Call Forward too!... RE: AW: Call hold and transfer in H.323 Anne xF. Too limited??
Chris Purvis
Chris.Purvis at MADGE.COM
Wed Mar 24 06:53:23 EST 1999
Karl,
> I do not see a limitation in H.450.3.
>
> If a called endpoint B is out of service (which is very
> likely for a PC based H.323 endpoint but which may be more an
> exceptional case for other endpoint types like "black
> phones"), a proxy function has to act on behalf of the
> endpoint B, provided you want to successfully establish the
> call.
> This is not specific to H.450.3 call diversion but applies to
> H.323 Basic call functions as well.
I disagree. As far as basic call functions are concerned (ie no forwarding
is set up) B's gatekeeper will reject any ARQ trying to reach B, and if it
is routing H.225.0 and receives a setup message without having had an ARQ,
fail the call by some suitable means. The point IS specific to call
forwarding. Without any forwarding set up, I don't see what a "proxy
function" is going to do.
> This proxy function may e.g. be co-located with the
> gatekeeper or may be located within an other endpoint (with
> the gk just performing routing to the proxy). The latter one
> may allow more flexibility and scalability. Anyway, this is
> an issue of your architecture and does not need to be
> standardized.
Agreed. The salient point here is that we agree the gatekeeper needs
knowledge of what's going on (either to provide the service or to perform
the routing to an external proxy).
> As an example, FIGURE 5/H.450.3 shows the forwarding function
> (i.e. the "served signalling entity") possibly being provided
> by a proxy function (e.g. for cases where the endpoint is out
> of service). Of course the proxy function needs knowledge
> about the activated supplementary services for a given user
> for which the proxy is acting, which again is an
> implementation issue.
I disagree with your last sentence here. The way the endpoint communicates
"all my calls need to be forwarded to Joe in my absence" to its gatekeeper
is certainly NOT just an implementation issue. An endpoint implementor
ought to be able to implement a dialogue box on his endpoint, which will set
up call forwarding whatever gatekeeper it uses (as long as the gatekeeper
has this functionality). (S)he will not be able to do this if that
particular communication is not standardised in some way - which seems to me
to be a pretty good measure to indicate that it is a standardisation, rather
than implementation, issue.
As for whether communications between the gatekeeper and the "proxy
function" need to be standardised, this is less clear (in my opinion) as it
seems a significantly less restrictive requirement for people to need to buy
"proxy function" and gatekeeper from the same vendor than to need to buy
endpoint, "proxy function" and gatekeeper from the same vendor. However,
given all the activity on gateway decomposition, I can imagine that there
will be people who disagree.
Regards,
Chris
> > -----Ursprüngliche Nachricht-----
> > Von: Chris Purvis [SMTP:Chris.Purvis at MADGE.COM]
> > Gesendet am: Montag, 22. März 1999 12:07
> > An: ITU-SG16 at mailbag.cps.intel.com
> > Betreff: Call Forward too!... RE: AW: Call hold and
> transfer in H.323
> > Anne xF. Too limited??
> >
> > Frank, Karl, Anyone else who's interested,
> >
> > A limitation in H.450.3 (Call Forward) recently became
> clear to me, and
> > the
> > solution may arrive through the sorts of things Frank's suggesting.
> >
> > Background:
> > What I see as a problem arises from the endpoint-centric
> nature of CFU
> > (Call
> > Forward Unconditional), especially in the case where the
> endpoint being
> > forwarded is PC-based (probably NOT a SET).
> >
> > The specific problem:
> > I would regard as a prime use for CFU to be the ability to set up
> > forwarding
> > and then switch off my PC, so that all my calls would then go (for
> > example)
> > to a colleague. Everything seems to be there in H.450.3 to
> allow this to
> > happen in the gatekeeper-routed model (obviously the
> GK-routed model is
> > likely to be required, because the GK appears to be the
> only "live" entity
> > that can do the forwarding), with the exception of the
> transaction between
> > my PC and its gatekeeper.
> >
> > The solution:
> > I don't know. Maybe an H.450.3 extension (which has
> dangers because a GK
> > is
> > not normally a callable entity), maybe a new RAS
> transaction type (but we
> > don't want proliferation of RAS messages)?
> >
> > The plea:
> > I'd like to see some serious suggestions on this, and
> really drive some
> > solution towards standardisation, either as an Annex to H.450.3 or
> > elsewhere. It seems to me that this is possibly the most important
> > application of Call Forwarding, so it seems a shame that it
> is missing.
> >
> > If consensus works towards a RAS-based solution, we may be
> able to do this
> > in a way that will also suit Frank's ideas?
> >
> > Regards,
> > Chris
> >
> > > -----Original Message-----
> > > From: Derks, Frank [mailto:F.Derks at PBC.BE.PHILIPS.COM]
> > > Sent: 22 March 1999 10:43
> > > To: ITU-SG16 at MAILBAG.INTEL.COM
> > > Subject: Re: AW: Call hold and transfer in H.323 AnnexF.
> Too limited??
> > >
> > >
> > > Folks,
> > >
> > > 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 lot
> > > 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 certain
> > > digit sequences as being the invocation of some service
> > > rather than a number
> > > 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 a
> > > 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 provide
> > > 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
> > >
> > > -----------------------------------------------------
> > > 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 pbc.be.philips.com |
> > > WWW: http://www.business-comms.be.philips.com |
> > > -----------------------------------------------------
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Klaghofer Karl ICN IB NL IP 7
> > > [mailto:Karl.Klaghofer at ICN.SIEMENS.DE]
> > > Sent: 18 March 1999 22:36
> > > To: ITU-SG16 at MAILBAG.INTEL.COM
> > > Subject: AW: AW: Call hold and transfer in H.323 AnnexF.
> Too limited??
> > >
> > >
> > > See comment below.
> > >
> > > Karl
> > >
> > > > -----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 mailbag.cps.intel.com
> > > > 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, I
> > > > 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. If
> > > > 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>
> > > > To: ITU-SG16 at MAILBAG.INTEL.COM <ITU-SG16 at MAILBAG.INTEL.COM>
> > > > 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 icn.siemens.de
> > > > >
> > > > >
> > > > >
> > > > >> -----Ursprüngliche Nachricht-----
> > > > >> Von: Gunnar Hellstrom [SMTP:gunnar.hellstrom at OMNITOR.SE]
> > > > >> Gesendet am: Dienstag, 16. März 1999 23:01
> > > > >> An: ITU-SG16 at mailbag.cps.intel.com
> > > > >> 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 in
> > > > >> 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 coding,
> > > > >> 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 would
> > > > >> 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 two
> > > > >> 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, the
> > > > >> current draft (APC 1504) specifies TCP or UDP. I realize
> > > that there are
> > > > >> 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 an
> > > > >> 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 omnitor.se
> > > > >> Tel +46 751 100 501
> > > > >> fax +46 8 556 002 06
> > >
>
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