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Re: Keep-Alive Notes

From: Dave Kristol <dmk@allegra.att.com>
Date: Thu, 12 Oct 95 12:27:27 EDT
Message-Id: <199510121628.AA224245306@hplb.hpl.hp.com>
To: frystyk@w3.org
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Henrik Frystyk Nielsen <frystyk@w3.org> wrote:
  > [...]
  > [argues that the relative values of timeouts can be used by the client
 to order requests]
  > Therefore at least the timeout does convey useful information. As HTTP is 
  > "measured in seconds" I don't think that roundtrip delays will have a 
  > significant influence in this game.

I'm not sure I follow your point.  When the network is slow and/or
congested, the delays can be that bad, I think.

Consider, also, the role of intermediaries.  What timeout value should a
proxy pass along?  Suppose we have the pipeline
	C -> P -> S	(client/proxy/server)
and the server says timeout=5.  What does the proxy say to the client,
assuming it keeps the whole pipeline open?  Timeout=5?  The client then
thinks it has five seconds to respond.  But that five seconds applies
only to the C-P connection.  Taking into consideration the proxy's
processing time and the propagation times S-P and P-C, that's a
misleading number.  So, should P say timeout=N for some N<5?  Certainly
it doesn't want to pick N>5.

(Roy, will you state rules for what an intermediary should say w.r.t.
timeout?)

Henryk argues that the relative values can be used to order requests.
But suppose C gets one response with timeout=5 and another with
timeout=6.  Suppose the latter has come through a connection that
involves several proxies.  The value of 6 may be well-degraded to the
point where a failure to respond on that channel first will render the
keep-alive useless.

I find it hard to imagine the timeout information to be useful.

Dave Kristol
Received on Thursday, 12 October 1995 09:30:59 EDT

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