Re: TCP maximum segment size determination

James B. VanBokkelen (JBVB@AI.AI.MIT.EDU)
Tue, 10 Nov 87 12:37:25 EST

The lower the performance of your network interface, the more trouble *any*
fragmentation means to you. On PCs, we try to eliminate fragmentation by
specifying a small MSS when routing via any gateway (subnets-are-local
would be nice to do, but we haven't yet). The IP option you propose would
help, but not until all gateways handled it properly.

If gateway gurus saw their way clear to do so, they might help some fraction
of the world by arranging that IP fragments aren't transmitted consecutively
(if there is other traffic to handle) or by inserting a little time delay
if the Ether or other non-serial media is idle. Presently, fragmenting an
IP datagram is the best simple way I know to determine how close together a
given hardware/software combination can send packets. If the gateway goes
faster than the host can handle, suddenly it is time for a TCP retransmit...

I can't say when/where I heard this, but I always thought that SATNET had an
MTU of 128 bytes.


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