Test Your Structured Cabling System

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.

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.

PCQuest had the opportunity to visit the manufacturing and testing facility

of Digilink in Goa and witness their testing procedures and processes.