On Thu, Feb 26, 2009 at 10:50 AM, Dale Worley <[email protected]> wrote: > On Thu, 2009-02-26 at 10:58 +0000, Gabor Paller wrote: >> Well, I am not sure whether this discussion belongs to here or to the >> dev list, or maybe somewhere else but I still press on. :-) > > You may want to consider the sip-implementors list: > <[email protected]> > > >> What are these for? These seem to be proxied "hold" re-INVITE requests >> from the Nortel 6812 desk phone but where is the body. > > Many phones, when executing a transfer, first put the existing call on > hold. That seems to be what is happening here. > > And you can send an INVITE with no SDP -- in that case, the recipient is > require to provide a SDP offer in the 2xx response, and the caller > provides a SDP answer in the ACK. See RFC 3264 and RFC 4317. > >> The second, more interesting question for me, what do the parties in >> question hear when the transfer is in progress. My understanding is the >> both the source and target1 call legs are established, therefore 183 or >> 180 messages without SDP cannot be proxied in any way. Therefore if the >> REFER target is a deskphone (that often does not produce early media for >> ringing), no party in the call (Source, target1) will hear ringing while >> the transfer progresses. > > That is true. However, the phone that is executing the REFER, since it > knows that a transfer is in progress, and sees the status messages from > the new dialog, can provide ringback to its user. This is much the same > as the way that phones, when establishing a new dialog, provide ringback > to the caller upon receiving a 183 response from the callee.
To add to Dale's observations above : If SipXbridge is handling the transfer ( i.e. fielding the REFER) AND managing MOH as well, the phone cannot provide ringback on blind transfer. Instead what SipXbridge does is to play Music On Hold (ie. signal the park server for MOH) for the period of time that the phone is ringing so that you hear no "dead air" while that is happening. Ranga > > Dale > > > -- M. Ranganathan _______________________________________________ sipx-users mailing list [email protected] List Archive: http://list.sipfoundry.org/archive/sipx-users Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users
