Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!FLORA.WUSTL.EDU!guru
From: guru@FLORA.WUSTL.EDU (Gurudatta Parulkar)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Re-fragmenting IP Datagrams
Message-ID: <8902230119.AA22877@flora.wustl.edu>
Date: 23 Feb 89 01:19:39 GMT
References: <8902211417.AA12976@etn-wlv.EATON.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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    Fragmentation is addressed in RFC 791 section 2.4.  All Internet
    hosts must be able to accept, at a minimum, a 576 octet packet.
    Re-fragmentation of an IP datagram is permitted as long as the
    "don't fragment" flag is not set. 

I believe the specifications also require all networks to be able to
forward a 576 octet datagram without fragmentation. I can understand
logic behing this requirement as part of IP specifications. But I
wonder what would happen when the first ATM network joins the internet
with packet size of about 64 bytes. Most of the high speed packet
switches being desinged plan to conform to the ATM standards. In such
a mixed environment, does it make sense for an internet layer to
require a minimum packet size of all component networks. Is the packet
size an attribute to be specified by an internet layer or left to
the underlying networks to decide. What are the performance
implications of doing it one way or the other ? 
(Jeff Mogul's paper in SIGCOMM'87 talks about some of the trade-offs
in the existing environment, but I am looking beyond.)

I would like to see some discussion on  this issue. Note that I am
talking about an internet layer in a generic sense and not challenging 
IP specifications.

-guru

Dr. Guru Parulkar
Asst Professor             guru@flora.wustl.edu
Dept of Computer Science   parulkar@udel.edu 
Washington University      wucs1!guru@uunet.uu.net
Campus Box 1045, Bryan 509
One Brookings Drive
St. Louis MO 63130-4899 
(314) 889-4621