Checksums


Brian Lloyd (rochester!cci632!rlgvax!dolqci!irs3!wb6rqn!brian@rutgers.edu)
23 Mar 88 09:37:25 EST (Wed)


The advantage to using checksums with tcp and ip is that generating a
checksum is a relatively low-cost operation (the addition instruction in
most processors requires relatively few t-cycles). When you begin to
talk about extracting pattern information from a bit stream you begin to
talk about an increase in processing overhead that is several orders of
magnitude greater.

To me the greatest feature of the Internet Protocol Suite is that it
tends to espouse the KISS principle: elegant simplicity. I would be
loath to bog down the protocol with a lot of additional algorithmic
baggage. I can see the point that it would be nice to determine that
someone is using an off-by-1 counter or has a pointer misalignment
problem, but that is not what goes on most of the time. The things you
really want to know in an operational network are link quality,
throughput, packet loss rate, and delays. What we REALLY need is a
protocol that allows us to gather information from the LLPs for
transmission so a network control center (either centralized or
distributed). We may also want to discuss the use of forward error
correction over some links so that you can extract additional
information from the bitstream but we would probably want to do that at
the link layer where it would be sensible to put it in a front-end
processor.

I guess that I am responding to a suggestion that smacks of making
things more complex. What we really need to do is to make things
simpler so that we can make things faster and more reliable. Additional
complexity should be compartmentalized in such a way that it can be
safely ignored :-).

Brian Lloyd, President
Sirius Systems, Inc.
(301) 540-2066
{bellcore, syscad, cp1, irs3, n3dmc}!wb6rqn!brian
Share and enjoy!



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