On Tue, 17 Jul 2001, Brandon Fosdick wrote:

> Olin Lathrop wrote:
> >
> > > For my project that uses an RS485 network I was planning to use a token
> > > ring system so I don't have to deal with collision detection.
> >
> > That's going to be tough because RS-485 is a multidrop bus, not a ring.  You
> > could implement a ring from individual point to point RS-232 connections,
> > but that would require two UARTs per node.
>
> Maybe "token ring" isn't the right term for what I'm thinking cause I seem to
> have sent everybody on a different path. "Token ring", as I understand it, isn't
> a network topology, its a communications protocol. We use it on several of our
> robots (www.ssl.umd.edu) and I think it was used for PC's back in the heyday of
> coax cabled LAN's, but that was before my time.

It's both a protocol and a topology.  It's a token-passing protocol on a
ring network.  Regardless of the fact that TR networks are usually (now)
cabled with Cat-5 and RJ45 connectors, it's a ring.  The earlier wiring
schemes used shorting connectors that would bypass an unplugged node, now
I think the switches take care of it for you.  In any case, the token is
passed from node to node in series on a ring network.

> The system I'm refering to, whatever its called, involves a series of nodes on a
> multi-drop broadcast network that need to communicate peer-peer. A node can only
> communicate when it has the "token", when its done with the network it gives the
> token to another node which then either uses the network or passes the token on
> to the next node. The token tends to move around the network in a ring, hence
> "token ring". Obviously there are some problems with this system, but it works
> for simple networks.

I think that's a valid concept, it's just not "token ring".  It's a
token-passing protocol on a bus network.  Now all you have to do is figre
out an addressing scheme so a node knows who gets the token next.

Dale
--
A train stops at a train station.  A bus stops at a bus station.
On my desk I have a workstation...

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