AW: TD-50/Osaka - Changes to the conferenceGoal field

Klaghofer Karl ICN EN HC SE 81 Karl.Klaghofer at ICN.SIEMENS.DE
Tue Jun 20 04:27:03 EDT 2000


H.323 procedures and H.450.1 procedures reference H.225.0 on how to set the
conferenceGoal for certain cases (e.g. for conference invitations, 450 call
independent signalling connections, ...). So far there is exactly one field
to be used for setting the appropriate value. With the original BT proposal,
we would suddenly in v4 have two ways on how to set the conferenceGoal
(depending on whether I send the new v4 optional neededFeatures package or
not).

Again, we should go with the alternative proposal provided by Rich keeping
the optional neededFeatures package out of the conferenceGoal construct. It
does not belong there. The guideline has always been that new optional
features shall not impact existing behaviour.

Karl Klaghofer
Siemens
karl.klaghofer at icn.siemens.de

> -----Ursprüngliche Nachricht-----
> Von:  Rich Bowen [SMTP:rkbowen at CISCO.COM]
> Gesendet am:  Tuesday, June 20, 2000 09:20
> An:   ITU-SG16 at mailbag.cps.intel.com
> Betreff:      Re: TD-50/Osaka - Changes to the conferenceGoal field
>
> Bob,
>
> If the v4 client supports the features listed in the needFeatures field,
> then it will respond with those same features listed in a
> supportedFeatures field, as an acknowledgement.  Presumably if it
> acknowledges features in this way, then it will not ignore packages
> related to those features.
>
> Rich
>
> "Callaghan, Robert" wrote:
> >
> > Rich,
> >
> > I question that the concept for forcing conferenceGoal to fail will even
> > work.
> >
> > The use of conferenceGoal will detect a v2 or v3 client through a
> failure.
> > But the version number will also detect the older versions.  A v4 client
> can
> > properly detect and decode the new structure.  However, support of
> packages
> > is optional, so the client can ignore the requirement to evaluate the
> > packages.
> >
> > Then what?
> >
> > Bob
> >
> > -----Original Message-----
> > From: Rich Bowen [mailto:rkbowen at CISCO.COM]
> > Sent: Sunday, June 18, 2000 5:14 PM
> > To: ITU-SG16 at mailbag.cps.intel.com
> > Subject: TD-50/Osaka - Changes to the conferenceGoal field
> >
> > All,
> >
> > In Osaka we agreed to add support for packages to H.225.0 along the
> > lines of TD-50 (ftp://standard.pictel.com/avc-site/0005_Osa/TD-50.zip).
> > There was some concern raised about the proposed modifications to the
> > conferenceGoal field in the Setup message.  The meeting report states:
> >
> > "Some issues were raised about conflicts in the usage of the conference
> > goal field between this new method and H.450.x.  A possible solution is
> > to create a new field in the ASN.1 to avoid conflicts.   The editors are
> > empowered to work with interested parties to resolve these conflicts in
> > the ASN.1 before the white paper is issued."
> >
> > The modification proposed in TD-50 was the addition of the
> > "neededFeatures" field to the confereceGoal field of the Setup-UUIE:
> >
> >         conferenceGoal          CHOICE
> >         {
> >                 create          NULL,
> >                 join            NULL,
> >                 invite          NULL,
> >                 ...,
> >                 capability-negotiation          NULL,
> >                 callIndependentSupplementaryService     NULL,
> > -->             neededFeatures          NeededFeatureGoal
> >         },
> >
> > where the NeededFeatureGoal structure is defined as:
> >
> > NeededFeatureGoal ::= SEQUENCE
> > {
> >         basicGoal       CHOICE
> >         {
> >                 create                                  NULL,
> >                 join                                    NULL,
> >                 invite                                  NULL,
> >                 capability-negotiation                  NULL,
> >                 callIndependentSupplementaryService     NULL,
> >                 ...
> >         } OPTIONAL,
> >         features        SEQUENCE OF SupportedFeatures,
> >         ...
> > }
> >
> > An alternative approach would be to add a neededFeatures field at the
> > highest level of the Setup-UUIE ASN.1 instead of inside the
> > conferenceGoal structure, similar to the way the desirededFeatures and
> > supportedFeatures fields will be added (see TD-50), like this:
> >
> > Setup-UUIE ::= SEQUENCE
> > {
> >         [snip]
> > -->     neededFeatures          SEQUENCE OF SupportedFeatures OPTIONAL,
> >         desiredFeatures         SEQUENCE OF SupportedFeatures OPTIONAL,
> >         supportedFeatures       SEQUENCE OF SupportedFeatures OPTIONAL
> > }
> >
> > The motivation for adding neededFeatures to the conferenceGoal field was
> > to force a call failure when trying to setup a call to pre-v4 endpoint
> > and there is some v4 or later feature that is *required* for the call.
> > The mechanism is intended to work like this:
> >
> > o The v4 EP sends Setup to the pre-v4 endpoint, and specifies some
> > required feature in the neededFeatures field of the conferenceGoal.
> > o The pre-v4 EP doesn't recognize the neededFeatures field as a
> > supported CHOICE for a conferenceGoal, so it sends Release Complete.
> >
> > There would not be any conflicts with H.450, as suggested in the meeting
> > report, because if the callIndependentSupplementaryService was needed,
> > it would still be specified.  The difference is that, if a neededFeature
> > was also required, the H.450 goals would be specified inside the
> > NeededFeatureGoal structure, which v4 and later endpoints would be aware
> > of.
> >
> > These are the pros and cons of adding neededFeatures to the
> > conferenceGoal vs. adding it to Setup-UUIE, IMO:
> > o Advantages:
> >     - *May* force an early call release if a required feature is
> >       not supported by a pre-v4 endpoint.
> > o Disadvantages:
> >     - ASN.1 and thus implementation would be more complex.
> >       Potentially have to check the conferenceGoal in two structures
> >       instead of one.
> >     - If pre-v4 EP sends Release Complete, there is no way to
> >       know whether it was sent because of an unrecognized
> >       conferenceGoal, because there is no ReleaseCompleteReason
> >       defined for that purpose.
> >     - H.323 does not require failing a call if the conferenceGoal
> >       is unrecognized, so the mechanism may not work at all.
> >
> > Although I think this mechanism is a good idea (and I supported it in
> > Osaka), at this point I don't think it would work reliably enough to
> > justify the added complexity.  So I would prefer the alternative
> > approach described above, adding the neededFeatures field directly to
> > the Setup-UUIE.
> >
> > Okay, fire away. :-)
> >
> > Regards,
> > Rich
> > --------------------------------------------------------------------
> > Richard K. Bowen                     Cisco Systems, Inc.
> > VoIP Session Protocols               Research Triangle Park, NC, USA
> > --------------------------------------------------------------------
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > For help on this mail list, send "HELP ITU-SG16" in a message to
> > listserv at mailbag.intel.com
>
> --
> --------------------------------------------------------------------
> Richard K. Bowen                     Cisco Systems, Inc.
> VoIP Session Protocols               Research Triangle Park, NC, USA
> --------------------------------------------------------------------
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> For help on this mail list, send "HELP ITU-SG16" in a message to
> listserv at mailbag.intel.com

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