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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide

OL-5169-01

Chapter 2 Troubleshooting Overview

Troubleshooting Strategy

Troubleshooting consists of determining the nature of a problem and then isolating the problem to a

particular device or component of a device. When a problem has been isolated and identified,

troubleshooting also consists of fixing the problem, usually by replacing the device, some component of

the device, or changing a setting or variable in the software.

Cisco telephony solutions include connections to external switches and to internal components, such as

call agents, signal processors, and trunking gateways. This is a complex environment involving many

connections, links, and signaling protocols. Connectivity and performance problems are very difficult to

resolve. The goal of this section is to provide you with a general troubleshooting strategy for isolating

and resolving connectivity and performance problems.

The cost of a network failure in a telephony environment can mount rapidly. Generally, the average cost

of a production network outage---using lost revenue due to loss of calls as the basis of calculation---can

be many thousands of dollars per hour. Restoring a network that has failed or has become impaired puts

a lot of pressure on network operators and administrators. Given this kind of pressure, the use of special

expertise and known shortcuts to rapidly restore network functionality is valuable. If you know how to

solve a production network problem directly, do so. Use your expertise. However, this expertise requires

a technical depth and a detailed breadth of knowledge about the network that does not result from

isolated, scattered, and unsystematic troubleshooting.

Unless you already know how to solve a problem, an unsystematic approach to troubleshooting can

result in wasting time lost in the network's maze of symptoms, interdependencies, and contingencies.

A systematic troubleshooting method, on the other hand, can help you understand the network's details

by going through a process that can help you identify facts, consider possibilities, act on likely causes,

and observe the results of your actions.

The general idea of a troubleshooting model is to systematically reduce a large set of possible causes of

trouble to a small set of causes or to a single cause. You can then fix the problem and restore network

function. After the problem is resolved, a systematic method of documenting the case helps to capture,

preserve, and communicate the troubleshooting experience gained while solving the problem.

As more advanced technologies and services are introduced into communication networks, the tasks of

designing, managing, and maintaining the resulting networks are also becoming increasingly complex.

The use of a systematic troubleshooting model increases the expertise of the organization and reduces

the time to solve similar problems in the future. This evolution of improving expertise and collaboration

can help mitigate the pressures of supporting crucial, complex networks.

Historically, telephone network architectures were switch-centric. These switch-based architectures

have evolved into distributed systems with the emergence of softswitches. New applications such as

video, audio, and multimedia are gaining popularity and are feasible due to the increase in processor

power on clients and servers.

The troubleshooting procedures provided in this guide assume that your network has been turned up and

is operating properly prior to experiencing the problem you are troubleshooting. For problems with

incorrect configurations or provisioning refer to the component documentation for procedures.

Symptoms, Problems, and Solutions

The symptoms of a problem can be general (such as being unable to access the SS7 network) or specific

(routes not in routing table). First you need to determine the cause of a symptom by using

troubleshooting tools and techniques. After identifying the cause, you can correct the problem.

Attempt to reproduce the reported symptoms if possible. If you cannot reproduce the symptoms, it will

be extremely difficult to analyze and solve the problem. If you cannot narrow the troubleshooting scope

to a particular subsystem or component, then you will probably be unable to determine how to fix it.

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