Date   : Wed, 19 Aug 2009 09:18:22 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: maximum econet packet size

Phil Blundell wrote:
> Does anybody know the maximum packet size that a Beeb will send or
 
Infinite. You can keep transmitting for ever until a end-of-frame
flag at any point.
 
> receive on Econet?  It seems to be 8k for normal transmissions under
 
Change the question to what the maximum practical packet size is,
and it depends. A server and client should negotiate between each
other to decide on an appropriate packet size[1]. Acorn bridges
will only propagate packets up to 8K, so the above negotiation
process means servers and clients use sub-8K packets over bridges.
 
As an example, *VIEW is capable of grabbing an entire 20K screen in
a single packet.
 
> that at the time the bridge was designed.  But it'd be useful to know
> for sure what the largest packet is that's likely to be encountered on a
> Beeb network.
 
20K for a whole screen grab is probably the biggest seen in normal
operation between 8-bit machines.
 
[1]For data transfer client->server (eg SAVE or WriteBytes), the
server sends a suggested block size. If the client can't cope with
that block size, it doesn't reply, and the server tries again with
a smaller block size. If the client replies with the requested
block size, but it can't be propagated through a bridge, the server
sees that as a missing reply and again tries again with a smaller
block size.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
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