Over the past years an expert system called LANES designed to detect and isolate faults in the Goddard-wide Hybrid Local Area Computer Network (LACN) was developed. As a result, the need for developing a more generic LACN fault isolation expert system has become apparent. An object oriented approach was explored to create a set of generic classes, objects, rules, and methods that would be necessary to meet this need. The object classes provide a convenient mechanism for separating high level information from low level network specific information. This approach yeilds a framework which can be applied to different network configurations and be easily expanded to meet new needs

Dominy, Robert

English

NASA Technical Reports Server

N89 - 1007 4
A Local Area Computer Network
Expert System Framework
Robert Dominy/Code 522.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771
!
/
/
/
Abstract
Over the past year I have been developing an expert system called LANES designed to detect and isolate
faults in the Goddard-wide Hybrid Local Area Computer Network (LACN). As a result, the need for
developing a more generic LACN fauh isolation expert system has become apparent. This paper explores
an object oriented approach to create a set of generic classes, objects, rules, and methods that would be
necessary to meet this need. The object classes provide a convenient mechanism for separating high level
information from low level network specific information. This approach yields a framework which can be
applied to different network configurations and be easily expanded to meet new needs.
Introduction
A hybrid local area computer network (LACN)
connects a variety of computers, ranging from
mainframes to micros, throughout several
buildings of the Goddard Space Flight Center.
The network is based primarily on an Ethernet
bus topology (Figure 1) but a star configuration
using the Cable TV (CATV) wiring and Applitek
equipment allows networks in different buildings
to be interconnected.
As this network grows, it becomes more and
more difficult to detect and isolate problems.
Currently operators do a small amount of
network checking manually, but to do a thorough
check of the entire network is tedious because of
the large number of items involved. As a result,
most fault isolation takes place after a user has
discovered and reported a problem.
The Local Area Network Expert System
(LANES) began in 1985 as an effort to automate
the process of fault detection and isolation.
Development work is being performed on a
Symbolics 3645 LISP machine using an expert
Transcelvere Brld ge Bo it Network Repeater r. m,_.. _,,_.1\ ___._1 _ L_
-- \=7 -
Computers App Illill
Figure 1 -- Portion of Goddard LACN
https://ntrs.nasa.gov/search.jsp?R=19890000703 2020-03-20T05:20:10+00:00Z
system development tool, the Automated
Reasoning Tool (ART) from Inference Corp. An
operationally useful prototype has been
completed and is available for demonstration and
USC.
The LANES screen is depicted in Figure 2. Each
network is depicted graphically and a global map
of Goddard Space Flight Center that shows
connections between buildings (Figure 3) can be
reached by clicking on the window connection
icon (the upward arrow) labeled Map. To tell the
system to begin checking the entire network a
user clicks on the START button by positioning
the mouse cursor over the START button and
pressing the left mouse button. The button
changes to STOP. The expert system heuristic
rules then attempt to detect and isolate problems
in the network. Results are displayed with text
and graphics. For example, in Figure 2 the
Bridge box CS1-D cannot be reached (an X is
placed in the box) and the Bridge box CS I-B has
a high statistical CRC (cycle redundancy check)
error count (a question mark is placed in the
box).
LANES checks each device on each network,
repeatedly cycling through all the networks, until
the user clicks on STOP. As each network is
checked, the window being viewed will
automatically be changed if the current network
is on a different screen and the Switch Screens
button is set. At any time the user can edit the
network design using NetEdit, an interactive
graphical network editor. Devices can be added,
moved, modified, or removed. The changes are
reflected immediately by the expert system and
can be used temporarily or saved to a permanent
OIta Systems Technology L.aboratory
In
CS1 -O
Edil _dds
Move
Change Connect
Remove
Figure 2 --LANES Screen
Goddlbrd SIIIICll FIl_k_ Cowl:or
Figure 3 -- Map of Goddard
ExpertSystem
t-_e.
Connectivity Algorithms
Object-Oriented Database
and Graphical Editor
Figure 4 -- Framework Layers
The current version of LANES checks networks
located in five different buildings. It gets the up/
down status and health statistics of seventeen
bridge boxes, gets the up/down status of ten
VAX computers, and derives the status of five
Applitek devices.
framework. To build a framework that is
reusable, highly modular, and easily modifiable
will require the base programming language to
provideobject-orientedfeatures such as dynamic
bindingof functions(methods)todata(objects),
inheritableobject and methods, and object
abstraction. A number of object-oriented
languagesprovideallofthesefeatures.l
Object-Oriented Framework
Demonstrating LANES has generated interest
within Goddard and at other NASA centers.
However, because LANES has been designed
specifically for the Goddard LACN much of the
code that was developed would have little
application to other LACNs. In addition, a
number of functions and rules within LANES are
replicated for similar object types. For example
two rules which get the status of an object may
only differ by the function which they invoke.
This not only duplicates code and effort, but also
makes global changes more difficult to make.
Improved knowledge abstraction with increased
modularity and ease of modification are being
added to help solve these problems.
The next step in the evolution of LANES is to
build a generalized LACN expert system
Framework Layers
Conceptually the framework is composed of three
primary layers (Figure 4), an object-oriented
database and graphical editor, a set of
connectivity algorithms, and the expert system.
This concept allows the lower layers to be fully
reusable without the upper layers, but not the
reverse since the expert system would need both
the database and connectivity layers to function.
The object-oriented database and graphical editor
are key elements of the system. The editor
provides the main portion of the user interface
with which users will create, modify, and add to
networks. The database defines the relationship
between network components and keeps track of
component attributes such as network addresses
and protocols.
1. In the computer science field, object-oriented programming is gaining popularity as a software
engineering methodology and programming style. The reason for this is that object-oriented
programming excels in software reusability, modularity, and ease of modification. Brad Cox discusses the
concept of using object-oriented programming to develop reusable software integrated circuits, Software-
ICs (Cox, Brad J., Obieet Oriented Pro2rammin_,: An Evolutionary Avm'oach. Addison-Wesley, 1986). A
commercially available product from Apple Computer called MacApp (Doyle, Ken, Wallace, Scott, and
Rosenstein, Larry, MacApprU: An Object-Oriented Application Framework, A_mpleReport No. 4, Apple
Computer, Inc., September 1986.) provides a highly reusable object oriented framework to implement the
standard Macintosh interface, reducing both the time and amount of code needed to build applications.
Connectivityalgorithms find paths between
components. For fault isolation on the Goddatd
LACN the main algorithm is a simple depth first
search (loops are not allowed in the network)
along connections that support the protocols of
the machines being tested. Another algorithm
would be used to find "backroads" between
equipment. An example would be to use a
modem to bypass default network components to
check the status of a computer. For other LACN
configurations (e.g., a network that allowed
loops), programmers could use the object-oriented
capability of overriding methods to customize the
algorithms.
The functions of the expert system layer are fault
other network object types. Each subsequent
child node or subclass, therefore, inherits methods
and fields from TComponent This, for example,
allows defaults to initially be set up in
TComponent and later customized in subclasses
as required. Some of the classes along with their
methods and fields are discussed below. A more
detailed design is currently under development.
TComponent has a field, fSubcomponents, which
can be used to define TComponent objects as
abstract entities such as a network or computer
that can be broken down into its
fSubcomponents. A polling method is then
defined to poll these subcomponents. Another
field, fConnectedTo, is a list of components that
TComponent
TDevice TPort TWire
TPassthrough
TAppIitTk e peaT::ansceiver
TActive
TMultiplexor
TBridgebox
TComputer
I
TDecnetDevice
Figure 5 -- Object
isolation, component monitor/polling, graphical
and text fault notification, and explanations.
Fault isolation is provided by both high-level and
low-level methods and heuristics. Monitor and
polling methods provide the capability to
continuously monitor specified components or
request an instantaneous diagnosis. Explanations
and fault notification are built upon the user
interface of the graphical editor.
Object Hierarchy
Each of these layers are built within the object
hierarchy shown in Figure 5. The top node,
TComponent, is the parent or superclass of all the
Hierarchy
the TComponent object is connected with.
TDevice, TPort, and TWire, are major subclasses
of TComponent and def'me high-level information
and knowledge. The TPassthroughDevice class is
for devices that act as information relays and are
essentially transparent to other devices on the
network. During fault isolation, the up/down
status for devices in this class would have to be
based on the ability of TActiveDevice objects to
communicate through the TPassthroughDevice
object. The TActiveDevice objects can be
communicated with directly to determine up/down
status. The bottom nodes of the hierarchy
(TApplitek, TMultiplexor, etc.) contain the most
network specific information and knowledge and -.,j
4
is where most modifications and additions will
place.
Future
Currently a detailed design of the framework is
under progress. In addition, a number of
potential application areas are being explored.
Once one is chosen, the hardware and software to
implement the framework will be selected.
Currently a variety of object-oriented
programming languages (C++, Objective-C,
Object Pascal, SmaUTalk, LISP Flavors, ART
3.0) which exist on a number of machines are
being considered.
When the LANES framework is complete, it
should be applicable to a variety of LACN fault
isolation problems. It could even be expanded
to handle LACN design and performance
analysis.
I suspect that fault isolation will not be the only
area where frameworks are built. Hopefully we
will see a number of frameworks being built to
handle other expert system areas such as
scheduling, planning, control. What will be key
to their success, however, will not just be
functionality, but ease of modification and
expansion. Object-oriented programming will
play a large part in that success.
-"N/
_ J
_j


A local area computer network expert system framework

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server