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From: BILLW@MATHOM.CISCO.COM (William "Chops" Westfield)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: TCP segment size -- user defined?
Message-ID: <12623634027.12.BILLW@mathom.cisco.com>
Date: 21 Sep 90 08:12:47 GMT
References: <1990Sep20.014208.7645@wrl.dec.com>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 18


    The upper limits on the size of a TCP segment are:
	:
	:
    (3) the "Path MTU"; basically, the largest packet that can be sent
    from source to destination without fragmentation.  


In theory, there isn't any reason the tcp segment size cannot be larger
than the path MTU.  (NFS essentially does this, though it doesn't use
TCP.)  In practice, there are several reasons why doing this is a rather
bad idea - see Jeff's paper "Fragmentation Considered Harmful".  Basically,
if you make the mss larger than the mtu, you force a lot of effort at the
routers (fragmentation), the destination (reassembly), and the network (if
it doesn't deliver all the fragments, the entire packet has to be retransitted)

BillW
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