Re: [rtcweb] I-D Action: draft-alvestrand-one-rtp-00.txt

On 08/12/11 05:37, Ross Finlayson wrote:
> Thanks, Harald, for this submission.
>
> A nit (I think).  Unless I'm misunderstanding the purpose of the 
> "a=group:TOGETHER" attribute, the port numbers in the two example 
> 'answers' are wrong.
I'm not sure. These examples came straight out of RFC 4317, including 
the port numbers; I noted the port number mismatch, and concluded 
(tentatively) that the port number of an offer means "I'll be using this 
port", while the port number of an answer means "I'll be using this 
port" - which means that they SHOULD be expected to be different.

When using ICE, the port number is moot anyway (the "candidates" 
overrides them), so the only purpose of the port number is that the 
special value zero in an answer means "offer not accepted".
> Example 1:
>    Answer, from an entity that understands TOGETHER
>
>           v=0
>           o=bob 2808844564 2808844564 IN IP4host.biloxi.example.com  <http://host.biloxi.example.com>
>           s=
>           c=IN IP4host.biloxi.example.com  <http://host.biloxi.example.com>
>           t=0 0
>           a=group:TOGETHER foo bar
>           m=audio 49174 RTP/AVP 0
>           a=mid:foo
>           b=AS:200
>           a=rtpmap:0 PCMU/8000
>           m=video 49170 RTP/AVP 32
>           a=mid:bar
>           b=AS:1000
>           a=rtpmap:32 MPV/90000
> Should be (I think):
>           ...
>           a=group:TOGETHER foo bar
>           m=audio 49170 RTP/AVP 0
>           a=mid:foo
>           b=AS:200
>           a=rtpmap:0 PCMU/8000
>           m=video 49170 RTP/AVP 32
>           a=mid:bar
>           b=AS:1000
>           a=rtpmap:32 MPV/90000
> Example 2:
>     Answer, from an entity that understands grouping, but does not
>     understand TOGETHER
>
>           v=0
>           o=bob 2808844564 2808844564 IN IP4host.biloxi.example.com  <http://host.biloxi.example.com>
>           s=
>           c=IN IP4host.biloxi.example.com  <http://host.biloxi.example.com>
>           t=0 0
>           m=audio 49174 RTP/AVP 0
>           a=mid:foo
>           a=rtpmap:0 PCMU/8000
>           b=AS:200
>           m=video 49170 RTP/AVP 32
>           a=mid:bar
>           a=rtpmap:32 MPV/90000
>           b=AS:1000
> Should be (I think):
>           ...
>           m=audio 49170 RTP/AVP 0
>           a=mid:foo
>           a=rtpmap:0 PCMU/8000
>           b=AS:200
>           m=video 51372 RTP/AVP 32
>           a=mid:bar
>           a=rtpmap:32 MPV/90000
>           b=AS:1000
>
> Ross Finlayson
> Live Networks, Inc.
> http://www.live555.com/
>
>
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