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Section 13.2.3

From: Ben Laurie <ben@algroup.co.uk>
Date: Mon, 03 Jun 1996 20:29:32 +0100
Message-Id: <31B33D1C.3D2B@algroup.co.uk>
To: HTTP Working Group <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
13.2.3

All HTTP implementations, but especially origin servers and caches, 
should use NTP[28] or some similar protocol to synchronize their clocks 
to a globally accurate time standard

This is unrealistic and besides is a requirement on the users of the 
implementation rather than the implementation itself, unless we are 
seriously suggesting that every HTTP implementation should run NTP 
internally. Unrealistic, BTW, because of firewalls, Intranets, and dumb 
operating systems, particularly at the client end (and, dont forget, 
there are more client caches than any other type).

If this point is accepted then much of the age calculation becomes 
wrong. I would suggest a simple fix. The responder includes in the 
header the local time at which the response is generated. The time slip 
between the responder and the client can be estimated by the following: 
time_slip=server_now-(request_time+response_time)/2. This can then be 
used to correct as appropriate.

Cheers,

Ben.

-- 
Ben Laurie                   Phone: +44 (181) 994 6435
Freelance Consultant and     Fax:   +44 (181) 994 6472
Technical Director           Email: ben@algroup.co.uk
A.L. Digital Ltd.            URL: http://www.algroup.co.uk
London, England.
Received on Monday, 3 June 1996 12:24:56 EDT

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