-----Original Message-----
From: Arunachalam Venkatraman [mailto:[EMAIL PROTECTED]]
Sent: Monday, May 14, 2001 4:34 PM
To: [EMAIL PROTECTED]
Subject: [Sip-implementors] Timestamp in PRACK
>The 100-rel draft's 03 version has this additional line (compared to 02) in
section 6.1,
>that puzzles me -
>
>If the provisional response contained a Timestamp
> header, this is copied into the PRACK.
>
>
>As per rfc2543bis-02 Section 6.43.
>
>The Timestamp general-header field describes when the client sent the
> request to the server. The value of the timestamp is of significance
> only to the client and it MAY use any timescale. The server MUST echo
> the exact same value and MAY, if it has accurate information about
> this, add a floating point number indicating the number of seconds
> that have elapsed since it has received the request. The timestamp
> is used by the client to compute the round-trip time to the server so
> that it can adjust the timeout value for retransmissions.
>
>
>Question:
>
>if the Timestamp is of interest only to the UAC (which sent the INVITE) and
it has
>received the value in a provisional response from the server, why is this
to be copied
>into the PRACK?
>
>
The purpose of the timestamp, in general, is to compute RTTs for the purpose
of modifying the retransmit interval. In this case, the UAS is the one
retransmitting periodically, so it needs to know the RTT from it to the UAC.
To determine this, it can insert a timestamp into the 1xx, and the UAC
mirrors it into the PRACK, which is generated immediately. This allows RTT
estimation.
-Jonathan R.
---
Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Ave.
Chief Scientist First Floor
dynamicsoft East Hanover, NJ 07936
[EMAIL PROTECTED] FAX: (973) 952-5050
http://www.jdrosen.net PHONE: (973) 952-5000
http://www.dynamicsoft.com
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