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List:       sip-implementors
Subject:    Re: [Sip-implementors] Query on processing ptime in SDP media
From:       "Bu, Wen Fei \(Leo\)" <wbu () lucent ! com>
Date:       2006-04-24 5:22:22
Message-ID: 2AC135F730C4A045BAE4F1C1CB83FD4B02F5970A () exch03 ! qd ! lucent ! com
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Venkatesh,

Per RFC 3264,
6.1 Unicast Streams, Page 10:
   The answerer MAY include a non-zero ptime attribute for any media
   stream; this indicates the packetization interval that the answerer
   would like to receive.  There is no requirement that the
   packetization interval be the same in each direction for a particular
   stream.
6.2 Multicast Streams, Page 11:
   The ptime and bandwidth attributes in the answer MUST equal the ones
   in the offer, if present.  If not present, a non-zero ptime MAY be
   added to the answer.

For unicast streams in your case:
when sending media, the offerer SHOULD send media according to the value of
any ptime in the anwser, if any is present. The answerer SHOULD also use a
packetization interval equal to the value of the ptime attribute in the offerer,
if any is present.

So, your understanding is correct. For the 2 directions, one uses 20 ms, while
the other 40 ms.

Regards,
Leo

-----Original Message-----
From: sip-implementors-bounces@cs.columbia.edu
[mailto:sip-implementors-bounces@cs.columbia.edu]On Behalf Of Venkatesh
Joshi
Sent: Sunday, April 23, 2006 2:37 PM
To: sip-implementors@cs.columbia.edu
Cc: Venkatesh Joshi
Subject: [Sip-implementors] Query on processing ptime in SDP media


Hi,

I have a query regarding the processing of ptime info (if present) in the SDP media.

We have a situation where the ptime attribute is present in the 200_OK message sent by the
called party. It is not present in the SDP message body of the INVITE from the  calling party.

In such a case, how should the ptime be processed ?

My understanding is:

Calling party                  Called Party
--------INVITE[ptime ms]----->
<-------200_OK[ptime@ms]------
--------ACK--------------------->
..............Media..............

.............40ms samples.........>
<............20ms samples.........

In the above case, the 2 sides send out different ptime values. And the packetization is
processed accordingly.

What happens if only 1 side sends out the ptime ?

thanks in advance,
Venkatesh
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