Subject: [Speechsc] MRCPv2 use in the case of 3pcc - problem

From: Sarvi Shanmugham <[email-masked]>
Date: Tue, 27 Jan 2004 18:13:58 -0800

The current draft does not seem to address the case where the MRCPv2 
client is dealing with a 3pcc INVITE from the endpoint without an 
m=audio line in the offer. But the client knows it wants to bring in a 
Player and Recognizer resource into the session to talk to the endpoint. 
The current call flows seem to have a problem with that.

Has this sort a problem been addressed before.

Option  1:
Can the client just offer m=control lines for the 2 resources with no 
m=audio line, and have the resource side add an m=audio line to the 
answer(i guess that would be more of an offfer with a counter offer or 
answer+offer. I am not sure if this is allowed in the SDP offer/answer 
model.

Option 2:
Send an INVITE with no SDP to the media server,  have the media server 
propose one m=control line for every resource the server supports and 
m=audio line for audio, in the 200 OK. Then have the client in its 
ACK(answer) essentially zero out the ports for the m=control 
lines(resources) it does not need and respond with a port only for the 
resource control line it wants to use.

Option 3:
Send an INVITE (no SDP) with the list of resources it wants to open in 
the code in the URI, the server then proposes m=control line and m=audio 
lines ONLY for the resources requested.

Option 4:
Look for an alternative way(other the URI) for the client to communicate 
that it wants to open X, Y, Z resource at the server so that it can do 
the initial offer. The problem I see here is that, If I wanted to add an 
additional resource later in the session, I don't think SIP allows a 
re-INVITE on the same session with different URI.

Option 5:
Setup only m=control line between the client and the server using SDP 
for all resources and and use an alternative mechanism such as URI or an 
additonal XML or other body to describe the resources to open.

What ever option we pick it needs to work for the case, that we may need 
to later add additional resources on the session, by a re-INVITE or UPDATE.

I am looking for suggestions/comments to address this.

Sarvi

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