Physical issues can be the origin of many problems. First, there are issues related to cabling. The most common form of network cabling and the form that is used in most homes and offices is unshielded twisted pair (UTP) cabling. Fiber optic cabling is the more expensive alternative. UTP cabling is prone to various types of interference; one form is crosstalk, when the signal from one cable bleeds into another cable.
Crosstalk is likely to occur when two UTP cables are run too close to each other. Near end crosstalk (NEXT) refers to when an outgoing data transmission leaks into an incoming one, whereas far end crosstalk (FEXT) occurs when a transmitting station at the far end of a transmission leaks into the receiving line. The solution, other than separating the cables as much as possible, is to purchase high-quality UTP cable. In these cables, the twisted pairs are twisted more tightly together. The greater the number of twists, the less crosstalk there is.
Electromagnetic interference (EMI) can also reduce the signal strength of cabling. Computer monitors, fluorescent lights, and electrical current are just some of the things that create an electromagnetic field and can cause problems with UTP cabling. Radio frequency interference (RFI) from objects such as cell phones can also be a factor. The best solution, other than buying high-quality UTP cabling, is to run network cabling away from such devices as much as is possible.
Keep in mind that the signal in UTP cabling is susciptible to attenuation, especially if the cable is too long. The maximum length for both Cat 5 and Cat 6 cabling is 100 meters. If you have noted intermittent network problems, you may want to check the length of the cabling. If the cables are too long, this may well be the problem. If you can't shorten the cable run, then try installing a repeater and see if this solves the problem.
Naturally, you can avoid all the problems associated with UTP cabling by installing fiber optic cabling. Fiber-based media uses light transmission instead of electronic signals. As a result, the issues discussed in this section such as crosstalk, EMI, and attenuation become non-issues with fiber optic cabling. It is also a secure medium; this is because accessing the data signals requires tapping into the media, which is usually difficult to accomplish.
Alas, the high cost of fiber optic cabling precludes many organizations from implementing it in their networks. In addition, fiber optic media is incompatible with most electronic equipment. This means that you must purchase fiber-compatible network equipment if you want to utilize it. The net effect of this is that while fiber optic cabling will continue to play a role in networking, particularly in serving as the primary medium for the internet as well as for WANs and MANs, its impact on smaller networks will likely to be limited, at least for the forseeable future.
Above all, be sure to check your cabling on a regular basis. If you suspect that Ethernet cabling is damaged, try swapping it with new cabling and see if it solves the problem. Investing in a network cable tester is also a good idea, there are many cable testers available relatively cheap, which will save you both time and money in the long run. Check to make sure that devices at both ends of the cable are on. Also check to make sure the ports are enabled and functioning. If you suspect that a device on your network is not performing autonegotiation of speeds correctly, you may want to plug in another device and see if it works.