Conflicting text in H.323 concerning the requirement for establishing a H.245 control channel??
Terry L Anderson
tla at LUCENT.COM
Wed Mar 21 10:31:29 EST 2001
Since there appears to be differing opinions about the current recommendation's
requirements for opening an H.245 channel when using fast connect (open ASAP,
open only if needed, ...) and discussion seems to recur every few months. It
would seem worth adding a clear statement about this through the Implementor's
Guide.
Roni Even wrote:
> All,
>
> H.323 mandates the support of H.245 for end points that comply with the
> standard. It does not mean, when using fast connect that it must be open
> immediately but can be opened at a later stage by any side. The reason for
> mandating H.245 is to supply a control channel and is important for gateways
> and MCUs as well as for control functions in point to point calls such as
> Video fast updates. H.323 annex F defines a simple end point that has H.245
> support as optional.
> I do not see the conflict between 6.2.8 and 8.1.7 if 6.2.8 means that you
> have to support it but not to actually open it as in simple fast connect
> calls.
> As for DTMF you can use the DTMF RTP payload to have it in band instead of
> H.245.
>
> Regards
> Roni Even
>
> -----Original Message-----
> From: Agboh, Charles [mailto:charles.agboh at EBONE.COM]
> Sent: Tuesday, March 20, 2001 6:59 PM
> To: ITU-SG16 at MAILBAG.INTEL.COM
> Subject: Re: Conflicting text in H.323 concerning the requirement for
> esta blishing a H.245 control channel??
>
> Chris,
>
> Part of establishing a "point-to-point" call involves opening 2 TCP
> connnections using the Fast Connect procedure as you described it. If that
> is the case, then the extract from H.323v2 below is misleading(I believe).
>
> H.323v2: 8.1.7 Fast Connect Procedure
>
> "..... The Fast Connect procedure allows the endpoints to establish a basic
> point-to-point call with as few as one round-trip message exchange, enabling
> immediate media stream delivery upon call connection."
>
> BR,
> Charles
> > -----Original Message-----
> > From: Chris Wayman Purvis [mailto:cwp at ISDN-COMMS.CO.UK]
> > Sent: Tuesday, March 20, 2001 5:47 PM
> > To: ITU-SG16 at MAILBAG.INTEL.COM
> > Subject: Re: Conflicting text in H.323 concerning the requirement for
> > esta blishing a H.245 control channel??
> >
> >
> > Charles,
> >
> > It does NOT defeat ANY of the stated aims of FastConnect.
> > These aims were to get agreed media channels in both
> > directions open as
> > quickly as possible. Doing FastStart AND H.245 gives you your media
> > quickly, and means you have the power of H.245 thereon.
> >
> > In-band DTMF transfer may be used. If you happen to be using
> > a codec that
> > supports it. If you assume it when you're using an
> > unsuitable codec you'll
> > have a problem. Which is a reason for using H.245 capability
> > negotiation.
> >
> > Regards,
> > Chris
> >
> > Agboh, Charles wrote:
> >
> > > which defeats the whole point of having a Fast Connect
> > procedure (FS +
> > > H.245). Why isn't in-band- DTMF transfer used instead (in FS)?
> > >
> > > -Charles
> > >
> > >
> > >> -----Original Message-----
> > >> From: Frank Derks [mailto:frank.derks at PHILIPS.COM]
> > >> Sent: Tuesday, March 20, 2001 4:40 PM
> > >> To: ITU-SG16 at MAILBAG.INTEL.COM
> > >> Subject: Re: Conflicting text in H.323 concerning the
> > requirement for
> > >> establishing a H.245 control channel??
> > >>
> > >>
> > >> Chris,
> > >>
> > >> I thought I was being clear enough, so let me try again.
> > >> 6.2.8/H.323 states
> > >> that an enpoint must open one (and exactly one) H.245 control
> > >> channel. When
> > >> Fast Connect is being used, I assume that the intention is
> > >> that no such control
> > >> channel is opened.
> > >>
> > >> To be compliant with 6.2.8/H,323 I would have to open a H.245
> > >> control channel
> > >> irrespective of which type of H.245 procedures I will be
> > >> using. So if I intend
> > >> to use Fast Start (and assuming that the other party also
> > >> supports this), I
> > >> still have to open a H.245 control channel.
> > >>
> > >> Frank
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >> cwp at isdn-comms.co.uk on 20-03-2001 15:17:14
> > >> To: Frank Derks/HVS/BE/PHILIPS at EMEA2
> > >> cc: ITU-SG16 at mailbag.cps.INTEL.COM@SMTP
> > >> Subject: Re: Conflicting text in H.323 concerning the
> > >> requirement for establishing a H.245 control channel??
> > >> Classification:
> > >>
> > >> Frank,
> > >>
> > >> Why do you consider this text to be "conflicting"?
> > >> Specifically, with what does it conflict?
> > >>
> > >> Regards,
> > >> Chris
> > >>
> > >>
> > >>> 6.2.8/H.323 states: "The endpoint shall establish exactly
> > one H.245
> > >>> Control Channel for each call that the endpoint is
> > >>
> > >> participating in."
> > >>
> > >>> 8.1.7/H.323 never states that when Fast Connect is being
> > used such a
> > >>> control channel should be established. As far as I understand the
> > >>> mechanism this is only required to switch to "normal" H.245
> > >>
> > >> procedures.
> > >>
> > >>> It would seem that section 6.2.8 should be rephrased to
> > >>
> > >> make clear that
> > >>
> > >>> the H.245 control channel shall only be established when
> > >>
> > >> "normal" H.245
> > >>
> > >>> procedures are being followed and not in the fast connect case.
> > >>>
> > >>> Frank
> > >>
> > >> --
> > >> Dr Chris Purvis -- Development Manager
> > >> ISDN Communications Ltd, The Stable Block, Ronans, Chavey Down Road
> > >> Winkfield Row, Berkshire. RG42 6LY ENGLAND
> > >> Phone: +44 1344 899 007
> > >> Fax: +44 1344 899 001
> > >>
> > >>
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >> For help on this mail list, send "HELP ITU-SG16" in a message to
> > >> listserv at mailbag.intel.com
> > >>
> > >
> > >
> > >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > For help on this mail list, send "HELP ITU-SG16" in a message to
> > > listserv at mailbag.intel.com
> >
> >
> > --
> > Dr Chris Purvis -- Development Manager
> > ISDN Communications Ltd, The Stable Block, Ronans, Chavey Down Road
> > Winkfield Row, Berkshire. RG42 6LY ENGLAND
> > Phone: +44 1344 899 007
> > Fax: +44 1344 899 001
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > For help on this mail list, send "HELP ITU-SG16" in a message to
> > listserv at mailbag.intel.com
> >
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> For help on this mail list, send "HELP ITU-SG16" in a message to
> listserv at mailbag.intel.com
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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--
------------------------------------------------------------
Terry L Anderson mailto:tla at lucent.com
Tel:908.582.7013 Fax:908.582.6729
Pager:800.759.8352 pin 1704572 1704572 at skytel.com
Lucent Technologies/ Voice Over IP Access Networks/ Applications Grp
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http://its.lucent.com/~tla (Lucent internal) http://www.gti.net/tla
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