By Dan Barrera, Global Product Manager, IDEAL Networks
www.idealnetworks.net

What does a LAN cable certifier test, and when should installers certify LAN cabling?

LAN cable certifiers continue to evolve and advance as the demands on networks develop. But despite progressing technologies, the reasons to certify cabling remain the same and this is due to cabling standards.

Understanding the standards

There are two main standardisation bodies that define the LAN cabling specifications. The ISO/IEC with the 11801 series of standards, and the ANSI/TIA with the 568 series, which define three types of performance requirements: components, cable and cabling.

Put simply, the first two elements of a LAN cabling system are the connectors and the cable. Component standards define the performance of jacks or outlets and plugs (connectors) for each performance category. Cable standards define the performance of the bare cable with no connectors attached. Manufacturers design and test their components and cables to these standards to ensure they meet the performance defined by ISO or TIA.

The third element of a LAN cabling system is the installation of cable and connectors in the field. This is what LAN cable certifiers test, and where the responsibility to check compliance with standards falls on the installer or engineer, rather than the manufacturers.

The cabling standard defines the performance of the completed links and channels when connectors and cable are installed in the field. Quality connectors and cable will provide their advertised performance when properly installed in laboratory environments, but installation in the field is very different from installation in a laboratory. In the field the cable can be stretched, kinked, crushed, installed in hot areas, exposed to water, and terminated with poor workmanship. Therefore, to ensure that the individual quality components form a completed, quality cabling system, installers need to test the performance of that cabling.

How it works

To set up a certifier to test cabling, the installer must select the desired performance standard as well as the configuration of the cable being tested. The two options for certifying commercial cabling are channel and permanent link (PL). Channel tests consist of the installed cabling, the patch cords that connect the cabling to the networking equipment and the connector that mates to the patch panel and work area outlet. The connection at the channel adapter is not included in the test.
When testing a PL, the installed cabling is tested using special PL adapters on the certifier. The connection at the patch panel and work area is also tested. This is the most common test performed in the field because it tests the elements of the cabling that the installer is responsible for, not patch cords which the end-user of the network could change, thereby invalidating certification test results.

What does a certifier test?

The key measurements for certifier tests are return loss and crosstalk. This is what separates certifiers from other types of network cable testers.

Crosstalk

Crosstalk is the measurement of a signal coupling from the intended pair of cable to another. It’s undesirable because it creates interference between the channels of the Ethernet transceiver at either end of the cable. The most common sources of excessive crosstalk are untwisting of the pairs during termination, poor quality connectors and cable or connectors that aren’t rated to the frequency at which they’re being tested.
Certifiers measure Near End Crosstalk (NEXT) for determining component quality in workmanship of the cable; Far End Crosstalk (FEXT) which is used in calculations for other measurements and Powersum NEXT, that’s a calculated value to simulate the combined crosstalk of any three pairs on the fourth pair of the cable. A certifier can also measure Alien Crosstalk where signal from one cable coupled onto a different cable, instead of the signal coupled from one pair onto another in the same cable, is measured.

Return loss

Return loss is the measurement of the signal reflected from the cabling back into the transmitting device – like an echo. High levels of return loss can create strong echoes that interfere with the transmission of the signal in one direction, but can also reduce the effective length of a cabling link or channel. Common causes of excessive return loss are plugs or jacks from vendors that aren’t compatible with each other, multiple connectors on a channel and poor contact between the cable conductor and contact of the connector (bad termination).

Beyond fault-finding

As well as finding faults in components or the installation itself, certifiers determine the true performance of an installed cabling system. Even where products appear to be labelled with a suitable rating, without field certification there’s no way of knowing if the actual performance matches what has been advertised.
To ensure the components purchased provide the required performance, installers should choose reputable brands. However, premium brand components don’t completely eliminate risk, so installations should be tested with a certifier to prove they meet the performance standard.

Why not qualify?

Unlike rigidly standardised certification, cable qualification has no defined tests or performance and accuracy specifications in the standards organisations. The manufacturer of the LAN qualifier simply decides what to test, how accurate the instrument is and how to report the results. This means the results from one brand of qualifier can’t be compared to another. Plus, without a definition for pass/fail limits, what does it mean when a qualifier fails a cable? For these reasons, no major cable or connector manufacturer will accept test results from a qualifier for their cable certification or warranty programmes.

Certifier or qualifier

An installer can easily check whether a tester is a certifier or qualifier. A tester is considered a certifier if it meets ISO/IEC 61935 and TIA 1152-A accuracy requirements and has ETL Level III/IIIe verified accuracy. Or, if the tester measures NEXT, PSNEXT, Return Loss, Insertion Loss and ACR-F, and specifies a test frequency range of at least 500 MHz, then it’s a certifier.
While certifiers are the best tool to guarantee installed cabling meets the stringent performance requirements defined by the ISO/IEC and ANSI/TIA standards bodies, installers should remember that a cable certifier is only an essential test tool on jobs where a certifier or cable manufacturer warranty is required. This is typically only the case in 25% of jobs. The rest of the time, a cable and network transmission tester can be used to create comprehensive proof of performance reports to industry recognised standards.

Certifiers are extremely important for finding faulty components and sources of installation mistakes, as well as helping to ensure that the materials are genuine, high-quality products and meeting customer requirements for warranties. However, installers should always carefully match their choice of tester to the needs of the job to ensure efficient and profitable operations.