[EMAIL PROTECTED] wrote:
Hi,
Query Regarding Connection lines in SDP
Related RFC 2327 & 3264
Scenario--> There are two Sip Endpoints, both of which put connection lines information at the media level rather than at the session level.
In the case when offer in the Invite is generated to the other endpoint there are two media streams and both of the these have corresponding connection line ("c="). The other endpoint supports only one of the media stream so it sends "m=audio 0 RTP/AVP 7" and the other accepted media in the answer.
Question --> So the question is whether there should be connection line for the rejected media stream as well has there is no session level connection line present. If yes than what is the use of the information in the connection line.
I think the simple answer is YES.
Offer/answer imposes some added constraints on SDP, but each offer and answer must be a valid SDP document in its own right. This means that there must be a connection for each media - either in that media section or at session level.
If the following is the offer (simplified):
m=audio 123 ... c=... m=video 456 c=...
Then the answer can be either
m=audio 789 c=... m=video 0 c=... or c=... m=audio 789 m=video 0
It doesn't matter what the value is for the connection of the rejected media, as long as it is syntactically correct. So you can use the same one as for the accepted media, or make something up. A simple thing to make up is 0.0.0.0.
You might get away without a connection attribute for the rejected stream, but don't count on it.
Paul
Relevant text from the RFC is below for reference Text from RFC 2327 Section 6 "Sdp Specification" \* A session announcement must contain one "c=" field in each media description (see below) or a "c=" field at the session-level. It may contain a session-level "c=" field and one additional "c=" field per media description, in which case the per-media values override the session-level settings for the relevant media." */ Text from RFC 3264 Section 6 "Generating Answer" \* For each "m=" line in the offer, there MUST be a corresponding "m=" line in the answer. The answer MUST contain exactly the same number of "m=" lines as the offer. This allows for streams to be matched up based on their order. This implies that if the offer contained zero "m=" lines, the answer MUST contain zero "m=" lines. */
Regards Saurabh
Saurabh Gupta - HSS Bangalore Campus
*********************** HSS-Private *********************** "DISCLAIMER: This message is proprietary to Hughes Software Systems Limited (HSS) and is intended solely for the use of the individual to whom it is addressed. It may contain privileged or confidential information and should not be circulated or used for any purpose other than for what it is intended. If you have received this message in error, please notify the originator immediately. If you are not the intended recipient, you are notified that you are strictly prohibited from using, copying, altering, or disclosing the contents of this message. HSS accepts no responsibility for loss or damage arising from the use of the information transmitted by this email including damage from virus."
_______________________________________________ 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
