Path: utzoo!attcan!uunet!ogicse!ucsd!usc!cs.utexas.edu!varvel
From: varvel@cs.utexas.edu (Donald A. Varvel)
Newsgroups: comp.realtime
Subject: Re: Realtime and fault-tolerance together?
Message-ID: <14348@cs.utexas.edu>
Date: 6 Nov 90 02:13:05 GMT
References: <720@dynasys.UUCP> <848@hrshcx.csd.harris.com>
Organization: U. Texas CS Dept., Austin, Texas
Lines: 21

One approach to getting realtime and fault-tolerance, within
certain assumptions, is self-stabilization.

The usual assumption for the investigation of self-stabilizing
programs is that the program will not be degraded, but that
any or all data may.  This assumes that ROM can be made not
to degrade, whereas RAM cannot.  Environments like the space
telescope come to mind.

A self-stabilizing system has a subset of states, usually
defined as those reachable from a predefined starting state,
which are acceptable.  The program in any unacceptable state
must eventually reach an acceptable state.

To make any claim to being "real-time", a self-stabilizing
program must reach an acceptable state within defined time
bounds.  I have a hard time visualizing such a system being
able to guarantee "hard" constraints, but there may be some
definition of "real time" that would be satisfied.

-- Don Varvel (varvel@cs.utexas.edu)