Amit Idnani wrote:
Franz,
There are devices that really don't start rendering media until media negotiation is complete. From what I understand, the device should be ready to receive media in any of the offered media codec in the INVITE request as soon as it is sent. (Paul please correct me if I am wrong)
Not sure I understand the point you are trying to make. But yes, the requirement is to be prepared to *receive* media once an offer (or answer) has been *sent*. There is in general no obligation to present that media to the user. So if a particular device chooses to delay presentation of received media until after negotiation is complete that is ok. However, while it is legal, it may not provide a good user experience - clipping may result.
Using option tag 100rel in the Require header provides for 183 being sent reliably but the behavior (in terms of opening media path) on receipt of a 183 response is again device specific.
Amit
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Shekar, Nagesh Soma (Shekar)** CTR ** Sent: Wednesday, March 30, 2005 1:00 PM To: '[EMAIL PROTECTED]'; [email protected] Subject: RE: [Sip-implementors] SDP in a 183 Session progress
Franz,
You will need to include an SDP answer (that you would normally include in a 200 OK). The SDP would contain the IP address, a port number on which to receive the media from the caller. It will also contain a CODEC list on the m= line. The Codec List contains a subset of the codecs from the received SDP in the INVITE.
Also, you will need to include a Require:100rel header in the
183 Session Progress. This will make sure that the UAC will act on the SDP in the 183.
Nagesh Shekar
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Franz Edler Sent: Wednesday, March 30, 2005 12:30 PM To: [email protected] Subject: [Sip-implementors] SDP in a 183 Session progress
Dear experts,
I have a question regarding SDP in a 183 Session progress response in case
of SIP-ISUP interworking (rfc3398).
rfc3398 states: ... the gateway will generate a 183 message towards the SIP
node; this contains SDP to establish early media cut-through.
But it is my understanding of offer/answer model that no SDP in a response
(answer) is necessary to cut-through in backward direction because the SDP
in INVITE (offer) already contains all information to send media to the
caller.
If an SDP is necessary in a 183 message in the above mentioned case: What
should it contain?
Thanks for you help.
Franz
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