Things You Must Know About Gigabit Ethernet 1

Things You Must Know About Gigabit Ethernet
1. Understanding Gigabit Ethernet
Today’s network managers know that modern demands on a network by its users can shrink
bandwidth dramatically. Faster computers, increased network resources and greater access to the
Internet can create an unbearable strain on networks with lowered bandwidth resources.
It used to be hard to believe that any network would require more than 10Mbit throughput. The
capacity of a 10Mbit network long outpaced the capacity of most computers and applications.
However, with today’s powerful computers, applications and peripherals, we know how quickly the
10Mbit bandwidth is filled up. Fast Ethernet evolved to provide networks with 100Mbit throughput,
and in fact, mixed 10/100 networks are the most commonly used in LANs. For a while, they
successfully solved bottlenecks at the backbone of the network.
Just as Fast Ethernet was introduced to increase bandwidth on 10Mbit networks, Gigabit Ethernet
is now being considered to again relieve the bottleneck caused by higher performing computers,
applications and peripherals. However, the decision to upgrade a network’s backbone requires
careful consideration of cost, interoperability and other factors that may affect performance
The Decision to Upgrade
Most decisions to upgrade a network follow the overall reduction in performance of the network.
Bottlenecks can occur at the backbone, servers, server connections and the connection to the
Internet. Network managers should assess their bandwidth needs based on the following:
Shared Files—Large or numerous data systems have a serious impact on the overall
performance of the network.
Shared Storage—Users must access the network to store or retrieve files, impacting
network traffic.
Large Server/Printer Farms—Servers, print servers and other network resources must be taken
into account in order to determine their individual bandwidth needs and evaluate their impact on the
Video and Audio over Ethernet—Improved video and audio technologies have increased users’
abilities to see and hear movies and music, increasing the strain on the network. Also, businesses
use these technologies for online training, meetings and teleconferencing.
Websites as Intranet/Internet Tools—Companies today use websites as a powerful sales and
marketing tool, and internal websites sometimes replace the corporate server as a place to post
company information. Interaction between the corporate intranet and the Internet add substantial
traffic on the network backbone. Quick and reliable access to web and ftp servers is vital to workers
and customers. Since these systems are most often connected directly to the network backbone,
ensuring enough bandwidth for these servers can be a problem with networks that are nearing their
bandwidth limits.
The Gigabit Solution
After having decided whether or not to upgrade, the network manager must decide which
high-speed LAN can offer the best value. Asynchronous Transfer Mode (ATM) is a well-known
alternative solution, but its higher costs associated with installation and maintenance has kept it
from being widely accepted. The Gigabit solution, on the other hand, has stemmed from existing
Ethernet standards with the same reliability and scalability of Fast Ethernet. IDC studies show that
by the late 1990’s, more than 85% of network connections were Ethernet, and Gigabit has become
accepted as a logical next step for those seeking higher speeds.
The Cabling Question
Upgrading your network to Gigabit may be the logical choice, but there is still a choice to make
regarding the types of Gigabit. Several cabling options are available.
1000BaseT Copper
Gigabit over copper may be the easiest, most cost-effective way to achieve Gigabit speeds. It
utilizes Category 5 UTP (Unshielded Twisted Pair), or better, cabling, but requires that all 4 wire
pairs be used.
Copper is less expensive than Fiber media, and is already widely used in many networks.
Therefore, Gigabit over copper can offer all the benefits of Gigabit Ethernet without significantly
restructuring existing cabling systems. UTP cabling is durable and easily maintained, but has the
same distance limitations (100 meters maximum) as Fast Ethernet.
Deploying Gigabit over Category 5 UTP is not difficult, physically, but special precautions must be
taken to prevent problems when adding 1000BaseT into a network.
As mentioned above, Gigabit requires the dedicated use of all four pairs of wires in the UTP cable.
With Ethernet and Fast Ethernet, it was possible to use only 2 pairs of wires for data transmission,
and the network manager could sometimes use the remaining pairs for secondary data
transmission, or for a Voice connection. Using all 4 pairs is necessary to overcome the following
issues that arise with Gigabit over copper:
Attenuation—Signal loss of the cabling from the transmitter to the receiver. In order to maintain
the 100m distance, attenuation increases with frequency; therefore, all 4 pairs are used to
maintain a low frequency, thereby keeping attenuation at an acceptable level.
Echo—An unwanted signal generated where both the transmit and receive signal occupy the same
wire pair. The signal bounces between the transmit and receive wires, and as echo builds, data
transmission degrades until the signal is lost.
Return Loss—Amount of the power reflected due to a mismatch in cabling impedance.
Cross Talk—An unwanted signal between adjacent wire pairs. Since Gigabit Ethernet utilizes
all 4 pairs, it is especially sensitive to cross talk of all kinds (near-end, far-end and equal level
far-end cross talk).
Protection from outside signal emissions becomes critical under 1000BaseT specifications. That
means that the network cabling must be installed in a manner that will avoid radiated energy
sources. Generators, fluorescent lighting, elevator motors, medical diagnostic equipment (X-ray,
MRI, etc.), AM and CB radio and other electrical devices can all affect wire signal quality, and
therefore, network viability.
Another specification to note is that Gigabit Ethernet only supports one repeater per collision
domain, whereas Fast Ethernet supports up to 2 repeaters, and 10Mbit Ethernet supports up to 4
repeaters in a collision domain.
Testing Your Existing Cable
Cabling runs conforming to current TIA/EIA-568A (1995) requirements should support 1000BaseT
operation. Individual links should be tested per ANSI/TIA/EIA-TSB-67 "Transmission Performance
Specifications for Field Testing of Twisted Pair Cabling System" with the additional tests
parameters for FEXT (ELFEXT) loss and return loss. This is due to be included as an addendum
to ANSI/TIA/EIA-568-A. The quality of the crimping job performed on cable ends is critical. For
example, the amount of untwisting in a pair as a result of termination to connecting hardware
cannot exceed 13mm (0.5in), or the connecting hardware may not meet current
ANSI/TIA/EIA-568-A requirements and may need upgrading. Likewise, it should be verified that
ALL 4 pairs are crimped.
It is also important to ensure that RJ45 wall jacks, horizontal cabling and connectors
(including all wiring closet components) meet or exceed the ANSI/TIA/EIA-568-A
Any parts of the cabling system that fail the ANSI/TIA/EIA-TSB-67 field test should be repaired
or replaced before continuing the migration to 1000BaseT.
1000BaseSX Fiber
One form of Gigabit over fiber is the 1000BaseSX specification, which employs short-wave light
lengths to transmit data. It uses 62.5-micron multimode fiber for operation at 160-200MHz. It has a
range of 2 to 275 meters (ISO/IEC 11801 building wiring standard). 1000BaseSX also operates
using 50-micron multimode fiber for operation at 400-500MHz and has a range of 2 to 550 meters
(ANSI Fibre Channel specification).
1000BaseLX Fiber
This more costly form of Gigabit over fiber uses long-wave light lengths to transmit data, and
uses both 62.5-micron and 50-micron multimode fiber. Its range is 2 to 550 meters for both
media types.
Using 9-micron single mode fiber under 1000BaseLX, the maximum distance reaches 5 km.
Fiber has the obvious advantage in distance (and is not susceptible to the signal issues mentioned
above), but the installation and maintenance of fiber-optic cabling is more difficult, and therefore
expensive. It generally requires professional installation and extra training, and is more
susceptible to breakage.
2. Assessing Interoperability
How the network manager implements the migration to Gigabit Ethernet will depend on the
existing network hardware. The following network scenarios describe how the Gigabit
Ethernet migration can be accomplished:
Legacy 10Mbit Networks
Virtually all 1000BaseT products on the market today support 100/1000 auto-negotiation. Adding a
couple 10/100 switches and network cards will convert your 10Mbit network to a 100TX. From here,
the network manager can continue to add Gigabit Ethernet switches as necessary to accomplish
higher speeds. Alternatively, you could choose a newer Gigabit switch that supports 10/100/1000
auto-negotiation, allowing your legacy 10Mbit devices to be connected directly.
Mixed 10/100 Networks
This network scenario is one of the most common, and also most likely to benefit from upgrading to
Gigabit. A Fast Ethernet backbone with multiple 10/100 switches can easily benefit from adding
one, or more, Gigabit Ethernet switches. Because most Gigabit switches support 100TX, they can
be linked to routers and other devices that support the 100TX link.
Vendor Compatibility
Some early Gigabit products that may exist in your network might have been on the market before
the standard for Gigabit Ethernet had been finalized. Broadcom, in particular, has early products
that may not now be compatible with standardized Physical Layer chip sets. Some companies
might not support Broadcom PHYs because of this (namely, Intel). Asante still supports use of
these early Broadcom PHYs, since you can work around the incompatibility by turning off the IEEE
802.3 compatibility in the driver of your Gigabit Ethernet network card.
3. Deploying Gigabit
A network employing both copper and fiber can benefit from Gigabit products that are now
available, using fiber at the backbone of the network or between buildings, and Gigabit
over copper to the desktop. Asante Technologies’ IntraCore switches support GBIC or
Module expansion slots for fiber and/or copper media.
The IntraCore 3524 Gigabit Ethernet switch is a 24-port 10/100 unit with 2
hardware expansion slots (type IC35). It supports the following Gigabit and
10/100Mbps media modules:
• 10/100/1000BaseT
• 1000BaseX GBIC
• 1000BaseSX
• 100BaseMMFX
• 100BaseSMFX
Gigabit Interface Converters (GBICs) are Gigabit only, and both fiber and copper GBICs
are supported on all IntraCore products.
4. Utilizing Multimedia Features
Now that your network will have such increased bandwidth, the next question becomes how to
manage a network’s higher priority traffic. Not every user requires sophisticated applications or
runs mission-critical programs, nor do they need the highest speed connections to the Internet.
Quality of Service
Quality of Service (QoS) refers to a network’s ability to provide improved and consistent services,
helping to manage network congestion and ensuring that throughput is maintained, even under
heavy traffic conditions. Multiple priority queues help shape the traffic to guarantee that
mission-critical applications get the bandwidth and priority that they need, while other
applications using the link still receive their fair service.
QoS service models differ from one another in how they enable applications to transmit and
networks to deliver data. A different service model applies to file transfer and e-mail applications
than to video conferencing and IP telephony.
Internet Group Management Protocol (IGMP) also is used to manage traffic on the network. It
optimizes multicast bandwidth by allowing multicast traffic only to registered users.
Per-port security may be configured with programmable action (i.e., new node detection trap) and
trusted MAC address tables. Network managers can control unauthorized access to network
devices by configuring "trusted" MAC addresses per port on switch models. When configured for
security, the ports "learn" trusted addresses either automatically through the connected stations, or
manually from the network manager. Only traffic from these trusted MAC addresses are allowed
through the port. If a violation occurs, network managers are able to configure ports to ignore the
violation, send a Simple Network Management Protocol (SNMP) trap, or block access.
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