Text File

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.