Date   : Sat, 04 Jul 2009 22:04:24 +0100
From   : philb@... (Phil Blundell)
Subject: econet bridge protocol

Thanks, that's interesting.  The thing about the length of broadcast
packets being a constraint makes it sound like the bridges would
probably forward an &81 packet but add their own far-side network number
to the end of the payload.

I guess I could experiment by sending some &81 packets to my bridge and
see what comes out on the other side.  Of course, that probably involves
locating some more working hardware, grumble.  

On that latter subject, does anybody happen to have a link to the
schematic for an SJ-style plugin terminator to hand?

p.

On Sat, 2009-07-04 at 21:42 +0100, Rob wrote:
> There's some discussion on Bridges in here:
> http://mdfs.net/Docs/Comp/Econet/RISCiX.txt
> 
> They definitely spread information about other reachable networks
> based on this paragraph:
> "There is a limit of eight on largest number of "hops" a frame could make on
> a connected set of networks. If there are more than 8 nets in any possible
> route, the protocol used by a bridge to ask all the other bridges where nets
> are falls over, because it uses broadcast packets which have a limit of 8
> bytes of data associated with them."
> 
> Unfortunately it's a bit thin on the detail...
> 
> I've not come across anything else, though I was only looking for AUN
> information...
> 
> Rob
> 
> 2009/7/4 Phil Blundell <philb@...>:
> > Does anybody have documentation on the port &9c protocol used by
> > bridges?  Chapter 10 of the MDFS book gives some details but doesn't
> > describe the messages with control bytes &80 and &81.
> >
> > Observing the single bridge that I have here, at power up it seems to
> > send a broadcast with control byte &80, containing in its payload the
> > number of its other local network; I guess this is the "reset packet"
> > that the MDFS book talks about.
> >
> > If I send the bridge one of those packets (cb &80) then it responds with
> > a series of packets with control byte &81 and, again, the network number
> > of its far side in the payload.  I'm not entirely sure what the meaning
> > of these packets is, or how (if at all) I am meant to respond to them.
> >
> > Can anybody shed any light on that?  Or, absent any documentation, is
> > there anybody with two or more bridges who would be prepared to capture
> > some packet dumps showing them talking to each other?
> >
> > thanks
> >
> > p.
> >
> >
> >
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