Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!RELAY.NSWC.NAVY.MIL!snorthc
From: snorthc@RELAY.NSWC.NAVY.MIL
Newsgroups: comp.protocols.tcp-ip
Subject: high cost of routing
Message-ID: <8908291343.AA07813@ucbvax.Berkeley.EDU>
Date: 29 Aug 89 12:33:07 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 44


	The cost of routing?

senario:
	I am collecting data on network protocols and applications.
The experiments are conducted on a test subnet only (128.38.45)
and from the '45' subnet to another (128.38.48).  The '45' cable has
only 4 computers, a sun, a dec 3100, a lanalyser and a lan watch.
The 48 cable is a "living lab" various protocols are allowed to
exist on it: decnet, novell_ipx, apple_localtalk, osi etc.  It is
also pretty quiet, a 2% peak for 1 second is the max traffic observed
to date (I haven't broken out the LAN MDs yet).  The router is
currently a Network Systems Corporation EN-641.  In a few more weeks
it will be replaced by a cisco box and the tests will be rerun.

question:
	There is a repeatable difference in the number of packets
required to conduct an operation on the 45 cable alone or routed
from the 45 cable to the 48 cable for certain applications.
The difference is fairly high for xterm and telnet, it cannot be
detected for ftp.  Below are two fragments of the test results
form.  They are fairly representative, I have been running tests for
three weeks and have collected a fair quantity of data.  
examples:	45 CABLE		45 -> 48 CABLE
	Traffic required to initiate an xterm connection:
		60 packets		71 packets
	Traffic telnet requires to transmit a known string:
		37 packets		45 packets	

YES! arps are stripped out and maintained as a separate stat.
YES! the test has been run to/from similar hw/sw platforms *
NO! fragments have not been observed... in fact in the case of
xterm or telnet you tend to have small packets anyway.

* there is only one dec 3100, so an ultrix vax was used on the 48 cable,
however there is a sun 2 sunos 3.5 on both cables and results are
quite similar.

So I am confused.  What causes this overhead?  Is there an RFC I should
have read on this subject?  Could it be the router?  Any ideas?

		Thank You,

		Stephen Northcutt (snorthc@relay.nswc.navy.mil)