How to thoroughly Test Copper "Twisted Pair" cabling - A step beyond standards compliance
Based on the application requirements of those that will run over the network, additional parameters may be specified in the Statement-of-Work/Field Testing Requirements. For example, we're seeing exponential growth in the area of Internet-of-Things (IoT) and Industrial-Internet-of-Things (IIoT). Devices are increasingly being powered remotely by Power-over-Ethernet (PoE). This is often preferred because separate power outlets no longer need to be installed. On the other hand, the measurement of Resistance Unbalance, not part of the standard Field Tester requirements, must be executed. Why? Because PoE operation at high loads is at risk if Resistance Unbalance is out-of-spec, and high loading can also cause poor electrical contacts to degrade over time. The Resistance Unbalance parameter test is activated by selecting the '+POE' option when selecting the appropriate test limit.
- With data transfer speeds going up, another measurement which is becoming increasingly important is Shield Integrity. This is especially true since the introduction of the IEEE 10GBASE-T application standard in 2006, which allowed transmission at speeds of up to 10Gb/s over a Cat 6A or Class EA cabling system. Legacy testers use DC Resistance measurements to ensure the shield is correctly terminated and presented in a cabling system. These testers will report the shield as connected, even if one of the ends is not. In the below image you can see that alternative electrical paths, such as through the building ground (earth) can cause some testers to incorrectly report that the shield is properly connected.
It is important to assess that the shield is connected at both ends of a link. If it is not a degradation of up to 10-20 dB loss in electromagnetic immunity (EMI) is likely and as a result the Alien Crosstalk parameter will become non-compliant. This is especially true in a data center environment, where this fault can be critical. The DSX CableAnalyzer has unique capabilities for confirming shield integrity. It ties the four pairs together and then sends a differential signal down the cable treating the shield as the second conductor. This allows the DSX CableAnalyzer to view the shield in the time domain. So even if the patch panels are grounded, it will report the shield open, if indeed there is a shield fault, you would see:
Selecting any shielded cable type will automatically select the 'Shield Integrity' test as one of the test criteria. This means that the test can result in a 'Fail' if the shield is damaged along the cable length, or is incorrectly terminated.
The arrival of the Cat8 standard in 2017 resulted in development of a nuymber of new, additional performance parameters, several of which are not directly required in field test applications, but which can provide valuable additional data regarding cable performance, and in some cases, the performance of cables with reference to adjacent cable runs (known as Alient Crosstalk.) These new parameters, which include TCL (Transverse Convergence Loss) and its far-end equivalent, ELTCTL, plus CDNEXT (Common-to-Differential Near End Crosstalk) and CMRL (Common Mode Return Loss) are all present and available to provide additional detail data about installation performance in both the DSX-5000 and DSX-8000 CableAnalyzers. These additional parameters can be accessed by selecting the '+ALL' option in the selected test limit.