Just to add a bit. Note that the "C=" may (in some interesting cases) be associated with a specific media stream, thus you may have multiple "C=", for instance one IP address to receive audio, and a diff one to receive video.
Regarding the IP Addr in the 'Via' and the 'Contact' headers, note that the 'via' has a hope to hope notion and is used by the next hope on the reply path, while 'Contact' has a end2end notion, and is designated to be used by consequent requests. ================================================================== Uri Baniel - Distinguished Member of Technical Staff - Motorola Tel: (847) 632 4616; Fax: (847) 632 3963; "Learning that does not daily increase will daily decrease. - EWC ================================================================== -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Wednesday, August 13, 2003 11:36 PM To: MINGHAO WANG, BLOOMBERG/ 499 PARK Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: Re: [Sip-implementors] About IP addresses in SDP content and SIP header Hi, Attempting to answer your question. Others can add if I missed something: Ans 1. Yes, the IP addresses can be different between the SIP headers and the SDP content. A typical case could be a gateway application where the signalling path and media path are different. Another example is the 3pcc cases where the scenario is as follows: +---------------+ | Controller | +---------------+ ^ ^ SIP / \ SIP / \ Caller <===============> Callee Media That said, in most cases 1 & 2 below are the same IP address (addr 1) while 3 & 4 are usually the same IP address (addr 2). Ans 2. o= line of the SDP conveys information about the creator of the session: his username and his *unicast* address (as per the appendix A of the sdp-new draft). The c= line, however, can be either unicast or multicast. So, in case user A creates a multicast session, the o= line in the SDP sent by him will contain something like: o=userA <sess-id> <sess-ver> IN IP4 <A's IP address> while the c= line is the actual multicast address where the media has to be received/sent. Regards, Siddharth. ------------------------------------------------------------ Siddharth Toshniwal Hughes Software Systems Ph (O): +91-80-2286390 Bangalore, India http://www.hssworld.com ------------------------------------------------------------ [EMAIL PROTECTED] wrote on 08/13/2003 07:05:41 PM: > A simple question about SIP header and SDP content. > When a caller sends an INVITE message, there are many places > containing IP > address info. For example, > 1) SIP header "via: SIP/2.0/TCP ***.***.***.***" > 2) SIP header "Contact: <sip:.....;maddr=***.***.***.***"> > 3) SDP content "o=- 0 0 IN IP4 ***.***.***.***: > 4) SDP content "c=IN IP4 ***.***.***.***" > My questions are: 1) Can they be different? If yes, give me an > example? 2) What > is the difference between SDP content "o=" and "c=", the two ip > addresses are > supposed to be the same or not? Is there any example that they > are different? > Thanks a lot. Howard. _______________________________________________ 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
