IMMO, since the timestamp of the original request was set by the same originating UAC, the UAC can simply substract the timestamp value when this particular response was received and the original value set in the Timestamp header (the one received in the response). This will help the UAC automatically estimate RTT, without the need of storing the value when sending the initial request -"storage" is actually achieved by mandating the UAS copy the value into the response. As Víctor indicates, this should be useful to adapt timers.
Furthermore, with the delay parameter added by the UAS, the UAC can even estimate what percentage of the total RTT was consumed as processing delay at the UAS.
-------- Original Message --------
Subject: Re: [Sip-implementors] How to parse "Timestamp" header?
From: Iñaki_Baz_Castillo <[EMAIL PROTECTED]>
Date: Wed, July 02, 2008 12:48 am
To: [email protected]
El Miércoles, 2 de Julio de 2008, Victor Pascual Ávila escribió:
> Hi Iñaki,
>
> On Wed, Jul 2, 2008 at 12:05 AM, Iñaki Baz Castillo <ibc@aliax.net> wrote:
> > My question is:
> >
> > - What does the first value mean?
> > 1*(DIGIT) [ "." *(DIGIT) ]
> > In the example above it's 0.4. What is it?
>
> It is the timestamp header field present in the request- It describes
> when the UAC sent the request to the UAS, and it is used by the UAC to
> compute the round-trip time to the UAS so that it can adjust the
> timeout value for retransmissions.
But the only useful information there is the "delay" field that the server
adds to the "Timestamp" header, but what is the "timestamp" value by itself?
I put an example:
INVITE sip:XXX
Timestamp: 12.34
It takes 0.5 seconds to the server to send the 100 Trying so:
SIP/2.0 100 Trying
Timestamp: 12.34 0.5
The useful information there (for the UAC) is the delay field (0.5 seconds)
added by the UAS. But what does "12.34" means?
Thanks.
--
Iñaki Baz Castillo
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