We all know that, when making a comparison, the items being compared need to be the same type. The same holds true for structured cabling. An apples-to apples comparison of structured cabling systems can only be valid if both system channels have the same topology.
Your cable topology – the cabling components you select, the way you physically lay out your cabling system and design your cable channels – can impact many things:
As opposed to a permanent link – the fixed part of a network made up of components that permanently stay in place (patch panels, outlets, etc.) – a cable channel refers to the entire connection between two devices (a switch and a computer, for example), including all connectors and patch cords.
When planning and installing a cable channel, we know it’s important to pay close attention to the components you choose. For instance, deploying high-performance Category 6A cabling along with Category 5e patch cords may negate the benefits of having a Category 6A cable, which will lower your network performance to a Category 5e level.
The length of cable channels can also impact network performance, such as return loss margins. When cable channels are far shorter than 100 m, for example, it provides an opportunity for connectors to have more impact on the cable channel, reducing the return loss margin. Return loss margin is directly related to your cable topology.
Below is an example of a 16 m channel, showing a short (10 m) permanent link with patch cords on either side. Below the 16 m channel is an example of a 24 m channel made up of a 15 m permanent link along with zone cords and patch cords – enough to make the connectors on the far end more attenuated so their impact is reduced. In this example, we see a higher return loss margin.
Looking solely at the numbers, the 16 m channel margins are better than the 24 m channel margins. With both channels made from the same components, this is a good example of how return loss margin is directly related to cable topology.
Cable channel test results can also be impacted by 100 m channels that aren’t designed in the same way (like placing patch cords and connectors in the middle of two permanent links, for example). Setting up the cable channel in this way attenuates the common-mode noise that causes alien crosstalk. In certain situations, this setup can give the impression that alien crosstalk performance is better than it really is.
A comparison can be made with these long channels as well by looking at channel alien crosstalk. In the first cable topology setup featured below, there are two permanent links (67 m and 20 m); in the middle are patch cords. This setup can achieve good alien crosstalk performance – better, in fact, than the second configuration – because of the location of the connectors. In the second configuration, which features an 85 m permanent link with patch cords on either end per TIA, you can expect a higher margin on alien crosstalk performance.
Again, with both channels being made from the same components, this is a good example of how alien crosstalk margin is directly related to cable topology.
It’s important to remember that your cable topology – the way you physically lay out your cabling system and design your cable channels – can impact many things, including the perceived performance of your cabling system for all cabling parameters, including alien crosstalk and return loss margin.
When comparing system performance to make a decision about the best cabling supplier, don’t just compare margins without including the cabling topologies. You may find out that you are not comparing “apples to apples.”
To learn more about how Belden can help you design your network and cabling system for the best performance possible, contact us.
Ron joined Belden in 2016 to help define the roadmap of technology and applications in the enterprise. Prior to this, he developed cables and connectivity for Panduit and Andrew Corp. Ron Tellas is a SME in RF design and Electromagnetic Propagation and has BSEE from Purdue University, a MSEE from IIT, and a MBA from Purdue University.