Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod!pacific.mps.ohio-state.edu!linac!att!bellcore!envy!karn
From: karn@envy.bellcore.com (Phil R. Karn)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: LAT
Message-ID: <1991Jan14.210236@envy.bellcore.com>
Date: 15 Jan 91 02:02:36 GMT
References: <12578@hubcap.clemson.edu> <1991Jan14.015852.26228@mdivax1.uucp>
Sender: usenet@bellcore.bellcore.com (Poster of News)
Reply-To: karn@thumper.bellcore.com
Organization: Packet Communications Research Group (Bellcore)
Lines: 21

In article <1991Jan14.015852.26228@mdivax1.uucp>,  writes:
|> A good question to ask is whether LAT performs checksumming. [...]
|> [...] rather CPU intensive nature of checksumming. 

Checksumming is a complete non-issue here. Its cost falls into the
noise when compared to all the other things that happen when you type
a character or refresh a screen.

Even in high bandwidth situations (i.e., FTP rather than TELNET) the
cost of TCP checksumming is usually minimal compared to, say, the cost
user/kernel context switches and of talking to the Ethernet hardware.

And Van Jacobson and Dave Borman have shown how TCP implementations
can combine checksumming with data copying. This all but eliminates
the cost of checksumming, especially on machines with fast processors
and slow memories.

Even if TCP checksumming weren't minimal, it would be a big mistake to
turn it off - the "end to end argument" reigns supreme.

Phil