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From: tcp-ip@ucbvax.ARPA
Newsgroups: fa.tcp-ip
Subject: Re:  ARPANET/MILNET performance statistics
Message-ID: <7958@ucbvax.ARPA>
Date: Sat, 8-Jun-85 06:28:33 EDT
Article-I.D.: ucbvax.7958
Posted: Sat Jun  8 06:28:33 1985
Date-Received: Sun, 9-Jun-85 02:47:16 EDT
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Organization: University of California at Berkeley
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From: CERF@USC-ISI.ARPA

Ron,

Hmmmm. the average byte statistics don't tell us about maxima or distribution
of 1822 message (see, I am being careful to distinguish 1822 MESSAGE from
IMP PACKET!) sizes. 

Perhaps Marianne Gardner has available more detailed statistics which
would tell us whether there is any significant amount of IP level
fragmentation going on.  Presumably one would not see the fragmenting
going on at MILISI, for instance. Rather, it would occur at the gateway
which interfaces the local area net to the ARPANET. 

If there were a significant number of 1536 byte IP messages being sent,
these would fragment into two IP datagrams of roughly 1000 bytes and
536 bytes.  [aside: I am no longer sure whether the present preferred
gateway fragmentation algorithm at IP level is to make datagrams
that just fit in the next net, in which case 1000 and 536 would be
more or less right for ARPANET, neglecting headers and stuff; or
whether the policy is to fragment to 576 maximum or to make all
IP fragments uniform in size and less than or equal to 576 or
less than or equal to the next net's maximum message size. Can
a knowledgeable source please set me straight on that? ]

It seems plain that something is causing the average IP datagram
size to be larger at MILISI than at other gateways.

Vint