by April 1, 2010 0 comments

Information plays a pivotal role in businesses and is the primary reason for
the emergence of bandwidth intensive applications like VoIP, IP based video
conferencing, etc. As networks evolve to support such intensive data
communication, so does the requirement of the cabling infrastructure to support
them. Whenever you plan to install a new cabling infrastructure for your
organization or upgrade the existing cable layout, you need to ensure that the
structured cabling in your building provides you the desired data transmission
capability and gives reliable performance.

The need for cable testing
Deploying structured cabling is not only about buying UTP cables and laying
them across the building. There’s much more to it. The biggest challenge is not
deciding whether you need fiber or copper, but how you can manage the web of
bulk fiber and copper spanning across your network. Structured cabling is mostly
seen as a one time investment by many organizations. However, about 78% of the
network related issues are because of the faults in the cabling infrastructure.
While implementing structured cabling, organizations need to  understand the
data transmission requirements for future. No matter what standard you are
implementiong, 10BASE-T, 100BASE-TX or 1000BASE-T, there are specific
requirements and potential pitfalls in implementing these technologies. And with
the introduction of 10GBASE-T, it becomes even more critical to keep a tab with
the latest developments in cabling.

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The Telecommunications Industry Association (TIA), is the governing industry
standards organization that deals with creating and maintaining standards and
specifications for various categories of telecommunications cabling. It is
mandatory for the structured cabling manufacturers to comply with the prevalent
industry standards. The tests performed by the Structured Cabling products
manufacturers are stringent and extensive as they have to adhere to the
guidelines of various International standards, and also have to get their
products certified by different globally recognized testing labs. As a network
architect, you should subject cables to performance tests before purchasing.

Testing performance
As networks evolve, so do requirements of the cabling infrastructure to
support them. Today devices like LAN testers, from Fluke and other brands are
available that network analysts and architects use readily to check for any
performance variance in the network setup within their infrastructure. These
advanced LAN testers generate signal from one end of the network and scan the
same from other end of the network; the device can then analyze and compare the
result with minimum required standard values. The parameters on which the
performance of the cable is judged is based on results of various tests like:
WireMap, Resistance, Attenuation to CrossTalk, Insertion Loss, Return Loss,
NEXT, etc. Though wiremap or ‘ping’ tests are age-old tests that are still good
enough to know where the fault or problem lies in the network infrastructure, to
decipher the reason behind the faults, one needs to refer to results of other
tests that are given by such advanced LAN tester devices.

Knowing crosstalk
A cable can give deteriorated performance because of crosstalk, which can
happen due to external noise that may have been introduced into the cable. The
reason could be a high-frequency device which is near to the cable, or at the
end-point there could be signal interference happening with another end-cable
outlet. The second factor is the length of the cable that may cause signal
attenuation, which is the decrease in signal strength from one end of the cable
to the other. It therefore becomes important to keep in mind the length of the
cable required for laying the network. Since, different types of copper cables
have variable length specifications; so, one has to opt for specific cable types
for installation over long distances and for shorter distances. Hence,
Attenuation to Crosstalk Ratio (ACR) is the most important result when testing a
link because it represents the overall performance of the cable. Other tests
that can help network architects in knowing performance of cables are:

Length: The length of the cable is sometimes the obvious cause for
attenuation. Since, the longer it gets the more resistance it will provide
resulting in less of signal reaching the other end. To measure length, the LAN
Tester devices use Time Domain Reflectometer (TDR), which sends a pulse through
the cable and when it returns it measures the time it took to travel down the
cable and back to the device/source. The network architects should know that due
to twists in the cable, the measured length through the device will be greater
than the physical length of the cable. Therefore, if you require to install a
cable for 80 meters which is specified to be free of attenuation till 100
meters, then doing this length test will help you know the actual measured
length of the cable to judge if this cable will be fine or to opt for a higher
specification cable.

NEXT: Near End Crosstalk occurs because alternating current flow
produces electromagnetic field around the cable that induces current flow in
adjacent cables. During transmission of data, the point where highest crosstalk
happens is the RJ45 connection, as it enters the cable or ‘Near-End’. The NEXT
effects are canceled out with twists in cables. Cable manufacturers also vary
the twist rates for each pair within the cable to combat crosstalk.

For any network architect planning to setup the network cable
infrastructure, the first fundamental step is to align his network design to
standard procedures. In physical layer designing there are two standards:
TIA-568-C and ISO/IEC-11080. Both would ensure bare minimum requirements
desired. Then there are guidelines, region dependent at times, for which an
excellent reference manual can be BICSI’s Telecom Distribution Methods
Manual, Telecom Cable Installation Manual, etc. CIOs or decision makers can
take a cue from various standards and certifications that a structured
cabling manufacturer adheres to. These are parallel standards and spell the
minimum performance levels for all recognized media, be it UTP Copper
solution or Lazer Optimized Multimode Fiber solution. There are neutral
testing agencies like UL, ETL, 3P who would verify the performance on
products simulating field conditions. End-user can take these as the
reference to compare amongst brands.

Milind Tamhane, Vice President – ITS Sales,

PCQuest had the opportunity to visit the manufacturing and testing facility
of Digilink in Goa and witness their testing procedures and processes.

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