While testing a large sample of patch cords recently, I was surprised by the degree to which performance varied from one patch cord to another. With my curiosity piqued, I tested those same patch cords in the channel--the sequence of cable and connections from hub to workstation--and found roughly the same degree of variability in overall channel performance as that which I had observed when testing the patch cords independently. The quality of the patch cord, it seemed, played a key role in determining the transmission quality provided by the channel as a whole.
Although it is a small, common component, the patch cord can cause big problems in performance and data transmission for networks. The good news for network users is that the industry is finally beginning to recognize the crucial role patch cords play in channel performance.
Patch cords are the short lengths of modular, plug-ended cable that connect personal computers to wall outlets and crossconnects to hubs. They are the element that turns the basic link into the channel. Difficult to manufacture consistently and difficult to test, patch cords are the cheapest channel components to replace, yet they can seriously contribute to network performance degradation.
Channel vs. cord performance
So why has it taken so long to focus attention on patch cords? Until recently, we had no practical method of quantifying a patch cord`s performance at the component level without destroying the cord. In the past, patch-cord performance was inferred solely from the performance of the overall channel. However, problems often arose when any of the patch cords in a compliant channel were replaced because the new patch cord could perform very differently from the patch cord that had been channel-tested and certified. The difference in patch-cord performance could cause the channel to test outside its recommended specifications--principally for return loss. Therefore, patch-cord testing independent of the channel is absolutely necessary, just as it is for other components of the physical layer, because all patch cords are not created equal.
It`s not difficult to understand why variations in patch-cord performance exist. The materials and practices used to manufacture patch cords differ from each other in a variety of ways. Some companies, for example, use scrap cable to manufacture patch cords. Others use inferior connectors and assembly techniques. Cords can even differ in performance from one end to the other.
Poor-quality patch cords can decrease the data-transmission rate or throughput of your network by reducing its overall bandwidth--and that remains true no matter how great your cable or connections are supposed to be. The high-speed channel you think you`ve bought may not be transmitting as fast as you think it is. Quite simply, having the right patch cords is an important step in establishing an efficient, cost-effective network.
How, then, do you determine which patch cords are right for your network? If you`re installing a new network, be sure to match the patch-cord cable type with the horizontal cable installed in the channel. Doing so will result in better impedance matching throughout the channel. Furthermore, electrical reflections, or return loss, due to inadequately matched cables will be minimized. In other words, when you use components manufactured to work together, they usually do, and you get better results.
Similarly, verify that the modular plug terminations of the patch cord are designed for use with the modular jacks they mate with. Quite often, connectivity manufacturers optimally tune their systems to perform best with their own components. When terminating patch cords with modular outlets or patch panels from different manufacturers, you will find that the mated performance is not as good because the components were not specifically designed to work with each other. The manufacturer, on the other hand, usually has very precise assembly procedures to ensure the plug is terminating consistently in the patch cord.
At Anixter, we test both the individual performance of components and their overall channel performance. To learn more about patch cords and their importance to the channel, call (800)-anixter.