You should also be aware that there are many issues related to cabling that can cause problems, and are often overlooked as a potential cause. The most common form of network cabling used in homes and offices is unshielded twisted pair (UTP), with fiber optic cabling being the more expensive alternative. UTP cabling is susceptible to various forms of interference. One such form is crosstalk, when the signal from one cable bleeds into another cable. This often happens when two cables are run too close to each other. Near end crosstalk (NEXT) is when an outgoing data transmission leaks into an incoming transmission. Far end crosstalk (FEXT) is when a transmitting station at the other end of a transmission line leaks into the receiving line. One of the ways you can minimize crosstalk is to purchase high-quality UTP cable, in which the twisted pairs are twisted more tightly; the greater the number of twists, the less crosstalk.

EMI can also reduce signal strength. Computer monitors and fluorescent lighting both create an electromagnetic field and can cause problems with UTP network cabling. Radio frequency interference (RFI) from objects such as cell phones can also be an issue. The solution to this problem is to run network cabling away from such devices.

The signal in a UTP cable is susceptible to attenuation if the cable is too long. Keep in mind that the maximum length for Cat 5 and Cat 6 UTP cabling is 100 meters. If there are intermittent network problems and you notice that the cables are too long, this may be the problem. If you can't shorten the cable run, then installing a repeater will solve this problem.

One way to avoid all these problems is to install fiber optic cabling. Because fiber-based media uses light transmissions instead of electronic signals, the issues discussed in this section, such as crosstalk, EMI, and attenuation become nonissues. Fiber optic cabling is also a secure medium, as accessing the data signals requires physically tapping into the media, which is difficult to do.

Unfortunately, the high cost of fiber-opting cabling precludes a lot of organizations from implementing it in their networks. Moreover, fiber optic media is incompatible with most electronic equipment, requiring you to purchase fiber-compatible network equipment. Thus, while fiber optic cabling will continue to play a role in networking, particularly in serving as the media for the internet, WANs and metropolitan area networks (MANs), its impact on smaller networks will likely be limited for the foreseeable future.

It is generally a good idea to check cabling. If you suspect that Ethernet cabling is damaged, try swapping it with new cabling. Make sure that you are using the right type of cabling for the connection. Check to make sure that devices at both ends of the cable are on and that the ports are enabled and functioning. If you suspect that a device is not doing auto-negotiation properly, you may want to plug in another device and see if it works.