Subject: SIP Provisional Responses

From: Eric Tremblay <[email-masked]>
Date: Tue, 19 May 1998 14:19:18 -0400

I think I just found small problem:

A SIP User Agent client (UAC)invites a remote user agent server (UAS).
The server's response to this request is Trying (100) and it then take
whatever action needed to see if the user is on the system.  The server
finds the user on the local system and alerts him.  The server now could
send 180 (Ringing) responses to the UAC, but how?  According to the
latest draft, the server has to wait for a retransmission by the UAC
(which is once every 30 seconds) before sending again a response.  I
think a remote UAC cannot wait such a delay before knowing that the
remote party is ringing.  How can the UAC be notified in time?

A quick and simple solution would be to have the UAC retransmit its
requests at a T1 interval (1 second) until it receives a response
GREATER than 100 or we could introduce another timer for the client(2-3
seconds).  

Comments?

Eric M. Tremblay    | Mediatrix Telecom
Ingénieur Stagiaire | -----------------
email: [email-masked]
Phone: +1(819)829-8749 ext. 238
Web: www.mediatrix.com

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 19 May 1998 17:22:07 -0400

> remote party is ringing.  How can the UAC be notified in time?

The user agent server *retransmits* its current response upon receiving
a retransmission of the request, but it can send a response at any time.
Thus, you would send the 180 whenever you want, and the 200 (if the call
is accepted) as soon as the user accepts - no need to wait for a request
retransmission. 

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX:   (732) 834-5379                       Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen