|
Problems such as alien crosstalk arise with most new technologies
when each of the systems is taken to its design limits. |
Now that the IEEE has approved the
latest LAN high-speed transport technology for running 10-Gigabit Ethernet
(10GigE) over unshielded twisted-pair (UTP) cabling, the quickest adoption
will probably be in the data center and server farm areas. This is because
aggregate backbone speed requirements have already surpassed the current
Gigabit Ethernet standard requirements. This is also due to the availability
of copper-based solutions that will reduce expansion costs that are
typically higher with fiber-based 10GigE systems.
The real hurdle for implementing this new copper 10GigE UTP technology is
the cable, connector and patching products required by the new standard. An
entirely new cabling system is mandatory in order to make 10GigE operate
correctly. The existing Category 6 cable plants might be useable at
distances less than 37 meters, but the current TIA 42.7 working groups are
still defining the component requirements for both the new 100-meter
Category 6A cabling standard, TIA 568-B.2-Ad10, and the 37-meter, existing
Category 6 mitigation TSB-155.
Early in the IEEE process, the physical layer performance requirements were
established for the entire cabling “channel†(i.e., the cable, connectors
and patching that go between the new 10GigE switching equipment and the end
device’s network interface card, or NIC). Ultimately, this enabled industry
working groups to come up with a firm channel model and propose a
performance specification.
In the steady progression of Ethernet, the demand for more capacity per
channel has been self-fulfilling. As the design moved away from coax-based
systems to UTP, the transmission hardware has been on an almost exponential
slope by factors of 10 times every four years or so.
The core electronics that make these Ethernet evolutions possible have
become more complex and demanding as the speed has increased. The switches,
routers and NICs into which they go are required to operate with tighter
design specifications and must compensate for more heat. Not surprisingly,
the increase in bandwidth has always come with an increase in the operating
frequency of the chips that make it work. This increase in frequency has
also made the design of the cabling systems more difficult.
The design of cables and connectors and how they interact with each other in
installed systems has also changed exponentially with the increase in system
frequency. As the frequency increases, the performance of copper-based
transmission systems degrades and becomes more susceptible to noise. To
offset this, manufacturers have developed physical and system designs to
enable this tenfold increase in bandwidth.
As a result, there has been a corresponding doubling of the transmission
frequency with each generation of Ethernet. Manufacturers have designed
these systems in concert with IEEE, and have also added new digital signal
processor technologies to increase signal strength and minimize noise so
that systems can operate with minimal errors.
The higher application frequency requirements associated with 10GBase-T
transmission have also increased the complexity of verifying the cabling
system’s performance in both the lab and real-world environments. The signal
modulation used by 10GBase-T, known as PAM-16, has multiple levels, where
bits of data are encoded onto the signal being transmitted.
With 16 discrete encoding levels, 10GBase-T copper systems need 500 MHz of
useable bandwidth to operate properly over the maximum UTP cabling distance
of 100 meters, the maximum distance requirement for Ethernet-based systems.
While 500 MHz may be considered a relatively low frequency for broadband
applications, it is twice the bandwidth of what Category 6 cabling can
deliver.
The 500-MHz transmission frequency of 10GBase-T has introduced a new type of
noise impairment on balanced UTP cabling systems called alien crosstalk,
which is signal or noise coupling between adjacent cables. Alien crosstalk
coupling occurs with respect to both the near end and far end of the
installed cabling system.
Transmission performance on the cabling can be verified with testing
conducted on a single Category 5e or Category 6 cable. Testing for alien
crosstalk requires that multiple cables (known as disturber or exciter
cables) be energized simultaneously in a cable bundle. This testing ensures
that they do not affect the transmission of 10GBase-T signals on adjacent
disturbed (i.e., victim) cables.
Problems such as alien crosstalk arise with most new technologies when each
of the systems is taken to its design limits. Operational tolerances can
overlap and result in system failures. The best way to avoid this is to
over-design the systems, and to install cabling infrastructures that exceed
the minimum design specifications whenever possible.
For the past six months, intensive independent testing has been performed on
the major 10GigE cabling systems currently available on the market. Data has
shown that there are some good-performing 10GigE systems being sold and
installed today that will fully meet the required channel performance
requirements. When the 10GigE switching hardware is fully available, buyers
will already have many viable solutions available on the market to choose
from.
Purchasing a 10GigE solution, however, can be somewhat of a daunting and
challenging task if you are not equipped with all of the latest facts and
statistics on all of the 10GigE solutions available on the market. How do
you know how or why to choose one manufacturer’s solution over another?
If a company says it meets 10GigE requirements in its collateral, should
that be enough? In reality, the answer is no. Buyers should always do their
due diligence on any 10GigE cabling solution prior to buying it. Dig beneath
the brochure hype, and require full disclosure from the manufacturer or
distributor. Buyers always have the right to request a copy of the
manufacturer’s spec sheets or test results that will verify that the 10GigE
cabling products meet the testing parameters as specified in ISO, TIA or
IEEE cabling standards.
There are also independent third-party companies that will provide these
test results to you at no additional charge. At the end of the day, the
manufacturer or distributor should prove that its 10GigE cabling solution
meets the standard requirements and will efficiently run your applications
today and well into the future.
Pete Lockhart is vice president, technologies, for Anixter, Glenview,
Ill.
For more information:
www.rsleads.com/611cn-250
|