Troubleshooting guide

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Cisco PGW 2200 Softswitch Release 9.8 Operations, Maintenance, and Troubleshooting Guide
OL-0800-14
Chapter 4 Maintenance and Troubleshooting Overview
Troubleshooting Strategy Overview
TDRs and OTDRs
TDRs are at the top end of the cable testing spectrum. These devices can quickly locate open and short
circuits, crimps, kinks, sharp bends, impedance mismatches, and other defects in metallic cables.
A TDR works by “bouncing” a signal off the end of the cable. Opens, shorts, and other problems reflect
the signal back at different amplitudes, depending on the problem. A TDR measures how much time it
takes for the signal to reflect and calculates the distance to a fault in the cable. Also, TDRs can measure
the length of a cable or calculate the propagation rate that is based on a configured cable length.
An OTDR performs fiber-optic measurement. OTDRs can measure accurately the length of the fiber,
locate cable breaks, measure the fiber attenuation, and measure splice or connector losses. An OTDR
can ascertain the “signature” of a particular installation, noting attenuation and splice losses. When you
suspect a problem in the system, you can compare the baseline measurement with future signatures.