Troubleshooting guide

2-17
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 2 Troubleshooting Overview
Troubleshooting Tools
Digital Interface Testing Tools
Several test tools can be used to measure the discrete digital signals that are present at PCs, modems,
printers, and other peripheral interfaces. Examples of this type of test equipment include breakout boxes,
fox boxes, and bit/block error rate testers (BERTs/BLERTs). These devices can monitor data line
conditions, analyze and trap data, and diagnose problems common to data communication systems.
Traffic from data terminal equipment (DTE) through data communications equipment (DCE) can be
examined to help eliminate problems, identify bit patterns, and ensure that the proper cabling has been
installed.
The line-powered Blue Box 100 breakout box from IDS, Inc. is a breakout box and cable tester that is
compact, handheld, and fully 100 percent LED. It accesses and monitors all 25 conductors of the
RS-232-C, EIA-232-D, CCITT, and V.24, and any other single-ended interface such as the Centronics
parallel printer interface. One hundred red and green LEDs monitor and display high, low, off, and signal
activity conditions for each of 25 conductors on the DTE and DCE sides of the interface.
Network Monitors and Analyzers
Network monitors continuously track packets crossing a network, providing an accurate picture of
network activity at any moment or a historical record of network activity over a period of time. Monitors
collect information such as packet sizes, the number of packets, error packets, overall usage of a
connection, the number of hosts and their MAC addresses, and details about communications between
hosts and other devices. Correlation of this data allows network administrators to create profiles of their
LAN traffic and find traffic overloads, plan for network expansion, detect intruders, establish baseline
performance, and distribute traffic more efficiently.
Not only must the monitor collect information about frames, but it must also be able to warn users if any
frames are dropped or flag users if certain events such as bad frames, protocol errors, or illegal addresses
occur. Visible and audible alarms for the entire network or for individual stations can be set, allowing
the network manager to be informed when certain parameters have exceeded predetermined thresholds.
The concept of baselining is becoming very important to network managers. To create a baseline, the
activity on a network is sampled over a period of time, and averages, means, and other statistical
calculations are used to establish a normal performance profile, or baseline. This baseline can then be
used as a reference if any abnormal performance is noted in the network, or it can be used to plan
expansion options.
Network monitors further enhance network management by gathering information from remote sites and
sending it back to a central management location.
Apart from gathering the standard traffic information, many monitors implement Simple Network
Management Protocol (SNMP), Remote Monitoring (RMON), and Management Information Bases
(MIBs) to gather information for central management stations. CiscoWorks can also supply network
monitoring functions.
The monitor screens of a Sniffer Pro product display charts and graphs that enable you to easily build
graphical baseline reports on your network.