[MUD-Dev] Transport layer (UDP vs TCP)

Ben Greear greear at cyberhighway.net
Tue Mar 17 22:04:02 New Zealand Daylight Time 1998

On Tue, 17 Mar 1998, Jon Leonard wrote:

> On Tue, Mar 17, 1998 at 10:58:58AM +0000, Niklas Elmqvist wrote:
> > > The question is, what is the packet size (max) that UDP can handle?
> > 
> > A good place to find information about anything that even remotely
> > pertains to networks and the Internet are the RFC docs. A bit technical
> > (but that's how we like them) but usually of good standard. You can find a
> > directory containing ASCII-text versions of all the RFCs at
> > <URL:http://ftp.sunet.se/pub/Internet-documents/rfc/> (the index is called
> > rfc-index.txt).
> > 
> > RFC 1180 is a TCP/IP tutorial, and a good one at that, but only brushes
> > through UDP. RFC 768 concerns itself solely with UDP, the answer to your
> > question might be found there.
> It's likely more complicated than that.  The maximum size of a UDP packet
> is about the maximum size of an IP datagram (quite large).  Realisticly,
> though, you want largest packet that won't get broken up into fragments.
> The largest non-fragmenting packet (MTU = Maximum Transfer Unit) depends
> on the networks involved.  For Ethernet, it's about 1500 bytes.  Most high
> speed networks have larger maxima, but you could see almost anything.

I'm definately looking for the MTU.  The whole point would be to ensure
that each packet arrived all at once, and was complete by itself.  I
think I can fit them into 512 bytes easily.  If I need to send larger
packets I can always chunk them over the tcp connection.

> A search for "MTU discovery" should probably find something on how some
> TCP implementations figure out what the optimal packet size is.  Anyone
> seriously considering a UDP tranport protocol should write something similar.
> The basic idea is set the "don't fragment" bit, and play with packet size
> until you find out what works.

I was mostly hoping that someone had a good 'working maximum' that they
had used with success.  However, most MUD's would deal wrather poorly
with a lossy protocol, so there may not be much experience with UDP
in the mud community....

> Jon Leonard

Ben Greear (greear at cyberhighway.net)  http://www.primenet.com/~greear 
Author of ScryMUD:  mud.primenet.com 4444

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