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Chapter 2. Network Media > Simplex, Half-Duplex, and Full Duplex - Pg. 24

24 CHAPTER 2 Network Media Perform a visual inspection of cabling. Replace the cable with a known good cable, and retry the connection. Retest communications. Examine network interface card (NIC) to ensure connectivity. Using tools that are designed for troubleshooting cable problems is another important factor in solving such problems quickly. Crunch Time Cable testers are tools that can analyze the capabil- ity of a cable to carry signals, and can find breaks or other problems in the wire. Examples of various cable troubleshooting tools include the following: Tone generator (Fox and Hound) This tool is used to perform tests and will aid in the identification of wires during the wire-tracing process. To use a tone generator, you begin by attaching the fox to the cable, jack, or panel that you would like to trace, and a signal is sent across a wire while you continue with the hound on the other end of the cable to find the fox's tone. Time domain reflectometer (TDR) This tool uses an electronic pulse, which travels down the cable until it is reflected back. The TDR then calculates the distance down the cable that the signal traveled before being reflected by measuring the amount of time it took for the signal to be returned. If this distance is less than your overall cable length, a cable problem exists at that distance from your location. Wire map tester This tool is used to test for opens, shorts, and crossed pairs, and will provide infor- mation that may indicate improper wiring. Because they are a low-cost cable tester, they generally pro- vide fewer features than other cable testers, such as TDRs. Oscilloscope This tool can determine if there are shorts, crimps, or attenuation in the cable. An oscilloscope formats its output in a graphical for- mat. Oscilloscopes are commonly used to test cables that have been recently run through walls to ensure there are no problems with the cable before using it. Cable tester This tool provides a variety of tests that can be performed on network cabling. The fea- tures of a handheld cable tester will vary, but some high-end testers will combine the features of sev- eral testers, such as providing the features of a wire map tester and a TDR or running auto-test features, which automatically perform a series of tests on the cable. Network monitors and protocol analyzers These tools monitor traffic on the network and display the packets that have been transmitted across the network. Crossover cable This tool is a twisted-pair cable with two wires crossed that is used to connect two com- puters to each other directly without the use of a hub. A crossover cable is also used to connect hubs together in the event you need to cascade them. Hardware loopback adapter This tool helps to test the ports on a system without having to connect to an external device. One example is a serial loopback adapter. SIMPLEX, HALF-DUPLEX, AND FULL DUPLEX When data travels across the medium, it travels in a certain direction. To describe the movement of data across communication channels, certain terms are used, including the following: