Subject: RE: [SIP] Timestamp header

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 31 Jan 2001 13:43:16 -0500

> -----Original Message-----
> From: Henning G. Schulzrinne [mailto:[email-masked]]
> Sent: Tuesday, January 16, 2001 10:25 AM
> To: Jonathan Rosenberg
> Cc: 'Grant McSheffrey'; Sip List
> Subject: Re: [SIP] Timestamp header
> 
> 
> Jonathan Rosenberg wrote:
> > 
> > The spec is not clear on this, saying simply that it should 
> be echoed. I
> > would imagine placing it in all responses, provisional and 
> final, makes the
> > most sense.
> 
> Note that because of the different origins, the delay for the 100 may
> differ from the other 1xx and the final response.

Hmm. This brings up some more issues.

If the purpose of the Timestamp header is to determine RTT for
retransmission rates, then what you really want is the delay between the UAC
and the *first stateful entity* (be it stateful proxy or UAS/redirect) on
the call path, since retransmissions terminate there. The final responses
are from UAS to UAC, which is going to have an RTT much higher than the UAC
to first stateful proxy. In fact, in this case, the 100 response is the ONLY
place that Timestamp would be useful.

Other applications of timestamp (not sure what they are, though) might make
an end to end measurement useful.

-Jonathan R.

---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
http://www.dynamicsoft.com

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