From: Attila Sipos [mailto:[EMAIL PROTECTED] > There must be some kind of channel allocated > somehow.
> Id doesn't matter whether what kind of telephone > system (LAN-based, ISDN or PSTN) you use, there must > be some kind of channel (RTP or ISDN bearer-channel > or just physical wires) otherwise you wouldn't hear > the ringback. This isn't entirely true. For DSS1, you can defer bearer channel allocation on the access interface right up until the call is answered. As a consequence (and also as a result of various other considerations), an ISDN terminal at A in the scenario would usually generate its own tones. I say usually, because there is a Call Progress signal to indicate that there are in-band tones on the bearer channel - i.e. tones generated elsewhere in the network. As a general rule, there is no rule. The position of the tone generation in a particular network is network and signalling scheme-dependent. International interworking complicates matters, and I believe this is usually resolved by bilateral agreement. Regards, Michael Procter _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
