Troubleshooting guide
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Cisco PGW 2200 Softswitch Release 9.8 Operations, Maintenance, and Troubleshooting Guide
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Chapter 4 Maintenance and Troubleshooting Overview
Troubleshooting Strategy Overview
A cable tester might also be able to perform any of the following functions:
• Test and report on cable conditions, including near-end crosstalk, attenuation, and noise
• Perform TDR, traffic monitoring, and wire map functions
• Display Media Access Control (MAC) layer information about network traffic, provide statistics
such as network utilization and packet error rates, and perform limited protocol testing (for example,
TCP/IP tests such as ping)
Similar testing equipment is available for fiber-optic cable. Because of the relatively high cost of
fiber-optic cable and its installation, the cable should be tested both before installation (on-the-reel
testing) and after installation. Continuity testing of fiber-optic cable requires either a visible light source
or a reflectometer. You can use a power meter with a light source that is capable of providing light at the
three predominant wavelengths, 850 nanometers (nm), 1300 nm, and 1550 nm. A power meter can
measure the same wavelengths and test attenuation and return loss in the fiber-optic cable.
Breakout Boxes, Fox Boxes, and BERTs/BLERTs
Breakout boxes, fox boxes, and BERTs/BLERTs are digital interface testing tools that are used to measure
the digital signals present at the interfaces of PCs, CSU/DSUs, and other devices. These testing tools can
monitor data line conditions, analyze and trap data, and diagnose problems common to communications
systems. Examine traffic from data terminal equipment (DTE) through data communications equipment
(DCE) to isolate problems, identify bit patterns, and ensure that the proper cabling has been installed.
These devices cannot test media signals such as those for Ethernet, Token Ring, or FDDI.
Network Monitors and Analyzers
Use network monitors to track packets that are continuously crossing a network. A network monitor
enables you to obtain an accurate picture of network activity at any moment, or a historical record of
network activity during a period. Network monitors do not decode the contents of frames. Monitors are
useful for baselining, in which the activity on a network is sampled during a period to establish a normal
performance profile or baseline.
Monitors collect information such as packet sizes, numbers of packets, error packets, overall usage of a
connection, and the number of hosts and their MAC addresses. A monitor also provides details about
communications between hosts and other devices. You can use the data to create profiles of network
traffic, locate traffic overloads, plan for network expansion, detect intruders, establish baseline
performance, and distribute traffic more efficiently.
A network analyzer (also called a protocol analyzer) decodes the various protocol layers in a recorded
frame and presents them as readable abbreviations or summaries. The analyzer provides details about
which network layer is involved (physical, data link, and so on) and what function each byte or byte
content serves.
Most network analyzers can perform many of the following functions:
• Filtering traffic that meets certain criteria so that, for example, all traffic to and from a particular
device can be captured
• Time-stamping captured data
• Presenting protocol layers in an easily readable form
• Generating frames and transmitting them onto the network
• Incorporating an “expert” system in which the analyzer uses a set of rules, combined with
information about the network configuration and operation, to diagnose and solve network problems