On Dec 6, 2004, at 4:58 PM, Anil Bollineni wrote:
Hi,
Thanks for the response. Actually I may confuse you. Specifically, if the callee sends the media after 183, and 183 is lost, will the caller should accept the media, because it don't know codec should the media expect or caller should decode whatever is coming, by finding the codecs in the list it offers. Sorry I don't know that it is the basic requirement, but in RFC can I find the statements that tell the media starts after the SDP negotiation is completed.
I believe the rule is "the caller MUST be ready to receive any media described in the SDP of an INVITE immediately after sending that INVITE." This is how we get all those neat early-media use-cases.
Note that this use case frequently occurs when placing a call from SIP through a PSTN gateway (with ISDN) that terminates on a PSTN IVR, like that used by American Airlines. The "answer" SDP arrives in a 200OK that is sent by the gateway after the PSTN circuit moves into connected state. However, the phone circuit is not in the "connected" state for the first round of engagement with the IVR. The gateway in my office will only tolerate this for about 32 seconds before it gives up on the INVITE, so I have to navigate the first level of the IVR quickly.
--
Dean
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