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Re: [Megaco] Sending tones via the other subscriber's ephemeral
Please bear in mind that call flows both in the Appendix of H.248/Megaco and
draft-ietf-megaco-callflows-00.txt are INFORMATIVE. Its not a particularly good
idea to base a commerical product around them as they are rather limited. For
good interoperability normative specifications are needed profiling how
SIP/ISUP/BICC/Megaco etc are used in a system. ITU Q.1950 and 3GPP 29.232 go
part of the way to acheive this for Megaco in BICC in ITU and 3G networks.
However even in the referenced BICC call flows in ITU are informative.
Regards, Christian
Raphael Tryster wrote:
>
> Thanks Al and Vivek.
>
> Your answers make sense to me, which leads me to ask if the examples in RFC
> 3015 and other places like draft-ietf-megaco-callflows-00.txt are wrong. All
> the examples I have seen show ringback being provided by MGA. Furthermore,
> some of the examples show the termination modes being recvonly until the
> called party goes off-hook. If this is the case, then the half-duplex
> connection to which Vivek refers is in the wrong direction. If EphB in my
> example is recvonly, then it cannot send the tone to EphA. Have all the
> example writers been oversimplifying to the point of misleading?
>
> Raphael Tryster
>
> -----Original Message-----
> From: Al Varney [SMTP:varney@ieee.org]
> Sent: Monday, 06 May, 2002 5:47 PM
> To: 'megaco@ietf.org'
> Subject: Re: [Megaco] Sending tones via the other subscriber's
> ephemeral
>
> At 01:04 PM 5/6/02 +0530, vibansal@hss.hns.com wrote:
> >It is recomanded that ringback tone id be played by the terminating
> media
> >gateway. So in this case, MGC controlling MGB tells MGB to send
> ringback
> >signal
> >on EphB, MGB at australia would play the ringback tone on the ephemeral
>
> >termination EphB, and subscriber A would hear Australian ringback tone
> >,as half
> >duplex connection is already open.
>
> I'm not sure where this is "recommended" rather than "required",
> except
> in cases where MGA and MGB operate together as a single logical switching
>
> entity (a distributed PBX, perhaps).
>
> >>Raphael Tryster <raphael@tdsoft.com> wrote on 05/05/2002 10:02:45 PM
> >>
> >>Is the following a realistic scenario?
> >>
> >>Subscriber A in U.S.A. wishes to speak with subscriber B in Australia.
> When
> >>the connection is established (MGA creates EphA in the same context as
> PhyA,
> >>and MGB creates EphB in the same context as PhyB) and B's phone is
> ringing,
> >>the MGC controlling MGA sends a ringback signal to PhyA. But this
> would be
> >>an American ringback signal, and A wants to know he is calling
> Australia.
> >>So instead, the MGC controlling MGB tells MGB to send ringback signal
> on
> >>EphB.
> >>
> >>Will this work, i.e. will subscriber A hear Australian ringback tone?
> And
> >>is it done in practice?
>
> If by "in practice" you mean "in the existing telephone network", you
>
> will find ringback tone ALWAYS comes from the terminating switch
> (pre-MGC/MG). There are several reasons for this:
>
> - MGA would never know when to apply ringback, since it has no
> knowledge
> of the status of the terminating line. In fact, it doesn't know if MGB
> is
> a terminating point or just an interworking point using traditional
> trunking to reach a third switching point (perhaps located in a third
> country).
>
> - MGA would not be aware (at ringback time) of cases where MGB is
> forwarding the call to another line somewhere in the world, or is
> interacting with an Intelligent Network service or is offering a voice
> announcement regarding the status of the called number. (E.g., "this
> number is disconnected, calls are being taken on XXX-XXXX-XXX".)
>
> - MGA (and any other MGs on the way to the final terminating MG) would
> have to be very quick in order for MGA to be able to remove ringback and
> cut through the connection before the called party's "Hello?" is
> transmitted.
>
> About a year ago (5/1/01), I discussed this same issue on the
> "megaco@fore.com" mailing list. Two years ago (6/27/00) it was discussed
>
> on the "MEGACO@standards.nortelnetworks.com" mailing list. And I've
> discussed it ad nauseam on several other standards lists (H.248, SIP,
> H.323, ISUP/BICC) over the past few years. Here's the rationale in a
> single sentence:
>
> "The PSTN does not, in general, provide a reliable
> out-of-band indication of when Alerting of the
> called party is occurring."
> - (quoting an ITU-T contribution)
>
> I assume this will continue to come up until the H.323, H.248 and SIP
>
> folks finally get something published that shows real-world examples of
> the
> need to provide ringback from the terminating end of a connection. (See
> the SIP "183 Session Progress" message for some examples.)
>
> Thanks, Raphael, for providing this year's version of the perennial
> question. Should you wish to examine other standards/requirements on
> this
> issue, note the ITU-T uses the term "Ring Tone" and Telcordia the term
> "audible ring tone" in many telephony documents. "Ringback" seems to
> have
> originated in PBX/ISDN documents in North America in the 1980s.
>
> Al Varney
>
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