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From: jamesp@wacsvax.OZ (James Pinakis)
Newsgroups: comp.protocols.tcp-ip
Subject: Building a reliable datagram protocol on top of UDP
Message-ID: <1486@wacsvax.OZ>
Date: 20 Dec 89 05:24:05 GMT
Reply-To: jamesp@wacsvax.uwa.oz.OZ (James Pinakis)
Organization: Comp Sci, University of Western Australia
Lines: 35

This may have been done to death previously but I can't find out
anything about it so here goes...

I'm trying to write a protocol which delivers variable size packets
reliably (i.e. in sequence, no dups, no dropped packets) using the
Internet UDP.  I opted to use UDP since I wanted a single (server)
process to be able to accept messages from any number of sites (clients),
rather than (using the tcp-ip client/server model) a process having
to accept a connection, then fork a process to talk on that connection.
I would also prefer to only have one socket to listen on, rather than
a pile of file descriptors to select on (since the number of clients
is potentially large).

I'm currently implementing a sliding window protocol (Tanenbaum's
protocol 6, actually) but this is getting nastily complicated.
It amounts to having to maintain a set of protocol state information
for every client which establishes a "connection" to the server.
This implies a reasonably large setting up operation every time
a new client wants to start talking with the server.

Basically, I'm wondering if anyone has experience/source code which
they would like to share with me.  How efficient is this protocol
likely to be?  Would I be better off sticking with tcp-ip and
accepting a limit to the number of client processes?

Thanks in advance

james
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