Hi,
The Figure 3 in RFC 3312 shown an example how to use precondition call flow
to change the IP address in the middle of the session. From this example
call flow, I was not very clear how SDP1 and SDP2 should look like if A
wishes to change codec or add a new media. Below is the assumed behaviour:
Case 1: change codec from PCMU (0) to PCMA (8)
======================================
(1) Re-INVITE SDP1: (A --> B)
m=audio 20000 RTP/AVP 8
c=IN IP4 192.0.2.1
a=curr:qos e2e none
a=des:qos mandatory e2e sendrecv
(2) 183 SDP2: (A <-- B)
m=audio 30000 RTP/AVP 8
c=IN IP4 192.0.2.4
a=curr:qos e2e none
a=des:qos mandatory e2e sendrecv
a=conf:qos e2e recv
Case 2: Add video media to this session
======================================
(1) Re-INVITE SDP1: (A --> B)
m=audio 20000 RTP/AVP 0
c=IN IP4 192.0.2.1
m=video 21000 RTP/AVP 34
c=IN IP4 192.0.2.2
a=curr:qos e2e none
a=des:qos mandatory e2e sendrecv
(2) 183 SDP2: (A <-- B)
m=audio 30000 RTP/AVP 0
c=IN IP4 192.0.2.4
m=video 31000 RTP/AVP 34
c=IN IP4 192.0.2.5
a=curr:qos e2e none
a=des:qos mandatory e2e sendrecv
a=conf:qos e2e recv
Could someone tell me if my understanding is correct? If not, what is the
expected behaviour?
Thanks,
Yong
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