Hi,
Please check in line.
regards
Peili Xu
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
[EMAIL PROTECTED]
Sent: Wednesday, September 14, 2005 5:46 PM
To: [email protected]; [EMAIL PROTECTED];
[EMAIL PROTECTED]
Subject: [Sip-implementors] query related to RFC 3264
Hi,
I have an query related to RFC 3264 regarding scope of modifying a media
stream.
Section 8.3.1 says "The port number for a stream MAY be changed."
1. Is it allowed to modify the port number or any parameter of deleted
stream?
Section 8.3.3 says "The media type (audio, video, etc.) for a stream MAY be
changed."
<peili>: media type, direction, port number, connection address,
parameters... can all be changed as long as the service requires.
2. What does modifying the media type indicate? Whether the old type is
deleted and new one added ?
If that's the case than how the end point will keep track of which all
media type got modified?
And beside that just like port modification should they continue sending
RTP packets of both old
media type and new type, unless they get some indication to stop sending
packets of old media type?
Example:
Alice sends offer with two bidirectional video streams, using H.261 (payload
type 31) and MPEG(payload type 32) v=0 o=alice 2890844526 2890844526 IN IP4
host.anywhere.com s= c=IN IP4 host.anywhere.com t=0 0 m=video 51372 RTP/AVP
31 a=rtpmap:31 H261/90000 m=video 53000 RTP/AVP 32 a=rtpmap:32 MPV/90000
Bob accepted both the video streams H.261 (payload type 31) and
MPEG(payload type 32) v=0 o=bob 2890844730 2890844730 IN IP4
host.example.com s= c=IN IP4 host.example.com t=0 0 m=video 53000 RTP/AVP 31
a=rtpmap:31 H261/90000 m=video 53004 RTP/AVP 32 a=rtpmap:32 MPV/90000
At some point later, Bob decides to modify the video stream H.261 (payload
type 31) to bidirectional audio stream v=0 o=bob 2890844730 2890844731 IN
IP4 host.example.com s= c=IN IP4 host.example.com t=0 0 m=audio 49920
RTP/AVP 0 a=rtpmap:0 PCMU/8000 m=video 53004 RTP/AVP 32 a=rtpmap:32
MPV/90000
So whether Bob is allowed to modify the existing stream or he have to add
the new one? What will be the Alice's interpretion from the modified offer
with audio stream PCMU(payload type 0) ?
<peili>: since the media is aligned by position. if you want to add a media,
you should add one m= line, in your example, you replace the type of first
m= line with audio/pcmu.
It should be interpreted to stop transmiting video packet and start
transmiting audio on that media.
Thanks in Advance.
Regards,
Ashish
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