Week 7: Day 021 - Installing a Physical Network #5

We're five posts into this chapter, and still not finished! To keep up pace, I'm gonna wanna finish this chapter quicker I would say. Thankfully, I'm not too stressed out with other classes as of now, so it shouldn't be too difficult to get back to my former pace.

Last time, I finished talking about Telecommunications Room and Making Connections. Today, I'm moving on to Testing Cable Runs. After you've completed the installation of the horizontal cabling, the best course of action is to see if all the jacks are plugged in, and then test the cable runs and assess their speeds. That's great and all, but network testing equipment can cost thousands of $$$ which sucks. However, there are less expensive ways of testing your network. According to my textbook here are some good questions to ask when dealing with potentially bad cables:

- How long is this cable? If it's too long, the signal will degrade to the point that it's no longer detectable on the other end.
- Are any of the wires broken or not connected in the crimp? If a wire is broken, it no longer has continuity (a complete, functioning connection).
- If there's a a break, where is it? It's much easier to fix if the location is detectable.
-  Are all of the wires terminated in the right place in the plug or jack?
- Is there electrical or audio interference from outside sources? UTP is susceptible to electromagnetic interference.
- Is the signal from any of the pairs in the same cable interfering with another pair?

In response to those questions, you must use a cable tester to answer them. Some are better than other, and can also answer more of those questions than others. Continuity testers are the economy ones, which are under $100, problem though is that it requires both ends to be connected in there (and I'm sure you don't want to unplug all those cables!) Now the more expensive testers run "wiremap" tests that pick up shorts and cross wires. The multimeter, which I've actually used before, is good to testing continuity. If there is no conneciton, you'll get infinite Ohms. So medium-priced tester cost around $400 and determine not only continuity and wiremap, but also the length of the cable! In addition to that, also if there's a break on any of the wire strands. One great advantage is that the tester works with already installed cables, so no unplugging. The more expensive ones detect some really specific issues, such as crosstalk, which is when when one of the UTP wires sends a signal, and the other wires pick up some of it (because they're so tightly closed together.) When crimping you should be wary, because a bad crimp will make it so the cable cannot do top speed due to a lot of crosstalk. To test the crosstalk the tester does a "near-end crosstalk" (NEXT) which detects and measures the amount of interferences on the near end of the connection. It also does a "far-end crosstalk" (FEXT) which listens on the far end of the connection. Other problems that occur in cables is "attenuation" which is when the signal gets weaker. When a cable run gets longer, there's more attenuation, unfortunately. To verify every cable run meets the TIA/EIA standards, tools known as "cable certifiers" are used. Most network techs will never use that (cause they don't need it!)

Finally, I want to go over testing fiber. In terms of testing, this is a very different thing. Fiber-optic technicians have to perform termination on the cables, and it's almost like an art, the amount of stuff that has to be done. In fact, I won't even get into that! The problems of a fiber-optic run is close to that of a UTP run. However, fiber-optic runs do not experience crosstalk or interference, because as said in earlier entries, they use light instead of electricity. However fiber-optic cables can still break, so a good network tech keeps an "optical time domain reflectometer" (OTDR) so if there does happen to be a break, it tells you where you can find it in the cable. The requirements for TIA/EIA are even more complex for testing fiber runs. The problems with fiber-optic cables are attentuation, modal distortion, and light leakage. Basically, if you accidentally bend a fiber cable you get light leakage, and the problem with attenuation is basically the same, except with light. The problem with modal distortion is however, specific to multimode fiber-optic cables. To install a cabling system, you'll need to be very skilled, and honestly, it should be left to the pros. But understanding this is great, so I can communicate with the pros when the time comes. On that bombshell, that's the end of my entry! Thanks for reading, and tschuss!