AW: Call hold and transfer in H.323 AnnexF. Too limited??

Paul E. Jones paul.jones at
Mon Mar 22 13:11:23 EST 1999


I do agree that two mechanisms for accomplishing the same task is a bad
idea.  I, too, would rather see one mechanism employed-- we do want to
create interoperable equipment, after all.  Unfortunately, we already have
two ways of doing "call hold"-- H.450.4 and "empty capability sets" (see
7.6.2 of Annex F).

The issues you raise with supplementary services echoes the concerns of
those also participating in the TIPHON work.  Essentially, service providers
would like to be able to add new services without upgrading software in the
endpoints.  Although it may be possible to upgrade IP phone devices, I can
assure you that the average person would never do that-- once the phone is
plugged in, it will stay there until it stops working.  More importantly,
why would one want to require somebody who purchased a hardware phone device
to upgrade periodically?

We need to engineer a solution so that the telephony service providers can
introduce new services without requiring software upgrades in the endpoints.
I would like to see SET device to take advantage of those newly introduced
services without software or hardware upgrades.


-----Original Message-----
From: Derks, Frank <F.Derks at PBC.BE.PHILIPS.COM>
Date: Monday, March 22, 1999 5:45 AM
Subject: Re: AW: Call hold and transfer in H.323 AnnexF. Too limited??

>when talking about a Simple Endpoint Type, I think we should aim for it to
>be something that closely resembles a black phone. This way it becomes a
>easier to define what its capabilities are and it makes life easy on the
>users and on those companies that will actually make (physical) IP-phones.
>These phones should probably look and act like the normal phones that are
>currently being used. Looking at how most supplementary services are
>accessed in both the public and the private (PBX) networks, I think it is
>safe to say that in most cases we are talking about "stimulus protocols".
>I.e. DTMF digits are sent to an exchange and the exchange interprets
>digit sequences as being the invocation of some service rather than a
>to be dialled. The big advantage over functional protocols (like H.450.x)
>being that services can be added from the exchange side, without the
>terminal having to be modified as well.
>Functional protocols never became a success in  the ISDN world and this may
>end up to be the same in the IP world. However, having said this, there is
>lot more potential for easy upgrading of e.g. terminal software in this
>domain, which reduces the side effects of functional protocols.
>It does not seem to make sense to define "alternative" mechanisms to
>services, so I would strongly opt for using H.450.x when possible and using
>a simple stimulus protocol otherwise. The latter would allow service
>providers to easily make services available and I see no reason why this
>should be standardised. In practice, today, we already see that certain
>digit sequences for service activation are identical in several countries.
>Frank Derks                    |Tel  +31 35 6893238 |
>Advanced Development           |Fax  +31 35 6891030 |
>Philip Business Communications |P.O. Box 32         |
>                               |1200 JD  Hilversum  |
>                               |The Netherlands     |
>E-mail: mailto:f.derks at           |
>WWW:       |
>-----Original Message-----
>From: Klaghofer Karl ICN IB NL IP 7
>[mailto:Karl.Klaghofer at ICN.SIEMENS.DE]
>Sent: 18 March 1999 22:36
>Subject: AW: AW: Call hold and transfer in H.323 AnnexF. Too limited??
>See comment below.
>> -----Ursprüngliche Nachricht-----
>> Von:  Paul E. Jones [SMTP:paul.jones at TIES.ITU.INT]
>> Gesendet am:  Donnerstag, 18. März 1999 18:57
>> An:   ITU-SG16 at
>> Betreff:      Re: AW: Call hold and transfer in H.323 AnnexF. Too
>> limited??
>> Karl,
>> Unfortunately, I will have to disagree with your comments.  While it is
>> true
>> that the H.450 supplementary services could be utilized in a SET device,
>> believe that introducing H.450 into a SET breaks the spirit of that work.
>> The goal of Annex F is to define a "Simple Endpoint Type".  There are
>> simpler ways to put a call on hold and to transfer a call.  Introducing
>> H.450 introduces a lot more complexity that I believe we want to have.
>> Annex F is not sufficiently clear on how to simply transfer a call or put
>> a
>> call on hold, we should work on that text-- I will absolutely disagree
>> with
>> introducing H.450 into a SET device.
>        [Klaghofer, Karl  PN VS LP3]  Whatever you mean with
"introducing" -
>H.450 as I sayd in my previous mail is a way of providing supplementary
>services like call hold and call transfer to a SET device. It IS already
>part of the H.323 Annex F!
>> Paul
>> -----Original Message-----
>> From: Klaghofer Karl ICN IB NL IP 7 <Karl.Klaghofer at ICN.SIEMENS.DE>
>> Date: Wednesday, March 17, 1999 3:27 PM
>> Subject: AW: Call hold and transfer in H.323 AnnexF. Too limited??
>> >Gunnar,
>> >
>> >You are referring to call hold and transfer in conjunction with H.323
>> Annex
>> >F SETs (Audio or Text) and clause 7.6 of H.323 Annex F.
>> >
>> >Talking about call hold, clause 7.6 of H.323 Annex F is not needed for a
>> SET
>> >at all. Call Hold works for a SET as it is defined in H.450.4.
>> >
>> >Talking about Call Transfer, clause 7.6 of H.323 Annex F is not needed
>> for
>> a
>> >SET, if the transfer is executed by the endpoints as defined in H.450.2.
>> >Codec re-negotiation you are referring to is no problem and takes place
>> >between the transferred and the transferred-to endpoint. This may cover
>> your
>> >case with wireless endpoints being involved.
>> >
>> >For call transfer, section 7.6 of H.323 Annex F is only needed if the
>> >gatekeeper or a proxy acts on behalf of the transferred SET endpoint B.
>> >However, media re-negotiation also should work here as part of the
>> fastStart
>> >method.
>> >
>> >Regards,
>> >Karl
>> >------------------------------------------------
>> >Karl Klaghofer, Siemens AG, Dpmt. ICN IB NL IP7
>> >Hofmannstr. 51, D-81359 Munich, Germany
>> >Tel.: +49 89 722 31488, Fax.: +49 89 722 37629
>> >e-mail: karl.klaghofer at
>> >
>> >
>> >
>> >> -----Ursprüngliche Nachricht-----
>> >> Von:  Gunnar Hellstrom [SMTP:gunnar.hellstrom at OMNITOR.SE]
>> >> Gesendet am:  Dienstag, 16. März 1999 23:01
>> >> An:   ITU-SG16 at
>> >> Betreff:      Call hold and transfer in H.323 AnnexF. Too limited??
>> >>
>> >> Dear multimedia experts.
>> >>
>> >> In my efforts to establish the simple IP voice and text telephone Text
>> >> SET,
>> >> I came across a section in H.323 Annex F (Simple Endpoint Type, TD11
>> >> Monterey) that I feel is causing a functional obstacle also to the
>> voice
>> >> users. Can anyone clarify if I am correct and why it is specified the
>> way
>> >> it is.
>> >>
>> >> In section 7.6.1 and 7.6.2 it is specified:"  The Audio SET device
>> shall
>> >> then resume transmitting its media stream(s) to the transport
>> address(es)
>> >> newly indicated in the OpenLogicalChannel structures."
>> >> I understand that this means that you cannot re-negotiate audio
>> >> and
>> >> you cannot add text conversation after rerouting the call from a Voice
>> >> only
>> >> SET to a Text SET.
>> >>
>> >> Re-negotiating the audio coding will probably be a desired function,
>> e.g.
>> >> when rerouting from a fixed to a wireless IP phone.
>> >> Adding a data channel for text will also be a desired function, after
>> >> answering a call in an audio-only SET, and then rerouting it to a
>> >> text-capable SET.
>> >> That action is very common in today's text telephone usage, and I
>> >> expect it to be just as common in the IP telephony world. You first
>> >> receive
>> >> the call in the terminal that is closest to you, and then you get a
>> reason
>> >> to start text mode. Then you transfer the call to another device with
>> text
>> >> capabilities, where you can switch mode.
>> >>
>> >> Questions:
>> >>
>> >> 1. Is that kind of call transfer that is handled by the mechanisms in
>> 7.61
>> >> and 7.6.2?
>> >>
>> >> 2. Are my conclusion right about the limitations?
>> >>
>> >> 3. Is this limitation a consequence of using Fast Connect?
>> >>
>> >> 4. Do you see any possibility to avoid the negative effects of it - to
>> >> make
>> >> re-negotiation possible?
>> >>
>> >> 5. Is the specified functionality acceptable in the voice world? If
>> >> devices have agreed on a voice coder, is it likely that the third
>> device
>> >> supports it? Will this not create a lot of unsuccessful call transfers
>> >> where the users will have a no chance to understand why they fail?
>> >>
>> >> ----
>> >>
>> >> Another question area:
>> >>
>> >> 6. When selecting the transport protocol for the text conversation,
>> >> current draft (APC 1504) specifies TCP or UDP. I realize that there
>> >> situations where TCP must be avoided. One such situation is a
>> sub-titled
>> >> H.332 transmission. Also other multi-casting situations is better off
>> with
>> >> a UDP based transport protocol.
>> >> I am therfore now leaning towards using RTP as the transport for text
>> >> conversation. With RTP we can discover dropped frames and possibly
>> invent
>> >> a
>> >> mechanism to mark that event in the text stream for T.140 to display.
>> If
>> >> we
>> >> have less than 3 % dropped frames, I think the users would accept it.
>> >>
>> >> 6.1 Do you agree that there are situations when TCP should be avoided,
>> and
>> >> a UDP based protocol preferred?
>> >>
>> >> 6.2 Do you agree that RTP is a good alternative, with a thin protocol
>> for
>> >> error indications to the user?
>> >>
>> >> 6.3 Most packets will carry only 1-4 characters . Can anyone give me
>> >> indication on the expected packet loss rates in different situations
>> for
>> >> such packets. Or a document giving such figures. Is max 3% loss
>> reachable?
>> >>
>> >> Please give your view on these questions.
>> >>
>> >> Best regards
>> >>
>> >> Gunnar Hellström
>> >> -----------------------------------------------
>> >> Gunnar Hellstrom
>> >> Representing Ericsson in ITU-T
>> >>
>> >> E-mail gunnar.hellstrom at
>> >> Tel +46 751 100 501
>> >> fax +46 8 556 002 06

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