Cabling Testing and Certification
Testing for a Category 6 Open Cabling System While there are many challenges in specifying a category 6 cabling system,
perhaps the most difficult is the interoperability between different category 6 component manufacturers. Unlike category 5 systems, where you can plug and play with your choice of connecting hardware and
still feel confident that your system will perform as required, category 6 systems usually require a proprietary cabling system to achieve the promised results. To avoid being tied to one supplier, network
owners and installers need to test and certify that their connecting hardware and patch cords are category 6 component compliant. Cat 6 connector performance is key
In order to achieve a category 6 open cabling system that is not vendor specific, both the TIA and ISO define both the physical properties and electrical performance
of the RJ45 plug. That's because the mated performance of the connector at the end of an installed cable is very dependent on the properties of the terminated RJ45 plug, especially the test parameter
near-end crosstalk (NEXT). As a result, connector manufacturers are required to design their connectors to a set of agreed physical properties for the RJ45 plug, while ensuring they will exceed the minimum
electrical performance of NEXT for the mated connection. The minimum NEXT performance for a mated connection is 52.5 dB @ 100 MHz. New category 6 testing tools benefit industry overall
The news of new category 6 testing tools and methodologies is good for the industry as a whole. Network owners and installers finally have absolute
assurance that the connectors and patch cords they are using are standards compliant and will work with their new category 6 cabling system. Similarly, connector manufacturers, cable manufacturers, and the
makers of quality patch cords now have the means to validate that their product is better than lower cost alternatives. The best way to ensure the quality of a category 6 open cable cabling system is to test
each step of the way using Fluke Networks standards-compliant centered
test plug and new DSP Patch Cord Test Adapters.
The Weakest Link In High Performance Cabling Systems Cabling is normally installed long before furniture or active
equipment, and over 95% of all new installations are tested to the permanent link model, which excludes the patch cords at both ends. The idea is that the link is tested and certified for the promised level
of performance (normally Category 5e or 6), and then patch cords are added later when the network is installed. This model works well if the performance of the patch cords meets the performance of the
installed link – which often is not the case.Most cabling professionals know that the TIA published TIA 568B in April of 2001, and that this standard includes performance requirements for Category 5e
cabling. What many don't know is why the standard took so long to be finished. One reason was the discovery that patch cord performance could vary in unpredictable ways. Tests of Return Loss were made on
Category 5 patch cords. Fluke Networks, a manufacturer of cable test equipment in Everett, Wash., measured the same patch cord in two different positions. There was no kinking, sharp bends, or cable abuse -
just a simple re-positioning of the patch cord. This is just the sort of repositioning that end users would commonly do as they move a cord between their PC and the wall outlet. The results were surprising.
Return Loss of the first position was over 4 dB better than in the second position! This was enough to mean one link passed and the other failed. This is a common error because in the TSB-67 days,
installers weren't required to measure Return Loss. This was a 'new' measurement, so its effects were not considered when patch cords were designed and manufactured. The Weakest Link
If you consider the entire structured cabling channel, from the PC to the switch, the weakest link is the modular plug. This is the point that has the potential for
the lowest performance. Why? Pairs get untwisted and jammed into a small space, they are crossed over each other and split, and then they are put in parallel with flat plates. Often, mechanical crimps are
used to hold the cable in the plug. These crimps can crush and deform the conductors, creating impedance changes that contribute to Return Loss. Cords take a lot of abuse; they are pulled around desks and
run over by chair wheels, stretched tight around fixtures and flattened by heavy furniture. Top 5 Causes of Cabling Failures
1. Modular plugs are not terminated properly
Use the right type of plug (stranded vs. solid conductor and follow the color code). 2. Pair-twists are not maintained
If needed, add an additional twist to
the pair when terminating the modular jack, when terminating ensure that the cutter on the termination tool is facing the right direction.
3. Too much cable jacketing is removed
Keep the cable jacket intact up to
the connector, only remove enough jacket to terminate the pairs.
4. Poor cable routing
Keep cable separation from power and other telecomm cabling as needed, do not exceed 25 lb of tension on cables being pulled, watch for cable twisting and
rubs on nails, screws, and even poorly drilled joists and studs.
5. Poor documentation
Keep good records of all cables placed in the job including all test data, leave a copy with the owner and in the distribution center. Trends in Fiber Network Certification Network certification is the process of testing certain network parameters and then comparing the actual results against an industry or user-defined standard. A
network is certified good if every tested link meets or exceeds (passes) the test limits as defined in the standard. Historically fiber network certification consisted of measuring insertion loss using a
power meter and light source. While this form of certification is still most common, fiber network installers and owners should be aware of emerging trends in fiber certification. Fiber Wiremap
As multi-fiber and duplex connectors gain in popularity, verifying proper orientation is increasingly important. Often called "polarity" in the fiber
world, it is analogous to UTP wiremap. You can use either a visual light source or an optical loss test set to verify the correct A-B fiber orientation to ensure that the transmitter on one end of a fiber
connects to the receiver on the other end. Installation Quality
While insertion loss testing provides an indication of whether a fiber link was
properly installed, an OTDR (optical time domain reflectometer) furnishes more details on cable installation and termination quality. An OTDR makes possible discovery of features along the length of a fiber
that may affect fiber reliability. You can use an OTDR to characterize features along a fiber link including attenuation uniformity and attenuation rate, segment length, location and insertion loss of
connectors and splices, and other events such as sharp bends that may have been incurred during cable installation. The TIA is contemplating incorporating an OTDR test in addition to an optical loss test as
a higher tier of network certification. Connector Condition
Every fiber connection is critical to network performance, especially in
high-speed, low power margin networks. It is essential to verify the condition of fiber connector endfaces. Recent studies show that more than 85% of all fiber failures encountered in LANs are due to
contaminated endfaces. Such contamination is easily seen with fiber microscopes. Documentation of the condition of connector endfaces may become a more common component of fiber network certification. |
