Alime.231
net.lan
utzoo!decvax!harpo!floyd!vax135!lime!martin
Fri Apr 23 09:25:34 1982
re: IBM local network

From: lime!vax135!houxi!ihnss!ihuxn!djmolny

The reliability questions Joe raised are mostly administrative in
nature.  I agree you can't get 99.999% reliability without duplex hardware
and related goodies, but good planning can get you 98%, which is by far
and away enough for most applications.

Here are some solutions for the problems Joe raised.  (Bear in mind that
the exact implementation is heavily processor- and medium-dependent.)

Master Down:	If the network master goes down, simply designate another
		node as master.  There doesn't have to be any special
		hardware associated with the master.  Assignment can be
		done manually or automatically, with only a brief pause in
		network traffic.

Two Machines Down: I'm not sure why this is more of a problem than one
		machine down.  To be sure, you need some way for other
		nodes to route around the downed system, but if implemented
		correctly, such a mechanism will work for any number of
		machines.  Typically, ring transmitters have a shunt
		to allow bits to go in one ear and out the other.

Sanity Timer Failure: Each machine should periodically check its own
		sanity timer by letting it fire.  Self-test, it's called.

Adding Machines: The answer to this question is dependent on the network
		hardware used, but again, can be solved by good hardare
		design.  All you need is an extra input and output path for
		each node, with a switch to select between paths.  Install
		the new machine on the alternate path, inform the other
		nodes of its existense, and flip the switch.


I'm not defending the IBM network (especially since I don't know anything
about it), but ring networks in general.  I'd also like to make it clear
that when I talk about ring networks, I mean logical as well as physical
rings.  A CSMA/CD transmission link can operate in ring fashion, if the
nodes grant transmit permission via tokens.  Simply a different protocol
on the same medium.

						-- DJ Molny
						ihnss!ihuxn!djmolny

-----------------------------------------------------------------
 gopher://quux.org/ conversion by John Goerzen <jgoerzen@complete.org>
 of http://communication.ucsd.edu/A-News/


This Usenet Oldnews Archive
article may be copied and distributed freely, provided:

1. There is no money collected for the text(s) of the articles.

2. The following notice remains appended to each copy:

The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 
 Bruce Jones, Henry Spencer, David Wiseman.