[SIPForum-discussion] [Sip-implementors] ptime/Maxptimesupp ortin SDP

Thu Jun 7 10:40:15 UTC 2007

Hi,

There is a draft in IETF MMUSIC WG discussing this problem:
http://www.ietf.org/internet-drafts/draft-garcia-mmusic-multiple-ptimes-
problem-00.txt. I've CC'd the authors. I guess there has been a debate
in the WG whether this is a real problem or not, so if people on this
list think it is, it would be good to express that also on MMUSIC list.

Regards,
    Markus

________________________________

	From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of ext Manpreet Singh
	Sent: 01 June, 2007 08:26
	To: Srinivas .; balasubramanian_neelakantan at quintum.com;
sip-implementors at cs.columbia.edu; discussion at sipforum.org
	Subject: Re: [SIPForum-discussion] [Sip-implementors]
ptime/Maxptimesupp ortin SDP

	I think we are digressing from the main conversation. Everyone
knows the priority is based on sequence in m line but the thread is
discussing how can we put different ptimes for different codecs. the
suggestion was to use different m lines and thats how the issue arose
that it wont be possible to find the priority. so if each m line has
only 1 codec, and there are multiple m lines, how is the priority
decided?

	But the bigger question is that if thats the right way to do and
if has been formally defined somewhere. 

	Manpreet

________________________________

	From: Srinivas . [mailto:nsrinivas at TechMahindra.com] 
	Sent: Friday, June 01, 2007 1:12 AM
	To: Manpreet Singh; balasubramanian_neelakantan at quintum.com;
sip-implementors at cs.columbia.edu; discussion at sipforum.org
	Subject: RE: [SIPForum-discussion] [Sip-implementors]
ptime/Maxptime supportin SDP

	As per RFC 3264, the offerer should place codecs in the order of
preference in "m" line.

	v=0

	o=carol 28908764872 28908764872 IN IP4 100.3.6.6

	s=-

	t=0 0

	c=IN IP4 192.0.2.4

	m=audio 0 RTP/AVP 0 1 3

	a=rtpmap:0 PCMU/8000

	a=rtpmap:1 1016/8000

	a=rtpmap:3 GSM/8000

	m=video 0 RTP/AVP 31 34

	a=rtpmap:31 H261/90000

	a=rtpmap:34 H263/90000

	In the above media attribute line codec 0 has high priority then
follows 1 and 3.

	It is answerer to negotiate based on this preference.

	Cheers

	   S

________________________________

	From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Manpreet Singh
	Sent: Friday, June 01, 2007 1:21 AM
	To: balasubramanian_neelakantan at quintum.com;
sip-implementors at cs.columbia.edu; discussion at sipforum.org
	Subject: Re: [SIPForum-discussion] [Sip-implementors]
ptime/Maxptime supportin SDP

	I was reading some threads on this last year and there is says
this way there is no way to find out the priority of the codecs to be
used. So if one does implement this how would the priority be decided?
So in the example below, which has higher preference, payload 18 or 4?

	Is this defined somewhere formally?

	thanks

________________________________

	From: Bala Neelakantan [mailto:neel at quintum.com] 
	Sent: Wednesday, May 16, 2007 10:34 PM
	To: 'Manpreet Singh'; sip-implementors at cs.columbia.edu
	Subject: RE: [Sip-implementors] ptime/Maxptime support in SDP

	For that, you have to have multiple m lines, with each having
just one codec, and the ptime can be specified for that. 

	In your example, you can try separate m= line for each codec in
the Offer.

	m=audio 22836 RTP/AVP 4
	c=IN IP4 216.168.161.230 
	a=rtpmap:18 G729/8000 
	a=fmtp:18 annexb=yes;

	a=ptime:20 
	a=maxptime:40 

	m=audio 22838 RTP/AVP 18

	a=rtpmap:4 G723/8000 
	a=fmtp:4 bitrate=6.3;annexa=yes;

	a=ptime:30 
	a=maxpime:60 

	Thanks,

	Neel

	-----Original Message-----
	From: Manpreet Singh [mailto:msingh at ibasis.net] 
	Sent: Wednesday, May 16, 2007 3:28 PM
	To: balasubramanian_neelakantan at quintum.com;
sip-implementors at cs.columbia.edu
	Subject: RE: [Sip-implementors] ptime/Maxptime support in SDP

	Well each codec is defined as the media attribute so for each
media attribute, one can define packetization to be used. Different
codec support different packetizations so they have to be defined
explicitly and we cant use a session level ptime for all media
attribiutes.

	So how does one specify packetization in the SDP for each codec
used is really my question. Lets assume a UA wants to use G723 with 30
ms packetization and G729 with 40 ms packetization.

	-----Original Message----- 
	From: Bala Neelakantan [mailto:neel at quintum.com] 
	Sent: Wednesday, May 16, 2007 4:15 PM 
	To: 'Manpreet Singh'; sip-implementors at cs.columbia.edu 
	Subject: RE: [Sip-implementors] ptime/Maxptime support in SDP 

	Ptime is media attribute.  It can't be specified per codec. 

	From 2327. 

	   a=ptime:<packet time> 
	       This gives the length of time in milliseconds represented
by the 
	       media in a packet. This is probably only meaningful for
audio 
	       data.  It should not be necessary to know ptime to decode
RTP or 
	       vat audio, and it is intended as a recommendation for the

	       encoding/packetisation of audio.  It is a media
attribute, and is 
	       not dependent on charset. 

	You can see some notes on usage of ptime in rfc3264. 

	From RFC 4040. 

	   Optional parameters: ptime, maxptime 

	             "ptime" gives the length of time in milliseconds 
	             represented by the media in a packet, as described
in RFC 
	             2327 [6]. 

	             "maxptime" represents the maximum amount of media,
which 
	             can be encapsulated in each packet, expressed as
time in 
	             milliseconds, as described in RFC 3267 [9]. 

	Thanks, 
	Neel 

	> -----Original Message----- 
	> From: sip-implementors-bounces at cs.columbia.edu 
	> [mailto:sip-implementors- bounces at cs.columbia.edu] On Behalf
Of 
	> Manpreet Singh 
	> Sent: Wednesday, May 16, 2007 2:22 PM 
	> To: sip-implementors at cs.columbia.edu 
	> Subject: [Sip-implementors] ptime/Maxptime support in SDP 
	> 
	> Whats the right implementation for ptime/maxptime in the SDP.
I read 
	> few recommendations but what is the correct way of doing it? 
	> 
	> m=audio 22836 RTP/AVP 4 18 
	> c=IN IP4 216.168.161.230 
	> a=rtpmap:18 G729/8000 
	> a=fmtp:18 annexb=yes;ptime=20 
	> a=maxptime:40 
	> a=rtpmap:4 G723/8000 
	> a=fmtp:4 bitrate=6.3;annexa=yes;ptime=30 a=maxpime:60 
	> 
	> OR 
	> 
	> m=audio 22836 RTP/AVP 4 18 
	> c=IN IP4 216.168.161.230 
	> a=rtpmap:18 G729/8000 
	> a=fmtp:18 annexb=yes; 
	> a=ptime:20 
	> a=maxptime:40 
	> a=rtpmap:4 G723/8000 
	> a=fmtp:4 bitrate=6.3;annexa=yes 
	> a=ptime:30 
	> a=maxpime:60 
	> 
	> is this how we can define ptime and maxptime per media
attribute? Any 
	> place this has been defined? 
	> 
	> Thanks 
	> _______________________________________________ 
	> Sip-implementors mailing list 
	> Sip-implementors at cs.columbia.edu 
	>
https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors 

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