Thank you Dean for your prompt response and making this source of confusion sound so simple.
Regards, Simon On 12/14/07, Dean Willis <[EMAIL PROTECTED]> wrote: > > On Dec 12, 2007, at 10:32 PM, Simon Flannery wrote: > > > > I would like to check my understanding of Early and Late media also > > know as Early (or Late) operating mode: > > > > - Using Early media, the inviting user may talk immediately, and the > > core network should buffer the media before the invited user (or > > users) accept the session > > - The received media is buffered until at least the first invited user > > accepts the invitation > > - The buffered media is also sent to all users that accept the > > invitation > > - Conversely, Late media mimics a traditional phone call where the > > inviting user must wait until at least one inviting user accepts the > > session before being allowed to send media > > > > Is my understanding correct? Are any of the dot points in error? > > > > > > Welcome to one of the most confusing aspects among the many confusing > aspects of SIP that were introduced by our attempts to compensate for > the broken signaling model of ISUP. Personally, I think we > unwittingly introduced a nightmarish level of complexity and should > have just said "no! If you need two stage signaling, finalize the > first stage with a 200 OK and then re-INVITE if the SDP changes for > the second session." But we didn't do that, so we have what we have. > > IETF seems to use the terms "early media" and "early session", > although I'm afraid I don't completely understand the nuances despite > having struggled with them for many years. I suspect I don't want to > understand just because the whole thing hurts my delicate > sensibilities. I'm told that RFC 3960 is a useful reference for this > discussion. > > Both uses of "early" refer to the transmission of media before > completion of some phase of the signaling. Sometimes this is mean to > be "before completion of the offer/answer phase" (that is, after an > "offer", but before an "answer", and sometimes (as defined in RFC > 3960) before the completion of a final response (generally a 200) to > an INVITE request. > > RFC 3960 uses the following definition: > > Early media refers to media (e.g., audio and video) that is > exchanged > before a particular session is accepted by the called user. > Within a > dialog, early media occurs from the moment the initial INVITE is > sent > until the User Agent Server (UAS) generates a final response. It > may > be unidirectional or bidirectional, and can be generated by the > caller, the callee, or both. Typical examples of early media > generated by the callee are ringing tone and announcements (e.g., > queuing status). Early media generated by the caller typically > consists of voice commands or dual tone multi-frequency (DTMF) tones > to drive interactive voice response (IVR) systems. > > In IETF and general IMS environments (AFAIK), there is no expectation > that early media will be buffered. Anything not received by a > listener is expected to be discarded. > > However, OMA's Push to talk Over Cellular (POC) specification does > (or at least did, the last time I looked) allow a predictive mode > where a POC controller (which is for all practical purposes a SIP > B2BUA with media handling) can "answer" on behalf of a POC terminal > with which it has an active relationship. The POC controller then > buffers media while it activates the radio bearer needed to send the > media on to the terminating POC client. Since the POC controller has > effectively "answered" the INVITE request with a terminal response > and media answer, I don't believe this mode qualifies as "early > media" by any of the definitions in use around the IETF. > > Good luck in sorting this all out. > > -- > Dean > > _______________________________________________ Sip mailing list https://www1.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip
