Livewire, You, and Your Facility
Introduction to Livewire
System Design Reference & Primer
Version 1.0
11 November 2004
i
NOTES:
ii
1 Livewire for beginners .............................................................................................................................. 1
Why Ethernet? ..........................................................................................................................................................1
Compared to AES ........................................................................................................................................................................2
Audio Routing...............................................................................................................................................................................2
The Livewire Advertising System .................................................................................................................................................2
Control..........................................................................................................................................................................................2
Livewire and PCs .........................................................................................................................................................................2
Support for Surround....................................................................................................................................................................3
Audio Quality ............................................................................................................................................................3
Fidelity..........................................................................................................................................................................................3
Delay ............................................................................................................................................................................................3
The Pac-Man Protocols: Internet Standards .............................................................................................................6
Converged Networks....................................................................................................................................................................6
2 What can you do with it? .......................................................................................................................... 7
Make a Snake...........................................................................................................................................................7
A High-performance Sound Card Replacement........................................................................................................7
Build an Audio Router ...............................................................................................................................................7
Build a State-of-the-Art Broadcast Studio .................................................................................................................8
Make a Flexible Two-Way Multi-Channel STL ..........................................................................................................9
Create a Facility-Wide audio network that Includes Integrated Studio Consoles ....................................................10
Create an Integrated National/Local Radio Network...............................................................................................10
3 The Axia Livewire components .............................................................................................................. 11
Livewire Hardware Nodes.......................................................................................................................................11
The Livewire Windows Suite...................................................................................................................................12
8-in/8-out Driver .........................................................................................................................................................................12
PC Router Selector ....................................................................................................................................................................12
Media Player Interface ...............................................................................................................................................................13
The SmartSurface On-Air Studio Console and Engine ...........................................................................................13
SmartEngine ..............................................................................................................................................................................13
SmartSurface .............................................................................................................................................................................14
PathfinderPC Router Control Application................................................................................................................14
Provisions for Redundancy and Back-up ...................................................................................................................................16
Timed Events .............................................................................................................................................................................16
Livewire Audio Router Control Protocol .....................................................................................................................................16
4 Nuts & Bolts: Making Livewire play ........................................................................................................ 17
Livewire’s Channel and Name System ...................................................................................................................17
Channels ....................................................................................................................................................................................17
Text Name..................................................................................................................................................................................17
GPIO ..........................................................................................................................................................................................17
Sources vs Destinations.............................................................................................................................................................18
Examples ...................................................................................................................................................................................18
Sample Source Configuration Screen ..................................................................................................................................18
Sample Destination Screen ..................................................................................................................................................19
Sample System and QOS Pages .........................................................................................................................................20
Sample Screens from the Axia IP-Audio Driver....................................................................................................................21
Sample Screen From the GPIO Node ..................................................................................................................................22
Hardware Node COnfiguration & Access................................................................................................................23
Front Panel Node Configuration.................................................................................................................................................23
Configuring Node IP address................................................................................................................................................24
Accessing a Node via a web browser...................................................................................................................................25
Plugs & Cables .......................................................................................................................................................25
Cat 5 for Audio?....................................................................................................................................................................26
Ethernet 100BASE-TX..........................................................................................................................................................26
Pin numbering, jacks, cables, and color codes.....................................................................................................................26
Crossover 100BASE-T Ethernet Cable ................................................................................................................................28
1000BASE-T Gigabit Copper................................................................................................................................................29
Audio connections......................................................................................................................................................................29
Installing RJ-45s.........................................................................................................................................................................31
5 Designing and building your Livewire Ethernet system ......................................................................... 32
Cabling ...................................................................................................................................................................32
Twisted-pair Cable Categories...................................................................................................................................................32
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Category 3 ............................................................................................................................................................................32
Category 5 ............................................................................................................................................................................32
Category 5e ..........................................................................................................................................................................32
Category 6 ............................................................................................................................................................................32
Special Care for Ethernet Audio.................................................................................................................................................33
To Shield or Not to Shield ..........................................................................................................................................................33
Unbalanced Connections ...........................................................................................................................................................33
More than Four Pairs in a Cable ................................................................................................................................................34
Patch Panels ..............................................................................................................................................................................34
Wall Jacks ..................................................................................................................................................................................34
Cat 6 Jacks ................................................................................................................................................................................34
Architecture Options ...............................................................................................................................................35
Simple One-Switch Network ......................................................................................................................................................35
Daisy Chained Multiple-Switch Network ....................................................................................................................................36
Hierarchical Multiple-Switch Network.........................................................................................................................................37
Options for Redundancy ............................................................................................................................................................38
Fiber .......................................................................................................................................................................38
Radio Links .............................................................................................................................................................39
Designing for Security.............................................................................................................................................39
6 The Ethernet switch................................................................................................................................ 40
Livewire Ethernet Switch requirements:..................................................................................................................40
Some Switches We Like .........................................................................................................................................40
Switch Configuration...............................................................................................................................................41
Configuring the HP Procurve 2650 Switch.................................................................................................................................41
Turn on IGMP – IP address must be assigned to the switch................................................................................................41
Enable IGMP querier on all VLANs ......................................................................................................................................42
IGMP Fast-Leave feature .....................................................................................................................................................42
Save configuration to the Flash ............................................................................................................................................42
7 Testing, 1-2-3…...................................................................................................................................... 44
General Ethernet Troubleshooting..........................................................................................................................44
Prevention ..................................................................................................................................................................................44
The Basics .................................................................................................................................................................................44
Link Test ...............................................................................................................................................................................44
Ping.......................................................................................................................................................................................44
Switch Diagnostics................................................................................................................................................................44
Some Things to Check .........................................................................................................................................................44
Cable Testers .............................................................................................................................................................................45
Four Cable Testers ...............................................................................................................................................................45
Sniffers .......................................................................................................................................................................................46
Diagnosing Problems using Livewire Components.................................................................................................46
Hardware Node Indicator LEDs .................................................................................................................................................46
LINK......................................................................................................................................................................................46
LIVEWIRE.............................................................................................................................................................................46
SYNC & MASTER ................................................................................................................................................................46
8 Network engineering for audio engineers .............................................................................................. 48
Ethernet/IP Networks..............................................................................................................................................48
Layering Model...........................................................................................................................................................................48
Layer 1: Physical Interface ...................................................................................................................................................48
Layer 2: Ethernet and Switching...........................................................................................................................................49
Layer 3: IP Routing ...............................................................................................................................................................49
Layer 4: Transport ................................................................................................................................................................49
Layer 5: Application ..............................................................................................................................................................49
Making Packets..........................................................................................................................................................................49
IP and Ethernet Addresses ........................................................................................................................................................50
IP Address ............................................................................................................................................................................50
Subnet mask.........................................................................................................................................................................50
Gateway address..................................................................................................................................................................51
DNS server address .............................................................................................................................................................51
Ethernet Addresses and Address Resolution Protocol (ARP) ..............................................................................................51
Multicast Addresses..............................................................................................................................................................51
Ethernet Switching..................................................................................................................................................52
Multicast .....................................................................................................................................................................................52
IGMP (Internet Group Management Protocol)......................................................................................................................52
Prioritization ...............................................................................................................................................................................53
The Role of TCP ...................................................................................................................................................................54
Virtual LANs (VLANs).................................................................................................................................................................55
Tagged vs. Port-Based VLAN Operation..............................................................................................................................56
Ethernet Switching vs. Routing ..................................................................................................................................................56
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Livewire Networks...................................................................................................................................................57
Quality of Service (QoS) ............................................................................................................................................................57
Source Advertising .....................................................................................................................................................................57
Synchronization..........................................................................................................................................................................57
Synchronizing to AES3 Systems ..........................................................................................................................................58
Network Standards and Resources ...........................................................................................................................................58
Layer 1..................................................................................................................................................................................58
Layer 2..................................................................................................................................................................................58
Layer 3..................................................................................................................................................................................58
Layer 4..................................................................................................................................................................................58
Layer 5..................................................................................................................................................................................59
Network Time Protocol (NTP)...............................................................................................................................................59
A Note about Protocol Design....................................................................................................................................................59
9 F.A.Q.s 62
General ...................................................................................................................................................................62
Can the network be used for general data functions as well as audio? .....................................................................................62
Of course, we would never mix on-air audio and business functions or open ourselves up to hacking. Can I make this a
completely separate network? ...................................................................................................................................................62
How do contact closures get in and out of the network?............................................................................................................62
Is there any problem with delay of control commands over the network? I’ve heard about other systems using TCP/IP that
have had problems in this respect. ............................................................................................................................................62
Can I use Livewire without the SmartSurface? ..........................................................................................................................62
How does Livewire compare to other audio networking systems? ............................................................................................62
So, what about that delay?.........................................................................................................................................................62
How can you promise live audio over Ethernet? Won’t it drop out?...........................................................................................63
But the Internet is a packet network and the quality is not very good for audio. ........................................................................63
Are you sure this is robust enough for 24/7 operation? My Windows networks always have downtime. ..................................63
Do you use any compression? I am concerned about codec cascading. ..................................................................................63
Can I connect two studios across town with a T1 line?..............................................................................................................63
How do I connect this to my Zephyr?.........................................................................................................................................63
PCs and Livewire....................................................................................................................................................63
Tell me about your “sound card” driver for workstations. ...........................................................................................................63
Building Livewire Facilities ......................................................................................................................................63
I’ve got a large facility. How many studios can I interconnect?..................................................................................................63
What about for smaller stations? This all sounds pretty sophisticated for a simple set-up. .......................................................63
This seems like a lot of IP to keep track of. What administration tools does Livewire have? ....................................................63
How do analog sources become part of the network? ...............................................................................................................63
What about AES?.......................................................................................................................................................................63
How do mix-minuses get generated?.........................................................................................................................................64
You said I can get RS-232 data through the system. How is that done?..................................................................................64
Ethernet Media .......................................................................................................................................................64
Are optical audio links supported? .............................................................................................................................................64
What Ethernet rates do you support? ........................................................................................................................................64
The Internet and Livewire .......................................................................................................................................64
What about hooking up over the internet? With my studio audio in IP form, can I just plug a port from the switch into an
internet router? Why do I need ISDN anymore? ........................................................................................................................64
The Studio Engine and Surface ..............................................................................................................................64
Can a single Mix Engine handle two or three SmartSurfaces?..................................................................................................64
You are using a PC motherboard for the Studio Engine, right? It’s hard to believe that an off-the-shelf PC can do high-quality
audio mixing. Are you sure there’s enough power there?..........................................................................................................64
Will it be as reliable as the cards-in-a-frame approach? I sure don’t want this thing to crash. ..................................................64
I like the SmartSurface’s features and design, but I’m not ready to commit to Livewire for my full facility. Can I just use your
Surface and Engine as a drop-in console replacement? ...........................................................................................................65
Analog Audio and AES on RJs and Cat 5...............................................................................................................65
You recommend an outer shield for analog audio. Why? ..........................................................................................................65
Is there any crosstalk between the pairs within the Cat-5 cable? ..............................................................................................65
So, must all the audio and digital signals be balanced? ............................................................................................................65
Is Cat-5 OK for AES3 digital audio?...........................................................................................................................................65
Is Cat-5 OK for analog audio?....................................................................................................................................................65
Livewire, Standards, and Other Vendors ................................................................................................................65
Is Livewire standards-based? ....................................................................................................................................................65
Are you planning to share information so that other vendors can make gear that directly plugs to Livewire? ..........................66
10 Resources .............................................................................................................................................. 68
Livewire/Broadcast .................................................................................................................................................68
Ethernet ..................................................................................................................................................................68
General Networking and Internet ............................................................................................................................68
Cabling Information and Standards ........................................................................................................................68
Cable and Connector Suppliers ..............................................................................................................................69
Cable Testers .........................................................................................................................................................69
Ethernet Switch Vendors ........................................................................................................................................69
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Network “Sniffers” ...................................................................................................................................................69
Ethernet Radio Equipment......................................................................................................................................69
Appendix A: Livewire tech details ............................................................................................................... 70
LW Packet Structures .............................................................................................................................................70
Standard Streams ......................................................................................................................................................................70
Livestreams................................................................................................................................................................................70
Network Link Capacity ............................................................................................................................................71
Multicast Address Translation.................................................................................................................................71
Index
................................................................................................................................................... 74
vi
A note from the president of Telos
built-in computer compatibility. You can use Livewire as a
simple soundcard replacement – an audio interface
connecting to a PC with an RJ-45 cable. But add an
Ethernet switch and more interfaces to build a system with
as many inputs and outputs as you want. Audio may be
routed directly from interface to interface or to other PCs,
so you now have an audio routing system that does
everything a traditional “mainframe” audio router does –
but at a lot lower cost and with a lot more capability. Add
real-time mixing/processing engines and control surfaces
and you have a modern studio facility with many
advantages over the old ways of doing things. Ok, maybe
this is not as thrilling as a wedding night – perhaps kissing
your first lover is a better analogy. (By the way, and way
off-topic, did you know that the person you were kissing
was 72.8% water?)
It’s been a tradition since Telos’ very first product, the
Telos 10 digital phone system, that I share a few words
with you at the beginning of each manual. So here goes.
In radio broadcast studios we're still picking up the pieces
that have fallen out from the digital audio revolution. We're
not using cart machines anymore because PCs are so
clearly a better way to store and play audio. We're
replacing our analog mixing consoles with digital ones and
routing audio digitally. But we're still using decades-old
analog or primitive digital methods to connect our gear.
Livewire has been developed by Telos to provide a modern
PC and computer network-oriented way to connect and
distribute professional audio around a broadcast studio
facility.
While were on the subject of history… you've probably
been soldering XLRs for a long time, so you feel a bit, shall
we say, “attached” to them. We understand. But no
problem – you'll be needing them for microphones for a
long while, so your withdrawal symptoms won’t be serious.
But your facility already has plenty of Ethernet and plenty
of computers, so you probably already know your way
around an RJ-45 as well. It's really not that strange to
imagine live audio flowing over computer networks, and
there's little question that you are going to be seeing a lot of
it in the coming years.
Your question may be, "Why Telos? Don't you guys make
phone stuff?" Yes, we certainly do. But we’ve always been
attracted to new and better ways to make things happen in
radio facilities. And we've always looked for opportunities
to make networks of all kinds work for broadcasters. When
DSP was first possible, we used it to fix the ages-old phone
hybrid problem. It was the first use of DSP in radio
broadcasting. When ISDN and MP3 first happened, we saw
the possibility to make a truly useful codec. We were the
first to license and use MP3 and the first to incorporate
ISDN into a codec. We were active in the early days of
internet audio, and the first to use MP3 on the internet.
Inventing and adapting new technologies for broadcast is
what we’ve always been about. And we’ve always been
marrying audio with networks. It’s been our passion right
from the start. In our genes, if you will. As a pioneer in
broadcast digital audio and DSP, we've grown an R&D
team with a lot of creative guys who are open-eyed to new
ideas. So it's actually quite natural that we would be
playing marriage broker to computer networks and studio
audio.
th
The 20 century was remarkable for its tremendous
innovation in machines of all kinds: power generators,
heating and air conditioning, cars, airplanes, factory
st
automation, radio, TV, computers. At the dawn of the 21 ,
it’s clear that the ongoing digitization and networking of
text, audio, and images will be a main technology story for
decades to come, and an exciting ride for those of us
fortunate to be in the thick of it.
Speaking of years, it has been a lot of them since I wrote
the Zephyr manual intro, and even more since the Telos 10
– almost 20 years now. Amazing thing is, with all the
change around us, I'm still here and Telos is still growing in
new ways. As, no doubt, are you and your stations.
Steve Church
January 2004
What you get from this is nearly as hot as a couple on their
wedding night: On one RJ-45, two-way multiple audio
channels, sophisticated control and data capability, and
vii
NOTES:
viii
A note from the president of Axia
to their analog predecessors. It took a fresh look from a
European company that had been outside broadcasting to
merge together two products – audio routing switchers and
broadcast consoles – into a central processing engine and
attached control surfaces. Eventually nearly every console
and routing switcher company began to follow this idea and
a wide variety of digital "engines" and control surfaces
flooded the market.
It's been nearly 20 years since I designed my first broadcast
console for PR&E. We were building bullet-proof boards
for the most prestigious broadcasters in the world – and
I’ve always looked back on that time with great fondness.
For a while, we were making each new console design
bigger and fancier to accommodate a wider variety of
source equipment and programming styles. The console
was the core of the studio and all other equipment was on
the periphery.
But as advanced as these integrated systems were, they still
didn't handle computer-based audio sources any different
than their analog ancestors. Sure the routing switcher and
console engine were now integrated, but the most important
studio element – the PC – was stuck in the past, interfaced
with 100-year-old analog technology. The PC and the
console couldn't communicate in a meaningful way –
which was pretty strange considering that PCs everywhere
were becoming networked and, thus, the world’s most
popular and powerful communication tool. But studio
evolution was stalled.
Then a group of Telos engineers developed a method using
Ethernet to interconnect audio devices, allowing computers
and consoles, controllers and peripherals to interact
smoothly and intelligently. The benefits of powerful and
flexible networks had finally come to our studios. As with
the transition from cart machines to computers, the benefits
are many and impressive. A few networked components
can replace routing switchers, consoles, processing
peripherals, soundcards, distribution amplifiers, selector
switches and a myriad of related devices.
Then things began to change. The personal computer found
its way into broadcast audio delivery and production. At
first, PC audio applications were simple and used only by
budget stations to reduce their operating expenses. Then,
predictably, the applications evolved and were embraced by
the larger stations. It didn't happen all at once, but slowly
the PC was taking over center stage in the radio studio.
Like many, I was captivated by the PC. Stations were
retiring cart machines, phonographs, open-reel tape
machines, cassettes and replacing all with PC applications.
Some were even using the computer to replace more
modern digital equipment such as DAT and CD players. I
watched with amazement as client/server systems emerged
and entire broadcast facilities used PC applications to
provide most – and in some cases all – of their recorded
audio. Yet consoles continued to treat the PC as nothing
more than an audio peripheral. I knew that we console
designers were going to have to rethink our designs to deal
with the new computer-centric studios. But it was not yet
obvious what needed to happen.
This deceptively simple networked system costs a small
fraction of other approaches, yet has capabilities far
surpassing anything else. The system is modular and can be
used to perform discrete functions in a traditional
environment. At the same time, the system easily scales
from the humblest to the very largest of facilities. The
console, router, and the computer work in harmony.
And so equipped with this new technology and countless
product ideas, we launch Axia, the newest division of
Telos. Axia is all about delivering innovative networked
audio products to future-minded broadcasters. On behalf of
every one on our team, I welcome you as a charter client.
Axia is the culmination of nearly 40 man-years of some of
the most ambitious R&D ever applied to the radio industry.
And this is only the beginning. We have more products,
innovations, and partnerships in the pipeline.
During this time, some of the traditional broadcast console
companies began to produce digital versions. Many
broadcasters thought the new technology would bring
operational innovations as the PC had done. But the early
digital consoles were nearly identical in form and function
ix
You already know your Axia system is unlike anything
else. So as you read through this manual, it will come as no
surprise to you that your new system is loaded with new
thinking, new approaches, and new ideas in virtually every
conceivable area. Some of the concepts will challenge your
traditional ideas of studio audio systems, but we are certain
that once you have experienced the pleasures of the
networked studio, you will never want to go back. And
now, for something completely different...
Michael “Catfish” Dosch
February 2004
x
About this manual
This manual is your introduction to Livewire. We
explain the ideas that motivated it and how you can
use and benefit from it, as well as nitty-gritty details
about wiring, connectors, and the like. Since Livewire
is built on standard networks, we also help you to
understand general network engineering so that you
have the full background for Livewire’s fundamentals.
After reading, you will know what’s up when you are
speaking with gear vendors and the network guys that
are often hanging around radio stations these days.
This covers topics common to all Livewire equipment.
It is only a part of your full documentation package.
You will also have manuals for each specific piece of
equipment you are using to build your system. From
this document, for example, you will not learn how to
install or operate a Smart Surface, but you will
understand the nature of the network it plugs into.
This is being written in early 2004, just as Livewire is
coming to market. Everything here is new and fresh.
There will no doubt be many updates to this document
over the coming months and years. New equipment
will be released that will need description. New ideas
for use of standard Ethernet components will be
explored and tested in our lab. As we assist with your
installations, we’ll find new and better ways to explain
things. So check our web site or contact our support
department for the latest version.
As always, we welcome your suggestions for
improvement. Contact Axia Audio with your
comments:
Axia Audio, a Telos company
2101 Superior Avenue
Cleveland Ohio 44114 USA
Phone:
Web:
eMail:
+1.216.241.7225
www.AxiaAudio.com
[email protected]
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1 Livewire for beginners
Livewire offers a revolutionary change in how studios can be built. But at the same time,
it’s a natural continuation of general trends and what you already know. This section
explains the basics and puts audio over Ethernet into context.
Within the next few years, it is certain that the transition to
digital now happening in our studios will be complete, with
all audio storage, mixing, processing and routing being
digital. We need a connection method that gets the
interconnection job done easily, effectively, flexibly, and
cheaply. So why not look to the computer and telephone
worlds to find the technology? We can then take advantage
of the huge manufacturing scale in those industries and can
piggyback on the billions of dollars (and Euros, Yen,
Yuan…) of R&D going on in those industries.
cable and has grown to today's modern 1 Gigabit star and
switched system. 10 Gigabit has already been introduced
and is likely to follow the usual curve to low cost as
volumes increase. While copper is the most common
Ethernet connection, fiber is popular as well and media
converters allow the two to be interconnected. Ethernet
switches cost $6000 for 8 ports a half-decade ago; now
high-end 24-port switches cost $600. And they include
advanced features that were unheard of only a few years
back.
There are radio links in many varieties, from WiFi for
short-range to sophisticated long-range systems like the
Canopy from Motorola. There are satellite links. And
LASER links. Ethernet opens the door to a world of
options.
Ethernet has proven to be the PC of networking: Initially
released with only basic capability – low speed and bussed
– it has been expanded to today’s fast, flexible, switched
architectures.
WHY ETHERNET?
Ethernet makes overwhelming sense. Today's computers
are near universally linked via Ethernet – and telephony is
decidedly moving that way as well, with VoIP rapidly
gaining market share. Even remote controlled stage lighting
is transitioning from the XLR-based DMX protocol to
Ethernet. Ethernet cables, plugs, cards, and chips are
produced in the hundreds of millions so we get tremendous
economy of scale. We get patch bays and cords, testers, and
all kinds of "structured wiring" components ready-made.
Plugs are easy to install and jacks are efficiently small.
The combination of huge R&D expenditures, open
standards, massive economies of scale, technological
evolution, and flexible multi-service packet design is hard
to beat. Not to mention the surprisingly appropriate name.
But much more important is that Ethernet allows us to
combine many channels of digital audio with whatever data
transmission we might need on a single cable. This data
could be as simple as a start command for an audio player
or could be anything that computers and Ethernet do, such
as file transfer, e-mail, web communication, etc.
As to the origin of ether… for many years after James
Clerk Maxwell’s discovery that a wave equation could
describe electromagnetic radiation, the aluminiferous ether
was thought to be an omnipresent substance capable of
carrying electromagnetic waves. In 1887 scientists Albert
Michelson and Edward Morley disproved its existence. The
ingenious experiment that did so was performed at Case
Western Reserve University, just down the street from
Telos’ main office in Cleveland.
Further, we are in the line of future development. Since its
invention over 30 years ago, Ethernet has been constantly
evolving. It started as a 2Mbps shared bus over coaxial
1
Ethernet was named by its inventor, Robert Metcalf. He
had been involved in a radio data network in Hawaii called
ALOHA. The first Ethernet was a bussed coax that carried
data packets similar to the way ALOHA had sent them over
the “ether.”
ONE: LIVEWIRE FOR BEGINNERS
Compared to AES
For digital audio transport, AES3 is the main alternative to
an Ethernet based system. Invented in the days of 300-baud
modems, it was the first practical answer to connecting
digital audio signals. But it's now over 15 years old and is
showing its age. Compared to Livewire's computerfriendly, two-way, multi-channel + high-speed data
capability, AES3 looks pretty feeble with its 2-channel and
one-way only limitation. Not to mention 50-year old
soldered XLR connectors. And no significant data capacity.
AES3 is a low-volume backwater, with no computer or
telephone industry R&D driving costs down and
technology forward. Your 300-baud modem has been long
retired; it’s well time to progress to the modern world for
studio audio connections as well.
That having been said, AES and Livewire may comfortably
co-exist in your facility. You can use Telos interface nodes
to connect from one to the other. If you are using a house
sync system for AES, Livewire may be synced to that
system also.
Audio Routing
Low-cost mass-market Ethernet switches offer us
something very interesting: Since their function is to direct
packets from port-to-port, we can use them to move our
audio signals from whatever source to whatever
destinations we want. This means we get a simple, flexible,
facility-wide audio routing system for almost free. Say
goodbye to racks of distribution amps or expensive
proprietary mainframe audio routers.
An audio source entered into the system from any point
becomes available for any number of receiving
destinations.
The Livewire Advertising System
Livewire has an audio advertising system. Every source has
a text name and numeric ID. These are transmitted from
source devices to the network. Receivers can build lists of
all available sources from which users can select.
With hardware nodes, you enter the names, numbers, and
other configuration information via an attached PC with a
web browser. With PC nodes, you open a configuration
window.
Control
Think about it… most audio these days needs associated
control. A delivery system needs a start input at minimum,
but could well benefit from a richer control dialogue such
as text identifying what is playing that can be sent to the
2
studio mixer and to the HD Radio and RDS encoders.
Satellite receivers have control outputs. Telephone systems
need dialing, line status, hold, transfer, etc. Even a simple
CD player needs ready indication out and start in. Even the
simplest source, a microphone, needs to convey on/off
status for the air lights. To now, this control has been done
with primitive GPIO parallel “contact closures.” As a first
step, Ethernet can transport GPIO data, reducing and
simplifying cabling, and Livewire offers this basic
capability to replicate traditional start/stop control.
But Livewire also supports sophisticated remote operation
of studio equipment over the Ethernet via a very modern
and powerful software tool from the computer industry
called XML. With this, the network can transport much
more advanced information than simple start commands.
For instance, we can send the song title from a delivery
system to a display on a mixing console’s fader channel.
Control of telephone systems and codecs can follow fader
assignment and be accessible from any location. With a
high-bandwidth network linking everything and a flexible
communication protocol, the door is open to many
interesting possibilities. Why couldn’t the satellite receiver
identify its content with “metadata” tags? Then an
automatic system could store a program along with the
information about it for later play. An on-air audio
processor might respond to program type information to
adjust its parameters. Microphones switched-on could
activate a logger. There are many possibilities yet to be
explored.
Livewire and PCs
One of the advantages of a LW system is that PC-based
audio may be directly connected to the network without
soundcards. This means radio station delivery systems can
use the Ethernet connection they already have to send and
receive audio. Soundcard problems such as noise and
multiple conversions are avoided – the audio remains in
digital form from the PC’s files to the network with no
alteration or degradation. Received audio may have
originated from another PC or from a hardware audio node.
Audio sent from a PC may be received by other PCs or
hardware nodes.
With so much audio in radio stations being either played
from computers or recorded into computers, isn't this a
tremendous advantage? Not only do you save the
soundcard, but also the port that it needs at the other end to
connect to your console or router. And you can pass control
and other information over the same connection.
ONE: LIVEWIRE FOR BEGINNERS
Support for Surround
Surround is probably coming to radio broadcasting. Recent
advances in multi-channel codec technology will make
surround a possibility over European DAB channels and
the USA HD Radio system. Experimental DAB surround
broadcasts are already underway in the UK and Sweden.
expensive. Not so with Ethernet and Livewire. In fact, there
is no additional cost for the core Ethernet switch because
the one you need for stereo would also be fine for surround.
Audio from PCs can be multichannel at no additional cost.
We have designed Livewire with the future well in mind. It
is ready today to provide the infrastructure for a modern
radio facility that needs surround capability – with
simplicity and low cost.
AUDIO QUALITY
Surround is big news in the home entertainment industry.
Audio showrooms and computer shops are full of 5.1
channel home theater systems. DVD-Audio and Super
Audio CD disks offer a surround reproduction format to
serious audiophiles today. Some high-end cars already offer
surround audio systems, such as the DVD-Audio player
pictured below from Panasonic in the Acura TL.
We're always asked, "Is Livewire like audio on the
internet?" Yes and no. While Livewire uses internet
transport standards, it is intended to operate only over
switched Local Area Networks (LANs). Without the
limitations of the public internet and with 100% control
over all parts of the system, we are able to achieve full
studio quality.
Fidelity
Internet streams are usually compressed for transmission
over public links with limited, variable bandwidth and low
reliability. LW audio is not compressed – we use studiograde 48kHz/24-bit PCM encoding. Telos audio interface
nodes have more than 100dB dynamic range, < 0.005%
THD, and headroom to +24dBu. LANs offer a safe,
controlled environment where there is no risk of audio
drop-outs from network problems and plenty of bandwidth
for many channels of high-quality audio without
compression.
Delay
AES 3 would be an impractical and expensive way to
handle multichannel audio. The 5.1 system needs 6
channels: 2 front, 2 surround, 1 center, and 1 subwoofer. It
might also be required to keep a separate stereo-mixed
version independently, so there could be 8 total audio
channels. Using a traditional approach, that’s a lot of plugs,
cables, router cards, and rack space!
On the other hand, Ethernet has plenty of bandwidth to
carry the multiple channels surround broadcasting will
require. All eight channels plus associated control could
easily be conveyed on one convenient Ethernet plug and
cable.
Expanding a traditional console or audio router from stereo
to eight channels would be either impossible or very
3
In packet-based systems, delay is an important issue and
certainly has an effect on your talent’s perception of
“quality.” Packetizing audio for network transmission
necessarily causes delay, and careful design of the system
is required to reduce this to acceptable levels. Internet
audio delay is often multiple seconds because the receiving
PCs need long buffers to ride out network problems and the
delays inherent in multiple-hop router paths. However, with
fast Ethernet switching on a local network, it is possible to
achieve very low delay. To do this, we must have a
synchronization system throughout the network. This also
avoids sample or packet slips that cause audio dropouts.
Internet streaming does not use this technique, so even if it
were to have guaranteed reliable bandwidth, you still
couldn’t achieve the very low delay we need for
professional studio application.
For Livewire, we generate a system-wide synchronization
clock that is used by all nodes. Within each node, a
carefully-designed
PLL
system
recovers
the
ONE: LIVEWIRE FOR BEGINNERS
synchronization reliably, even in the case of network
congestion. Hardware nodes provide this clock and in each
system, there is one master node which sends the clock
signal to the network. If it should be disconnected, or stop
sending the clock for any reason, another node
automatically and seamlessly takes over.
In broadcast studios we care very much about audio delay
in the microphone-to-headphones path for live announcers.
Maximum delay must be held to around 10ms or
announcers will start to complain of comb-filter or echo
problems. We need to consider that this is a total “delay
budget” and that multiple links and some processing will
often be in the path. So we’ve decided to have a link delay
around 1ms end-to-end for anything in this path, allowing
us a few links or maybe a couple of links and a processor
before we get into links: one from the mic node to the mix
engine and one from the engine to the headphones out
node. Thus, 2ms total.
Delay
Effect
1-3 ms
Undetectable
3-10 ms
Audible shift in voice character (comb filter effect)
10-30 ms
A slight echo turning to obvious slap at 25-30ms
30-50 ms
Disturbing echo, disorienting the announcer
>50 ms
Too much delay for live monitoring
Here are the air-talent reactions to delay in a test conducted by Jeff Goode at
WFMS in Indianapolis
In our experience, delays to around 10ms are not a
problem, from 10-25ms announcers are annoyed but can
work live, and anything above 25-30ms is unacceptable.
Another way to think about delay: Audio traveling 1 foot
(0.3 meters) in air takes about 1ms to go this distance.
And another data point: A common professional A-to-D or
D-to-A converter has about .75ms delay.
But, as is universally the case in engineering, there is a
tradeoff – otherwise known as the “if you want the
rainbow, you gotta put up with the rain” principle. To have
low delay in a packet network, we need to send streams
with small packets, each containing only a few
accumulated samples, and send them at a rapid rate. Bigger
packets would be more efficient because there would be
fewer of them and they would come at slower rate. But they
would require longer buffers and thus impose more delay.
Big packets would also have the advantage that the
necessary packet header overhead would be applied to
more samples, which would more effectively use network
bandwidth.
With Livewire, we enjoy our rainbow and avoid the rain by
having two stream types: Livestreams use small and fast
packets, while Standard Streams have bigger and slower
packets. Livestreams require dedicated hardware and
achieve the required very low delay for microphone-toheadphone paths. PCs are not able to handle these small
4
packets flying by so quickly, therefore they use the
Standard Streams. As the name says, these are compatible
with internet standards and can be directly received into the
network from PCs running standard delivery software. The
network delay in this case is around 5ms and the PC’s
latency is likely to add perhaps 50-100ms more. Since PCs
are playing files and are not in live paths, this is not a
problem. Our only concern is how long it takes audio to
start after pressing the On button, and delays in this range
are acceptable. Standard Streams can also be sent from the
network to PCs for listening and recording. Again, this
small delay is not an issue – especially given that PC media
players have multiple seconds of buffering.
However, off-the-shelf PC hardware with a special
operating system and software optimized for real time
audio is able to handle the fast streams. Indeed, we use this
approach for our studio mixing and processing engine.
All LW hardware devices transmit both stream types and
can receive both stream types. There is no inefficiency
from having both available because all streams stop at the
Ethernet switch and take no system network bandwidth
unless they are subscribed to by a receiver. Each receiver
takes only the one it needs, taking the low-delay version if
available, or the higher-delay version, if not. The selection
happens transparently with no user action needed. Users
ONE: LIVEWIRE FOR BEGINNERS
just select the channel they want and audio is delivered by
whichever is appropriate to the equipment they are using.
THE PAC-MAN PROTOCOLS: INTERNET
STANDARDS
We use the internet’s IP standard for streaming media
called RTP/IP for Standard Streams. RTP stands for RealTime Protocol. It is the internet’s standard way to transport
streaming audio and video, just as TCP/IP is the standard
for general data. Both use the same underlying IP packet
structure, but each has a header and transmission method
appropriate to the content.
Since we adhere to internet standards, your audio may be
played by PC players such as Windows Media and Real
that support standard protocols and uncompressed PCM
audio.
Converged Networks
The headline below taken from the Wall Street Journal
nicely captures what is happening in the telephone and
networking worlds: IP has become the “Pac-Man” of
protocols, eating up everything in sight.
traffic only to where it is needed. Even on a single link,
traffic can be mixed because we use modern Ethernet’s
priority mechanism to be sure audio packets have first call
on the link’s bandwidth. A studio audio delivery system
could use this capability, for example, to download an
audio file from a server while simultaneously playing
another live.
Until a few years ago, there was skepticism that Ethernet
would handle convergence with services like telephone and
live media being assured reliable bandwidth while sharing
the network with computers. A network technology called
ATM was proposed as a better solution. But it was
expensive, difficult to administer, and would have required
a “fork-lift” upgrade to existing systems. So it never caught
on and has pretty much faded from sight for local networks,
although it has a role at the core of some Telco networks.
Ethernet’s
switching,
priority
mechanisms,
and
increasingly fast speed has put most concerns to rest, and
all the vendors who offer VoIP telephones connect them
over Ethernet, not ATM.
Livewire adds to the convergence possibilities in a
broadcast facility. We predict that you eventually will have
your computer data, telephone, audio, and control on a
single network and that this will use computer/telephone
industry standard wiring.
Major networking companies like Cisco, 3Com and HP are
dedicated to the idea that a facility needs only one network
for data, telephones, and media. They are building products
today that deliver on this notion.
Meanwhile, PBX companies like Lucent, Nortel, Mitel,
Alcatel, and Siemens are moving headlong into IP transport
for their telephone products.
The result is almost certain to be a converged network,
serving all needs. Traditional telephone PBXs are likely to
go away.
Ethernet might just as well be said to be the Pac-Man of
local networks. It has nearly a 100% share of new LAN
installations and is the network that all VoIP phone systems
we know about use for connection to the desktop.
An Ethernet network being used for Livewire audio may be
shared with any other data transmissions such as file
transfers, web browsing, and the like. An Ethernet system
with a switch at the center may have a mix of audio nodes
and normal servers, PCs, etc. The Ethernet switch directs
6
TWO: WHAT CAN YOU DO WITH IT?
2
What can you do with it?
Imagine everything that you can do with a PC connected to a network: Share files, send
and receive emails, chat, surf the web, listen to audio, etc., etc.. PCs and networks are
designed to be general-purpose enablers. You have a similarly wide range of
possibilities for audio applications using Livewire. Here are examples, starting with the
most simple, and continuing to the most interesting.
MAKE A SNAKE
Concert sound guys need to get a lot of audio from the
stage to their mixing consoles in the center of the house.
They call the multi-conductor cables they traditionally use
for this function a “snake”. LW lets you put such a snake
on a diet! A single Ethernet cable connects multiple audio
Audio in x8 (line or mic)
Audio out x8
channels. Add a switch at each end and you can have as
many nodes as you want. Use gigabit Ethernet and you can
have hundreds of channels. Add fiber optic media
converters and cable to extend the distance between units to
many kilometers. Maybe you need to get something from
here to there?
Audio in x8 (line or mic)
Audio out x8
Ethernet – Copper,
Fiber, or Radio
Basic Ethernet Snake
A HIGH-PERFORMANCE SOUND CARD
REPLACEMENT
Livewire can talk directly to PCs, making the network look
like a soundcard to delivery systems, editors, etc. Telos LW
nodes have excellent audio performance: Balanced I/O with
more than 100dB dynamic range, < 0.005% distortion,
headroom to +24dBu, etc. They make excellent multichannel “soundcards” for professional applications. You
can position the node at a distance from the PC, and you
get balanced audio on connectors that are a lot more
reliable than mini phone jacks.
Ethernet Sound Card Replacement
With the addition of an Ethernet switch you can feed your
audio to multiple computers and/or have multiple I/O boxes
– which takes us to the next application…
7
BUILD AN AUDIO ROUTER
A system with Livewire nodes, one or more Ethernet
switches, and PC-based routing controller software make
an excellent facility-wide audio router. PCs send and
TWO: WHAT CAN YOU DO WITH IT?
receive audio directly to the network without soundcards or
audio ports, thus lowing cost and eliminating conversion
steps. Telos and Omnia telephone, codec, and processing
equipment will also eventually connect directly. To
interface conventional analog and AES signals, LW
interface nodes come in a number of versions.
One LW node operates like a traditional audio router X-Y
control panel. But with a difference: audio in and out is
available on the same box.
A PC-based router control package is available that makes
your whole system look like a single entity. You can
control which outputs are connected to which inputs just as
if the system were a single location box.
Since there is no requirement for a mainframe, the base
cost is low – you can make a small system at very
reasonable cost and expand it over time. Indeed, the total
cost of a large system will be much lower then older
approaches due to the use of commodity switches at the
core. Just as using standard PCs to play audio makes much
more sense than any proprietary approach, building routers
from common computer industry parts makes similar sense.
Indeed, this approach gives you a true “audio network”
quite unlike other approaches.
PC with Telos PC
Audio s/w Direct
Connects Audio
Router-style Audio Terminal
8x8 AES in/out
8x8 Analog in/out (mic in opt)
Control PC
Basic Ethernet Audio Router
BUILD A STATE-OF-THE-ART BROADCAST
STUDIO
to be controlled depending upon source
characteristics.
Plug an audio processing engine and a control surface into
the network and you have a modern radio studio with many
advantages over the old way:
Tighter integration with delivery systems
means that mixing, scheduling, and playing
may work together. For example, song titles
can appear on the mixer surface, start and other
control functions may be conveyed over the
network, and logging can confirm that an audio
piece was really played on the air.
Simplified and unified cabling for audio,
control, general data, and telephone.
No sound cards, multiple conversions, etc.
With most studio audio coming from or going
to PCs, audio is kept in the networked digital
domain. Audio may be monitored on any PC
with a player such as Windows Media, Real
Audio, etc.
Troubleshooting
and
repair
are
transformed. Extensive diagnostics are
available over the same network that connects
the audio. A suspect surface or engine may be
swapped by re-plugging only one Ethernet
cable.
Integrated data means you are ready for
synchronized text and metadata, such as will
be needed for HD-Radio in the USA. It will
also be possible for audio processor parameters
Low-cost
machines
powerful,
technical
8
power. Computers replaced cart
because they are a lot more
convenient, reliable, and cheap. The
side of radio broadcasting is tiny
TWO: WHAT CAN YOU DO WITH IT?
compared the computer and networking
industries. We get tremendous value by
plugging into the massive R&D and production
scale offered by the computer world.
Leveraging low-cost mass-produced computer
components makes the same sense for studio
mixing and audio distribution as it did for cart
machine replacement.
In the example below, a Livewire-based system is being
used as a studio console. Sources such as microphones and
CD players are interfaced to the network with a node in the
studio, while sources such as network feeds interface with a
node in an equipment room.
Certain peripheral equipment connects directly to
the network. Audio from the delivery PC goes to
the network via an Ethernet connection and control
is also over the network. The network also supports
file transfers to the delivery system from a server.
The studio operator surface controls a rack-mount
mixing engine, which has a single Ethernet
connection for both control and audio.
Surround-ready. As one would expect from
its flexible computer technology-based origins,
Livewire readily adapts to future technologies
such as 5.1 surround.
Delivery PC
Mixing/processing Engine
Production Studio
To other studios
Server
Complete Broadcast Studio
MAKE A FLEXIBLE TWO-WAY MULTICHANNEL STL
Studio and transmitter sites may be linked with “Ethernet
STLs”. LW nodes provide audio interface to Ethernet
point-to-point radios. These are off-the-shelf today from
such companies as Motorola, Adtran, Proxim, and Redline.
9
In addition to the audio, anything that can be carried over
Ethernet can be conveyed over the radio link, such as VoIP
telephones, email, file transfers, and transmitter remote
control.
TWO: WHAT CAN YOU DO WITH IT?
Ethernet radio systems are available that can connect at up
to about 50Mbps. This data rate would support around a
dozen stereo uncompressed audio channels in each
direction, with capacity remaining for VoIP telephone and
facilities control. Seems these radios would make an
interesting two-way RPU also. For co-owned stations that
are not co-located, these could be an effective way to link
studio facilities.
NOTE: Many of these systems are optimized for speed vs
low error rate and therefore may not work. Axia has
evaluated several units and we can offer guidance if you
are interested in pursuing this option.
CREATE A FACILITY-WIDE AUDIO
NETWORK THAT INCLUDES INTEGRATED
STUDIO CONSOLES
Combine all of the above for maximum power,
convenience, and flexibility. You get facility-wide audio
10
routing, state-of-the-art studio mixing, a single wiring
infrastructure for audio, computer data, control, and
telephone.
Audio processors with Livewire ports may easily have
multi-channel outputs, such as for simultaneous analog FM,
HD Radio, and low-delay monitoring feeds. A single
Ethernet would serve for all needed inputs and outputs.
With a data capability alongside the audio, it would be
possible to control processing parameters depending upon
which audio source is active.
CREATE AN INTEGRATED
NATIONAL/LOCAL RADIO NETWORK
Imagine a satellite transmitting IP packets. Now live audio,
audio to be stored for later play, and identifying data can be
delivered. Wouldn’t this transform radio networks into
something much more interesting, useful, and powerful?
Including an internet-based return path adds another
dimension.
THREE: THE AXIA LIVEWIRE COMPONENTS
3
The Axia Livewire components
Livewire is not only a technology. It is a solution, made for broadcast. Here are the
essential pieces that put Livewire to work for you.
A Livewire system usually has a mix of hardware nodes
and PCs with driver software that lets them send and
receive LW audio streams. There will also be one or more
Ethernet switches, unless you are making only a very
simple 2-box snake or a PC soundcard replacement. This
section gives an overview the available nodes as of January
2004. Switches are covered in another section.
We expect that in the future much broadcast equipment will
have on-board Livewire jacks. We are planning to include
these ports in most new products, so there will soon be
Telos telephone hybrids and systems, Zephyr ISDN codecs,
and Omnia audio processors with LW connectivity.
LIVEWIRE HARDWARE NODES
These interface analog and AES audio to the LW network.
Some are used to interface GPIO such as for starting CD
players or lighting on-air signs.
Configuration and monitoring is via a networked web
browser.
Analog 8x8 Node
Eight balanced inputs and outputs with more than 100dB dynamic range, < 0.005%
distortion, headroom to +24dBu. Software controlled gain lets you trim adjust to
accommodate different levels. Front panel LED audio level metering.
AES 8x8 Node
Eight AES3 inputs and outputs. An input can be used to sync your Livewire network to your
house AES clock, if desired.
Mic + Line Node
Eight microphone inputs with very high-grade pre-amps, phantom power, and eight
balanced line outputs. Intended mainly for on-air studios.
11
THREE: THE AXIA LIVEWIRE COMPONENTS
Router Selector Node
Emulates the function of traditional x-y audio router controllers, but includes on-board input
and output in both analog and AES3 digital forms. The LCD presents a list of active audio
channels, which are selected with the adjacent knob. Programmable “radio buttons” offer
immediate access to often-used channels. For equipment room monitoring and production
studio or newsroom audio interface. Also useful as a test instrument to check and generate
audio streams.
General Purpose Input/Output Node
This GPIO interface for parallel closures has eight DB-15 connectors, each with five inputs
and five outputs. Interfaces control to CD players, delivery systems, on-air lights, etc. that
need simple parallel control. The SmartSurface power supply also offers identical GPIO
functionality
THE LIVEWIRE WINDOWS SUITE
This is the software interface between your PC audio
applications and the Livewire network. Components are
included that provide various interface capabilities.
8-in/8-out Driver
This is a driver that interfaces eight inputs and eight
outputs. It provides these functions:
Interface for audio sent to Livewire from audio
applications such as delivery systems and other
audio players.
Audio applications see the LW network as if it were one or
more standard sound cards. A sample rate converter and
clock generation functions are included.
PC Router Selector
The second application in the LW Windows Suite is an
interface to display and select LW streams – essentially a
software version of the Router Selector. The selected audio
is sent to any audio application that works with standard
Windows sound cards. The Preview function lets you listen
directly without another application.
Sources are listed for selection with a mouse click. They
may be filtered by category.
Interface to receive audio from Livewire into
applications such as audio editors.
There is a capability similar to the radio buttons on the
hardware Router Selector. Dragging a listed source to one
of the buttons allows it to be used to quickly select a
desired source.
A GPIO function to convey “button-press’ data
from the network to applications, such as from
a control surface fader start button to an audio
player.
12
THREE: THE AXIA LIVEWIRE COMPONENTS
PC Router Selector user interface
Media Player Interface
Streams can be adapted for listening by standard internet
audio players such as Microsoft Windows Media and Real
players. The list of Livewire streams is presented within the
player’s usual interface as if they were standard internet
streams.
THE SMARTSURFACE ON-AIR STUDIO
CONSOLE AND ENGINE
With all audio sources in your facility available on a single
Ethernet jack, the door is open to new ways of mixing and
processing audio signals. We are now able to build a lowcost, but very powerful mixing/processing engine that
subscribes to networked audio streams, modifies them and
presents the resulting streams back to the network. On that
same jack.
SmartEngine
The StudioEngine is a powerful processor designed to add
console functions to a Livewire audio system. The Studio
Engine performs all the mixing and signal processing
functions that would have been performed in the past by an
audio console. Of course, a LW-based routing system may
be used with any traditional console, but integration brings
many advantages.
StudioEngine
13
THREE: THE AXIA LIVEWIRE COMPONENTS
Each engine can perform all the mixing and processing
functions needed by even the largest console, with perchannel mix-minus feeds, multiple outputs and monitor
feeds, EQ, etc. There’s plenty of headroom to support
future features. Generally, one Studio Engine is required
for each radio studio.
components, web-based interaction is used for more
advanced configuration.
Operators still need to have control interfaces. The Telos
SmartSurface shown below is a Studio Engine-compatible
control surface. It, too, connects with a single Ethernet
plug.
The front panel display on the StudioEngine provides
confidence feedback. The selector knob allows you to
easily perform basic configuration. As with all LW
SmartSurface
SmartSurface
Designed for the needs of live programming, SmartSurface
provides your on-air staff with a familiar and comfortable
set of controls in an uncluttered and intuitive format. With
a lot of broadcast experience under our belts, we worked
carefully to keep the basic functions simple and troublefree,
but still have all the sophisticated functions of large
traditional consoles supported in a deeper layer. The two
high-resolution color LCD displays usually show metering,
time, timer, and essential status. But they are also used for
source selection and other functions. Pressing the Option
button on monitor or fader channels brings up all the fancy
stuff. All sources in your LW system are listed and
available for selection, and there is pan, EQ, L/R select,
send bus access, etc.
But it goes further. As you would expect from Telos,
SmartSurface has a smart approach to mix-minus for
phones and codecs. Every channel has the ability to provide
a mix-minus output automatically. Operators simply select
a phone or codec source and the backfeed is automatically
generated based on preferences established when the user
profile was configured. There is a single button that selects
a Phone Record mode for the common case that a DJ needs
to record phones off-air for later play.
14
LED text labels show the active source for each monitor
and fader, and icons show the status.
SmartSurface can save profiles for each user, allowing
different preferences, layouts and defaults for a variety of
shows and talent.
In addition to console functions, SmartSurface provides
controls and displays that interact with phone systems,
codecs, editors, PC delivery systems, etc.
Together with the Studio Engine, SmartSurface was
designed to meet all the console/control needs of the most
demanding live and live-assist radio operations.
PathfinderPC ROUTER CONTROL
APPLICATION
You can control a distributed Livewire system as if it was a
traditional centralized audio router. In this case, you will
need a way to control the multiple nodes as if they were a
single device.
We offer a PC software package called PathfinderPC,
developed in cooperation with a partner, Software
Authority, that specializes in this. It is a client-server
system that serves as a front end for X-Y style router
switching. The server communicates will all of the LW
nodes in your system, and offers a common point of control
THREE: THE AXIA LIVEWIRE COMPONENTS
to clients. Multiple clients can connect to the server to
provide any number of control points. Each client may be
optimized for a particular style of operation. For example, a
master control client will probably be very different from a
controller within a studio.
Scenes (presets) can be created and recalled allowing local
studio or global changes. A virtual patch bay function
provides an intuitive way to manage routes. The server and
clients run on Windows PCs.
PathfinderPC user interface for selecting routes throughout an entire Livewire
Network
Because LW nodes put audio level information onto the
network, PathfinderPC clients are able to display audio
level metering. This is shown on the crosspoint icons above
– the green dots indicate the presence of audio. Users may
also select accurate multi-segment meters for audio sources
they want to check carefully.
You can use PathfinderPC to make “virtual routers.”
Virtual routers can be subsets of the real routers. So, for
example, if a Livewire system has 128 different sources
and destinations on the network, a particular studio area
may only wish to use a small number of these points. You
can create a virtual bay specifically designed with the
sources and destinations required by this studio. This
virtual router can have its own set of snapshot (scene
changes). The virtual router also allows you to map
multiple points to a single virtual point. For example you
15
can make a virtual source and destination that contains both
the audio inputs and outputs for a particular device, but also
the GPIO points. Thus when the route is made, both audio
and GPIO is routed simultaneously.
PathfinderPC supports non-Livewire routers including
video routers and machine control routers. Thus you can
make routing points in the virtual bay which will
simultaneously route audio, video, GPIO, and Machine
Control. This makes the software ideal as a master
centralized router control package. Software Authority is
continuing to expand our list of supported products, and the
software is designed to allow us to add support for
additional protocols and routers quickly.
PathfinderPC supports the use of tie lines or gateways
between routers. For example if a system has both an
analog video router and an SDI video router, one or several
THREE: THE AXIA LIVEWIRE COMPONENTS
tie lines can be wired through Analog to SDI converters
between the two routers. PathfinderPC will then combine
the routing tables and automatically use the tie lines when
necessary to get analog sources to the SDI router. The
complexity is hidden from the end user. This capability
allows Livewire terminals to extend an older and already
filled router.
Provisions for Redundancy and Back-up
There is a silence detector. You can place a “watch” on a
particular Livewire destination. If the audio level falls
below a specified threshold for longer than a specified
period of time, the system will switch to a backup audio
source. This lets you build automatic redundancy into a
signal path. If the primary and backup sources and
destinations in the silence detector are assigned to different
Livewire units and these units are wired to different AC
power sources, the signal path can be maintained even in
the event of a failure of a terminal or power source.
In addition, multiple Pathfinder servers can be
simultaneously monitoring the Livewire network, building
redundancy into the control system as well. The Livewire
system is an ideal system for building a redundant audio
chain. Since every audio unit is an independent device, the
server can automatically switch audio to a different unit if
the usual one fails. With careful planning, you can arrange
your system so that the primary and backup audio units are
connected to different LAN switches which are chained
together using the inherent Ethernet redundancy protocols.
Thus audio is continuously and reliably passed, even in the
event of a LAN switch failure.
Timed Events
PathfinderPC has a simple timed-event system built into the
server. You can program events to happen at specified
times. Individual routes or snapshots (scenes) can be
triggered at a particular time and date or on a rotating
schedule on certain days and times of the week. Events can
also be created which will monitor a GPIO and initiate a
snapshot (scene change) or route whenever a GPIO
condition changes.
For more sophisticated timed operation, external
automation systems will be able to access and manipulate
the routing tables provided by the Pathfinder server using
the protocol translator. Multiple protocols may be
simultaneously translated and connection may be on either
IP/Ethernet or serial ports.
16
Livewire Audio Router Control Protocol
We also provide a documented protocol for those who want
to develop their own controllers.
Applications designed for controlling traditional audio
routers can implement LW Audio Router Protocol directly
or use a software gateway between this protocol and their
native protocol. The first solution may be preferable, as it
enables applications to fully control every LW unit and is
free from potential problems with the gateway reliability.
To avoid multiple TCP/IP connections, the gateway
solution may be used. In this case, there must be
gateway/translator software developed for each protocol
that has to be supported.
Livewire Routing protocol assumes multiple audio
input/output nodes. Every node has its unique IP address, N
input ports and M output ports.
We offer a software interface that emulates a traditional
router and does the mapping and translation. Input to this
module can be either serial port or TCP/IP over a network.
Network configuration of Livewire devices can be
communicated to this program using command line or a
text configuration file. There is a TCP/IP server waiting on
every LW node. The client simply writes text commands to
the appropriate device.
FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
4
Nuts & Bolts: Making Livewire play
Now we move to making audio happen. Time to take the gear out of the shipping carton
and make it play. This section gives you practical information. Details about the
underlying tech are reserved for later.
LIVEWIRE’S CHANNEL AND NAME SYSTEM
An advantage of having a data network carrying our audio
streams is that we can send identifying information on the
same cable and system. Receivers can build tables of
available audio, and testers can identify specific streams on
a cable. In Livewire, we have both a numeric and a text ID
for each audio source.
Hardware LW devices are configured either using a
networked PC's web browser, or with local pushbuttons and
displays. PC LW nodes will have a configuration window
that opens when you click on the application icon. Details
for each are in the manual specific to the product, but the
general approach is the same for all audio and GPIO.
Channels
Channel numbers may range from 1 to 32767. You assign
these to audio sources as you wish.
New units are pre-configured from the factory to start with
channel 1, thus an 8-channel node will come assigned to
channels 1-8. Two new units can be connected to each
other with a “cross cable” (described later) for immediate
out-of-the-box testing. For your network, you should
reserve channels 1-8 for testing and not assign them for
routine use. Then, if you plug a new unit into the network
before you configure the channels, there will be no problem
with conflicts.
In a large system, you will probably want to have a peoplefriendly naming and numbering system that reflects studio
use or location and to help prevent accidental duplication of
channel assignments (a big no no by the way). You have
plenty of numbers to use, so you don't have to conserve
them. For example, the channels associated with Studio 1
could start with 100, Studio 2 with 200, etc. There is no
requirement that channels be assigned in order or
contiguously from a multi-channel device.
Devices such as telephone hybrids and codecs need audio
in both directions, so when appropriate, a single channel
contains a “to device” audio stream as well as the usual
“from device” audio. In this case, you can think of the
channel as something like a telephone number that connects
17
a call with audio in both directions. The advantage of this
“bundling” of the two audio directions is that the
association is naturally maintained when studio mixers are
in the picture. Mixers generate the feed to devices (usually
mix-minus, but not always) and automatically assign it to
the source channel number, and this association is kept
regardless of which fader is being used, etc.
Text Name
The text name may be up to 24 characters and you choose it
as you wish. This is what will appear on the Router
Selector’s LCD, studio mixing surface source select lists,
etc. Most devices are not able to display all 24 characters,
so will truncate to show what they can. The Router
Selector, for example, can display 16 characters. You may
wish to include in the name the rack number or room name
of where the Node is located, to help orient yourself in the
case of a future emergency.
A typical name might be: ST1CD2 for Studio 1, CD Player
2.
Our studio mixing systems (Smart Surface, for e.g.)
automatically generate return feeds to devices that need
them, creating the text name for these in the form “To:
name”. For example, if you have a source called “Hybrid
1”, the mixer will generate an audio stream named “To:
Hybrid 1” and advertise it to receivers.
GPIO
There are also GPIO (General Purpose Input/Output)
channels and text names. These work in a fashion very
similar to the audio source channels and names.
GPIO channels often share the same channel number as an
audio source. A typical situation would be when you have a
CD player that needs start control from an audio mixing
console. The mixer automatically generates the start
command and puts it on the channel number you assigned
to the audio source. To cause a particular hardware GPIO
to output this command as a contact-closure pulse, you
configure the GPIO device to listen to this channel. As with
the back audio, control follows the audio source to
whichever fader is being used.
FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
But GPIOs may also be independent of audio sources. In
this case, the Livewire system provides a pass-through
function where outputs follow inputs – sort of like a GPIO
distribution amplifier.
Sources vs Destinations
We’ve always struggled with terminology when referring
to audio input/output from devices such as codecs and
hybrids where there’s local audio I/O as well as a combined
network I/O port. We will try to be consistent within the
Livewire realm by using the following terms:
Destination – this is an audio output from a
hardware Node and therefore represents
playback of some stream from the network. Of
course a StudioEngine or Livewire capable
audio device may access a livewire stream and
in these cases there would be no associated
hardware audio output.
So, to reiterate, sources represent the feeding end of the
audio stream equation whereas destinations are just that,
one or more destinations where that stream is used.
Examples
Source – this is an audio input to a hardware
Node and therefore available on the Livewire
network as an audio stream that can be
accessed by other LW nodes. Of course a
StudioEngine can generate new audio sources
and in this case there is no associated hardware
audio input.
Following Gauss’ dictum that “an example is worth two
books,” let us now turn to some to show you how
Livewire’s channel and name identification work.
Here are some of the web configuration pages for the 8x8
analog I/O node:
The first is the home page that is displayed once you have logged into the
node. It simply lets you navigate to the other configuration screens.
Sample Source Configuration Screen
Pictured on the next page, the Configure Sources page
permits your to configure locally generated sources.
The Name entry at the top is where you put the
text ID for the node.
if you know you won’t use a particular type,
you can switch it off to conserve bandwidth.
For example, a satellite feed will never be in a
mic-to-headphones path, so only the Standard
Stream would be required.
The Bits selection is an advanced option for
RTP streams. Usually Livewire audio is 24
bits. But some PC players might not be able to
handle this high resolution. This option lets
you adjust the bit depth to 16 or 20 for such
players. Normally this is set to the default auto
position, which causes 24-bit words to be
output.
There are 8 Source Name entries, one for each
audio channel. This is the text name for the
individual audio source.
Source Channel is where you enter the channel
number for each source.
Livestream and Standard Stream Enable allow
you to decide which of these you want to put
onto the network. Usually both are enabled, but
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FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
Our example node has selectable gain for
inputs. You can choose the appropriate value
with Input Gain (the range of values will
depend on the node to be configured). This can
also be set on the Meter screen, in case you
desire to set gain “by eye”.
And here is the source configuration page. It allows you to assign names
and channels to the sources that will be generated by this node, and to
configure the audio inputs associated with those sources, as described
below.
Sample Destination Screen
This page, pictured below, is used to configure the local
units outputs
Here is the Destinations page, where you configure the output channels,
with the menu options described below.
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As with sources, you can enter a text Name to
be associated with the destination associated
with each output port.
Channel is where you tell the unit which audio
stream is to be output from each audio output.
As previously discussed, each Livewire stream
is identified by both a text name and with
audio channel number. You can enter the
channel number directly, or you can use the
button to the right of the channel entry to open
a page that gives you a list of all the active
audio channels and can choose from among the
channels listed within it. Usually the list
contains text names of audio streams, but if no
text name has been assigned, you will see the
device type and IP number instead.
Hot Tip! You will only have a complete list of audio
sources if you have already configured all your source
nodes and have them connected and operating so that they
are advertising to the network. You can always just enter
the channel number here if you don’t yet have your source
nodes working, but it will be more convenient if you
prepare all your sources before moving on to destinations.
The Meters page for our example audio node let’s you monitor the levels for
each input and output channel. This is also an alternative to the source page
for setting input gain.
Sample System and QOS Pages
Pictured on the next page, the system screen permits
checking the IP address and related settings. The QOS is an
advanced feature page.
20
FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
The System and QoS pages let you set some other values such as the IP
number for the unit, stream characteristics, and clocking mode. These are
described in detail in the unit’s manual, but to appreciate the context, you will
also need to understand more of the Livewire and networking basics
described later in this document.
Sample Screens from the Axia IP-Audio Driver
Our samples so far have been from the 8x8 Analog Node.
Next let’s look at how sources and destinations are handled
by the IP-Audio Driver used on Windows™ computers.
Soundcard Emulation – The IP-Audio Driver looks like a
standard sound card to Windows™. Each of the Drivers
eight sources (e.g. streams originated by this computer)
shows up as a sound card, called Telos Audio Out x. You
can define one of these LW sources as Windows’ Preferred
Sound Playback Device from the Windows™ Sounds and
Multimedia Properties Control Panel as shown here:
Driver Configuration – The Axia IP-Audio driver is
configured for sources and destinations much like the Axia
audio nodes. The driver is configured from the window
shown on the next page.
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The Axia IP-Audio Driver is configured from this window.
This various settings are described below.
Livewire channel instead. In the example, an audio player
that has selected Telos Audio out 01 will put its audio into
Livewire stream channel 1491 and will be available to all
LW devices on the network.
Sources and Destinations – You can see that
the node and source naming and channel idea
is the same as for the hardware nodes. Any
audio channels you want to receive are entered
into the Destinations boxes. If you don’t know
the ID number, you can choose from text lists
instead, by clicking on the Browse button.
Sample Screen From the GPIO Node
The GPIO node is a hardware box with 8 DB-15
connectors, one for each port. Each has 5 inputs and 5
outputs. Here is the home page for this device.
Livewire Network Card – A PC running this
driver may have two network cards, one for
general data and another for audio streams.
The Livewire Network Card entry let’s you
associate Livewire audio with the appropriate
card.
Advanced – Clicking this brings up a screen
that lets you set stream characteristic values.
This is covered in greater detail in the Axia IPAudio Driver manual.
Statistics – This button brings up a screen with
lots of information useful for debugging
network problems.
When you have finished configuration, the Livewire
network looks like a sound card to any Windows
application that uses the standard wavin/out audio
interface. In Windows applications where you normally
select the soundcard you want to use, you will select a
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The GPIO home page. From here you can access the GPIO screen:
GPIO channels may be associated with audio channels or
may be independent. If they are independent, they must not
use the same number as any audio channel – they share the
same “channel space”.
snake application we need not access the nodes’ web pages.
However in most cases we will need to do so, but we will
need to assign an IP address first.
You can monitor the status of each with the indicators at
the top of the page.
A number of items can be programmed from the front panel
of most of the hardware nodes. This is covered in more
detail in the individual manuals. However we will cover
setting the IP address here since you’ll need to assign and
IP address to enter via the web browser, and we’ll cover
that next. Here’s how to assign an IP address to a typical
hardware node, such as the 8x8 Audio Terminals (the GPIO
node must have it’s IP address configured using a BootP
server, see the GPIO Users Manual for details).
HARDWARE NODE CONFIGURATION &
ACCESS
As shown in our examples above, you’ll need to configure
various parameters in the hardware nodes. Some very basic
parameters such as the name and IP address can be
configured from the front panel. In fact, for the basic audio
23
Front Panel Node Configuration
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Configuring Node IP address
Each Livewire™ node must have a unique IP address. The
only exception is when two nodes are connected in the
point-to-point configuration.
by the cursor. Continue until all digits of the
IP address have been entered.
4.
To program the node’s IP address follow these steps:
1.
Starting from the metering screen, press the
<SELECT> button once. The default IP
address is "0.0.0.0", so unless the unit has
previously been programmed, the screen will
show "000.000.000.000".
2.
Press and hold the <ID> button for 4 seconds.
A blinking cursor will appear below the first
digit. Use <SELECT> to change the digit
indicated by the cursor (each press of this
number will increment the displayed digit by
one).
3.
Press the <ID> button to jump to next digit.
Use <SELECT> to change the digit indicated
2.
Hit ID button on GPIO front panel. You will
be prompted for new IP address entry:
3.
Enter new IP address and press ENTER:
Once the changes are complete, press the
<ID> button repeatedly until no cursor is
shown then press <SELECT> to exit.
If you do not wish to save your changes do not
press <SELECT> after reaching the last digit.
After approximately 10 seconds the display will
return to the meter screen and the old settings
will be restored.
The node’s IP address can also be remotely assigned over
the network using a program included with the your node
called BootP (with some nodes this is required). To do so
follow these steps:
1.
Make note of the IP address you have entered so that you
can access the Node using a Web browser, see below. You
24
Start bootps.exe program on any Windows
2000/XP PC. You will see the following screen:
can now continue to assign additional Node IP addresses,
or shut down the Bootp program.
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Accessing a Node via a web browser
To access the built in web server from a computer, the
computer and node must be connected to the same LAN (or
the computer and node can be connected using a “crossover
10/100 Base-T” Ethernet cable). To connect enter the
following in your browser:
http://123.456.789.101 where “123.456.789.101 is the IP
address of the node to be configured.
NOTES:
The IP range (e.g. the first three numbers of the
four numbers of the IP address of the computer
and the node must match, or additional
configuration will be required.
Microsoft Internet Explorer version 5 and later
has been tested with the Livewire™ 8x8
Analog Node. Other browsers may work,
however they have not been tested.
Your browser should now display the login window to
allow you to access the node:
Enter a valid user name and password and click on “OK” to
log in.
The default user name for all Axia nodes is:
“user”
The default password for all Axia nodes is:
<enter>
Once you have logged in you will see the Axia node home
page as shown earlier.
PLUGS & CABLES
Livewire systems use primarily copper cables, but you can
add fiber where it makes sense. We’ll start here with
copper.
An important goal in the design of Livewire was to
simplify installations. One of the ways we do this is to let
you standardize on a single cable type, plugs, patchfields,
etc. This is consistent with the modern way of thinking
about cabling in office buildings where a common type can
serve different applications. You can use the same
connectors and cables for everything in your plant. And for
big new installations, outside contractors can install and
test the wiring infrastructure for everything. In fact this is
one reason why we suggest that Broadcast Engineers
should become familiar with the relevant standards such as
EIA/TIA-568-A & B.
The 100BASE-T Ethernet we need for most Livewire
devices requires RJ-45 8-pin modular plugs and jacks. So,
we’ve standardized on RJ-45s for balanced high-level
analog and AES connections as well. There are a lot of
connectors being used for analog audio these days, so why
did we go this route? The reasons are cost, density,
compatibility, and convenience. RJ-45 sockets and plugs
are a lot cheaper than other choices, both for us at the
manufacturing level and for you at the time of installation.
Density is an important advantage: We can get only a few
XLRs across the rear panel of a 1U rack box and we need
two of them for each stereo connection. Our basic nodes
would have to be 2U to have the same channel capacity as
we have now with 1U nodes. A single RJ can do both
channels on one jack and we can fit dozens of them on a
1U box. XLRs and DBs need to be soldered, and shells
assembled, etc. Molexes need a separate crimp for each
wire and are not standard. RJ crimping is convenient
procedure compared to the others. And you will already
have the plugs, cables, and tools at hand.
The tables below summarize the cable types that could be
used in a LW system and their applications:
Description
Cable
Analog Audio, balanced, highlevel
Usually shielded Cat. 5, but unshielded with
care
AES3 Digital Audio
Usually shielded or unshielded Cat. 5 or 5e
Non-Ethernet Cabling Relevant to the LW Systems
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Name
Description
Max
Length
Where Used
10BASE-T
10Mbps on 2 pairs Cat. 3
copper. Obsolete for new
installations.
100Mbps on 2-pairs Cat 5
copper (Cat. 6 recommended
for LW to add a safety
margin).
Most
common
Ethernet media.
100Mbps on fiber
‰ multi-mode
‰ single-mode
1Gigabit on 4 pairs Cat 5e
copper (Cat. 6 recommended
for LW to add a safety
margin).
1 Gigabit on short wavelength
fiber, multi-mode
1 Gigabit on long wavelength
fiber, single-mode
100m
Not used
100m
LW Nodes, PCs
100BASE-TX
100BASE-FX
1000BASE-T
1000BASESX
1000BASE-LX
2km
20km
100m
220550m
5km
LW nodes with ext.
media converters
Studio Engine to
switch,
PCs,
switch-to-switch
Switch-to-switch
Switch-to-switch
Ethernet Cabling Relevant to Livewire Systems
Cat 5 for Audio?
Using Cat. 5 “digital cable” for audio may seem strange at
first, but it does make sense. The low capacitance and tight
twisting requirements necessary for high-speed networks
are good for analog and AES audio as well. Because you
have a single cable and connector type for everything in
your facility, as your studios evolve, the same cable that
was once used for analog may be used for AES, LW digital
audio, general Ethernet data, or whatever else might come
along.
Does this work in the real-world? Sure it does – as
demonstrated in the many installations that have been done
using the Radio Systems “Studio Hub” product family. We
use the Studio Hub 2 format for our connectors by the way,
to allow convenient use of their system by Livewire users.
More on this below.
Ethernet 100BASE-TX
Livewire uses 100BASE-TX copper wiring with RJ-45
style plugs and jacks for connections from audio nodes to
switches.
26
100BASE-T with the final X being dropped is oftentimes
used as shorthand for 100BASE-TX. The 100BASE-T
designation officially refers to both copper and fiber
formats at 100Mbps rate, with TX the specific designation
for copper. The abbreviation in popular use arises from the
fact that the copper formats on either side are called
10BASE-T and 1000BASE-T. And that the -T is supposed to
stand for “twisted pair” – except here for some reason.
Leave it to standards bodies to be non-standard.
You must use Category 5 cable and accessories or better.
For any new installation, we strongly recommend Cat 6
because you will have a better performance margin and you
will be ready for 1000BASE-T. Cat. 6 is not much more
expensive that 5e and it has much better performance,
particularly when a run has a lot of bends that could disturb
the pair relationships within the cable jacket, or has many
punch blocks and/or patch cables.
Pin numbering, jacks, cables, and color codes
Modular wall jacks are normally installed so that the pins
are at the top of the cavity. This helps to protect the
contacts from water when baseboards are mopped and from
dust. When the jack is oriented in this position, looking into
FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
the jack with the contact pins at the top, the pins are
numbered 1 to 8 from left to right. Some jacks may not
have all pin positions populated, but the numbering would
still begin with the first position. For instance, the "RJ-11"
style jack is a 6-position 4-pin jack. Therefore it has pins 23-4-5 and pins 1&6 are usually absent.
You should take care not to plug an RJ-11 into an RJ-45
jack. It will work to connect the pairs that are supported in
the plug, but the plastic part on both sides will push the
outer pins on the jack up, and they may not make good
connection when the jack is again used for an RJ-45 plug.
cables. The T568A color code is “preferred” by TIA/EIA
but is not so usual in the USA for business installations.
The TIA/EIA T568B color code cable specification has the
same electrical connections, but has the green and orange
pairs swapped. This is also known as the AT&T 258A
wiring sequence and has been widely used in the USA. It is
used by the Radio Systems Studio Hub system for analog
and AES connections, so we recommend it for all new
installations.
Either sequence will work just fine if you have it on both
ends. In either case, you have a cable with 4 pairs wired
straight through, both ends wired identically.
Ethernet uses 8-position 8-pin modular connectors.
TIA/EIA specifies two standards for wiring RJ-45 style
TIA/EIA-588-A T568B RJ-45 Wiring Sequence
Depending on the cable manufacturer, the color conductor
of each pair may or may not have a white stripe. The other
half of the pair is usually white with a colored stripe, but
sometimes can be only white. Both formats are shown in
table form here:
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TIA/EIA-568-A T568 Wiring Standard
(preferred for LW)
standard, which has the same two pinout standards within.
Pin
TIA/EIA-568-A T568 Wiring Standard
(Optional)
Shield
Something to watch out for: The old telephone USOC
wiring code has the pairs in the wrong place, with the
wiring in simple one-pair-after-the-other sequence. You’ll
have a split-pair if you have this sequence – and a lot of
crosstalk and interference problems. You need to be sure
that the pairs correspond to Ethernet’s requirements.
Why does Ethernet have such a strange wiring sequence?
Because the center two pins, 4 & 5, are where telephone
voice circuits are wired. The designers of the standard
thought that some people would want to use a single cable
Pin
Shield
Function
Function
Color
Protective ground
1
Transmit +
White/Orange
2
Transmit -
Orange
3
Receive +
White/Green
4
N/C
Blue
5
N/C
White/Blue
6
Receive -
Green
7
N/C
White/Brown
8
N/C
Brown
Couldn’t these guys have been a bit less confusing?
Color
Protective ground
Crossover 100BASE-T Ethernet Cable
1
Transmit +
White/Green
2
Transmit -
Green
3
Receive +
White/Orange
4
N/C
Blue
5
N/C
White/Blue
6
Receive -
Orange
7
N/C
White/Brown
8
N/C
Brown
Sometimes you want to connect two LW nodes directly
together without a switch, such as for testing or when you
want to make a snake. Or you might want to connect a node
directly to a PC for initial configuration or as a sound card.
In this case, the Transmit of one device must be connected
to the Receive of the other.
For this, you'll need the special crossover cable wired as
shown below.
for voice and data, so they kept Ethernet clear of the
telephone pins. There is also this: if a user plugs his PC’s
network connection into the phone jack, he doesn’t blast
the network card with ringing voltage.
Even though you have two unused pairs in the standard Cat
5 4-pair cable, you should not share the cable with any
other service since 100BASE-TX was not designed to
withstand additional signals in the cable. The reason for the
extra pairs is that you might want to upgrade to
1000BASE-T or some other yet-to-be-introduced service
later.
Finally, on this topic, something really nuts… The overall
cabling specifications standard and document from
TIA/EIA was called TIA/EIA-568-A Commercial Building
Telecommunications Standard. Within this were the T568A
and T568B pinout standards. Note the dashes and lack of
same. Now there is a new TIA/EIA-568-B overall
28
Pin
Color
Pin
1
White/Green
3
2
Green
6
3
White/Orange
1
4
Blue
Not
Used
5
White/Blue
Not
Used
6
Orange
2
7
White/Brown
Not
Used
8
Brown
Not
Used
100Base-T Crossover Cable
Many modern Ethernet switches have ports that
automatically sense the need for a crossover function and
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configure their ports appropriately. So when you are
connecting ports from two switches, you probably will not
have to use a crossover cable.
1000BASE-T Gigabit Copper
We use 1000BASE-T to connect studio processing engines
to switches. If your LW network consists of multiple
switches, you will also want to use it to link switches to
each other.
1000BASE-T works with Cat. 5e, but again we recommend
Cat. 6. It uses the same RJ-45s as 100BASE-TX, but needs
all four pairs. Either the T568A or T568B wiring sequence
will work, but you will have to be sure all four pairs are
wired through and working. Again here, the advantage of
choosing one scheme and using it for everything (e.g.
T568B on Cat. 6) is obvious.
Nevertheless, 1000BASE-T is more sensitive to certain
performance issues owing to the hybrids and twice the
number of signals in a 4-pair cable. That’s why Cat. 5e or
Cat. 6 is recommended. And you should always use highquality factory-made patch cables.
You shouldn’t ever need a 1000BASE-T crossover cable,
but who knows? Anyway, a universal crossover cable can
be made (or better, purchased) that works for both 100 and
1000BASE-T.
Pin
Color
Pin
1
White/Green
3
2
Green
6
3
White/Orange
1
4
Blue
7
Pin
Color
Function
5
White/Blue
8
1
White/Orange
BI_DA+
6
Orange
2
2
Orange
BI_DA-
7
White/Brown
4
3
White/Green
BI_DB+
8
Brown
5
4
Blue
BI_DC+
5
White/Blue
BI_DC-
6
Green
BI_DB-
7
White/Brown
BI_DD+
8
Brown
BI_DD-
Universal 1000Base-T/100Base-T
Crossover Cable
Audio connections
1000Base-T Signal Designations
There are no separate send and receive pairs for
1000BASE-T. Each pair both sends and receives with a
hybrid at the ends to separate the two signal directions.
Thus, there are effectively four paths each way. The
signaling rate for 1000BASE-T is the same as for
100BASE-T – which is why it can be run over the same
cable.
29
We use the pin-outs established by the Radio Systems
Studio Hub+ wiring system, which has become a de-facto
standard. Since we follow this standard, Studio Hub wiring
components may be used for the analog and AES part of
LW installations. Radio Systems offers an extensive line of
single “dongle” and multi-pair harness cables pre-wired to
connect to a variety of popular studio gear. They also make
balanced-to-unbalanced, AES to S/PDIF, and AES to
TOSLINK adapters, headphone amps, etc.
We do stay with traditional XLRs for microphone inputs,
however. We don’t think RJs would be sufficiently reliable
for such low signal levels. And we sometimes have parallel
XLRs for your convenience when panel space allows us to
do it, such as with the LW Router Selector node.
FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
Router Selector Node Rear Panel – Both XLR and RJ-45 connectors are
present for inputs and outputs.
While unbalanced connections can be used be very short
runs with unshared and shielded cables, balanced
connections are essential for anything over a few feet in
length. The input stage of any attached analog equipment
needs to have good CMRR (Common Mode Rejection
Ratio) and high-frequency filtering in order for balanced
connections to effectively cancel crosstalk and interference.
With 60dB CMRR, Telos LW node inputs are designed to
be no trouble in this respect.
The pinouts for the RJ-45 style audio connectors is shown
on the next page:
30
FOUR: NUTS & BOLTS: MAKING LIVEWIRE PLAY
Pin
Function
Color
Shield
Protective
ground
White/Slate &
Slate/White*
1
L+
White/Orange
2
L-
Orange
3
R+
White/Green
4
N/C (GND)**
Blue
5
N/C
White/Blue
6
R -
Green
7
N/C (15-)**
White/Brown
8
N/C (15+)**
Brown
Nevertheless, you’ll probably find yourself installing your
own plugs at some point, so here is some advice:
If you are making a patch cord, use strandedconductor cable. Solid is likely to break after
some time being plugged and unplugged.
However solid cable should be used for
backbone wiring as it has less loss.
Be sure you are using plugs designed for the
cable type you are using. Plugs for solid and
stranded wires are not the same.
Plugs from different manufacturers may have
slightly different forms. Be sure your crimp
tool correctly fits. In particular, the crimper
made by AMP will only work with AMP
plugs. Buy a high-quality crimping tool.
* Optional
** Used to power “spoke” devices such as
balanced-to-unbalanced converters. LW
nodes do not supply this voltage, but
external supplies can be used when needed.
Telos/Radio Systems Standard for Analog
and AES wiring on RJ-45s
Off-the-shelf or homemade RJ-45 cables together with the
adapter dongles connect the nodes to audio equipment. It
would be possible to wire a sophisticated studio full of gear
without ever soldering an audio connector.
The outer jacket should be cut back to about 12
mm (.5 inch) of the wire tips. Check to be sure
there are no nicks in the wires’ insulation
where you cut the jacket (an appropriate tool
can be purchased to permit you to do so rapidly
without fear of damaging the inner insulation).
Slide all of the conductors all the way into the
connector so that they come to a stop at the
inside front of the connector shell. Check by
looking through the connector front that all the
wires are in correct position.
After crimping, check that the cable strain
relief block is properly clamping the outer
cable jacket.
When checking the cable either with a tester or
a real device, wiggle the cable around near the
plug to be sure that connector is working
reliably with stress.
You’ll probably need a couple of times to get it right the
first time, but after some experience, it will start getting
pretty easy. Certain RJ connectors include a small carrier
that the wires can be fed into first, and then slid into the
connector itself. These are recommended as the speed
installation and improved accuracy.
RJ to XLR Adapter
Installing RJ-45s
It would be possible to build a sophisticated multi-studio
facility without ever wiring a single RJ-45 plug – you
would use modular patch fields or jacks at each end of the
long “horizontal” cable with punch-down 110-style
connections. Then factory-made patch cords would be used
to get from the switch or LW node to the patch jack. And
this might not be a bad idea!
31
FIVE: DESIGNING & BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
5
Designing and building your Livewire Ethernet
system
As with analog audio installations, Livewire set-ups range from the very simple to
complex facility-wide installations with hundreds of ports. This section is aimed primarily
at those who will be building large systems.
CABLING
Category 3
Ethernet is balanced and transformer coupled, so has quite
good resistance to interference and has no problem with
ground loops. However, frequencies ranging to tens of
megahertz are being used, so care must nevertheless be
taken.
Charles Spurgeon in Ethernet: The Definitive Guide says
that you should consider wiring to be the essential skeleton
for your network installation. He goes on to point out that
network cabling skeletons are often hidden in the timehonored place for skeletons: a closet. Rim shot.
In the bad old days, wiring was specific to the task – and
often to the vendor. Each telephone, network, and audio
had its own cable type and wiring protocols. The idea at
standards bodies like the Telecommunications Industry
Association (TIA) and the Electronic Industries Association
(EIA) in the USA is to define classes or categories of
cables and accessories that can be used for all applications
specified for that class. With this, you have a vendorindependent way to wire buildings and facilities so that
services from many vendors can be supported over time
without replacing cabling and connectors. The name for
this concept is structured wiring.
The long cables that go from equipment rooms to node
locations are called horizontal cables. They usually
terminate in RJ-45s, either in patchfields or on wall jacks.
Patchcords with RJ-45s at each end complete the system,
connecting the nodes and central equipment to the jacks.
Twisted-pair Cable Categories
Cable categories are key to the structured wiring concept.
The cabling specifications for the various categories are in
the TIA/EIA-568-A (and B) Commercial Building
Telecommunications Cabling Standard. The following
categories are defined:
32
These are used only for telephone and Ethernet 10BASE-T,
so are not useful for Livewire installations.
Category 5
This designation applies to 100 ohm unshielded twisted
pair cables and associated connecting hardware whose
transmission characteristics are specified up to 100MHz.
Cat 5 cables are today’s most common because they
support Ethernet 100BASE-TX.
Category 5e
This is enhanced Category 5 cable. The main application is
for gigabit 1000BASE-T. While Cat 5 is acceptable for
1000BASE-T, 5e is officially preferred.
Category 6
We recommend Cat 6 for all new LW installations. Cat 6
provides significantly higher performance that Cat 5e. The
main difference is that this cable has a plastic pair separator
inside that holds the wires in correct relation to each other.
This is what makes Cat 6 larger in diameter than Cat 5
cables.
Belden has a Cat 6 cable called Mediatwist that looks very
interesting. This cable has a half-moon shape and the pairs
are tightly held in molded channels. This product also has
the two wires in each pair glued together so that the twist
characteristic is fixed and stable regardless of
manufacturing tolerances, cable flexing, etc.
The most significant difference between cables from each
category is the number of twists per foot and the tightness
with which the twists and the spacing of the pairs to each
other are controlled. The wire pairs in a voice-grade
Category 3 cable usually have two twists per foot, and you
may not even notice the twists unless you peel back quite a
lot of the outer insulation. Category 5 is tightly twisted,
something like 20 per foot. This results in superior
crosstalk performance at higher frequencies.
FIVE: DESIGNING AND BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
Another characteristic of twisted-pair cables is the type of
insulation used on the wires and the cable jacket. “Plenum
rated” cables are more stable with changing temperatures
due to their using Teflon rather than PVC insulation.
Plenum rated cables are required in air handling spaces in
order to meet fire regulations. Teflon produces less smoke
and heat in the case of a fire than PVC and does not support
the spread of flames.
Special Care for Ethernet Audio
“Normal” data over Ethernet is usually TCP/IP protocol.
As discussed later, TCP has a re-transmission mechanism
that detects errors and fixes them by requesting and
obtaining replacement packets when one has been received
with a defect. This mechanism is not used for audio – it
can’t be when you need low delay and multiple receivers.
So it could be possible that a network could apparently be
OK with computer data, yet exhibit errors with audio
because TCP is covering-up underlying problems.
A particular concern is to prevent impedance reflections at
cable termination points and to not disturb too much the
position of the wires inside the cable. Here are some
specific recommendations:
Use the minimum number of terminations and
patches that will support your application.
Avoid stretching the cable. The official
recommendation is to use less than 25 lbs.
pulling pressure.
Avoid close proximity to power cables and
equipment that generate significant magnetic
fields. The official recommendation is
minimum 6.4 cm (2.5 inches) from power
cables when the Cat 5 is either inside a conduit
or shielded. Care should be taken also with
fluorescent lighting fixtures, motors and
transformers.
The pins on RJ-45 plugs are gold plated. But
not all connectors are. For maximum
reliability, use connectors with 50m gold
plating.
To Shield or Not to Shield
Unless you are in a high RF environment or you intend to
run your network cables close to audio cables with
equipment that has poor balancing on the inputs, you
should be able to use unshielded twisted pair for your
Ethernet connections. If you decide to shield, the usual
procedure to attach it only at one end applies in order to
prevent ground loops.
Unbalanced Connections
Use patch cables, connectors, and other
accessories rated at the same or higher
category level as the cable you are using.
Generally, your best bet is to buy pre-made
patch cables to both save money and time as
well as assure reliability.
The Livewire nodes have very good common mode
rejection. This coupled with the highly twisted cat. ?? cable
works extremely well in the balanced pro-audio
environment. Unbalanced interconnections are problematic
however and should be avoided for the usual reasons. If
you need to interconnect a Livewire node to unbalanced
gear we strongly recommend that you use a balanced to
unbalanced buffer amplifier or transformer located as close
as practical to the unbalanced equipment. There are a
number of commercial off-the shelf options to accomplish
this. In particular the Radio Systems Studio Hub Matchjack
series (pictured below) offer plug and play compatibility
between the RJ-45 balanced and consumer unbalanced
worlds.
Keep a wire pair’s twist intact to as close as
possible to any termination point. For Category
5, this should be to within 1.3 cm (.5 inch).
Maintain the required minimum bending
radius. For a 4-pair 0.5 cm (.2 inches) diameter
cable, the minimum bend radius is 4 times the
diameter, or about 2 cm (.8 inches).
Minimize jacket twisting and compression.
Install cable ties loosely and use Velcro
fasteners that leave a little space for the cable
bundle to move around. Do not staple the cable
to backboards. If you tightly compress the
jacket, you will disturb the twists inside and
the relationship of one pair to another, which
could cause crosstalk.
Do not overfill conduits.
33
FIVE: DESIGNING AND BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
Paladin 3570 punch tool for
110-style IDC connectors
Wall Jacks
More than Four Pairs in a Cable
Back in the 10BASE-T days, it was usual to have phonetype 25-pair cables carrying data signals. But the standards
for Cat 5 and better call for individual cables for each
connection due to the possibility of multiple disturber near
end crosstalk – or many signals adding up to create
combined crosstalk at too high a level.
Again 110-style IDC connectors terminate the cable. Then
these wired-up “Keystone” RJ-45 jacks are pushed into a
hole in the wall plate to complete the job. The diagram on
the next page shows the simple steps involved in
terminating these.
On the other hand, Belden has some papers on their website
proposing that their finest cable, Mediatwist, would support
even 100BASE-T and analog audio inside a shared sheath.
Nevertheless, they offer the cable in only 4-pair versions at
this time.
Patch Panels
Patch panels come in versions for rack or wall mount and
with varying numbers of jacks. Cat 5/5e cables are punched
down at the rear into 110-style insulation displacement
connectors using a tool very similar to the one that is used
with traditional “66 blocks.”
Cat 6 Jacks
Cat 6 cables and their accessories need more care to
maintain the twists as close as possible to the end.
Cat 5e RJ-45 Patch Panels,
in Rack and Wall-mount
Versions
Above is a high-end Cat 6 jack assembly ready for
installation into either a rack-mounted patch-field or a wall
jack. This is a shielded version, so the shell is made from
34
FIVE: DESIGNING AND BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
metal to maintain the shield all the way to the edge of the
jack.
Assembling one of these can be done in a minute or two.
First the wires are put into the slots and the ends are
trimmed. Then this piece and the front part of the jack are
pushed together. The shell is then placed over these pieces
and pushed over them, which draws the wires into the
insulation displacement forks and locks everything
together.
ARCHITECTURE OPTIONS
There are a lot of ways to build a Livewire network. For
many people a simple one-switch layout will be perfectly
sufficient. Others will want to build sophisticated networks
to support multiple studios and perhaps hundreds of audio
channels. Fortunately, Ethernet scales easily– so too your
LW installation.
Here are some examples and ideas to get you started.
Next, you can see the components that make up the jack
disassembled. This is now the non-shielded version, so the
shell is plastic, the blue piece in the photo below.
Here is a closer look at the part that holds the wires:
Simple One-Switch Network
Common 1U switches can have as many as 48 ports. That
is a lot of audio! Here’s a setup that supports an on-air
studio and a production studio.
The switch is a 24-port 100BASE-TX + 2-port 1000BASET/GBIC fiber version.
There is the microphone version of the LW node in the onair studio and the 8x8 line version in the central rack. The
production studio connects with a Router version node,
which has one send channel and a selectable receive
channel.
The Surface power supply includes plenty of GPIOs for
Production Studio
Central Equipment Rack
On-Air Main Studio
Example of a single-studio Livewire Routing/Mixing Solution
35
FIVE: DESIGNING & BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
starting CD players, lighting on-air lamps, remote mic onoff, etc.
initially attach for now. But soon this equipment and others
will have direct LW connection ports.
The Studio Engine connects with a 1000BASE-T copper
link to one of the two 1000BASE-T ports.
You could expand this to two Surfaces and Engines to
support two studios since the switch has two 1000BASE-T
ports. Or you could substitute an all 1000BASE-T switch to
support as many studios as you want.
The delivery PC connects directly to the audio network
with the Livewire PC Suite software. Control for it may be
directly over the network or could be with a hardware
parallel connection. Servers and additional PCs can be
connected to the switch.
Peripherals such as codecs, telephone systems, and satellite
receivers may be connected into the network wherever it is
convenient. In the diagram, the Zephyr codec is shown
attached to a LW node and that is how most equipment will
In the next photo you can see a typical set-up with a node,
engine, switch, and patchbay. The patchbay is being used to
terminate cables from remote locations before being
connected to the switch with short patch jumpers, while the
node and engine connect directly using longer patch cords.
Using a patchbay and off-the-shelf patch cords in this
fashion minimize the need to install RJ-45 plugs.
Photo of central hub of the Livewire System at WEGL, Auburn University.
Daisy Chained Multiple-Switch Network
While one switch can support multiple studios, you would
have a single point of failure. Here’s another approach that
gives each studio its own switch. The example below uses
three switches, one for each studio group. This layout style
could easily be expanded to any number of switches and
studios.
36
The switches are connected together so that audio sources
are shared. A 1000BASE-T link between the switches
allows hundreds of audio channels to flow from one group
to another. With more than two switches you could have a
“circular backbone” with redundant spanning-tree links
(described below) between the switches.
Peripherals that are used in common such as codecs could
be plugged to any of the studio switches, or there could be
a separate switch to pick up such feeds.
FIVE: DESIGNING AND BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
Daisy-chained Ethernet Switches Support Multiple Studios
Hierarchical Multiple-Switch Network
This is a layout that could support a very large facility. A
gigabit switch is at the center and 100/1000 switches are
used at the edge with one for each studio or logical group.
A Router Selector node is kept in the central equipment
room for test and monitoring. Additional nodes could link
audio from non-Livewire studios.
While we could plug the Engines into the central switch, if
A Two-level Hierarchical Network for Support of Larger Studio Facilities.
37
FIVE: DESIGNING & BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
we keep them coupled to the individual studio switches,
there is no single point of failure for any studio.
they also can solve problems that might crop up in difficult
locations with copper cables.
Gigabit links are used between the edge switches and the
center. These could be copper or fiber with a suitable
switch.
External media converters can be very simply plugged to
LW node and switch 100BASE-T ports to convert copper
connections to fiber.
The physical location of the switches is a matter of taste
and trade-off. Putting the edge switches near the studios
saves cable runs, but locating all the gear in a central room
simplifies engineering activities.
This unit from Allied-Telesyn uses 100Mbps ST
multimode fiber for up to 2km range. Units supporting SC
single mode fiber can extend up to 75km.
As this is written, an appropriate switch for the center costs
$2k and the studio switches $700. So this is a quite
reasonable-cost option that provides a lot of power,
flexibility, and expandability. Dozens of studios and
thousands of audio channels are possible.
Options for Redundancy
Ethernet switching has a built-in scheme for redundancy,
called spanning-tree and standardized as 802.1D. A newer
variant is called fast spanning-tree. Switches with
spanning-tree enabled exchange information with each
other about the topology of the overall network. You can
have redundant backup links that are automatically
activated in the case that a main link has failed. Depending
on the switch and layout, it could take as little as a second
or as much as a half-minute for a redundant link to be
connected.
Link aggregation (sometimes called port trunking) is
another method. With spanning-tree, even if you have two
links between two switches, only one of them at a time will
be active. But, it’s often better to have both active
simultaneously because you get twice the bandwidth during
normal operation and instantaneous backup should one fail.
The link aggregation standard is 802.3ad. To use it, you
usually have to specifically enable it on your switch.
Incidentally, this is supported on some PC network
interface cards intended for servers, so its not only for
switch-switch links.
Most Ethernet switches offer a redundant power supply
option.
We’ve been talking here about automatic on-line
redundancy, but there is also manual swap-out as a
reasonable option. Because RJ-45s are so easy to unplug
and re-plug and because switches and other Livewire
components are much cheaper than traditional alternatives,
you can have spare units on the shelf for fast substitution.
FIBER
Fiber optic links can extend the range of Ethernet. Because
they are not subject to crosstalk and magnetic interference,
38
Modern Ethernet switches often have the option to plug a
media converter directly into a special socket so that fiber
may easily be connected from switch to switch. This is
useful to make high capacity backbone links without any
external boxes.
Here is a typical case. There are two “uplink” ports for
1000BASE-T copper paired with SFP/mini-GBIC sockets.
When the fiber adapters are plugged-in, the copper ports
are automatically disabled. In the photo, there are no fiber
adapters installed into the Mini-GBIC slots and the “T”
LED is illuminated to show that the copper jacks are active.
FIVE: DESIGNING AND BUILDING YOUR LIVEWIRE ETHERNET SYSTEM
The devices above are typical modern media adapters in the
“SFP/mini-GBIC” size – about the same in width and
height as an RJ-45 jack. The one on the left is for
1000BASE-SX and the one on the right is for 1000BASELX. Generally, SX cables have a range to 500 meters, LX
to 5km, and LH to 70km.
You probably expect something with “multi” in the name to
have more capability than the same thing designated
“single”. But this is not the case with fiber optics: singlemode cables are better and more expensive than multimode. These names refer to how light is contained within
the fiber. Single-mode strands are smaller and more
carefully control the light so that it doesn’t bounce around
so much inside, thus are more efficient and permit longer
ranges.
RADIO LINKS
There are Ethernet radios with surprisingly high bandwidth
– and at surprisingly low cost. Not all units are capable of
achieving true Ethernet performance in terms of error rates,
so some caution is in order. Most of these operate in the
unlicensed ISM bands, but with modern spread-spectrum
technology and elevated directional antennas, interference
doesn’t look to present much problem. Licensed radios
following the new IEEE 802.16 “Wimax” standard are
starting to appear.
Bitrates range to 48 Mbps and distance to 25 miles
depending on power level, antenna, and terrain.
For studio-to-transmitter link, remote pick-up, and studioto-studio applications, these offer multiple channels of
uncompressed audio, two-way transmission, and the ability
to multiplex VoIP telephone, remote control, and general
data. When audio and general data are mixed, the Ethernet
switch provides the prioritization function. As with all LW
elements, you can check them with a web browser on a
network-attached PC.
We are studying these radio systems now. We will have a
number of them in our laboratory and will test for Livewire
compatibility and general performance. You should
consider these like the Ethernet switch – please let us
advise you on the best choice and help with your
application. If you are thinking about this option, contact us
for our latest advice.
DESIGNING FOR SECURITY
You will have 100% security if you keep the Livewire
system completely isolated from any other network, local
or wide area. Those very concerned with protecting the
studio system may well want to take this approach.
39
But there are advantages to sharing with or linking to an
office network. You can configure and monitor the system
from any connected PC and audio can be monitored on any
desktop. In this case, separate switches or VLANs
(described later) can be used to provide isolation. An IP
router passes only the correct packets from one to the other
and thus provides a firewall function.
The next step up in connectivity would be to have a
network linking co-owned or otherwise affiliated stations.
In this case, a network engineer is probably in the picture
and he can take the necessary steps to protect your audio.
Connection to the public Internet brings the advantage that
you can monitor and configure from a remote site, but you
now have much risk from unwanted intruders, viruses, etc.
A qualified network engineer should be consulted to be
sure you have an appropriate firewall and other protections
in place.
In LW nodes, web and Telnet access are password
protected to provide some measure of security. But we do
not use exotic techniques like SSL (Secure Sockets Layer),
so please understand that our devices were not designed to
be exposed to the public internet without external
protection.
SIX: THE ETHERNET SWITCH
6
The Ethernet switch
This is what makes it all possible. Here are some details on requirements for a capable
Livewire switch.
Livewire uses only network Layer 2 functions, with the one
exception: IGMP snooping, which almost all managed
Layer 2 switches have.
IGMP control for multicast. Traffic must be
under IGMP control – strictly no flooding of
ports with multicasts under any circumstances.
Routers and so-called “Layer 3 switches” offer additional
functionality because they operate at both the Ethernet and
IP levels. They may be used for LW systems if they meet
the timing and backplane requirements. These may become
more interesting in the future as their cost continues to fall,
but for now basic Layer 2 switches make more sense
because they are both simpler and cheaper.
Support for both port-based and tagged-framebased VLAN. This latter is the IEEE 802.1Q
standard and is what allows the switch to
determine priority on a frame-by-frame basis.
Port-based VLAN can also be useful: it lets
you “hardwire” a particular port for a single
VLAN, useful to be 100% sure an office PC
can’t get onto the LW audio VLAN.
LIVEWIRE ETHERNET SWITCH
REQUIREMENTS:
If you will use a separate VLAN for Livewire,
the switch needs to have an “IGMP querier” on
each one, which also means that you can assign
an individual IP number to each VLAN. This is
a rare capability and its absence disqualifies
many switches.
Sufficient backplane bandwidth, preferably
fully “non-blocking” to handle all ports at full
capacity.
Sufficient frame forwarding rate. LW
Livestreams have small packets at a fast rate.
The switch needs to handle this.
Management. This is how you get remote
monitoring.
Correct handling of IEEE 802.1p/Q frame
prioritization. LW audio frames must be given
priority without too much delay or jitter. The
IEEE standard specifies 8 levels of priority, but
few switches support all the levels. Many
support only 2 or 4, lumping some of the
incoming levels together. We recommend 4 as
the minimum for a LW system.
The practical bottom line is that you should use a switch
that has been selected and tested by Telos unless you have
the capability and inclination to carefully study data sheets
and verify performance yourself. When we check a switch,
we have a laboratory setup that lets us send frames on a
number of ports at a high rate, while switching channels
on/off with IGMP, etc. We have a lot of experience with
different switches and know what to look for. Using a
recommended switch will also help you when you need
customer support because we will be familiar with it, will
have one we can plug into a test setup to try to reproduce
your problem, etc.
Support for multicast, with sufficient filter
entry capacity to cover the total number of
audio streams you need. This latter is
important, because when the filter capacity is
exhausted, switches forward multicast packets
to all ports, subscribed or not. This would
cause serious problems. You will probably
want 256 minimum.
SOME SWITCHES WE LIKE
As this is written in August 2004, anyway. There are new
switches introduced everyday it seems, with ever increasing
performance and falling prices. Please check our web site
for the latest recommendations.
40
SIX: THE ETHERNET SWITCH
HP Procurve 2650 Switch
The Procurve 2650 switch has everything we need. The
color even matches our Livewire components! 48
10/100BASE-T ports + 2 1000Mbps copper/fiber ports.
Includes a built-in simple router and IGMP Queriers on
every VLAN. There is a 26-port version also, the model
2626. About $700 for the latter. Also comes in a poweredport version that can be used with VoIP phones.
HP Procurve 2828 Switch
Though it looks much like the first one, the 2828 switch has
44 10/100/1000BASE-T ports and 4 1000Mbps ports that
can be used either with copper or fiber with SFP/miniGBIC adapters. The 2824 is a 24-port version. All the
features we need. About $2k.
SWITCH CONFIGURATION
Most switches offer three connection options: an RS-232
console port, Telnet over Ethernet, and web over Ethernet.
For Telos-supported switches, we offer a configuration
“cheat-sheet” that gives you the basics. We also will be
happy to pre-configure your switch and test it at Telos
before shipping it to you. Since the above HP switches are
what we are currently recommending to customers the
correct configuration information is include below.
switches web browser based user interface to configure
certain basic features of the device.
A more universal way is to use the serial cable supplied
with the switch to connect the switch’s console port to a
PC. Then, you can access it using a text terminal, such as
HyperTerminal. This method allows access to all
parameters that must be configured for full LW support.
The switch will auto detect serial communication
parameters. Using the console port gives you an access to
all the features while the WEB user interface presents only
the basic. The following instructions assume you are using
the console port command line interface (CLI). See the
ProCurve switch manual for details on connecting to the
console CLI.
Turn on IGMP – IP address must be assigned to the
switch.
Configuring the HP Procurve 2650 Switch
This switch, like most, requires configuration before being
used with the Livewire system. Switches purchased directly
from Telos have been pre-configured and this will be
indicated on the box. New switches are configured to
obtain IP address from DHCP server. If your local network
includes a DHCP server you will be able to use the
You can do this configuration from the console (CLI)
interface, only.
Use supplied serial cable to connect to the switch RS-232
port. Once you have established communications type,
“setup” to start the basic configuration screen.
Configure IP Address as shown below:
41
SIX: THE ETHERNET SWITCH
than 1, do the VLAN configuration as described in
following sections, first.
The above will configure the IP address for the
default VLAN. Now Hit “Save” and exit the
configuration screen.
Save configuration to the Flash
Enable IGMP querier on all VLANs
You can do this configuration from the console (CLI)
interface or the WEB. See below for what to enter (you will
be entering the information in italics)
HP ProCurve Switch 2626(config)# vlan 1
HP ProCurve Switch 2626(vlan-1)# ip igmp
HP ProCurve Switch 2626(vlan-1)# show ip igmp
IGMP Fast-Leave feature
Enabling IGMP Fast-Leave on Livewire ports helps to
immediately stop multicast flooding when Livewire device
unsubscribe from a channel.
The syntax for this command is following:
setmib hpSwitchIgmpPortForcedLeaveState.<vlan>.<port> -i 1
Example (VLAN=1, Port=3):
HP ProCurve Switch 2626# setmib
hpSwitchIgmpPortForcedLeaveState.1.3 -i 1
hpSwitchIgmpPortForcedLeaveState.1.3 = 1
HP ProCurve Switch 2626#
This command should be repeated for all the Livewire
ports. If you decide to put Livewire on different VLAN
42
After the entire configuration is done, you need to save it to
permanent Flash memory in the switch. To do so enter:
HP ProCurve Switch 2626# write memory
SIX: THE ETHERNET SWITCH
NOTES:
43
SEVEN: TESTING, 1-2-3…
7
Testing, 1-2-3…
There are tens of thousands of people installing Ethernet networks every day, and many
millions of working installations. So there are a lot of tools to help you. Livewire
equipment have a lot of diagnostic functions built-in as well.
GENERAL ETHERNET TROUBLESHOOTING
Switch Diagnostics
Ethernet is a mature technology, with years of proven
reliable service. You are not very likely to see problems in
the fundamental technology if you follow the network
wiring and layout recommendations.
Ethernet switches have many diagnostic tools, ranging from
front panel LEDs to sophisticated software monitoring
functions. See the switch manual and software description
for details for your unit.
Prevention
Simple Network Management Protocol (SNMP) and
Remote MONitoring (RMON) are part of the TCP/IP
internet suite. (RMON is built on SNMP so they are closely
related.) They offer a way to probe and monitor network
equipment operation in a vendor-independent way. For
example, an Ethernet port has a standard way of
communicating its status that is supposed to be used by all
products with these ports.
The best way to avoid downtime is to build the network
well in the first place. Use high-grade cables, good quality
factory-made patch cords, etc. And be careful with the
punchdown and plug installation.
More on the topic of patch cords. If you really must make
your own, they should be built with stranded wire cables.
Solid conductors are likely to crack when flexed a lot,
usually right at the RJ-45 plug. From this you can get
intermittents and bit errors. Also, as mentioned in the
cabling section, be sure you have the right plug for the
cable you are using. An RJ-45 plug designed for stranded
wire will cut through a solid conductor.
But you know all that. So let’s get on to troubleshooting,
when despite all due care something still goes wrong.
The Basics
Link Test
A layer 2 test, this checks the connection between the
switch and a designated network device on the same LAN.
During the link test, IEEE 802.2 test packets are sent to the
designated network device in the same VLAN or broadcast
domain. The remote device must be able to respond with an
802.2 Test Response Packet. Most switches support this
test via a web or command line interface.
Ping
A layer 3 test, a simple and effective way to check basic
“reachability” of an IP-enabled device. Ping sends a test
packet to a device and waits for an echo response. A
Windows PC can do this within the command prompt
window. Just enter ping x, where x is the IP number or
the domain name (if a DNS server is available) and see the
result. If you get the echo, the basic connectivity (including
Layers 1, 2, and 3) is OK. Most switches and almost all IPenabled devices support this test.
44
Almost all sophisticated Ethernet switches offer these, and
they are useful tools to monitor traffic, check operation, etc.
You can do a lot of this with web and Telnet based
communication but SNMP usually offers a deeper look.
You will encounter the acronym MIB, for Management
Information Base. This is how information is organized
within SNMP.
To use SNMP and RMON, you will need a software
application that presents the information. A popular tool is
H-P’s OpenView, for example. HP ships a simple version
called TopTools with many of its switches.
A full discussion would be too much for this document, but
there is a lot of info that comes with Ethernet switches, and
a lot more in bookstores and on the web.
Some Things to Check
Switch configuration must be correct. IGMP
must be switched on, VLAN parameters set if
you are using them, etc. In our experience to
date, this is the most common cause of
problems. (With the exception of cables, of
course.)
Ethernet links can be 10, 100, or 1000 Mbps,
and full or half-duplex. We always want the
maximum rate and full duplex. You can
configure the Ethernet ports on some devices
SEVEN: TESTING, 1-2-3
for specific modes – but you should not do
this. The Auto mode is the correct setting,
which will cause the device and node to
automatically negotiate to the appropriate
condition. If you manually set the mode to fullduplex, the switch – in compliance with a
flawed IEEE standard – will set itself to halfduplex (!), leading to many problems. Telos
Livewire h/w nodes are always set to the auto
mode, so this problem will arise not with them,
but with other equipment such as PCs.
probably a bit higher in Ethernet systems. Indeed, a number
of surveys have put the “network medium” to blame 7080% of the time. This being the cables, connectors, and
hardware components that make up the signal-carrying
portion of the installation.
Wiggling and unplug-plug operations are legitimate and
effective troubleshooting methods. But there are plenty of
cable testers to help you perform more elaborate checks.
These range from simple conductivity testers to
sophisticated units that test cables for adherence to the
TIA/EIA standards, detect breaks with a Time Domain
Reflectometer, and more. Contact info for the main
manufacturers of these are listed in the Resources section.
If you want and have multiple redundant links
using port trunking or spanning-tree, you have
to set up the switch to support them. Taking
the default will usually not work.
Four Cable Testers
The testers shown here represent something of the range
available.
The “activity” LEDs (usually amber) on many
network cards and switches will be on
continuously when any LW audio streams are
present on the link. That is because the logic
that drives the LED extends the on time so that
you can see it with normal traffic. LW packets
are traversing the network at such a fast rate
that the LED never has a chance to turn off.
First, is the Agilent Framescope 350, and the second from
the Fluke DSP-4000 family, can certify that your cable
meets the appropriate category requirements with regard to
crosstalk, attenuation, etc. and perform a number of
sophisticated tests. The adapter at the top of the Fluke can
be changed to allow the unit to work with both copper and
fiber cable type.
Mode of the Axia Livewire hardware nodes
have status LEDS. The provide useful
information and should be checked. This is
covered later in this section.
Cable Testers
“It’s the cable – it’s always the **@@ cable!” said my first
boss. About half the time, he was right. That percentage is
45
The third unit is a much simpler and cheaper variant from
Fluke that checks for conductivity and correct wiring. It can
also tell you the distance to a break with a TDM function
and can do tone trace with an optional remote unit. The
ByteBrothers 2-piece set on the right is a basic wiring tester
and tone line-finder.
SEVEN: TESTING, 1-2-3…
Sniffers
These are s/w applications that run on PCs and can listen-in
on the packets flowing on an Ethernet link. Usually used in
conjunction with an Ethernet switch’s port-mirroring
function. This lets a designated monitoring port to mirror
that traffic on any other port you select. Livewire audio
packets are small in length and very frequent compared to
general data traffic so are quite challenging for a sniffer. To
be useful, you will need a good one and a fast computer to
run it. Very useful, but expensive. Perhaps best borrowed
from your company’s network guys’ kit.
DIAGNOSING PROBLEMS USING LIVEWIRE
COMPONENTS
All Livewire components have built-in diagnostic tools. For
example, audio nodes have a loop-back testing procedure
that measures audio noise and distortion. The web interface
lets you check a number of internal values.
The LW Router node is a useful device for displaying
available audio streams and listening to them. It has one
channel of send, so is useful as an audio source injector as
well.
The LW PC Suite has a diagnostic window that tells you a
number of things about the system clock and audio streams.
Hardware Node Indicator LEDs
Four LEDs indicate the status of the Livewire™ and
Ethernet connections, as well as system synchronisation as
follows:
LINK
When illuminated continuously, this LED represents the
presence of a live Ethernet link to another Ethernet 100
Base-T device. This LED indicates that a connection is
present and some device is connected. It does not indicate
the quality of the connection however. If no Ethernet link is
present, this will flash slowly.
LIVEWIRE
This LED indicates that the connected Ethernet segment
has Livewire™ traffic present. If the link LED is
illuminated, and the LIVEWIRE LED fails to illuminate,
there are either no other Livewire™ devices connected, or
the Ethernet switch has not been programmed to pass such
traffic through to the port to which this node is connected.
SYNC & MASTER
Only one of these two LEDs should be illuminated. If
neither LED illuminates, something is not correct. The
SYNC LED indicates the receipt of clock information from
another (Master) Livewire Node. The MASTER LED
46
indicates that this node is acting as the master clock source
for the Livewire network. More specifically:
SYNC – If Sync packets are being received by the
Livewire™ node, this LED will begin to flash. The LED
will continue to flash until the Livewire™ node has locked
its local clock to the network master. Once the local node’s
PLL is locked, the LED will illuminate solidly.
MASTER – The Livewire™ system employs a
sophisticated master/slave clocking system over the
Ethernet network. By default any device may become the
clock master, however this can be changed if desired. The
system has the ability to automatically change to a different
clock master should the current master become
disconnected, or otherwise inoperable. This happens
transparently without audio glitches. This LED indicates
that this node is currently acting as MASTER.
SEVEN: TESTING, 1-2-3
NOTES:
47
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
8
Network engineering for audio engineers
You don't need to know most of what’s in this section to use Livewire. Just as a beginner
can plug analog XLRs successfully together without knowing anything about op-amps,
you can connect and use LW without knowing details about packets. But just as fixing
tricky problems in the analog world calls for higher-level understanding, so does an
awareness of Livewire's internal technology help you to solve problems and build
complex systems.
This section introduces basic concepts – enough for you to get a feel for how data
networks work and to understand the lingo so you are ready to ask intelligent questions
of network guys and vendors. It also explains a lot of Livewire-specific points.
Livewire is built upon standard components, so if you
understand data networking generally, you'll be ready for
the specifics of Livewire audio networking. Network
engineering is a rich topic, abounding with information and
nuance, and in constant flux. Fortunately, Livewire uses
only a small subset that is easy to learn and understand.
That is mainly because most of the complexity comes with
IP routing and wide-area networks such as the internet –
and we don’t use much of that, staying only with the much
simpler Ethernet LAN level. Even if you don’t know
anything yet, you’ll get pretty much what you need in the
next few pages. If you want to know more, bookstores have
shelves loaded with networking advice and information.
We offer a few starting points in the Resources section.
As always, Telos support is at your side to help with any
specific practical issues that may come your way.
If you are developing for Livewire, this will offer only a
brief introduction, and you'll want to know more. Please
contact us for any of your needs, such as software API
documents.
ETHERNET/IP NETWORKS
Layering Model
You need to know layers to know networks. The notion of
layers and the open systems they support are central to
network engineering. Because layering is a key to enabling
multiple vendors for each function, this design has also
been a major factor in the growth and operation of the
internet. It’s also one of the keys to Livewire, allowing us
to build our professional audio transport application on
existing standard lower layers.
For many years, the Open Systems International (OSI)
model was the reference paradigm for data networking. For
example, the ISDN D-channel communication between
48
nodes and the telephone network is loosely based on this
model.
Layer
Function
7
6
5
4
3
2
1
Application
Presentation
Session
Transport
Network
Data Link
Physical
The OSI Layering Model
But this proved to be too complex for most practical
applications, and an architecture has evolved that is simpler
than the OSI model. Here is how that simpler model applies
to the IP-over-Ethernet combination we are using:
Layer
Function
Example
5
Application
4
3
2
Transport
IP Routing
Switching
1
Interface
HTTP (Web),
POP (mail),
etc.
UDP/TCP/RTP
IP
Ethernet
Addressing
Ethernet
Physical
The Modern Layering Model for
IP/Ethernet
Layer 1: Physical Interface
This layer is responsible for hardware connectivity, which
is provided by Ethernet.
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
Layer 2: Ethernet and Switching
This layer is Ethernet’s end station addressing and
everything related to it. An Ethernet switch is working at
Layer 2 because it forwards packets based on Ethernet
Media Access Control (MAC) addresses which are unique
ID numbers assigned by the Ethernet-capable equipment
manufacturer.
Layer 2 does not ordinarily extend beyond the corporate
boundary. To connect to the internet requires a router. In
other words, scaling a Layer 2 network means adding Layer
3 capabilities.
Officially, the transmission units comprising header and
data are called frames at this layer. At Layer 3, the correct
designation is packets. But, since Ethernet frames are
almost always carrying IP packets, the word used to
describe the combination most often depends upon the
context or the author’s preference. Unless we are referring
to layer 2 functions, we usually use “packets” because
Livewire audio has the IP header – and because “packets”
has become the usual way to describe this sort of thing
generally.
Layer 4: Transport
This layer is the communication path between user
applications and the network infrastructure and defines the
method of communicating. Transmission Control Protocol
(TCP) and User Datagram Protocol (UDP) are well-known
examples of elements at the transport layer. TCP is a
"connection-oriented" protocol, requiring the establishment
of parameters for transmission prior to the exchange of data
and providing error recovery and rate control services.
UDP leaves these functions to the application.
Layer 5: Application
Web browsers, audio editors, and email clients, for
example. And our Livewire audio.
Layer 3: IP Routing
In addition to Ethernet addresses, each IP packet on a LAN
also contains source and destination IP addresses. These
were intended to be used by routers to forward packets
along the most efficient route and link LANs of different
types. When the internet was invented, there were dozens
of LAN technologies in use and this was an important
capability. Now, IP addressing is used both within LANs as
a way to access servers from clients, etc, and to connect to
internet resources offsite.
Ethernet
header
IP in itself is not a particularly complex protocol, but there
are numerous capabilities supplied by the other components
of the IP suite. The Domain Name System (DNS) removes
the burden of remembering IP addresses by associating
them with real names. The Dynamic Host Configuration
Protocol (DHCP) eases the administration of IP. Routing
protocols such as Open Shortest Path First (OSPF), Routing
Information Protocol (RIP), and Border Gateway Protocol
(BGP) provide information for Layer 3 devices to direct
data traffic to the intended destination.
IP
header
UDP
header
Applications developers decide on the type of Layer 4
transport necessary. For example, database or Web access
require error-free access and use TCP, while live streaming
media use Real-Time Protocol layered on top of UDP/IP.
Making Packets
Livewire Standard Streams use all of the recommended
internet protocols and are constructed in the usual layered
fashion. Here is one representation of the packet structure:
RTP
header
RTP Payload (audio)
UDP payload
IP payload
Ethernet payload
In the next graphic you can see this structure in more detail.
This is the way network engineers usually visualize a
49
packet. It’s not important to know what each of the fields
means; the idea is for you to see how a packet is
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
constructed generally. Each of the horizontal bars are 4
bytes. At each layer, devices are operating only with the
information contained within the associated header. An
Ethernet switch only cares about the layer 2 headers and
everything else is just payload. An IP router only “sees” the
layer 3 header and doesn’t care about the lower-level
Destination Address
Source Address
Destination Address (cont)
Layer 2 - Ethernet
Source Address (cont)
Type/Length
Version
IHL
Priority/VLAN
Type of Service
Identification
Time to Live
Total Length
Flags
Protocol
Fragment Offset
Layer 3 – UDP/IP
Header Checksum
Source Address
Destination Address
Options
V=2
P
Padding
Source Port
Destination Port
Length
Checksum
X
CC M
Sequence Number
PT
Layer 4 – RTP Transport
Timestamp
Data
Audio Data (6 to 1480 bytes)
Layer 2
Check
transport. Applications don’t care about headers at all –
they just deliver their data to the network and expect to get
it back at the other end. (There are, however, exceptions,
such as sophisticated Ethernet switches that can inspect
layer 3 headers for some advanced functions.)
IP and Ethernet Addresses
As with everything connected to IP/Ethernet networks,
Livewire devices require both IP addresses and Ethernet
MAC (Media Access Control) addresses.
IP Address
IP addresses are four bytes long and are written in “dotted
decimal” form, with each byte represented decimally and
separated by a period. For example, in the IP address
193.32.216.9, the 193 is the value for the first byte, 32 for
the second, etc. Since a byte can hold values from 0 to 255,
this is the range for each decimal value. Host IP addresses
are assigned to your organization by your internet service
provider and parceled out to individual host computers by
your network administrator. He may give you this number
to be entered manually, or could opt for DHCP (Dynamic
Host Configuration Protocol) to let your computer get the
address automatically from a pool. Because Livewire
devices are permanently attached and because it is more
convenient to know the IP address attached to a particular
50
node and perhaps assign them in some kind of logical
pattern, we do not support DHCP for our hardware nodes.
Therefore, you will need to enter an IP address into each
node.
In addition to the address, there are a few more numbers to
enter into an IP configuration:
Subnet mask
Subnets allow a network to be split into different parts
internally but still act like a single network to the outside
world. There are three logical parts to any internet address:
the main network address, the subnet address, and the
particular device address. The mask marks the dividing
point in the address between the subnet part and the device
(host) part. What is meant here by “network” and “subnet”
depends on your internet provider. A network in this
context could mean all of the address space allocated to the
provider, and the subnets could delineate the individual
customers. Or the network could be all the addresses
allocated to a university or major corporation and subnets
could divide the address space to correspond to
departments. Network addresses are assigned by IANA, the
internet names and numbers authority, while subnets may
be changed without any official approval.
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
10
Network
Subnet
Host
11
11111111111111
111111
0000000000
s Subnet mask
32-bit (4-byte) IP address space
The mask is written in the same dotted-decimal form as IP
addresses. In the example a very large network supporting
64k hosts is divided into 64 subnets, each with 1k hosts.
The subnet mask would be 255.255.252.0, which is just
another way of writing the binary ones and zeros value
shown above.
As a practical matter, you usually just take the number
given to you by you network administrator or service
provider and enter it.
Gateway address
This is the IP address of the device that passes traffic out of
your local network to the internet. This is usually a router.
are written in “dashed hexadecimal” form like this: 5C-66AB-90-75-B1. (Sometimes colons are used as the
separators.) Hex notation is just another way to write binary
values. Single digits range from 0 to 9, A, B, C, D, E, F and
byte values from 00 to FF. The value FF means all the bits
in a byte are 1s and is equivalent to decimal 255. While this
notation may seem strange at first sight, it is very useful to
programmers, who need to think in powers of two.
There is a unique Ethernet MAC address for each and every
network adapter ever made in the world. IEEE handles the
allocation among manufacturers and each manufacturer is
responsible to ensure that they make no two alike within
their assigned range.
DNS server address
This is the address of the computer that provides name
look-up service, translating text domain names like
www.telos-systems.com to IP address numbers.
In careful language, devices that attach to the internet and
have IP addresses are called hosts, a name that probably
made sense in the early days. (They “host” the IP stack and
interface.) And Ethernet-connected devices are officially
called stations to keep the radio/ether analogy going. But
what do you call something that is both host and station, as
almost everything is? “Host” doesn’t sound very natural
for our audio devices and “station” would be very
confusing, indeed. As you’ve noticed, we usually just say
Livewire node in the context of our audio equipment, which
should be clear enough. But we will be in trouble when
hybrids, codecs, processors, etc. have direct Livewire
connections. They won’t be nodes, will they? Unless
something better comes along, we’ll probably say Livewire
device. As to “host” and “station” for other devices, we’ll
just use connected PC or some variant, thank-you very
much.
Ethernet Addresses and Address Resolution Protocol
(ARP)
Machines that use IP and are connected to an Ethernet have
two addresses, IP and Ethernet MAC. While the IP address
is user-determined, the Ethernet address is usually
programmed into the network card or interface by the
manufacturer.
You will probably never have to deal with them directly,
but who knows? Ethernet addresses are 6 bytes long and
51
I (Steve) used to feel bad about all those wasted addresses
from obsolete and thrown-away network cards – guess
that’s the Protestant USA mid-westerner in me – but
supposedly 6 bytes is enough that each of Earth’s grains of
sand could have its own address, so not to worry.
There is a need to translate between IP and Ethernet
addresses. Consider a server sending data to a machine it
knows only by IP address. To communicate, it has to
generate an Ethernet frame including the Ethernet
destination address corresponding to the desired IP address.
To do this, every IP-based device has an ARP module,
which takes an IP address as input and delivers the
corresponding Ethernet address as output. It maintains a
local table with the associations. When it encounters one it
doesn’t yet know, it broadcasts an ARP query packet to
every device on the LAN and the device that owns the
specified IP address responds with its Ethernet address. If
there is no owner, the packet is presumably intended for an
off-site device and is sent to the gateway address of a
router. How does the transmitting device find the router’s
Ethernet address? With ARP, of course.
Entering arp -a into Windows command prompt will
give you the current list of IP addresses and associated
Ethernet addresses – the ARP table for that machine.
Multicast Addresses
All of the above discussion was only relevant to the usual
unicast situation that is used for web surfing, emails, file
transfers, etc. We also use it in LW for configuration and
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
control, such as when a web browser is connected to a
hardware node. But audio is multicast because we want it
to be available to multiple destinations. The principle is
simple: rather than specifying a specific destination, a
special “virtual” multicast address is used that is not
assigned to any particular device. Audio nodes can listen-in
in a party-line fashion by receiving any packets at this
address.
Our audio streams are multicast at both Layer 2 and Layer
3, using the set-aside multicast addresses at each layer. The
Livewire channel number is automatically translated to the
appropriate addresses at both layers internally.
Livewire uses the IP address range starting from
239.128.0.0. This choice is based on the assigned numbers
from the IANA (Internet Assigned Numbers Authority)
allocation of this range for use within organizational and
site specific scopes. These addresses are to be used for
multicast applications that are not used across the global
Internet. Since our application will be used within a single
facility on a single switched LAN, this range is appropriate.
Over 8 million unique IP multicast addresses are available
with each address mapping to a globally unique Ethernet
multicast address.
Even so, IP is relatively stingy with its multicast space.
Ethernet has set aside half of all destination addresses for
multicast - 140,737,488,355,328 addresses, which should
be enough for even the very largest broadcast facility! The
designers clearly had big plans for multicast that have not
yet been realized.
The distinction is made in the first transmitted bit of the 48bit address that divides the total available address space in
two: a 1 in this position signifies a multicast.
ETHERNET SWITCHING
Ethernet switching has caused a revolution in data
networking. With switching, each device owns all the
bandwidth on its link. No sharing and no collisions.
Incoming frames are forwarded only to the nodes that need
them.
Despite their amazing power, the invention of switching
was more akin to falling off a log than sawing one in two…
The switch builds up a table of what addresses are attached
to what ports, which it does by merely by examining the
source addresses of sent packets. When frames come in, the
switch looks into the table, discovers what port owns the
destination and forwards the data only to that port. In the
rare case that no entry exists for an address, the frames are
52
“flooded” to all ports to be sure the intended recipient gets
it. If a connection is unplugged or there is no data for a long
time, the entry is removed. Pretty simple, eh?
Multicast
The operation described above is for the common unicast,
or point-to-point, communication that you have for typical
traffic such as web, email, etc. But Ethernet supports three
communication types:
Unicast means point-to-point. The usual mode
for traffic.
Multicast means that multiple receivers may
"tune in" to the transmission from a source so
that a selected subset of nodes is served.
Broadcast means that packets are sent to all
receivers, which is quite common on Ethernets.
Microsoft file sharing, for example, advertises
the PCs on a network this way. ARP uses this
to get a query to all machines on the network.
We use multicast for Livewire audio streams because we
want to emulate distribution amps and audio routers, with
multiple receivers being simultaneously able to listen in to
a source. The automatic procedure described above does
not work for multicasts because they are not associated
with a particular output port and node. Fortunately,
switches offer a way to control these one-to-many streams.
A multicast Ethernet frame has a “virtual” destination
address that is just stopped inside the switch if there are no
interested receivers. When receivers want to tune-in, they
send a message to the switch telling it to turn on the stream
to their port.
The switch knows what frames are multicasts because the
destination address belongs to the set-aside multicast pool.
Livewire uses one Ethernet/IP multicast address for each
audio stream. These are derived automatically from the LW
channel numbers you assign. Streams are multicast at both
Ethernet and IP layers using the assigned multicast
addresses at each.
IGMP (Internet Group Management Protocol)
We need some way to tell the switch what streams go to
what ports – that is, a way to control multicast switching.
IGMP was designed for just this purpose.
IGMP is part of the IP suite and is a Layer 3 function that
was designed to communicate with IP routers to control
multicasts. But switch manufacturers started to implement
“IGMP snooping” on the messages between hosts
(computers) and routers as a way to control multicasts at
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
Layer 2. In recent switch implementations of IGMP, this is
taken further and a router is not necessary as long as a
switch is configured to support IGMP with the “Querier”
feature enabled. We want this because there is often no
router in the system. Even were there to be one, better to
have this capability in the switch as a back-up.
IGMP uses three types of messages to communicate:
Query: A message sent from the querier
(multicast router or switch) asking for a
response from each host belonging to the
multicast group. If a multicast router
supporting IGMP is not present, then the
switch must assume this function in order to
elicit group membership information from the
hosts on the network.
switch automatically ceases Querier operation if it detects
another Querier. A switch with IGMP querier capability
will become a Querier in the absence of any other Querier
on the network. If you disable the Querier function on a
switch, ensure that there is an IGMP Querier (and,
preferably, a backup Querier) available. If the switch
becomes the Querier, then subsequently detects queries
transmitted from another device on the same VLAN, the
switch ceases to operate as the Querier for that VLAN. In
the above scenario, if the other device ceases to operate as a
Querier, then the switch detects this change and can
become the Querier as long as it is not pre-empted by some
other IGMP Querier.
In a Livewire system, it is the responsibility of the audio
nodes to generate the IGMP messages.
Prioritization
Report (Join): A message sent by a host to the
querier to indicate that the host wants to be or
is a member of a given group indicated in the
report message.
Leave Group: A message sent by a host to the
querier to indicate that the host has ceased to
be a member of a specific multicast group.
An IP multicast packet includes the multicast group
(address) to which the packet belongs. When an IGMP
client connected to a switch port needs to receive multicast
traffic from a specific group, it joins the group by sending
an IGMP report (join request) to the network. (The
multicast group specified in the join request is determined
by the requesting application running on the IGMP client.)
When a networking device with IGMP enabled receives the
join request for a specific group, it forwards any IP
multicast traffic it receives for that group through the port
on which the join request was received. When the client is
ready to leave the multicast group, it sends a Leave Group
message to the network and ceases to be a group member.
When the leave request is detected, the appropriate IGMP
device will cease transmitting traffic for the designated
multicast group through the port on which the leave request
was received (as long as there are no other current members
of that group on the affected port).
Thus, IGMP identifies members of a multicast group and
allows IGMP-configured hosts (and routers) to join or leave
multicast groups.
The function of the IGMP Querier is to poll other IGMPenabled devices to elicit group membership information.
The switch performs this function if there is no other
device, such as a multicast router, to act as Querier. The
53
Within a link, we sometimes want to have audio mixed
with general data. This happens, for example, when a
delivery PC is playing audio and downloading a file at the
same time, or when our Studio Engine is sending and
receiving audio and control messages simultaneously. To
be sure audio always flows reliably, we take advantage of
the priority functions that are part of the switched Ethernet
system.
Compared to the original, modern Ethernet has an
additional 4 bytes of data inserted into the frame's header.
One field provides a 3-bit priority flag, which allows
designation of eight possible values.
Priority
Level
IEEE
Recommendation
Livewire
Assignment
7
Network control
6
Reserved
LW audio
5
Voice
Telephone
audio
4
Video conferencing
3
Call signaling
2
High priority data
1
Medium priority
data
0
Best effort data
LW control &
advertising
Ethernet Priority Assignments
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
Input
Port
Classify
High-priority Queue
Input
Port
Mux
Output
Port
Classify
Low-priority Queue
Output Section per Port
Highest-priority packets have first call on the link’s
bandwidth. If high-priority packets are in the queue and
ready to go, the lower-priority ones wait. If there is not
enough bandwidth for both, low-priority packets will be
dropped – but this is not a problem, as you will soon see.
The graphic above shows only two queues, but the idea is
the same for four or eight. Switches used for Livewire must
support a minimum of four queue and priority levels. Some
low-end switches have no support or may have only two
queue levels.
If you have multiple switches in a
configuration, the priority information
automatically to all the switches in a system.
hierarchical
is carried
This prioritization scheme works only within a facility’s
local area network. Because it is at the Ethernet layer, it has
no effect past the router boundary into the internet.
However, we also set the priority bits in the IP header to
match the Ethernet priority so that as LAN switching
evolves to use more Layer 3 intelligence, our packets will
be ready.
The Role of TCP
TCP is a key to sharing high-priority audio with bestefforts data on a single network link. Because the acronym
TCP/IP is so often written, many people think that they are
necessarily and always joined. This is certainly not so. IP is
independent from TCP and may well be used without it.
For example, RTP/IP is specified for streaming media, and
UDP/IP is used for a variety of transmissions, such as DNS,
the internet’s name look-up service.
TCP has two functions: Ensuring reliable transmission and
controlling transmission rate.
Routers and switches may drop packets when there is not
enough bandwidth to transmit them or when they are
overloaded.
They also do not guarantee to deliver packets in the same
order as they were sent. And there is no protection for bit
errors from signal corruption. None of this is a mistake or
oversight in the design of the internet. The inventors knew
what they were doing: they wanted control of any needed
correction process to be as close as possible to the
endpoints, consistent with the general internet idea to move
as much as possible from the center to the edges.
Certainly we need 100% reliable transmission for most data
files – even a missed bit could have bad consequences.
TCP gets this done by using a checking and re-transmission
approach. Whenever TCP detects any corrupted or missing
data, it requests another copy to be sent and holds any data
it might already have in its queue until the replacement has
arrived. Packets are numbered by the sender so that they
can be delivered to the application in correct order. The
application always gets good data – but it could be after
significant delay.
Transmission rate control is essential for most internet
applications because the bandwidth of the many
transmission “pipes” from sender to receiver are almost
always different. And the available bandwidth to a
particular user is constantly changing as the demands from
the many users sharing the net ebb and flow. Think of the
common case that you are at home with a 56k modem
connected to your office server. The server and its local
network can certainly send data faster than your modem
can take it. And the available bandwidth on the public part
of the net is varying. So something needs to slow the
sending rate to match both the network and your modem’s
ability to receive. That function is performed by TCP. This
is called flow-control. While the details are complicated,
the principle is simple: a TCP sender monitors the
condition of the buffer at the receiver so it knows how fast
the data is arriving and can adjust its transmission rate to
maintain the correct average buffer fill.
TCP also has a function called congestion-control. While it
also controls rate, it does it with a different mechanism and
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EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
for a different reason. The re-transmission procedure we
discussed earlier addresses a symptom of network
congestion, but not its cause – too many sources trying to
send at too high a rate. To treat the cause of congestion, we
need to have some way to throttle senders when needed.
TCP’s congestion control is unusual in that it is a service to
the network at large rather than to the individual user. It
was conceived as a way to fairly ration network bandwidth
to all users. To do this, TCP monitors dropped packets,
assuming that lost packets signal congestion. When a new
connection is established, a slow-start function causes the
rate to start low and ramp up until a lost packet is detected.
Then the rate is cut in half and the ramp up begins again. In
this way TCP is always probing for the maximum available
bandwidth and always adjusting its transmission rate to
match. Its really a very slick technique, one that is very
well suited to getting the fastest transmission of bursty data
over a shared links.
We’ve gone into a lot of detail on TCP because it is one of
the keys to Livewire’s audio being able to share a network
link with other general data. The Ethernet switch handles
congestion in a similar way to the routers in the internet –
when there is too much traffic, it drops packets. But we
have something very important: Priority. Audio packets are
assigned higher priority than general data. So they are
never dropped before all TCP packets are. The usual
condition is that some percentage of the link is filled with
constant audio streams and the remaining capacity is left
for data. For example, an 8-audio channel LWIO with all
channels active will take about 40% of its 100BASE-T link,
leaving 60% for data. But, we could have one or we could
have a dozen audio streams active on a link – and this
number could well change over time. TCP automatically
finds how much bandwidth it can use and adjusts it rate
naturally to match.
You might be thinking, “All well and good, but what if we
put too many high-priority packets into the link? Won’t we
have drop-outs then?” Yes, we would. But we never allow
this to happen. Remember that each Livewire node knows
about the link attached to it because it “owns” it. The link
from a node to a switch is full-duplex point-to-point with no
sharing. The node knows how many streams can fit and
never is allowed to send more into or request for reception
more than can be supported by the link.
All of the above applies to a shared link, such as for a
delivery PC that needs both audio and data. It is the
Ethernet switching function that allows the overall network
to be shared, since general data never even gets to a port
connected to a Livewire node.
55
Virtual LANs (VLANs)
This is a technology that came to Ethernet along with
switching. It is a way to have “virtual” isolated LANs,
while using common hardware.
Remember those Broadcast packets? They go to all
devices, even with an Ethernet switch in the picture. If
there are a lot of computers on the network, there could be
a lot of traffic generated by these transmissions. VLANs
can be used to contain broadcast packets, since they are not
propagated outside of their assigned VLAN.
VLANs can also be used for security. If the LW network is
on a different VLAN than the internet, a hacker would not
be able to gain access to your audio streams or send traffic
on the audio network.
In a LW network that is shared with general data, VLANs
offer protection against a computer that could have a
problem with its network software or interface card. The
Ethernet switch can be configured so that the ports to which
general computers are connected are not able to forward
packets outside of the assigned VLAN, so can never reach
LW audio ports.
Finally, VLANS protect against the rare case that an
Ethernet switch has not yet learned an address and has to
flood all ports until it knows the specific destination.
All LW devices allow choice of VLAN. We recommend:
If you have a separate network for Livewire
audio, you can just stay with the default VLAN
1 and pay no more attention to this topic.
If you have your Livewire network connected
to the internet, or shared with a large group of
office computers, use the default VLAN 1 for
general data and VLAN 2 for LW audio and
control.
A router must be used to bridge the traffic between
VLANs, while providing a “firewall” function. So if you
have PCs on the LW network that will be used for audio
and web surfing, etc, you will need to provide this bridge.
You will also need this to access LW devices on VLAN 2
with PCs connected to VLAN 1 for configuration,
monitoring, etc.
A router that bridges VLANs is sometimes called a “onearmed” router because it has only one Ethernet port,
rather than the usual two. But you can use the same router
that you have for your internet link to provide this function.
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
Or maybe better: Some sophisticated Ethernet switches
provide an internal routing capability that can be used to
bridge VLANs. Simpler and saves boxes.
Tagged vs. Port-Based VLAN Operation
When the VLAN information embedded in the Ethernet
frame is used to direct the switch, this is called tagged
VLAN operation. With LW devices, when you configure a
VLAN value, the device will transmit Ethernet frames with
the embedded value you specify. But some devices are not
able to do this. As if this writing, Windows does not
support VLAN tagging, for example. That means the
switch itself has to insert the tag – a procedure called portbased VLAN. In this case, all frames that enter from a
particular port are tagged with a certain value, defined by
switch configuration. To enable this, you must configure
the switch appropriately.
There is one special case: Frames tagged with VLAN=0 are
called priority frames in 802.1p standard. They carry
priority information, but not the VLAN ID. The switch will
translate to whatever VLAN is default for that port. This is
useful if you want to use port-based VLAN assignment at
the switch, rather than tagging from the LW device.
Many switches allow a combination of port and tagged
VLAN. In this case you assign a default value to the port
and frames either with no tag or with tag=0 go to this
default VLAN, while tagged frames override the default.
It would be possible to use port and tagged VLAN in
combination. For example, you use LW node configuration
to put all your audio devices onto VLAN 2. But since
Windows doesn’t support tagged VLANs, how would you
connect a PC for configuration and monitoring? Using the
port-based assignment, you can set a port to be always
VLAN 2 and plug your PC into it.
Some switches have other options for assigning VLANs.
Assignment could be “hard-coded” to MAC addresses with
a configuration set-up. Or layer 3 protocols (TCP, RTP,
etc) could be detected and used as a way to make VLAN
assignments. These may have their place, but since
Livewire devices provide the tagging, it doesn’t seem that
these methods make much sense. The less you have to
configure the switch, the better.
Ethernet Switching vs. Routing
Both switches and routers examine packet addresses and
send them appropriately on their way. So what is the
relationship between these technologies? Why and where
would you use one versus the other? Routing works at
Layer 3, where IP information resides, while Ethernet
switching works at Layer 2. Routing is a much more
complex operation than switching, where multiple paths
from one site to another are the norm, and it is the job of
the router to find the optimum route (get it?), which may
well be changing from minute-to-minute. On the next page
is a comparison of the two side-by-side:
As do switches, routers also support multicast and
prioritization. So it would be possible to have a routed LW
network on top of a switched one. You’d still need the layer
2 switching because Ethernet would still be the transport
layer. Livewire fills the IP header with all required
information and does it in a standard way. So if it ever
becomes a good idea to route LW, we are ready.
Switch
Router
Layer
Layer 2 / Ethernet
Layer 3 / IP
Function
Determines to which port the
addressed node is connected and
switches incoming frame to it
Finds the best route from among
many and forwards packet to
next router along the path
Terminology
“Switching”
“Forwarding”
Technology
Simple table look-up in hardware
Complex dynamic best-route
determination in software
Standards
IEEE
IETF
Ports
Many, connecting mostly to end
nodes
A few, connecting to networks
and Telco lines
Cost
Low
Expensive, but coming down
Ethernet Switch vs IP Router Comparison
56
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
Cisco is the most famous and by far the most widely
deployed router brand. They pretty much have a lock on the
router market, while there are a bunch of vendors selling
Ethernet switches. Is it any surprise that Cisco wants you to
do everything at Layer 3?
Traditionally, routers did their work with software, while
switches had dedicated hardware chips. Now there is
something called Layer 3 Switch, a hybrid of traditional
routers and Ethernet switches. Layer 3 switches perform
their forwarding – whether Layer 2, Layer 3, unicast,
multicast, or broadcast – in hardware. Software handles
network administration, table management, and exception
conditions.
As the cost of such devices falls, it could well be useful to
have them at the core of a LW audio system. Indeed,
already some low-cost switches have basic Layer 3
functions such as simple routers that can pass packets from
one VLAN to another.
LIVEWIRE NETWORKS
So now we are ready to consider all that has gone before in
the context of Livewire. And to begin the discussion of
Livewire-specific technologies.
Quality of Service (QoS)
An important concept in a converged network is Quality of
Service. When general data is the only traffic on a network,
we only care that the available bandwidth is fairly shared
among users and that the data eventually gets through. But
when our studio audio and general data are sharing the
same network, we need to take all the required steps to be
sure audio flows reliably.
Our method for achieving QoS is system-wide, with the
following components each contributing a part of the
whole:
Ethernet switch. Allows an entire link to be
owned by each node. Isolates traffic by port.
IGMP. Ensures that multicasts – our audio
streams – are only propagated to Ethernet
switch ports that are subscribed.
Limiting the number of streams on a link.
Nodes have control over both the audio they
send and the audio they receive, so they can
keep count and limit the number of streams to
what a link can safely handle.
The result is rock-solid QoS, combined with the ability to
share audio and data on the same or interconnected
networks.
Source Advertising
Audio source nodes advertise their streams on a special
multicast address. Receive nodes listen to these
advertisements and maintain a local directory of available
streams. The advertisements are sent when the streams first
become available and at 10-second intervals after that.
(Actually, only the data version number is sent every 10
seconds. The full data is advertised only upon entering the
system, on any change, and on explicit requests from those
having detected the data version number increase.) If a
node’s advertisements are not received for 3 consecutive
periods, it will be assumed to be removed from service.
There is also an explicit “stream unavailable”
announcement.
Receive nodes maintain a local table of available streams
and their characteristics, updated as any new information
arrives. Sources are cleared from local tables when an
explicit message is received announcing that a stream is no
longer available, or when three consecutive advertisements
have been missed.
A receive node may be configured to be permanently
connected to particular multicast streams, or users may
select audio sources from a list. The list may display all
available sources, or a filtered subset.
Synchronization
You may ignore this matter completely – and your LW
system will work automatically “out of the box”. But there
are times when you might want to modify the default
behavior of the clock sync system, so here is some detail on
how the system works.
Full-duplex links. Together with switching,
eliminates the need for Ethernet’s collision
mechanisms and permits full bandwidth in
each direction.
Ethernet Priority assignment. Audio is
always given priority on a link, even when
there is other high-volume non-audio traffic.
Livewire needs careful system-wide synchronization in
order to have small buffers for low-latency streams. If we
did not have a distributed way to derive a bit clock, we
would eventually have buffer over or under-flow, resulting
57
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
from the input and output node clocks being not exactly the
same frequency.
A PLL (Phase Lock Loop) in each LW node recovers the
system clock from multicast clock packet that is being
transmitted at a regular interval. At any given time, one
Livewire hardware device is the active system clock
master. In the event the master develops a fault or is
removed from service, the local PLLs in the nodes are able
to “ride out” the brief interruption and there will be no
problem with operation.
Jitter in the timing and PLL functions ultimately set a lower
bound on output buffers and therefore audio delay. And any
drift in the time calculation produces buffer pointer drift.
Further, jitter in the derived A-to-D and D-to-A bitclocks
causes sampling uncertainty that can generate unwanted
noise in the audio.
The LAN network is a “noisy” environment with packets of
various kinds and lengths being numerous and
unpredictable. Thus, the PLL system needs to be quite
smart so as to generate a reliable, consistent, low-jitter
output, while not being confused by dropped or jittered
time packets.
Our method for handling this PLL problem is subject to a
patent application, to give you some idea of the novelty and
complexity.
Factory default is 4. So all units have equal
priority out of the box, and the following is
used to break ties (in descending order):
lowest LW audio transmit base channel, then
lowest IP address, then lowest Ethernet
address.
Livewire nodes have an LED labeled Master on their front
panel that illuminates when that unit is the clock master.
Synchronizing to AES3 Systems
To avoid passing audio through sample-rate-converters, we
recommend that LW be synchronized to your AES master
clock, if you have one. Our LW AES node provides this
function, recovering the clock from an attached AES input
and creating a LW sync packet. The LW AES node must be
active clock master.
Here’s an interesting application of LW AES nodes: Two
LW AES nodes can be used as a way to synchronize two
AES systems located apart, but with an available IP path
between them. One becomes the master, connecting to a
LW AES input. The slave attaches to a LW AES output and
is configured to recover clock from it.
Network Standards and Resources
All nodes are capable of being a clock source, and an
arbitration scheme ensures that only the unit with the
highest clock master priority is active. Clock mastership
priority may be set by the user, or left to the default case of
all being equal priority.
We use standards whenever possible. Ethernet is
standardized by the IEEE and information is available on
their website at www.ieee.org. Internet Protocol and
associated technologies are standardized by the Internet
Engineering Taskforce (IETF) and much can be learned
from their website at www.ietf.org. Documents are a free
download. Bookshops are full of books on Ethernet, IP, and
networking and we offer a list of suggested reading.
When the clock goes away for 3 consecutive periods, all
capable units begin transmitting clock packets, after a delay
skewed by their clock mastership priority.
Livewire operates at both Ethernet and IP network layers,
taking advantage of appropriate standards-based resources
at each layer.
When a unit sees clock packets from a unit with a higher
mastership priority on the network, it stops its own transmit
of clock packets.
Here are the resources we are using at the various layers:
You can specify the clock mastership priority behavior.
The clock mastership can be made predictable, rather than
end up being any node in the plant – maybe the one down
in an out of the way equipment closet.
Each node has a clock mastership configuration setting that
can range from 0 to 7.
'0' means never - slave only
Layer 1
IEEE Ethernet Physical
Layer 2
IEEE Ethernet switching
IEEE 802.1p/Q prioritization
IEEE 802.1p multicast management
Layer 3
IETF IP (Internet Protocol)
7 means “always” - forced master (Don't use
multiple forced masters in a system.)
Layer 4
IETF RTP (Real-Time Protocol)
58
EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
IETF UDP (User Datagram Protocol)
believe firmly in this principle. We tried very
carefully to add nothing unnecessary.)
IETF TCP (Transport Control Protocol)
IETF IGMP (Internet Group Management
Protocol)
3.
Make clear choices. If there are several ways
of doing the same thing, choose one. Having
multiple ways to do something is asking for
trouble. Standards often have multiple options
or modes or parameters because several
powerful parties insist their way is best.
Designers should resist this tendency. Just say
no. (It was just us – and we did say no. No
committees or politics to cause bloating.)
4.
Exploit modularity.
This principle leads
directly to the idea of having protocol stacks,
each of whose layers is independent of all the
other ones. In this way, if circumstances
require one module to be changed, the other
ones will not be affected. (We built Livewire
on all of the available off-the-shelf lower
layers.)
5.
Expect heterogeneity.
Different types of
hardware,
transmission
facilities,
and
applications will occur on any large network.
To handle them, the network design must be
simple, general, and flexible. (We had to
accommodate both dedicated hardware audio
nodes and general-purpose PCs being used as
audio nodes.)
6.
Avoid static options and parameters.
If
parameters are unavoidable, it is best to have
the sender and receiver negotiate a value than
defining fixed values. (These were avoidable –
we don’t have any such negotiated parameters.
We do have the receiver selection of stream
types, but this is simple one-ended selection.)
7.
Look for a good design, not a perfect one.
Often designers have a good design but it
cannot handle some weird special case. Rather
than messing up the design, the designers
should go with the good design and put the
burden of working around it on the people with
the strange requirements. (Steve, Mike, and
Greg’s mantra! Make it work, make it solid,
build just enough flexibility to get the job done
– and no more.)
8.
Be strict when sending and tolerant when
receiving. In other words, send only packets
that rigorously comply with the standards, but
expect incoming packets that may not be fully
Layer 5
IETF NTP (Network Time Protocol)
IETF DNS (Domain Name Service)
IETF HTTP/Web
IETF ICMP Ping
IETF SAP/SDP (Session Announcement
Protocol/Session Description Protocol) (in the
Windows PC Livewire Suite application)
Network Time Protocol (NTP)
This is the internet’s standard for conveying time. There are
a number of servers on the net that users can connect to in
order to retrieve accurate time. There are also boxes from
manufacturers such as EXE that receive radio time signals
and translate them to NTP packets. Livewire does not need
NTP, but some peripherals do. For example, our studio
mixing surfaces and Omnia processors use NTP to
automatically synchronize to the correct time.
A Note about Protocol Design
There is no question that among network protocols, the
internet has been an impressive success. One of the reasons
for this was the approach its designers took – and still use –
when inventing its protocols. These are outlined in the
IETF RFC 1958 document. We’ve taken the principles to
heart in the design of Livewire. Here they are, in priority
order, and with our comments in parenthesis:
1.
2.
Make sure it works. Make prototypes early and
test them in the real world before writing a
1000-page standard, finding flaws, then writing
version 1.1 of the standard. (Telos is a practical
commercial oufit, not an academic or
governmental organization. We had two years
extensive lab tests of prototypes in two
locations and then real-world field tests at
radio stations before locking the core tech
down.)
Keep it simple. When in doubt, use the
simplest solution. William of Occam stated this
th
principle (Occam’s razor) in the 14 century.
In modern terms, this means: fight feature
creep. If a feature is not absolutely essential,
leave it out – especially if the same effect can
be achieved by combining other features. (We
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EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
conformant and try to deal with them. (We told
the s/w guys to do this. Hope they did!)
9.
Think about scalability.
No centralized
databases are tolerable. Functions must be
distributed as close to the end-point as possible
and load must be spread evenly over the
possible resources. (We kept very close to this
idea – which is the main spirit of the internet.
We don’t have any central databases or other
pieces along these lines. We have a fully
distributed system. If one part fails, the others
keep going.)
10. Consider performance and cost. If a network
has high costs and there are cheaper variants
that get the job done, why gold-plate?
(Compare the power and cost of our solution
with others. Using simple off-the-shelf
commodity parts was the guiding principle for
our work.)
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EIGHT: NETWORK ENGINEERING FOR AUDIO ENGINEERS
NOTES:
61
NINE: F.A.Q.S
9
F.A.Q.s
We know there will be questions. Here are some we’ve already heard, and some we
imagine.
GENERAL
Can the network be used for general data
functions as well as audio?
Most certainly, should you choose to do so. The Ethernet
switch naturally isolates traffic. You may even use one link
for both audio and data, since the audio is prioritized. This
will probably be the case when a PC is connected to the
network – you will sometimes want to download files,
receive email, etc. in addition to the audio stuff. Switch
selection is important, though, and you must use one tested
and recommended by us. You could have two networks and
link them as described below.
Of course, we would never mix on-air audio
and business functions or open ourselves up
to hacking. Can I make this a completely
separate network?
Yes, we understand and agree. You have a few choices:
Have a completely separate and isolated
network for Livewire. Take advantage of
Ethernet, but don’t combine any internet or
business functions with studio audio.
text or other information flowing between the systems. A
satellite receiver could have program information and
requests for specific local tasks, not just a “start something”
closure.
Is there any problem with delay of control
commands over the network? I’ve heard
about other systems using TCP/IP that have
had problems in this respect.
No, Livewire control latency is very small – no more than
50ms for hardware GPIO closures from Surface button
pushes. We are using a special network protocol we
invented called R/UDP (Reliable UDP) rather than TCP/IP,
in part to be sure control delay is low.
Can I use Livewire without the
SmartSurface?
Yes, of course. You could just use it as a snake or router
system and connect whatever consoles and other equipment
you like.
How does Livewire compare to other audio
networking systems?
Livewire is an audio networking system which allows realtime uncompressed digital audio to be conveyed over
standard Ethernet hardware. Livewire is extremely low
latency, which is especially important for broadcast facility
operation, where live monitoring and cascaded links are
common. Second, Livewire includes all the technology you
need for practical studio application: Switches are
controlled, sources are ID-ed and advertised to receivers,
GPIO over the network is covered, etc. Third, Livewire
connects directly to PCs – no soundcard or other hardware
is required.
Have two physical networks and link them
with an IP router. Correctly configured, the
router provides a security barrier.
Share the network hardware for audio and
general functions but isolate Livewire to its
own VLAN. Again, an IP router could be used
to link the two networks.
How do contact closures get in and out of
the network?
The SmartSurface power supply also has 40 GPIO
connections. We make the same box without the power
supply, so if you need more GPIOs elsewhere, such as in a
Tech Center rack, just install a GPIO box there.
But we expect more and more, control functions will move
from “dumb” contact closures to smarter network
transactions. For example, a delivery system that now uses
a closure to start play could just take a packet over a
network for this function. But, beyond this replacement of
today’s closure-based functions, you could have song title
62
Livewire is a not just a technology, but rather a get-the-jobdone solution. We offer you all the pieces you need to build
a modern broadcast studio. Nodes, Engines, Surfaces, PC
drivers. We are experienced broadcasters, so we know how
to support radio studio applications.
So, what about that delay?
For live monitoring, such as when an air talent hears his
own microphone in headphones, 10ms is the limit before
noticeable problems. We’ve kept Livewire link delay to
below 1ms, so a number of links can be successfully
NINE: FAQS
cascaded. To put this in perspective, a normal professional
A-to-D or D-to-A converter has about .75ms delay.
How can you promise live audio over
Ethernet? Won’t it drop out?
No. We wouldn’t be proposing any system that wasn’t full
broadcast quality. With Ethernet switching, each device
owns all of the bandwidth on a link so there is no
possibility of contention or audio loss. If a node needs both
audio and data, such as a PC running an audio editor and a
web browser, audio is prioritized and always has
precedence. We’ve had thousands of hours of testing in our
lab with careful logging of packet transmission. So we can
assure you that it works.
But the Internet is a packet network and the
quality is not very good for audio.
Right. Internet bandwidth is not guaranteed, so there can be
problems when there is not enough. But you completely
own and control all the pieces of a Livewire system and
there is more than enough bandwidth on a switched
Ethernet LAN, so performance is fully reliable.
Are you sure this is robust enough for 24/7
operation? My Windows networks always
have downtime.
Livewire equipment is based on tight, embedded hardware
and software. The Ethernet switches we recommend are
fully professional devices with high reliability and options
for redundancy.
Do you use any compression? I am
concerned about codec cascading.
Livewire audio is uncompressed 48kHz/24-bit. It would be
possible to have compressed streams sharing the Ethernet,
but this is not a part of Livewire.
Can I connect two studios across town with
a T1 line?
Yes, but not the way you’re probably thinking. Remember
that LW audio is uncompressed 24-bit 48kHz, so each
stereo stream is 2 Mbps. A T1 is 25% less than that. To get
this done over a reasonable phone line, you’d use Telos
Xstreams to reduce the bit rate for connection across town
via T1 or fractional T1. We’ll probably have a compressed
gateway some day to specifically handle this function. And
you could possibly use an Ethernet radio link.
How do I connect this to my Zephyr?
Easy. Use any analog or AES I/O node ports.
PCS AND LIVEWIRE
Tell me about your “sound card” driver for
workstations.
The official name is “Telos Livewire Suite for Windows”.
It makes the Livewire network look like a sound card to a
PC Windows application. Most audio applications should
work unmodified.
BUILDING LIVEWIRE FACILITIES
I’ve got a large facility. How many studios
can I interconnect?
There is no limit. You may have as many studios and audio
channels as your Ethernet switch can support. Switches
come in all sizes, some with hundreds of ports. And
multiple switches may be cascaded to expand ports. We
recommend that you use a switch per studio to isolate any
problems to a defined area. These are then interconnected
with a backbone. Switches may be physically associated
witch each studio or may be all in a central location, as you
prefer.
What about for smaller stations? This all
sounds pretty sophisticated for a simple setup.
Look at Ethernet for data applications… You have
everything from a single PC connected to a printer to a few
PCs in a small office tied to the internet and a couple of
printers to huge campus networks with thousands of nodes.
This is one of the reasons we went with Ethernet – you can
use it for big and small facilities. The technology and
economics naturally scale to suit the application size. We
figure, in fact, that small stations may benefit the most as
they gain routing capability at a very modest cost.
This seems like a lot of IP to keep track of.
What administration tools does Livewire
have?
All Livewire devices have a web browser control and
monitoring capability. Keep the IP numbers in a “favorites
list” and you can easily check them. Or make your own
web page with all the links.
How do analog sources become part of the
network?
With Telos Livewire nodes. These come in variants for line
and microphone application. Over time, you can expect that
codecs, hybrids, processors, etc. will have direct Livewire
connection ports.
What about AES?
We have a node that interfaces your AES audio to the
network. This is a direct bit-to-bit procedure with no
63
NINE: FAQS
conversion of any kind. You can also sync a Livewire
system to an AES master clock.
How do mix-minuses get generated?
This is a software function within studio processing
engines. We provide one for each channel as standard.
You said I can get RS-232 data through the
system. How is that done?
Using 3rd party devices, such as from Lantronics, your serial
data can go anywhere across the network and be used
where it’s needed.
ETHERNET MEDIA
Are optical audio links supported?
Livewire is fully compatible with copper and fiber
connection types. We imagine a common configuration to
be switches dedicated to studios with 100BASE-T copper
connecting nodes, engines, surfaces, etc. A fiber backbone
connects the switches in order to share audio among the
studios.
What Ethernet rates do you support?
Nodes connect with copper 100BASE-T links. PCs may
use 100Mbps or 1000Mbps, copper or fiber. Our processing
engines use 1000BASE-T. Switch-to-switch links may be
any supported Ethernet media. Media converters allow the
use of fiber on nodes, such as for extended-range snake
applications.
THE INTERNET AND LIVEWIRE
What about hooking up over the internet?
With my studio audio in IP form, can I just
plug a port from the switch into an internet
router? Why do I need ISDN anymore?
As the internet becomes ever more ubiquitous and
bandwidth more plentiful, arguments for using it for audio
transmission become more convincing. A gateway device
could perform compression from LW’s PCM to a lowerrate bitstream using a codec like MPEG AAC. The main
problem to be overcome is the internet’s lack of any
Quality of Service guarantees; a “net storm” that starves
bandwidth and drops audio might not be a big deal to a kid
at home with his computer, but it sure wouldn’t be good for
an important on-air feed. Private networks with reserved
capacity are one answer. Another could be the “resource
reservation” and “differentiated services” technologies that
has passed out of the laboratory and might eventually be
implemented by Internet Service Providers – at a cost, of
course.
In theory, RSVP, diffserve, mpls, IPV6, and other emerging
technologies will in due course offer us reliable audio
64
transmission. However, given the slow pace of new tech
adoption at the core of the public internet (nothing much
has changed for a decade) and the problems with scaling
the lab work to the real world, perhaps the following
observation applies: Sometimes there is a gap between
theory and practice. The gap between theory and practice in
theory is not as large as the gap between theory and
practice in practice.
In our view, the wait for ISPs to offer QoS guarantees at a
reasonable price is likely to be long. And when they do,
transmission delay is still probably going to be an issue for
live interactive broadcasts. So, it looks as if ISDN is going
to be the best option for most remote hook-ups for awhile.
Our Zephyr codecs support direct LW connection, so you
can use them to get a remote link into your Livewire
network that way and effectively have the same result –
albeit at ISDN’s per-minute cost.
All that having been said, for some non-critical apps, an
occasional drop-out might be acceptable and a gateway
with appropriate buffering and error recovery might be
useful. We’re engaged in some research on this topic now.
Please stand-by…
THE STUDIO ENGINE AND SURFACE
Can a single Mix Engine handle two or three
SmartSurfaces?
Each Mix Engine allows a huge amount of power and
flexibility to each SmartSurface, so it’s a one-to-one ratio.
You are using a PC motherboard for the
Studio Engine, right? It’s hard to believe that
an off-the-shelf PC can do high-quality audio
mixing. Are you sure there’s enough power
there?
The amount of processing power in a Pentium-4
motherboard is staggering. If you don’t burn it up with
fancy graphic user interfaces, it’s amazing what you can
do. With optimized software design, a single P4 can
outperform the largest, multi-DSP consoles and routers. We
use a special realtime and minimized version of Linux as
the operating system, so there is no overhead needed for the
graphic displays, etc. that burden desktop PCs.
Will it be as reliable as the cards-in-a-frame
approach? I sure don’t want this thing to
crash.
Modern PC hardware is very reliable. The parts and board
count of the PC solution is much lower than a card-frame
approach, so statistically the h/w failure rate is almost sure
to be lower. The most failure-prone device in a PC is the
hard drive and we don’t use one; our software is loaded
NINE: FAQS
from Compact Flash memory. There are no plug-in PCI
cards to cause connector-related problems. We have
redundant large panel-mounted fans turning at a relatively
low RPM, rather than the usual small heatsink-mounted
high-RPM cooler. But more important for reliability is the
software. We are using an off-the-shelf Intel-made PC
motherboard and processor, but we are treating it from the
software perspective as if it were an “embedded DSP”
platform. We’re running a pared-down and highlyoptimized version of the Linux operating system and our
engine processing application code is carefully “written to
the metal”. Unlike general PCs that must host a lot of
different application s/w, which are coming and going,
sharing and releasing resources, and potentially causing
conflicts, we have only one application running in a
carefully controlled environment.
I like the SmartSurface’s features and
design, but I’m not ready to commit to
Livewire for my full facility. Can I just use
your Surface and Engine as a drop-in
console replacement?
Sure, you can. Take a Surface and Engine, add the audio
I/O you need and an Ethernet switch and you have a standalone console that interfaces via analog or AES to your
other equipment.
ANALOG AUDIO & AES ON RJS AND CAT 5
You recommend an outer shield for analog
audio. Why?
As a precaution. Shielded cable protects against RF and
eliminates any possible crosstalk between cables in multicable bundles.
Is there any crosstalk between the pairs
within the Cat-5 cable?
As long as your circuits are balanced, there is almost no
left/right crosstalk inside the cable. With a balanced input
circuit that has 50 dB CMRR (Common Mode Rejection
Ratio), separation will be greater than 90 dB.
So, must all the audio and digital signals be
balanced?
Generally, yes, or crosstalk will degrade. Unbalanced
connections can be used for short runs only and preferably
with separate cables for left and right if you care very much
about stereo crosstalk. Radio Systems makes small devices
that adapt unbalanced RCAs to balanced RJs for their
StudioHub system that could be used to convert any
unbalanced sources you have. AES3 digital audio signals
are always balanced and require no conditioning.
65
Is Cat-5 OK for AES3 digital audio?
A 1997 report, Review of Cables for AES/EBU Digital
Audio Signals, conducted by the BBC Research and
Development Department, concluded that Cat-5 shielded
twisted audio pair cable “offered the highest performance
of all the cables tested here.” Their tests included coaxial
cables and special cables specifically designed for digital
audio. They preferred Cat-5 cables for their consistent
performance and because they have the flexibility to
support other signal formats.
Cat-5 cables are engineered for data rates up to 100 Mbps
to support networks such as 100BASE-T. Since AES3
signals have a bandwidth of about 3 Mb/sec (depending on
sample rate), AES3’s requirements are well within the Cat5’s guaranteed performance parameters. Dependable errorfree transmission is possible at lengths up to 920 meters
(over ½ mile). Cat-5 cables perform well for AES3 because
they are engineered to have characteristic impedance of 110
ohms and extremely low capacitance – in the 12 pF/ft
range. This yields low signal reflection and excellent high
frequency response, thus lowest error rates.
Is Cat-5 OK for analog audio?
Sure, it is! The low capacitance, needed for data’s high
velocity and wide bandwidths, yield exceptionally flat
analog audio frequency response, even over very long cable
lengths. The tight, controlled twists are good for hum and
crosstalk rejection. Steve Lampen, a senior audio video
specialist for Belden Wire & Cable writes, “Digital cables
make the absolute best analog cables. You can go farther
with flatter frequency response than with any cable
designed for analog”.
(See Belden’s web site for
interesting and revealing papers on the subject of using Cat
5 and 6 cables for analog signals.)
LIVEWIRE, STANDARDS, AND OTHER
VENDORS
Is Livewire standards-based?
As much as it can be, yes. Standard Streams use all the
relevant internet standards, the main one being the RTP
format defined in the IETF document RFC1889. Thus
standard PC audio players can play this audio. But, there is
no standardized way to convey low-delay full-fidelity audio
over Ethernet because you need a synchronization system
and that doesn’t exist in either the Ethernet or internet
standards. So we had to invent that. Still, they are as
standard as is possible to be.
Also, we needed to implement a protocol for tagging audio
sources with names and advertising these to receivers.
Nothing was available off-the-shelf, so we had to invent
NINE: FAQS
something for that, too. Same for the GPIO-emulation
functions.
Are you planning to share information so
that other vendors can make gear that
directly plugs to Livewire?
Yes. Software vendors for PCs can use our driver to easily
make their applications compatible. Makers of audio
hardware would have to coordinate with us to be
compatible. Of course, you can use whatever equipment
you want via the analog and AES nodes.
66
NINE: FAQS
NOTES:
67
TEN: RESOURCES
10 Resources
Networking is a field well covered by books and web sites. There’s plenty of information
out there. Here is a selection of some resources we’ve found useful. The links are active
and the list is larger and up-to-date on the Telos Livewire website.
LIVEWIRE/BROADCAST
Telos Systems
www.telos-systems.com/livewire
Weekly email update by request at: [email protected] or by phone at +1 216 241.7225
Radio Systems
www.studiohub.com
Vendor of Studio Hub components
ETHERNET
IEEE
www.ieee.org
The standards body for Ethernet. The documents are now a free download, but will cost you a lot of paper and toner – the basic
Ethernet standard is 1,268 pages!
Charles E. Spurgeon, Ethernet: The Definitive Guide; O’Reilly & Associates, 2000
www.bellereti.com/ethernet/ethernet.html
Living up to its title, it is pretty definitive on basic Ethernet topics. Stops short of much detail on switching and multimedia,
however, and has a lot of coverage of older Ethernet technologies we don’t use.
GENERAL NETWORKING AND INTERNET
IETF (Internet Engineering Task Force)
www.ietf.org
The Internet’s main standards organization. Look for the RFC (Requests For Comment) documents to see in detail how the
internet is built.
Andrew Tannenbaum, Computer Networks; Pearson Education/Prentice Hall, 2003
Our favorite general networking book. Popular college textbook covers it all, including multimedia, with a breezy style and at
just the right level of detail: enough to be useful, but not so much as to be overwhelming.
J. Naughton, A Brief History of the Future; Overlook Press, 2000
Not really so interesting for audio and Ethernet, but still worth reading for perspective. This history of the internet tells how it
happened in a friendly – even charming – way. Lots of stories and anecdotes. We particularly love AT&T’s repeatedly making
clear that digital communication had no future. (Something a lot like what we expect to hear from certain quarters regarding the
future of computer networks for studio audio.)
CABLING INFORMATION AND STANDARDS
Cabling Business
www.cablingbusiness.com
68
TEN: RESOURCESS
This magazine, targeted to cabling contractors, is a good way to keep abreast of the latest TIA/EIA cabling specs. It is also a great
source for innovative cabling accessories, testers, and installation techniques. Those located in the USA can sign up online for a
free subscription on the web site.
Jim Abruzzino; Technician’s Handbook to Communications Wiring; CNC Press, Chantilly VT, 1999.
This book is concise yet contains a lot of great information including proper technique for working with Cat. 5 cable and
connectors. Small enough to keep with your toolbox.
Cabling Design
www.cabling-design.com
Cabling tutorials
TIA
www.tiaonline.org
cables
Standards organization for
Global Engineering
www.global.ihs.com
standards
Sells the TIA/EIA cabling
CABLE AND CONNECTOR SUPPLIERS
AMP
www.amp.com
RJ plugs and tools
Anixter
www.anixter.com
Distributor of cables, etc.
Belden Cable
www.belden.com
Leading cable supplier
Hubbell Premise Wiring
www.hubbell-premise.com
Devices for Cat 5, etc
Panduit
www.panduit.com
products
Marking and installation
Siecor
www.siecor.com
components
Fiber optic cabling and
Siemon
www.siemon.com
Punch blocks
CABLE TESTERS
Fluke
www.flukenetworks.com
Full range of testers
Agilent
www.agilent.com
Top-end tester
ByteBrothers
www.bytebrothers.com
Low-end tester
Acterna
www.acterna.com
Fancy sniffers, too
ETHERNET SWITCH VENDORS
Hewlett-Packard
www.hp.com/go/hpprocurve
NETWORK “SNIFFERS”
Shomiti
www.shomiti.com
Network Associates
www.nai.com
ETHERNET RADIO EQUIPMENT
Adtran
www.adtran.com
Motorola
www.motorola.com/canopy
system)
Redline Communications
www.redlinecommunications.com
Proxim
www.proxim.com
69
(look for the “backhaul”
APPENDICES
Appendix A: Livewire tech details
You don’t need to read any of this unless you want to know about the internal details.
LW PACKET STRUCTURES
The speed of the link, the bit requirements of the header
and payload, and the number of samples that are combined
into a packet determine link capacity. The more samples
that are combined, the less the header overhead per packet,
and the higher the efficiency and capacity.
There is a fundamental tradeoff: When we have more
samples per packet, we have more capacity – but at the
expense of more delay. Good design means finding the best
compromise.
Packet-time = 1/sampling-rate * samples-perpacket
There is one packet send buffering, two packets receive
buffering, and the switch latency, therefore:
Link-delay = packet-time *3 + switch latency
Standard Streams
Standard Streams are compatible with internet standards.
They use large packets so as to be very efficient with both
computer
resources
and
network
bandwidth.
The sampling rate and the number of samples that are
combined into a packet determine delay:
Function
Bytes
Notes
Interpacket delay
12
This is not actually transmitted, but must be taken
into account for network bandwidth calculations
Ethernet header
30
Includes the VLAN/priority fields
IP header
20
Standard
UDP header
8
Standard
RTP header
12
Standard
Audio
1440
240 samples @ 48kHz, 24-bit, stereo
Audio (variant)
720
120 samples @ 48kHz, 24-bit, stereo
Standard Stream Packet Format
Livestreams
Total bytes per packet = 1498. Core delay = 5ms.
(720 and 2.5ms with the variant format)
An Ethernet frame’s maximum data length is 1500 bytes,
so you can see that we have chosen to pack the Ethernet
frame to nearly the maximum possible. There are two
reasons for this: 1) the frame rate is lowest possible to put
the least burden on PC receivers, 2) the header overhead is
applied to the most data so the proportion of capacity
devoted to audio vs. overhead is highest.
70
Livestreams are specialized for low delay, so we can pack
only a few audio samples into each packet. Because they
are smaller, less buffering is needed and that means the
time delay is lower.
APPENDICES
Function
Bytes
Notes
Interpacket delay
12
This is not actually transmitted, but must be taken
into account for network bandwidth calculations
Ethernet header
30
Includes the VLAN/priority fields
IP header
20
Standard
UDP header
8
Standard
RTP header
12
Standard
Audio
72
12 samples @ 48kHz, 24-bit, stereo
Livewire IP Packet Format
Total bytes per packet = 118. Core delay = .25ms.
The header load for RTP/UDP/IP is 40 bytes per packet,
which is a significant piece of the network bandwidth given
that our audio is only 72 bytes. Most of the time this is of
no consequence, since we have plenty of bandwidth.
However, there are some situations where a “lean and
mean” approach makes sense. So some Livewire equipment
offers a pure Ethernet layer 2 option.
Function
Bytes
Notes
Interpacket delay
12
This is not actually transmitted, but must be taken
into account for network bandwidth calculations
Ethernet header
30
Includes the VLAN/priority fields
Telos timestamp
4
Audio
72
12 samples @ 48kHz, 24-bit, stereo
Livestream Layer 2-only Packet Format
All of the above has been concerned with per-link
bandwidth. The system bandwidth is effectively unlimited
with appropriate switches.
Total bytes per packet = 118. Core delay = .25ms.
NETWORK LINK CAPACITY
Each Standard Stream has a bitrate of 2.304Mbps. A
100Mbps link can therefore carry 43 such channels at full
capacity and a 1000Mbps link can carry 430 channels.
Each Layer 2-only Livestream has a bitrate of 3.776Mbps.
A 100Mbps link can therefore carry 26 such channels at
full capacity and a 1000Mbps link can carry 260 channels.
In practice, links to hardware nodes will have a mix of
Standard Streams, Livestreams, and control data. Our
biggest node has 8 channels, so there is plenty of link
capacity. PCs use the more efficient Standard Streams and
maybe only 6 of them maximum, so again there is plenty of
capacity to handle both audio and simultaneous file
transfers, etc. Our Studio Engines connect with 1000Mbps
links, so the sky is the limit there.
71
MULTICAST ADDRESS TRANSLATION
Livewire streams are multicast at both layer 2 and layer 3.
The Livewire channel number is automatically translated to
the appropriate addresses at both layers internally. You
might want to know the translation algorithm because
maybe you or your network engineer might need to check
packets with a “sniffer” or Ethernet switch diagnostics. So
here are the details.
Livewire channels range from 0 to 32767. Audio streams
are mapped into IP and Ethernet multicast addresses using
the channel numbers for the lower 15 bits as follows:
APPENDICES
IP address
Type
239.192.000.0/15
Standard Streams
239.192.128.0/15
4 addresses are our system defaults, other not used
(left for expansion)
239.193.000.0/15
Back Standard Streams
239.193.128.0/15
not used (left for expansion)
239.194.000.0/15
Livestreams
239.194.128.0/15
not used (left for expansion)
239.195.000.0/15
Back Livestreams
239.195.128.0/15
not used (left for expansion)
...
239.251.000.0/15
not used
239.251.128.0/15
not used (left for expansion)
The following special addresses are assigned:
IP Address
Function
239.192.255.1
Livestream clock
239.192.255.2
Standard Stream clock
239.192.255.3
Advertisement channel
239.192.255.4
GPIO (UDP port 2060)
These all are within the range specified for “OrganizationLocal Scope” use by IANA – the Internet Assigned Names
and numbers Authority. Routers do not propagate traffic on
these addresses to the internet; they stay contained within
LANs. (We also set the “link local” bit and TTL=1 in the
IP header to further ensure that streams stay local.)
The range supports our 32k channels, with up to 120 stream
types per channel. We are only using four types now, but
there is plenty of room for growth.
Our motivation for mapping each type to a contiguous
block rather than having the type in the lower-order bits is
to allow configuration of switches and routers on a per-type
basis by specifying an address range. This direct mapping
of channels to addresses also makes sniffing easier: it is
simple to know where to look for a particular audio stream.
IP addresses are mapped into an Ethernet MAC layer
multicast, according to a de-facto standard process for this
procedure. This process is as follows:
72
Using the Class D address, identify the low order
23 bits of the class D address.
Map those 23 bits into the low order 23 bits of a
MAC address with the fixed high order 25 bits of
the IEEE multicast addressing space prefixed by
01-00-5E.
Example:
Assume: Channel = 80
Assume: stream type is Standard Stream
Then: IP address = 239.192.0.80 (dotted
decimal)
And then: Ethernet MAC Address = 01-00-5e00-00-50 (dashed hex)
Ethernet addresses are transmitted most-significant byte
first, but least-significant bit first within the byte, so in our
example it is the 1 in the leftmost MAC address byte 01
that signifies a multicast address.
APPENDICES
NOTES:
73
INDEX
Index
Advertising System.
See: Livewire
AES, 3, 57
Cat. 5, 64
Livewire compared
to, 2
Analog Audio, 64
Applications
Audio router, 7
Boradcast
Studios, 8
Facility-wide audio
network with
consoles, 10
High performance
sound-card
replacement, 7
make a snake, 7
STL, 9
ARP, 50
Audio
Unbalanced, 32
Audio Connections,
29
Audio Quality, 3
Audio Routing, 2
Backup, 16, 37
Cabling, 31
Cabling installation
guidelines, 32
Cat. 3, 31
Cat. 5, 25, 31
AES, 64
AES Cable, 29
Analog audio, 64
Analog audio on,
64
Audio Cable, 29
Cat. 5 for audio?, 26
Cat. 5e, 31
Cat. 6, 31, 33
Category. See: Cat.
Channels. See:
Livewire Channels
Church, Steve, 50
Color codes, 27
Color Codes, 26, 29
Control, 2
Converged Networks,
6
Crosstalk, 33, 64
Delay, 61. See
Livewire & delay
Air-talent response
to, 4
Destination
configuration
screen, 19
Destinations, 18
Ethernet, 25, 39, 47
1000Base-T, 28
100Base-TX, 26
Addresses, 50
Audio over, 32
Broadcast, 51
Cabling, 31
Crossover cable,
28, 29
Crossover Cable,
28
FAQs, 63
Fullduplex links, 56
IGMP, 51, 56
Multicast, 51
Packets, 48
Prioritization, 52
Priority
assignment, 56
QoS, 52
Radio links, 38
Radio Links, 68
Redundancy, 35,
37
Resources, 67
Switches, 56
Switches
(recommendati
ons), 39
Switches,
configuring, 40
Troubleshooting,
43
Unicast, 51
Why Ethernet?, 1
Ethernet Switches
Requirements for,
39
Ethernet switching
vs IP routing, 55
FAQs, 61
Analog Audio and
AES on RJs and
Cat. 5, 64
Building Livewire
Facilities, 62
Ethernet, 63
General, 61
PCs and Livewire,
62
Studio Engine and
Surface, 63
The Internet and
Livewire, 63
Fiber optics, 37
Frequently asked
questions. See:
FAQs
Hardware nodes
74
AES 8x8, illus, 11
Analog 8x8, illus,
11
Configuration and
access, 23
Configuring IP
address, 24
General Purpose
Input Output
(GPIO), illus, 12
Mic + Line, illus,
11
Router Selector
Node rear
panel, illus, 29
Router Selector,
illus, 12
Hardware Nodes
GPIO, 21
IEEE 802.1p/Q, 39
IGMP, 40, 41, 51
Fast leave feature,
41
Leave group, 52
Query, 51
Report (Join), 52
IP, 6
DNS server
address, 50
Gateway address,
50
IP address, 49
RTP, 6, 53
subnet mask, 49
TCP, 53
The Pac Man
protocols, 6
UPD, 53
IP address, 24
IP Networks, 47
IP Routing
vs Ethernet
switching, 55
Layer 1
Physical Interface,
47
Layer 2
Ethernet and
switching, 48
Layer 3
IP Routing, 48
Layer 4
Transport, 48
Layer 5
Application, 48
Layering model, 47
Link Capacity, 70
Link LED, 45
Livewire
Advertising
System, 2
Audio Router
Control
Protocol, 16
Channel and name
system, 17
Channel names, 17
Channels, 17
Examples of
sources and
destinations, 18
GPIO Channels, 18
Hardware nodes.
See: Hardware
nodes
IP-Audio driver,
illus, 21
Link capacity, 70
Livestreams, 69
Livestrwam packet
format, 70
Multicast address
translation, 70
Networking
Engineering, 47
Networks, 56
Packet structures,
69
PCs and, 2
Security, 38
Source advertising,
56
Sources vs
Destinations, 18
Standard streams,
69
Stream types, 4
Synchonization, 56
Synchonizing to
AES, 57
Systems, 34
Diasy chained
switches, 35
Hierarchical
network, 36
Simple oneswitch
network, 34
Livewire IP-Adio
Driver
Media Player
Interface, 13
Livewire IP-Audio
Driver
8x8 Driver, 12
Configuration, 21
PC Router
Selector, 12
INDEX
PC Router
Selector, illus,
13
Livewire LED, 45
Livewire QoS. See:
QoS
Master LED, 45
Multicast
Address
translation, 70
Network Engineering
For Audio
Engineer, 47
Network standards,
57
Layer 1, 57
Layer 2, 57
Layer 3, 57
Layer 4, 57
Layer 5, 58
Network Time
Protocol (NTP), 58
Packets, 53, 62, 69
Ethernet, 48
Pathfinder Router
Control
Application, 14
Pathfinder Router
Control
Application, illus,
15
PCs, 2
Axia IP-Audio
driver for, 12
Axia IP-Audio
Driver for, 21
Pathfinder Router
Control
Application.
See: Pathfinder
Router Control
Application
Sound cards, 8
Sound-card
replacement, 7
Plugs, 26
Plugs and Cables, 25
Protocol Design
Principles, 58
QoS, 21, 39, 52, 53,
56
Quality of Service.
See: QoS
Redundancy, 16, 35,
37
Resources, 67
Cabling
infomration and
standards, 67
Ethernet, 67
Ethernet Radio, 68
General
networking and
Internet, 67
# 1490-00037-000
Ver 0.9 SC/RKT 09/04
1.0 RKT 11/04
75
Livewire/Broadcast
, 67
Test equipment,
68
RJ-11, 26
RJ-45, 25, 26
Installation tips,
30
Routers, 55
RTP, 53. See: IP RTP
Security, 38
Shielding, 32
Smartsurface, 13
SmartSurface, 63
Smartsurface, illus,
14
Sound cards. See:
PCs
Source, 18
Source configuration
screen, 18
Sources, 18
STLs, 9
Streams, 6
Livestream, 18
Livestreams, 4, 69
Standard stream,
18
Standard streams,
69
Standard Streams,
4
Structure wiring, 31
StudioEngine, 13, 14,
63
StudioEngine, illus,
13
Surround, 3, 9
Sync LED, 45
TCP, 53
TIA/EIA-568, 28
Timed events, 16
Troubleshooting, 43
Cable testers, 44
Hardware node
LEDs, 45
Link test, 43
Ping test, 43
Some things to
check, 43
Switch diagnostics,
43
UDP, 53
Unbalanced
Connections, 32
Virtual LANS. See:
VLANS
VLAN, 39, 41
VLANs, 54
VLANS, 55
WEGL
Livewire
installation,
illus, 35
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