Re: [MMUSIC] Scope of RTP payload types in BUNDLE?

Colin Perkins <csp@csperkins.org> Mon, 27 May 2013 12:59 UTC

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From: Colin Perkins <csp@csperkins.org>
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Date: Mon, 27 May 2013 13:59:04 +0100
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Subject: Re: [MMUSIC] Scope of RTP payload types in BUNDLE?
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On 27 May 2013, at 13:52, Christer Holmberg wrote:
>>> There were a number of comments in the call last week, and on the list, about unique payload types in BUNDLE. I'd like to explore this further.
>>> 
>>> Case A: Within a single RTP session, I think we'd all agree that an offer that uses the same RTP payload type for two payload formats on a single m= line is problematic: 
>>> 
>>>  v=0
>>>  o=alice 2890844526 2890844526 IN IP4 host.anywhere.com
>>>  s=
>>>  c=IN IP4 host.anywhere.com
>>>  t=0 0
>>>  m=audio 49170 RTP/AVP 96
>>>  a=rtpmap:96 AMR-WB/16000
>>>  a=rtpmap:96 G7291/16000
>>> 
>>> If this were done the receiver would have no way of distinguishing what payload format is meant by payload type 96. Accordingly, unique payload formats need to be used for each payload format.
>> 
>> That should be "...unique payload types need to be used for each payload format" of course.
> 
> What if you have two m- lines, with identical encoding in both? Both represent the same payload format, don't they? :)
> 
> v=0
> o=alice 2890844526 2890844526 IN IP4 host.anywhere.com
> s=
> c=IN IP4 host.anywhere.com
> t=0 0
> m=audio 49170 RTP/AVP 96
> a=rtpmap:96 AMR-WB/16000
> m=audio 49170 RTP/AVP ???
> a=rtpmap:??? AMR-WB/16000


Not sure I get your point. You can have two different payload types that map to the same payload format in a single RTP session, since you can always distinguish what payload format is intended. You can't have the same payload type mapping to two different payload formats in a single RTP session, since you can't then infer what payload format was meant. 

-- 
Colin Perkins
http://csperkins.org/