A--->CO ----- CO ---> B What I understood is that In order to play tones to A from B's CO, a pre-allocation of bearer channel is a prerequisite.
So if a telephone system does not allow such early assignment of bearer channel (like DSS1) then tones from B's CO cannot be played to A, instead A's CO will take care of that job. Though that seems to be an ineficient way of carrying tones all the way on international circuits while a just tone indicator (and country indicator) would have solved the purpose. Thanks guys for reponse. regards Mandeep --- Michael Procter <[EMAIL PROTECTED]> wrote: > 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 > __________________________________ Do you Yahoo!? Free Pop-Up Blocker - Get it now http://companion.yahoo.com/ _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
