There are no good, current studies on LAN behavior that I've seen.
There have been a number of papers on WAN behavior. The usual result
of those is that ~40-50% of packets are about 40-44 bytes, but most of
the bytes are carried by packets of ~500-576 or 1500 bytes.
--Steve Bellovin
In some traces I did for my PhD work about three years ago, I found that
51% of the packets were 40 or 41 bytes long (i.e. mostly TCP acks or
one-byte TCP payloads). Only 15% of the packets were maximum-sized. The
average packet size was 273 bytes. This workload was probably heavier on
telnet than today's networks; however even when doing bulk file transfer,
one packet in three is still an ack.
Stuart Cheshire <cheshire(_at_)apple(_dot_)com>
* Wizard Without Portfolio, Apple Computer