System Verification

System verification means documenting and managing your system. You should always test your network thoroughly and maintain detailed written documentation.

System verification begins at installation. Even the smallest systems need to be documented as they're installed so that records are available when those systems are modified. First, record cable type and network topology. Then make a wiring map of all connections and endpoints, as well as the locations of network hadware - repeaters, bridges, hubs, and concentrators. You should also include information about the network's limitations - the maximum number of nodes, maximum and minimum cable lengths, and other specifications.

Check the play in all mechanical connectors to ensure good contact. Also be aware of the locations of all AC power lines, motors, transformers, and fluorescent lights, and route cable around their electromagnetic fields. When you install a system, check the integrity of the new cable twice - once on the spool for the entire cable length and once along each segment after installation to check for stresses that might have damaged the cable during installation.

Check the cable on the spool with a Time-Domain Reflectometer (TDR) test, which sends a fast rise-time pulse down a cable and measures the intensity of reflections. The greatest reflection indicates the end of the unterminated cable. Reflections appearing too soon could indicate changes in crimping, stretching, corrosion, or breaks in shielding, among other defects. TDR testing is particularly useful for cable that's already in place to detect bad vampire taps, changes in cable type, pair splits, and other problems.

Unshielded Twisted-Pair (UTP) cable installed before July 1991 was not subject to EIA/TIA standards. Since its performance is unknown, you should test preinstalled cable for suitability as a LAN medium.

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