Hardware Tools and Media Testers
Network media test equipment is available to install and verify new cabling systems as well as to diagnose and maintain the existing physical infrastructure. At the lower end of the spectrum, there are breakout boxes, cable testers (scanners), volt-ohm meters (VOMs), and digital volt ohm meters (DVOMs). At the higher end of the spectrum, there are time domain reflectometers (TDRs) and optical TDRs (OTDRs). Go to websites such as www.flukenetworks.com, www.blackbox.com, and www.microtest.com for more information.
Breakout boxes check signals and pinouts for RS-232 serial devices.
VOMs and DVOMs test continuity, voltages, current, resistance, and physical connectivity.
Cable testers and scanners, although at the lower end of the troubleshooting spectrum, are good in continuity situations, whether it be installation, maintenance, or support. A cable tester may help you determine whether the port is actually bad on the router or switch, for instance. Many handheld testers today display helpful address and protocol statistics as well. Figure 2-11 shows the Fluke handheld device.
TDRs are at the higher end of spectrum and are good for cable-break issues. They test for consistency in the impedance over the length of the cable. An electronic pulse is sent to quickly detect shorts, breaks, and throughput issues. You used to really need TDRs for coax cable, but cable scanners work just fine today for twisted-pair cable.
An OTDR is a time domain reflectometer for fiber. It uses optical pulses to check signal loss. A good flashlight, believe it or not, will get you most of the problems. Figure 2-12 shows a fiber tester. TDR products are great, but are normally very expensive. If you are the wiring contractor, however, this is a must for your tool bag.
