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.
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