Hi All,
Quick question about the "pager mode" IMs which are outlined in RFC3428.
I understand that IMs are not supposed to be dialog-creating requests, the RFC is quite clear about this. However, they mention in section 2:
The authors recognize that there may be valid reasons to send MESSAGE requests in the context of a dialog. For example, one participant in a voice session may wish to send an IM to another participant, and associate that IM with the session. But implementations SHOULD NOT create dialogs for the primary purpose of associating MESSAGE requests with one another.
And again, in section 4:
A UAC MAY associate a MESSAGE request with an existing dialog. If a MESSAGE request is sent within a dialog, it is "associated" with any media session or sessions associated with that dialog.
So it seems that in some circumstances, it is OK to "piggyback" IMs on existing sessions. Presumably, this is done by using the same Call-ID and maybe from and to tags (although I'm not sure about the to-tag), and of course ensuring the CSeq is properly incremented. I think the authors are suggesting that an existing voice call (for example) may carry IMs as part of its session.
I am wondering about a situation which does not seem to be outlined here. Let's say I have two users, which are having a "conversation" using pager mode IMs. Let's call them A and B.
A sends an IM to B, a new Call-ID is created, CSeq is set to one.
A sends another IM to B, in the same "conversation".
Question: do we use the same Call-ID here and increment the CSeq (even though we did not create a dialog)?
I would think this is a bit like being in the same Call but not the same Dialog (since no dialog was created).
B sends an IM to A
Question: should B use the same Call-ID (the same call) as A, even though no dialog was created?
IMs in general are a source of much confusion during SIP integration. If anyone could help out, I'd appreciate it.
-- David Stuart, SIPquest Email: dave (at) sipquest (dot) com Phone: 254-8886 x234 Web: http://www.sipquest.com/ Address: 106 - 350 Terry Fox Drive, Kanata Ontario, K2K 2P5
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