Subject: [SIP] Re: SIP INFO: What is "mid-session"; sessions w/o media

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 03 Apr 2000 03:24:56 -0400

This issue isn't really specific to INFO. In general, the question is
whether you can send a request immediately after sending an INVITE, and
can the UAS send a request in the reverse direction after receiving the
INVITE?

We discussed this issue as it relates to BYE. I believe the issues here
are similar. If the UAC waits for a provisional or final response, it
will have both a Route and a tag, and can thus insure that the request
gets to the right place. If the UAC sends a request out before waiting
for that response with the tag and route, it might work, but it becomes
dependent on the consistency of call processing logic at intermediate
proxies. 

The issue is similar for the called party. If it sends the request
before the caller gets a provisional or final response to the initial
INVITE with a tag, the caller won't know from whom the new request is.
So, its a good idea for the called party to wait for an ACK before
sending a new request, but its not mandatory.

Do you have a specific need for sending INFO right away? Remember, INFO
cannot be used to modify session or call state.

Regarding your second question, sure. No m lines in the SDP.

-Jonathan R.

[email-masked] wrote:
> 
> 1. The draft on the INFO method says that the INFO method may be used
> "mid-session"; exactly what that means is not clear to me. Does it mean that
> the UAC may send an INFO right after sending an INVITE, and the UAS may send
> an INFO right after receiving an INVITE?
> 
> 2. Is it possible to create a session without a media stream, solely for the
> purpose of sending one or more INFOs, and if so, is there a standard or
> preferred way of doing so?
> 
> Thanks,
> 
> Cliff Harris

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (732) 741-4778
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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