> -----Original Message----- > From: Paul Kyzivat [mailto:[EMAIL PROTECTED]] > Sent: Wednesday, March 14, 2001 5:02 PM > To: Jonathan Rosenberg > Cc: [EMAIL PROTECTED] > Subject: Inviting on hold > > > I was looking at draft-rosenberg-sip-app-components-01.txt, > and noticed a couple of places where an interesting pattern > was used: > > - invite A on hold > - use returned SDP to invite B > - reinvite A using SDP from B > > One example of this is in section 6.4.2 Web Enabled Message Drops: > > The controller then calls the user (3) using an SDP with a single > media stream on hold initially. This is accepted (4), and the > resulting SDP is used in an INVITE to the messaging server (6). > > I have a couple of questions about this potentially useful > technique: > > 1) Is it kosher to invite on hold? Depending on signalling > delays, this could be somewhat disconcerting to the > called party. It is fine; I think the user experience is reasonable for applications of this sort. > > 2) How can media formats be properly dealt with? > The SDP returned by A will be a subset of what is > initially offered. And that then limits what B may > choose from. But at the time of the initial invitation > there is no knowledge of what B supports. This issue has been discussed extensively in the context of third party call control (3pcc), which is one the core concepts in app components. As a result of list and meeting discussion, there appeared some amount of consensus around the call flow now documented in: http://search.ietf.org/internet-drafts/draft-rosenberg-sip-3pcc-02.txt which does not invite on hold, rather, it invites with no SDP. This resolves the problem you mention. In fact, the draft specifically discusses the problem. App components is lagging a bit in terms of its usage of 3pcc; it still references the flows originally described in the older 3pcc drafts. This will be corrected in later versions. I just didn't have time this round. -Jonathan R. --- Jonathan D. Rosenberg 72 Eagle Rock Ave. Chief Scientist First Floor dynamicsoft East Hanover, NJ 07936 [EMAIL PROTECTED] FAX: (973) 952-5050 http://www.cs.columbia.edu/~jdrosen PHONE: (973) 952-5000 http://www.dynamicsoft.com _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
