Ethernet is still one of the most utilized and reliable forms of digital communication in the world. Virtually every network has at least some Ethernet these days, and because of that, it’s important to know what kinds of things can inhibit Ethernet communication.
The Basics of Crosstalk
To begin with, crosstalk is interference in an electrical signal that messes with the flow of data. That interference can come from a number of different sources, but when it is present, digital communication suffers.
In Ethernet connections, the cable itself (or other Ethernet cables in the area) can create crosstalk. Since Ethernet is made from twisting pairs of copper wires, there are multiple electrical signals present in a single Ethernet cable. Those signals can interfere with each other and disrupt the flow of data. That’s the essence of Ethernet crosstalk.
Types of Ethernet Crosstalk
Even though Ethernet crosstalk primarily comes from electrical signals in other copper wires, there are different types of crosstalk that impact Ethernet lines. For the most part, you can break them into near-end, far-end, and alien crosstalk, but as we break down each type, you’ll see that there are variations and different things to consider.
The most common crosstalk that plagues Ethernet communication is near-end crosstalk (NEXT). This is crosstalk that is measured at the transmitting end of the cable, and it’s at this point that we need to be specific.
NEXT does not occur specifically at the transmitting end of the cable; that’s just where the measurement is made. The truth is that crosstalk happens across the full length of all Ethernet cables. The question is how much crosstalk is present, and how much is it interrupting communications?
NEXT is one of the best measurements to answer those questions, primarily because crosstalk is most pronounced at the ends of an Ethernet cable. This is because the copper wires are untwisted and unshielded in order to plug into devices.
Moreover, crosstalk is stronger at the transmission end than the receiving end because the overall signal is stronger at transmission. So, if you want a good picture of crosstalk in an Ethernet line, start with NEXT.
While near-end measurements are valuable, they don’t tell the whole story. You can also measure far-end crosstalk (FEXT), and as you might have guessed, this measurement is made at the receiving end of the cable.
Crosstalk is usually weaker here, primarily because the electrical signal loses a little bit of power as it travels through the cable.
Nevertheless, FEXT is a useful measurement and will often tell you about crosstalk in your line. FEXT is usually at its best when compared to NEXT. It gives you a better idea of how much of your crosstalk is coming from the transmitting connection in your cable.
The third primary type of crosstalk is alien. As the name implies, this is crosstalk that comes from external sources. In other words, this crosstalk doesn’t come from within a single Ethernet cable.
While alien crosstalk can technically come from any external source, the most common culprit is other Ethernet cables. If you pack large, tight bundles of Ethernet cables together, there’s a good chance that they will induce crosstalk among each other. That’s alien crosstalk, and it’s just as important as any other.
How Crosstalk Hurts
Before we start talking solutions, it’s probably worthwhile to understand just why this problem matters. Why would you consider investing in things to prevent crosstalk if it isn’t a big deal?
The truth is that the scope of crosstalk issues varies from one network to the next — even one cable to the next.
But, when crosstalk is pervasive enough, it causes major disruptions to your Ethernet signal. It can slow down your data rates, cause packet losses, and in extreme cases, it can shut down an entire network and force you to restart everything.
None of those consequences are fun, so if you’re having those problems, you can test for crosstalk to see if it’s a likely cause. In the case that crosstalk is your culprit, you can follow the tips below to mitigate it.
How to Avoid Crosstalk
Now that you’re sold on managing crosstalk, let’s talk methods. What can you actually do?
Battling crosstalk boils down to two concepts: shielding and distance. We’ll go through both ideas and then show you an example of how they work.
Shielding is your most powerful tool. Technically speaking, crosstalk occurs in copper wires because copper is a good conductor. When a signal runs through one wire in a cable, that current can induce magnetic and electric fields in the other wires. That’s the source of crosstalk.
This is why shielding is so useful. If you put any type of shielding between the copper wires, it dampens (or even completely stops) those inductions, and your crosstalk problem gets smaller quickly.
The easiest way to shield Ethernet equipment is to pay for it. You can get shielding cables that reduce crosstalk. You can also invest in shielded connectors to keep your endpoints from creating too much crosstalk.
Because crosstalk has to do with electric and magnetic induction, it involves the inverse square law. This is a fancy physics phrase that basically says distance mitigates crosstalk very quickly. If you double the distance between your cables, you cut the crosstalk into a fourth. The returns come very quickly.
So, any chance you have to spread things out is good for you and reduces crosstalk.
You can apply both concepts to your bundles when you run a lot of Ethernet cables in a network. This solution is specific to alien crosstalk, but the denser a network is, the more this idea matters.
One simple solution you can deploy is to group your bundles loosely. It might be tempting to sinch everything together nice and tight with a zip tie, but that exacerbates alien crosstalk. Loosen your bundles and even use velcro ties to that effect. The looser cables aren’t quite as close to each other, and that really does make a difference with crosstalk.
Keep these ideas in mind, and you can mitigate crosstalk and keep your networks fast and reliable.
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