Conflicting text in H.323 concerning the requirement for esta blishing a H.245 control channel??

[Chris Wayman Purvis]

Roni, Frank, Paul Jones et al,

Having reread 8.1.7.2 (as referenced by Roni) I believe that Frank was right
all along in saying there is a conflict.  8.1.7.2 saying that a device "may"
establish an H.245 session at any point during a call is, I would argue,
clearly at odds with 6.2.8 stating that such a session "shall" be
established.  After all, having not bothered to bring one up until an
instant before the end of the call (clearly permitted by 8.1.7.2), why
create one at that stage (except because 6.2.8 tells you to...)?

There is an alternative reading: the implication of 6.2.8 is that some sort
of H.245 session should start immediately (the start and end are the only
"special" times in an ordinary call, so if you must start one it's pretty
well a requirement to do it immediately).  What I don't recall is whether
it's permitted to drop an H.245 session during a call.  I think it is.  So
is there an alternative reading, saying "start the H.245 channel at the
beginning of the call, but you may drop and restart it as you like during
the call"?
I don't like this reading, though, it's probably the worst of all worlds.

However I don't like the delay of setting up an H.245 session being added to
the time taken to transmit the first DTMF tone in a call either...

Paul,

I think this really needs tidying up one way or another - I think it's a job
for the implementors guide...  Consensus currently seems to be against me,
and to be that we should dump the relevant text in 6.2.8.

Regards,
Chris

Roni Even wrote:

> Chris,
> About your comments
>
> 1. B can make A start H.245 by using facility message with reason
> startH.245. See H.323 8.2.3   Switching to a separate H.245 connection.
> 2. About 6.2.8 I agree that it states the H.245 shall be established, it
> does not say when. The when is mentioned  in 8.1.7.2.
> Roni Even
>
>
> -----Original Message-----
> From: Chris Wayman Purvis [mailto:cwp at ISDN-COMMS.CO.UK]
> Sent: Wednesday, March 21, 2001 3:31 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??
>
>
> Roni,
>
>
>
>> 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.
>
> Except that it states exactly the opposite in the section under discussion.
>
> Also, consider the following scenario:
> Two endpoints, A and B.  B does not support tunnelled H.245.  A calls B,
> without giving any H.245 address in its Setup message.  B accepts the call
> on the basis of fastStart.  No H.245 channel is set up, as you suggest.
> Suppose now B wishes to send a UII (or any H.245 message) to A.  It can't.
> It can't set up the H.245 channel.  A could set it up, but doesn't see the
> need.
>
>
>> 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.
>
> But 6.2.8 does not mean that.  It clearly states that an H.245 channel SHALL
> be opened.
>
>
>> As for DTMF you can use the DTMF RTP payload to have it in band instead of
>> H.245.
>
> If the person you're talking to happens to support this.  Of course you
> don't know whether or not it does if you haven't exchanged TCS.
>
> Please let's not break this!
>
> Regards,
> Chris
>
>
>
>> -----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
>>>>>
>>>>
>>>>
>>>>
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>>>
>>>
>>>> For help on this mail list, send "HELP ITU-SG16" in a message to
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>>>
>>>
>>> --
>>> 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
>>>
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>>> For help on this mail list, send "HELP ITU-SG16" in a message to
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>>
>>
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>
>
>
> --
> 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


--
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

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