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Re: Section 8.2

From: Ben Laurie <ben@gonzo.ben.algroup.co.uk>
Date: Fri, 31 May 1996 20:58:27 +0100 (BST)
To: Jeffrey Mogul <mogul@pa.dec.com>
Cc: ben@algroup.co.uk, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <9605312058.aa02703@gonzo.ben.algroup.co.uk>
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/633
Jeffrey Mogul wrote:
>     'HTTP/1.1 servers SHOULD maintain persistent connections and use TCPs 
>     flow control mechanisms to resolve temporary overloads, rather than 
>     terminating connections with the expectation that clients will retry. 
>     The latter technique can exacerbate network congestion.'
>     On a practical note; how do I distinguish between an idle client, a dead 
>     client, and one that is avoiding network congestion? Should the standard 
>     give some guidelines?
> Actually, the real question is "how do I distinguish between an idle
> client, a dead client, and one that can no longer be reached over
> the network?"  (Network congestion tends to result in slow but not
> totally failed communication.)

A host that detectably can't be reached over the network will produce a "host
unreachable" response. An undetectable one is indistiguishable from a dead
host or one that is avoiding network congestion (I think).

> The answer to the real question is "you can't, so don't bother to try."
> Treat them all the same: when you get tired of waiting, give up.  Many
> servers seem to use a timeout of about 20 minutes for this.

20 minutes seems like a very long time to tie up valuable resources.

> I mean, you could use the TCP keepalive mechanism to disinguish between
> idle clients and the other cases, but it's pretty pointless, and it's
> not a good way to reduce network congestion.




> -Jeff

Ben Laurie                  Phone: +44 (181) 994 6435
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Received on Friday, 31 May 1996 13:45:21 UTC

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