Structured Cabling Design Considerations

Structured Cabling Design Considerations
Structured Cabling
Design Considerations
BLACK BOX
®
Planning your structured
cabling system.
Planning
Topologies
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Ethernet Standards
Introduction
Table of Contents
Planning your structured cabling system
Important design considerations................................................................................................................................................................ 3
Other factors to consider........................................................................................................................................................................... 4
Total cost of ownership.............................................................................................................................................................................. 4
Physical network topologies....................................................................................................................................................................... 5
Logical network topologies........................................................................................................................................................................ 7
Ethernet standards..................................................................................................................................................................................... 8
Ethernet nomenclature............................................................................................................................................................................... 9
This guide is intended to provide an overview of the design considerations that govern structured cabling systems. For expert
advice on your new or upgraded structured cabling system, and for complete services ranging from design and products through
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Structured Cabling Design Considerations
Important design considerations.
A structured cabling system is the wiring network that carries all your communications systems, including unified communications,
VoIP, data, voice, multimedia, security, PoE, and even wireless, throughout your office, building, or campus. It’s a critical
component of your organization. Proper planning, design, installation, and maintenance of this infrastructure can have a positive
impact on your company’s day-to-day operations and can contribute to its success.
A structured cabling system that’s smartly designed takes careful planning, even for the most seasoned professional. It’s much
more than just pulling cable through the ceiling. It’s a complex undertaking that involves integrating different technologies and
cabling types, projecting future capacity requirements, and making sure the whole system operates smoothly and reliably. The
more complex your network is now, the more important it is to successfully plan for growth. No matter if your network consists
of a two-room office or a multi-building campus, decisions you make now will impact your business’s or organization’s success for
many years to come. The system you plan today should support new and different applications, including migrating to 40-/100GbE, even 1-TB systems.
The question is, how do you plan for the future? The first step in designing and implementing a new or upgraded network
infrastructure is to step back and assess your needs.
Plan on using the best cable, hardware, and components your budget can afford. The latest technologies you install today will be
old hat by the time you’re ready to replace your cabling system. And, most importantly, plan for more capacity and space than
you think you’ll need. Consider these factors during your planning.
Lifespan. Consider how long you want your structured cabling system to serve your facilities.
Plan on a life span of 10–20 years, with 10 years being the minimum, and 15 years being typical. While the cabling itself
represents only about 5% of the total network budget, it is also the most difficult and expensive part of the network to
replace, requiring extensive labor and major workplace disruption. Your cabling system should have the longest life cycle of any
component in your network. You can expect to replace network electronics at least two to three times over the lifespan of your
cabling infrastructure. Electronics have an average lifespan of five years.
Bandwidth. The demand for it just keeps growing. The more the better. Consider how much capacity and speed you need
now, and how much you are going to need in the future. Remember, recabling is a very expensive proposition. Or in some
instances, you may have to plan on shorter cabling runs to achieve higher speeds.
BYOD/wireless. Plan for complete coverage with as much bandwidth as possible. Gartner estimates that tablet sales will reach
369 million by 2016. Forrester Research Inc. estimates that about 25% of computers used for work globally are tablets and
smartphones, not PCs.
Media. What media will you use? Fiber, copper, or both? The types and mixtures of cable you choose will depend on the
applications, architecture, environment, and more. Carefully consider any trade-offs of price for performance. The lowest-cost
cable may not be the most economical long-term choice, particularly as you migrate to 40-/100-Gbps in the future. Labor is the
most expensive part of installing new cable, so choose the best grade cable you can that will serve you for years to come as your
organization grows.
Location and number of users. How many users do you have now and how many do you anticipate adding over the next 10
years. Where are users and how far are they from the network switches? Will a collapsed backbone work better? Centralized
cabling? Zone cabling? Your architecture may also affect your cabling choices.
Usage. Consider how your network is to be used. A network in educational buildings has far different requirements than a
network in healthcare facilities. Other factors that can affect network planning include peak load periods, number of ports,
particular usage patterns, security, even outlet density.
Unified Communications/VoIP. The question isn’t if, it’s when. Plan on using the best cable you can to carry your voice, data,
and multimedia transmissions.
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Structured Cabling Design Considerations
Standards. ANSI/TIA. State and local building codes. NEC codes. They exist for a reason and will make your life easier in the long
run when it comes to performance, maintenance, upgrades, etc. If you follow the standards for distance limitations, installation,
and best practices, you should get good performance and conform to all safety regulations. Don’t forget cable management,
documentation, and testing requirements. Also, if you are in healthcare, education, or another specialized vertical, be aware of
specific standards that apply to you, such as TIA 1179 for healthcare facilities.
Other factors to consider.
Documentation. Don’t forget proper documentation, diagrams, labeling, color coding, and other administrative duties. Doing it
right in the beginning will make your life so much easier in the future.
Power over Ethernet (PoE). Consider where you may need to run power over your data lines. Also consider where you want to
locate networking devices, especially if it's in an area where there is no power or would be difficult to install power. PoE devices,
such as security cameras, alarms, and locks, solve the problem of no power availability.
Physical plant. Consider available space for data centers, equipment, telecommunications rooms, and cable runs. Also consider
any unusual physical constraints, such as power lines, EMI influences, seismic activity, or industrial activity. Make sure to factor in
plenum runs, additional air ducts, suspended ceilings, etc.
Security. Plan on current and emerging data, network, and physical security systems, including PoE and wireless applications.
Redundancy. Do you need to run duplicate pathways?
Pay particular attention to this if you are in healthcare, finance,
industry, or education.
Structured cabling system with mixed media
Warranties/manufacturer support. Be aware of product
warranties. What is the length of the warranty? What components
does it cover? How long will the manufacturers will support the
cabling?
CAT6A: 500 MHz
Single-mode fiber
(campus backbone)
Total cost of ownership.
This can be tricky. The lowest initial installation cost is not always
the least expensive or most economical solution. You have to factor
in the cost of upgrades and recurring costs over the lifetime of the
system. One of the greatest initial expenses is the labor to pull the
cable. Carefully consider what media you’re going to use. What may
initially seem to be a bargain may end up costing you much more in
the long run if you have to tear out and replace cable. You may be
better off spending more now on the highest category cable you
can afford, as it will serve you longer and better as you migrate
to higher bandwidth applications.
50-micron OM3,
10-GbE
(recommended
backbone)
Alternately, CAT6A
is also
recommended
The greatest expenses after your original investment will be
MACs and equipment upgrades. Plan on replacing your electronic
equipment two to three times over the life of the cabling system.
When all totaled, these ongoing costs can actually equal or exceed
the cost of your original investment.
CAT6A: 500 MHz
CAT6A: 500 MHz
CAT6A: 500 MHz
You also have to consider the quality of the installation. The
lowest bid may not necessarily be the best. A well-planned and
documented installation will more than pay for itself by lowering
long-term maintenance, eliminating problems from poor
workmanship, reducing downtime, and most importantly,
giving you peace of mind.
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Structured Cabling Design Considerations
Physical network topologies
A physical network topology describes how the devices in a network are physically connected and how the network is physically
laid out. Physical topologies include star, bus, ring, mesh, hybrid, and point-to-point. There are advantages and disadvantages
to each.
Star
In the star topology, all the network devices (individual workstations or peripherals) are connected to a central device, such as a
switch, in a point-to-point fashion. The star topology is one of the most commonly used today. ANSI/TIA 568-C.0, the Generic
Telecommunications Cabling for Customer Premises standard, recommends the star network. It specifies that there be no more
than two hierarchical levels of cross-connects between the main cross-connect and the equipment outlet. This is called a
hierarchical star topology.
Advantages of the star topology include its simplicity in installation. You can centrally manage the star network and will find it
easier to troubleshoot than other topologies. If one node/device goes down, it doesn’t bring the entire network down. You can
also add and remove network nodes without disrupting the entire network. In addition, a star topology is easier to troubleshoot.
Its major disadvantage is its single point of failure. If the central device goes down, the network goes down. To provide
redundancy and resiliency, star networks are often deployed in an ”extended” star, in which multiple stars are attached to the
central star. Think of this network as a snowflake pattern. The star topology can be more expensive than other topologies
because of the need for more network switches. When planning for future growth and flexibility, plan on using a star topology
for your campus network. You can always add redundancy with a secondary bus or ring network. This is called a hybrid network.
Star topology
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Structured Cabling Design Considerations
Ring
A physical ring topology links a series of devices in a
continuous loop, and the network sends the signals around
the ring. One of the main disadvantages of a ring network is
if the main cable or a single device goes down, so does the
entire network. To counteract this, often a second, counterrotating ring is added for resiliency and redundancy. A
counter-rotating ring will continue to operate even if a node
fails or a cable is cut. This is seen in Fiber Distributed Data
Interface (FDDI) networks.
Ring topology
The ring topology is mostly remembered as being used in
legacy Token Ring networks. If you’re concerned about
reliability, consider installing a counter-rotating campus
backbone ring to be used as a hybrid topology with your
star networks.
Bus
Mesh
The physical bus topology consists of one continuous, linear
backbone cable with devices connected it. All the devices are
linked to each other and the line is terminated at each end. In
the bus, when data is transmitted, it is received by all nodes in
the network. The bus topology is the oldest and was the
original Ethernet topology because it was easy and
inexpensive to set up. It is now out of date in favor of a star
topology. The bus has some disadvantages such as a limited
cable length and nodes, a single point of failure if there is a
cable problem, low security, and inefficient transmissions.
In a physical mesh topology, every node/device is connected
to every other node or device. The main advantage of this
topology is its high reliability. It is one of the most redundant
topologies available. If one node goes down, the network
doesn’t go down. Mesh networks are mostly used in wide
area networks where high availability is required. The major
disadvantage of a mesh network is that it requires much more
cable and is difficult to implement, manage, and troubleshoot.
To add a node, you have to connect the new node to every
other existing node. Partial mesh networks, ones in which not
all nodes are connected, are a trade-off between redundancy
and administrative management.
Bus Topology
Mesh topology
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Structured Cabling Design Considerations
Logical network topologies
The logical topology (also referred to as signal topology) describes how data flows through the network without regard to the
physical network configuration or topology. The logical topology refers to the data transmission path, which may or may not be
the same as the physical topology. Logical topologies are governed by network protocols, such as Ethernet, rather than by the
physical configuration of the network devices. The protocols also describe the media access method used by the network. The
two primary ones are shared media and ring (token based). You can have one physical topology and a different logical topology.
Logical topologies include bus, ring, star, and point-to-point.
Bus
This is the most common topology and is used by Ethernet and defined under IEEE 802.3. Ethernet is configured with a logical
bus topology that operates over a physical star topology.
Under a bus topology, a node broadcasts simultaneously to the entire network and each receiving node checks to see if it
the data is intended for them. Collision detection software directs traffic so network stations do not try to send and receive
simultaneously. Ethernet uses a protocol called Carrier Sense Multiple Access/Collision Detection (CSMA/CD).
Ring
In this topology, a node gains access to the network by grabbing a token that attaches itself to the data packets (frame)
being sent around the ring. Each node receives the signal and repeats it forward until it reaches the intended node. An
acknowledgement is added to the frame, which continues around the ring to the originating node. One advantage of a ring is
that if a node is down, the frame bypasses that station and continues. Only one node can send data at a time to avoid collisions.
Token based networks typically have latency problems and are usually configured in a physical ring topology.
In a counter-rotating ring, signals travel in one direction on one path and in the opposite direction on another path.
Token Ring networks are slow and are rarely used. FDDI is like a Token Ring network, but for fiber.
Star
In the star topology, all components are connected to a central switch that distributes traffic back out.
Point-to-point
This is literally a simple connection between one point and another, although it can connect multiple devices,
such as in a Fibre Channel network.
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Structured Cabling Design Considerations
Ethernet Standards
Network
Ethernet
Fast Ethernet
Gigabit Ethernet
10-Gigabit Ethernet
40-Gigabit Ethernet
Standard
IEEE
Media
Speed
Distance
10BASE5, 2
802.3
Coaxial
10 Mbps
500 m/185 m
10BASE-T
802.3i
CAT3
10 Mbps
100 m
2000 m/500 m
10BASE-F, -FB, FL, FP
802.3
Fiber
10 Mbps
100BASE-TX, T4
802.3u
CAT5
100 Mbps
100 m
100BASE-FX
802.3u
MM Fiber
100 Mbps
400 m half-duplex,
2 km full-duplex
1000BASE-T, TX
802.3ab
CAT5e/6
1000 Mbps
100 m
550 m/2 km
1000BASE-LX
802.3z
MM, SM Fiber
1000 Mbps
1000BASE-LX-10
802.3z
SM Fiber
1000 Mbps
10 km
1000BASE-SX
802.3z
MM Fiber
1000 Mbps
Up to 550 m
10GBASE-SR, -LR, LX, -ER, -SW, -LW,
-EW 10GBASE-CX4
802.3ae
CAT6, MM, SM Fiber
10 Gbps
65 m to 40 km
10GBASE-T
802.3an
CAT6 plus
10 Gbps
100 m
10GBASE-CX4
802.3ak
(4) lanes (8 twinax pairs)
4 x 2.5 Gbps
15 m
10-BGASE-LX4
802.3ae
MM, SM Fiber
10 Gbps
300 m/10 km
10GBASE-LR
802.3ae
SM Fiber
10 Gbps
10 km
10GBASE-ER
802.3ae
SM Fiber
10 Gbps
40 km
26–82 m
10GBASE-SR
802.3ae
OM3 MMF
10 Gbps
10GBASE-KRN
802.3aq
500-MHz MMF
10 Gbps
220 m
40GBASE-KR
802.b1
(4) lanes backplane
40 Gbps
1 m over a backplane
40GBASE-CR4
802.ba
(4) lanes (8 twinax pairs)
40 Gbps
7m
40GBASE-SR4
MMF
40 Gbps
100 m
40GBASE-SR4
(8) OM3 lanes
40 Gbps
125 m
SM Fiber
40 Gbps
10 km
40GBASE-FR
SM Fiber
40 Gbps
2 km
40GBASE-LR4
SMF
40 Gbps
10 km
SMF
40 Gbps
2 km
(10) Twinax lanes (20 pairs)
100 Gbps
7m
(10) OM3 MM pairs
100 Gbps
100 m
(10) OM4 MM pairs
100 Gbps
150 m
100GBASE-LR4
(4) SMF lanes
100 Gbps
10 km
100GBASE-ER4
(4) SMF lanes
100 Gbps
40 km
40GBASE-FR
100GBASE-CR10
802.bm
100GBASE-SR10
100-Gigabit Ethernet
1-Terabit Ethernet
Expected by 2015
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400 Gbps to 1 Tbps
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Structured Cabling Design Considerations
Ethernet nomenclature.
Ethernet nomenclature is fairly easy to follow, although the standards do not spell out the meaning of all the letters. Informal
terms have been adopted by the industry, but they don’t always coincide with the original intent. (This information is based
on a presentation by the Ethernet Alliance in 2012.)
Ethernet nomenclature: ATYPE-BCM1
ATYPE-BCM1
ATYPE-BCM1 = Data rate
10 = 10-Mbps
100 = 100-Mbps
1000 = 1000-Mbps (1-Gbps)
10G = 10-Gbps
40G = 40-Gbps
100G = 100-Gbps
B = media type or wavelength
C = Twinaxial copper
E = Extra-long wavelength (1550 nm)/
extended reach
F = Fiber
K = Backplane
L = Long wavelength (1310 nm)/Long
reach
S = Short wavelength (850 nm)/Short
reach
T = Twisted pair
ATYPE-BCM1
BASE = Baseband modulation
ATYPE-BCM1
C = Reach or PCS encoding
R = ScRambled coding
X = EXternal sourced coding
e = Energy Efficient Ethernet
ATYPE-BCM1
M = Multimode
ATYPE-BCM1
1 = 1 pair or lane
4 = 4 pairs or lanes
10 = 10 pairs or lanes, or 10 km
Example of Ethernet nomenclature for 100GBASE-LR4
Data Rate
Modulation type
Other distinctions
100G (100-Gbps) BASE (Baseband)
-LR4 (Long Range, 4 pairs)
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