Hi Prakash, You are absolutely right about the proxy replying with the stored response in case there is a re-transmission of REGISTER. As per bis09 (sec 17.1.2.1) a non-INVITE (REGISTER in this case) request is retransmitted at an interval starting at T1 (500 ms) & doubles till it hits T2 (4s). So, I guess the minimal time for which a proxy must maintain a registration dialog is T2.
Also, as per bis09 (sec 12), a dialog consists of the tuple call-id, local tag, & remote tag. So, I can think of the following scenarios: 1. If the re-REGISTER request is sent within T2, and it contains the *same* local tag as the original REGISTER request (as also same remote tag & call-id), the proxy will consider it as a re-transmission & will reply with the stored response. The existing registration will be left untouched. 2. If the re-REGISTER request contains the *same* local tag, but is sent beyond T2, it will be treated as a new request, a new dialog will be created at the proxy, and the existing registration will be updated. 3. If the re-REGISTER request contains a *different* local tag (your case), it doesn't matter if it is sent within T2 or beyond it. It will be treated as a new request, a new dialog will be created, and the existing registration will be updated. Sharad -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Prakash GS Sent: Tuesday, July 02, 2002 1:48 PM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Cc: Nirmalya (E-mail) Subject: RE: [Sip-implementors] Refreshing Registration query Hi sharad, Thanks for your opinion. However the proxy must maintain the dialog for some minimal time at least. This is because it might have to take care of a retransmission scenario where the User-Agent sends the same REGISTER again. The proxy in this case can send a stored response back to the User-Agent instead of processing the REGISTER for the 2nd time. In the scenario that I have described below, there is nothing to deter the User-Agent from having the same call-id and Cseq in the REGISTER when it restarts. That leaves me with some more questions : (1)So what actually constitutes a dialog ? Is it composed of the following: (a)From( URI+ tag and NOT any other parameter) (b)To( URI+ tag and NOT any other parameter) (c)Call-ID (2)What should be the minimal time for which a proxy must maintain a REGISTRATION dialog to take care of retransmission? Thanks and Regards Prakash GS -----Original Message----- From: Sharad Goklani [mailto:[EMAIL PROTECTED]] Sent: Tuesday, July 02, 2002 12:56 PM To: Prakash GS; [EMAIL PROTECTED] Cc: 'Nirmalya (E-mail)' Subject: RE: [Sip-implementors] Refreshing Registration query I guess the proxy/registrar will/should *not* be maintaining any information residing in the REGISTER request, except, of course, the From (excluding tag), Contact & Expires fields. The tag parameter is actually significant when there is a possibility of 2 or more REGISTER requests, from different sources, having the same call-id, arriving at a proxy at the same time. In this case, however, once the first REGISTER is executed, the proxy forgets about the dialog, and thus the next request will be treated as a new/update request and it will update the registration expiry time. Sharad -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Prakash GS Sent: Tuesday, July 02, 2002 11:23 AM To: [EMAIL PROTECTED] Cc: Nirmalya (E-mail) Subject: [Sip-implementors] Refreshing Registration query Hi all I have a doubt regarding a refreshing registration. Assume that a User-Agent A has registered using the following REGISTER message with a proxy+registrar. REGISTER sip:proxy.com SIP/2.0 Via:SIP/2.0/UDP ua1:5060 From:<sip:3251@ua1;User=phone>;tag=278100000000000000000715 To:<sip:3251@ua1;User=phone> Contact:<sip:3251@ua1;User=phone> Call-ID:01B2270D4881400000000000@ua1 CSeq:1 REGISTER Expires:180 A goes down and comes up again. It attempts to register and sends a registration with the SAME call-id and Cseq as before but with a DIFFERENT tag in the From header . How should the proxy treat the REGISTER and why ? Should it : (a)Consider the REGISTER as a retransmission from A or (b)Should it keep track of the 'Tag' and so treat the request as a new REGISTER ? In essence what is the role of the 'Tag' field in such a scenario, if any ? Thanks Prakash GS _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
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