[e2e] TCP in outer space

Vernon Schryver vjs at calcite.rhyolite.com
Tue Apr 10 07:55:50 PDT 2001

> From: Fred Baker <fred at cisco.com>

> ...
> The other is that both HTTP and SMTP are fairly chatty transaction 
> protocols, which kill time for several RTTs before doing much of anything. 
> HTTP is materially improved by the use of tcp pipelining, which is commonly 
> implemented in servers but is not often used by browsers. SMTP generally is 
> implemented in a chit-chat fashion - one says "EHELO" and waits, then sends 
> the "FROM", then says (often individually) who the message is to, and 
> finally sends the (usually one or two) segments of data. There is a round 
> trip in between each, and if it is on the order of 560 ms as Mark suggests, 
> that will dominate the other link characteristics. In the general case, all 
> of these commands generally "work", so it would be sufficient to send all 
> the commands in a batch, receive all the responses, and determine what to 
> do next. ...

There is also the other than new "SMTP Service Extension for Command
Pipelining" which currently seems to be defined by RFC 2920.   It talks
about an explicit mechanism and reasons to not just blast the SMTP
commands, which you might or might not find convincing.  (I have doubts.)

The release notes for sendmail version 8.12 include the comment:
       Implement SMTP PIPELINING per RFC 1854.  It can be turned off
                at compile time or per host (ruleset).

For HTTP, there's the recent draft-mogul-http-ooo-00.txt

Vernon Schryver    vjs at rhyolite.com

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