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10GBASE-T: What does it mean for my network?
10 Gigabit has been much in the news recently. This
makes sense, given the flurry of industry activity and standards emerging on the topic in the last few months.
None of this activity has generated more interest than
10GBASE-T, the next generation of Ethernet speed over
copper unshielded twisted pair (UTP) cabling. UTP's
winning combination of low cost, robust usability and
easy termination has driven such a prolific installation
rate that it dominates most networked environments today
as the cable infrastructure of choice.
Copper UTP has given us many capabilities in its short
history. Today's UTP will support equipment and devices
operating at 10Mbps, 100Mbps and 1Gbps speeds. It
supplies power to our IP phones and wireless access
points. And by aggregating multiple links together, it
provides a very cost-effective uplink capability for
runs of up to 100 meters in length.
No surprise, therefore, that 10 Gigabit speed — the
logical option to uplink all those edge Gigabit ports —
is eagerly anticipated by networking vendors and
customers alike.; You'd think translating this anticipation into action
would be easy. The standard has been published, and it's
just a straightforward process of installing some new
switches or modules out there, then lighting up the
lines at 10G speeds, when and where you need it, right?
Unfortunately, it's not quite as simple with
10GBASE-T as it has been with its predecessor
technologies. Understanding the conditions and expected
behaviour of this new standard is critical to planning
for deployment of 10G, in addition to saving a lot time
troubleshooting should a problem occur.
Cabling considerations
Generations of copper cabling have been getting better
at solving these challenges as we've moved through
Category 5, 5e and now Category 6 UTP, while at the same
time maintaining their "usability" in terms of
termination and flexibility.
The technology envelope has been pushed back far enough
with 10GBASE-T that it requires new cabling to go the
full 100 meters, but this doesn't necessarily mean that
you need to rip out your Cat 6 cable just yet.
The 802.3AN standard for 10GBASE-T defines two modes of
operation: short haul, at 30 meters, and long haul, the
full 100 meters. Short-haul interfaces will remain
useful due to the lower power required, which therefore
allows higher densities of ports per rack space. It will
work very well in a server rack or data centre
application.
To hit 100 meter distances and not be affected by
interference from the higher power levels required to
run 10Gig, a new type of cabling had to be defined,
called Augmented Category 6 (or Cat 6A). The standard
goes on further to define support for older cabling and
offers some guidance on what to do to avoid possible
interference.
Long-Haul 10GBASE-T
|
Cable type |
Supported Length |
Comment |
|
Category 6 |
55 meters |
|
|
Augmented Category 6 |
100 meters |
|
|
Category 7 |
100 meters |
Shielded cable (needs shield management)
|
Short-Haul 10GBASE-T
|
Cable type |
Supported Length |
Comment |
|
Augmented Category 6 |
30 meters |
*expected that Cat 6 will also run to 30m,
although not specified in the standard
|
|
Category 7 |
30 meters |
Shielded Cable (needs shield management)
|
Does this realistically mean that if you try to run 56
meters of Cat 6 your link will fail? Probably not.
Because these limits were designed with "worst case"
scenarios in mind, it's possible your existing links
will work; however, testing will be essential to ensure
the performance of the link for this new technology.
The key capability delivered with Cat 6A is immunity to
10GBASE-T's biggest challenge: external interference,
called "alien interference" or "alien NEXT." This type
of interference happens when cables are bundled tightly
around one or many central cables. Typically, the
largest source of alien NEXT comes from the first 20
meters of cable from the active equipment. The picture
below demonstrates the problem.
(Source;
Procurve Networking by HP – Technology, March 2007) | 
