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Re: [CACHING] corrected_initial_age computation question

From: Jeffrey Mogul <mogul@pa.dec.com>
Date: Fri, 26 Apr 96 16:00:17 MDT
Message-Id: <9604262300.AA23047@acetes.pa.dec.com>
To: Anselm Baird-Smith <abaird@w3.org>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
    I am having a little problem with the proposed computation for the
    correction to the received_age. Draft02, p. 87 states:
    
    corrected_initial_age = corrected_received_age + (now - request_time)
    
    If I don't miss something: 'now-request_time' measures the round time
    trip between the receiver and the sender, while what we want to
    measure is only the time between the sender and the receiver (since
    the Age value at the sender is supposed to be updated right before the
    sender emits it - see paragraph 5 of the same section).
    
    While I understand that as an approximation, this is on the safe side,
    I would like to know if this was intentional (in which case it 's
    probably safer to state it in the text).

This *is* intentional.  The Age calculations are meant to be as
conservative as possible, and because it is not true that all
Internet paths are symmetrical, the most conservative assumption
is that all of the round-trip delay is in the server-to-client
direction.

There are existing examples of highly assymetrical paths in the
Internet.

-Jeff
Received on Friday, 26 April 1996 16:11:14 EDT

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