Re: [reSIProcate-users] About the codec ptime of SDP

["Justin Matthews" <jmatthewsr@xxxxxxxxx>]

I’m not sure exactly how this would be done.  The SDP rfc defines ptime as an a: attribute on its own, so it applies to the entire m-line.  I couldn’t find any formal documentation, but others have suggested using the fmtp for the codec or use separate m-lines (1 codec per m-line, or <n> codecs with the same ptime per m-line).

 

Fmtp example:

 

a=fmtp:18 annexb=yes;ptime=20

 

You should be able to specify the fmtp line using resip as well as the multiple m-lines.  Unfortunately unless you can find it documented as standard somewhere, I’m not sure that it will work as intended because other vendors may not use the fmtp line, or even adhere to the different ptimes in the multiple m-lines.   Another issue with the multiple m-line approach is that you would need to find out if the order of m-lines implies priority.  It is stated that the order of codecs listed on an m-line implies priority, but not sure about multiple m lines ordering.

 

If you come across a definitive answer, let me know.

 

-justin

 

From: resiprocate [mailto:resiprocate@xxxxxxxxx]
Sent: Thursday, August 02, 2007 12:42 PM
To: Justin Matthews
Subject: Re: [reSIProcate-users] About the codec ptime of SDP

 

Thanks for your answer. So it's means I can't set the ptime for every codec? For example, set the G729 ptime is 20ms. and set the PCMA ptime is 30ms ?

 

2007/8/2, Justin Matthews <jmatthewsr@xxxxxxxxx>:

I believe that ptime applies to the entire m-line scope so it is only needed once as it applies to all codecs for that m-line.

 

-justin

 

From: resiprocate-users-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:resiprocate-users-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of resiprocate
Sent: Thursday, August 02, 2007 10:15 AM
To: resiprocate-users@xxxxxxxxxxxxxxxxxxxx
Subject: [reSIProcate-users] About the codec ptime of SDP

 

Hi all. I have created this SDP contents before I make the invite(I want to set the ptime for every codec):

 

v=0
o=- 10974059 10974059 IN IP4 192.168.1.100
s=CALL
c=IN IP4 192.168.1.100
t=0 0
m=audio 21524 RTP/AVP 4 18 3 98 8 0 101
a=fmtp:101 0-15
a=rtpmap:4 G723/8000
a=ptime:20
a=rtpmap:18 G729/8000
a=ptime:20
a=rtpmap:3 GSM/8000
a=ptime:20
a=rtpmap:98 iLBC/8000
a=ptime:20
a=rtpmap:8 PCMA/8000
a=ptime:20
a=rtpmap:0 PCMU/8000
a=ptime:20
a=rtpmap:101 telephone-event/8000

 

//////////////////////////////////////////////////////////////////////////////////////////////////////

Data content(SDP.c_str);

 HeaderFieldValue hfv(SDP.data(), SDP.size()); 

 Mime type("application", "sdp");
 SdpContents sdp(&hfv, type);

///////////////////////////////////////////////////////////////////////////////////////////////////////

 

But I used this SDP to make the invite and check the SIP mesage by ethereal, the invite SDP contents is :

 

v=0
o=- 12370334 12370334 IN IP4 192.168.1.100
s=CALL
c=IN IP4 192.168.1.100
t=0 0
m=audio 20104 RTP/AVP 4 18 3 98 8 0 101
a=fmtp:101 0-15
a=ptime:20
a=ptime:20
a=ptime:20
a=ptime:20
a=ptime:20
a=ptime:20
a=rtpmap:4 G723/8000
a=rtpmap:18 G729/8000
a=rtpmap:3 GSM/8000
a=rtpmap:98 iLBC/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000

 

 

Why reSIProcate modify my SDP ?

 

If I just want to set the ptime for  iLBC and G723, then how can I make the SDP contents?

 

Thanks.