Dear colleagues, we've discussed about Call Waiting some time ago, but I think we didn't really came to a conclusion at that time. So I'm still looking for a solution how to inform a calling user that the called user is already involved in a call.
The background was and is, as the behaviour of the called user in the case of call waiting is different from the situation the phone rings and the user just answers the call (the time until the call is answered will be longer in average, because the user realises that a call is waiting, then he brings the call he is involved in on hold or ends it, probably saying some words to the other user, and only then he answers the waiting call), in the PSTN there is an indication in the backward 'Ringing' message, saying "call is a waiting call", defined in the Generic Notification Indicator element in ITU-T recommendation Q.763. In some networks this leeds to a call waiting announcement to the calling user. Anyway the calling user is informed that the time until the call is answered might be a littlebit longer, and he will wait a littlebit longer until he hangs up. On the other hand the called user knows the the calling user has information about the call waiting situation, and that gives him some more time to answer the waiting call. When we discussed this issue, I think the proposed solutions were the following - usage of a 182 Queued response Con: it not sure the the 182 will cause a ringing tone at the calling user - usage of an Alert-Info header Con: Alert-Info shoulf be used to provide Ringing tones, possible conflict between providing a ringing tone and rendering the information to the user - Usage of presence information <activities> <on-the-phone/> </activities> Con: Presence is a subscription based service and it may not be possible to interwork this information to other Networks, esp. PSTN - I proposed (as usual) to use a P-header for this purpose, as a possibility to interwork the Generic Notifiaction Indicator element in general Con: another new P-header; possible interactions with the event notification framework; So in my opinion the best solution would be an indication in the 180 Ringing response. Something like the Alert-Info header without the mentioned difficulties. In other discussions it was proposed to use the Call-Info header for a similar purpose. This could perhaps be done by using a special URI and defining a new CW specific purpose value. Another solution could be to re-use the presence XML schema as defined in RFC 4480 with <activities> set to <on-the-phone/> and include it in a MIME body in the 180. Regards, Martin _______________________________________________ BLISS mailing list [email protected] https://www.ietf.org/mailman/listinfo/bliss
