Subject: [MMUSIC] a=mptime not needed ? FW: [Sip-implementors] Multiple ptime attributes in the SDP

From: "Lyons, Terry" <[email-masked]>
Date: Fri, 9 Sep 2005 13:56:56 -0400

Is this a valid concept, "codec specific attribute"?
SDP says ptime "is a media attribute".

- [email-masked]

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of
[email-masked]
Sent: Wednesday, September 07, 2005 1:33 AM
To: Kool Guy
Cc: [email-masked];
[email-masked]
Subject: Re: [Sip-implementors] Multiple ptime attributes in the SDP

Hi,

ptime is a codec specific attribute. The ptime value corresponds to the
previous codec specified in the
attribute list. The multiple ptime attribute can be represented as follows:

              m=audio 49230 RTP/AVP 96 97 98
              a=rtpmap:96 L8/8000
              a=ptime:20
              a=rtpmap:97 L16/8000
              a=ptime:25
              a=rtpmap:98 L16/11025/2

In the above, ptime=20 corresponds to L8 codec and ptime=25 corresponds to
L16.

Regards
Partha

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From: Colin Perkins <[email-masked]>
Date: Mon, 12 Sep 2005 13:46:35 +0100

Terry,

The "a=ptime:" is a media level attribute, which makes it specific to  
the "m=" line. It does not work on a per-codec basis, and the  
suggestion that "the ptime value corresponds to the previous codec  
specified in the attribute list" is incorrect.

Colin

On 9 Sep 2005, at 18:56, Lyons, Terry wrote:
> previous codec specified in the attribute list. The multiple ptime  
> attribute can be represented as follows:
>

---

From: [email-masked]
Date: Wed, 14 Sep 2005 00:01:31 +0530

Hi Colin/Christer,

In case ptime needs to be treated as a media level attribute, I have doubt
in SDP negotiation
of UA which support RFC 2327 and RFC 3264.

When UA receives the message with multiple ptime, please let me know which
ptime needs to
be selected for that media line (First ptime or last ptime in the set of
ptime for that m line) .
I faced this issue in Sipit 15 with one UA as I always select the last
ptime attribute in the m line.
This issue is already discussed in the mailing list but I could not figure
out the final conclusion
in the thread at
http://lists.cs.columbia.edu/pipermail/sip-implementors/2003-March/004747.html

Could you please clarify the expected UAS behavior.

Regards
Partha

             Colin Perkins                                                 
             <[email-masked]                                             
             g>                                                         To 
             Sent by:                  "Lyons, Terry"                      
             sip-implementors-         <[email-masked]>               
             [email-masked]                                          cc 
             ia.edu                    [email-masked],   
                                       [email-masked]                     
                                                                   Subject 
             09/12/2005 06:16          Re: [MMUSIC] a=mptime not needed ?  
             PM                        FW: [Sip-implementors] Multiple     
                                       ptime attributes in the SDP         

                                                                           

Terry,

Colin

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From: Colin Perkins <[email-masked]>
Date: Thu, 15 Sep 2005 09:29:48 +0100

On 13 Sep 2005, at 19:31, [email-masked] wrote:
> in SDP negotiation of UA which support RFC 2327 and RFC 3264.
>
> ptime needs to be selected for that media line (First ptime or last  
> ptime in the set of ptime for that m line).

SDP does not define an interpretation for multiple "a=ptime:"  
attributes in a single "m=" line.

Colin