Communications Magazine

A Symptom-Driven

Expert System for

Isolating and

Correcting Network

Faults

Todd E. Marques

March 1988-Vol. 26, NO. 3

IEEE Communications Magazine

Introduction

To day a single data network c m c onsist of d o ~ e n s of geographically distributed switching nodes

and concentrators, and can support numerous nichespecific

communications protocols, terminal devices,

and network access facilities. The task of isolating

faults within large and complex networks can be

extremely demanding. Competency in this area requires

a general command of data communications princ iples

and sectionalization strategies, as well as specific

knowledge about the operations and diagnostic capabilities

of a wide variety of network components. The

demands of this task are likely to grow as new and varied

product offerings are deployed, and as the sheer size

and topological complexity of networks increase.

This article discusses recent work geared toward the

simplification of fault isolation within data net\+-orks.

Traditional approaches to task simplification have

focused on properties of the user interface. The use of

color, graphics, pan and zoom, and many othcr coding

and display techniques can provide users with the critical

information required to make sound and timely

decisions. Yet the judgment processes, which c Iearly

are among the most difficult aspects of man) tasks,

remain the purview of the user. Thus, i t is not clear

that advanced interface techniques actually reduce the

skill level required to perform complex problem solving

tasks such as fault isolation. The approach

reported in this paper focuses less on the presentation

of key information and more on the interpretation of

key information.

SturKeeper@ Network Troubleshooter is a real-time

interactive expert system that was developed to simplify

the task of fault isolation by mechanizing many of thc key

judgment processes. Based on a symptom description and

situation-specific background data supplied by the user,

Troubleshooter identifies all suspicious components,

formulates a plan designed to minimize the amount of

time taken to isolate the fault, executes the plan, and

terminates after the fault has been isolated and corrected.

The system is designed to be used by individuals

with widely varying skill and experience levels.

As shown in Fis. 1, Troubleshooter is positioned

between a clerk, technician, or administrator staffing a

help desk and a conventional operations system (OS).

Troubleshooter interacts with the OS much like a

human user. It has access to the entire OS command

set as well as all reports and displays available to any

other authoriLed user. Troubleshooter determines which

OS commands should be executed in a given situation,

executes the commands, and interprets OS responses.

System input consists mainly of (i) symptom descriptions

that either are reported to the help desk by network

end-users, or are derived from network-generated messages,

and (ii) specific inquiries about the operational

state of a designated component. System output consists

of (i) a diagnosis that identifies the physical address of

the faulty network component, describes the fault, and

provides evidence upon which the diagnosis is based,

(ii) rrsults of any system-initiated proceduies intended

to clear the fault, and in the event that human intervention

is drcmed neccssary to clcar the fault, (iii) adLice on

the appropriate corrective procedures.

6 0163-6804/88/000S-0006 $01 .OO 0 1988 IEEE

Fzg. 1. TroubleJhooter: An Intrllzgent Front-End to an

Erzstzng 0prratzon.c SyJtfm.

Initial Task Domain

Troubleshooter is currently operational in the Datakit@

Virtual Circuit Switch (VCS) networking environment.

Datakit VCS provides data communication

between host computers and terminals of various types.

Datakit VCS networks may range from a simple star

configuration where hosts and terminals are interconnected

via a single node, to a wide area network consisting

of many nodes linked by digital data service or

high speed fiber