# Calculating Age Question

From: Paul Hethmon <phethmon@utk.edu>
Date: Mon, 25 Nov 1996 20:46:20 EST
Message-Id: <199610252046.2122933.7@hops.ag.utk.edu>
To: HTTP-WG <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/1957
```I don't mean to bring this up for discusion, rather clarification.
In going through the mailing list archives and over draft 07, I
wanted to be sure I understood the calculations of the Age value
correctly.

Given the request/response chain:

UA ----> A ----> B ----> C ----> OS

And time values as indicated:

UA request_time  = 0
A  request_time  = 1
B  request_time  = 2
C  request_time  = 3
OS request_time  = 4  (date_value)
C  response_time = 5
B  response_time = 6
A  response_time = 7
UA response_time = 8

Age at C:
apparent_age = max( 0 , 5 - 4 ) = 1
corrected_received_age = max( 1 , - ) = 1
response_delay = 5 - 3 = 2
corrected_initial_age = 1 + 2 = 3
resident_time = 0
current_age = 3 + 0 = 3 (age_value)

Age at B:
apparent_age = max( 0 , 6 - 4 ) = 2
corrected_received_age = max( 2 , 3 ) = 3
response_delay = 6 - 2 = 4
corrected_initial_age = 3 + 4 = 7
resident_time = 0
current_age = 7 + 0 = 7 (age_value)

Age at A:
apparent_age = max( 0 , 7 - 4 ) = 3
corrected_received_age = max( 3 , 7 ) = 7
response_delay = 7 - 1 = 6
corrected_initial_age = 7 + 6 = 13
resident_time = 0
current_age = 13 + 0 = 13 (age_value)

So when the User Agent receives the response, the Age value
should be 13? Basically, at each cache, the Age value will
be increased by the response_delay of that cache (plus
resident_time if applicable).

And if the User Agent calculated the Age value:

Age at UA:
apparent_age = max( 0 , 8 - 4 ) = 4
corrected_received_age = max( 4 , 13 ) = 13
response_delay = 8 - 0 = 8
corrected_initial_age = 13 + 8 = 21
resident_time = 0
current_age = 21 + 0 = 21 (age_value)

I know this is suppose to be an especially conservative
algorithm so I wanted to make sure I'm interpreting the
spec correctly.

thanks,

Paul

Paul Hethmon
phethmon@utk.edu
phethmon@hethmon.com
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```
Received on Monday, 25 November 1996 17:55:43 UTC

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