Chris,

Actually I agree with you, getting a list of conferences to Join in response to a create is kind of odd...

The reason this occurs is that unlike T.120 there is no initial query function in H.323 call setup for the calling terminal to find out the nature of the called terminal. In general terminals (H.323 and H.320 for that matter) provide users a simple phone call model UI. The user provides an address and the terminal calls it. In this interface (unless the terminal requires or caches information about the nature of the target) the terminal is not aware of the intent of the call. In fact the user may not be aware of the ultimate intent of the call. Much of the time the user just wants to make a simple point to point connection and so one model is that the calling terminal simply asks the called party/terminal to create a conference. If the called party does not want to create the conference it refuses the connection and provides potential information on how to proceed. One of these possible responses is a list of conferences the terminal software can present to the user allowing the user to select conference he or she would like to join.

I should point out there are terminals that make the user determine a priori the nature of the call (i.e., the user must indicate they are calling an MCU (or conference service) and would like to join a conference). While obviously being technically clean and correct, I personally, find them difficult to use. The model provided above, although "strange", is actually more intuitive in my opinion.

glenn

-----Original Message----- From: Chris Purvis WVdevmt-WS [mailto:cpurvis@madge.com] Sent: Tuesday, June 23, 1998 5:10 AM To: gstewart@sonusnet.com Cc: mbozier@madge.com; jim.toga@intel.com; gthom@delta-info.com; gkajos@videoserver.com Subject: RE: conferenceListChoice

Glenn,

Thanks for the response. It still seems a little strange offering an endpoint a choice of conferences to JOIN when it has asked to CREATE a new conference, but at least it now seems reasonably clear what you intended. Don't worry about lack of clarity, by the way - that's the fault of everybody who had a chance to comment on the text, not just the person who submitted it in the first place. Would you like to squirt some clarification back out on the reflectors?

Jim: Can something go in the implementor's guide on this, please?

Chris

Chris,

The conferenceListChoice element is only to provide a list of conferences that the calling endpoint can join. The ability of the calling endpoint to create a conference at the MCU is a choice left to the MCU manufacturer. Assuming the MCU will allow a "create" then use of the supplied GCID is sufficient.

Your second (more serious) point reveals a lack of clarity in the text (supplied by me I'm afraid). Not explicitly stated is that the "Facility" message is a routeCallToMC in which the MCU Call Signaling Address and the conference list are supplied. The calling endpoint then sends new Setup to the supplied Call Signaling Address with the selected conference (see section 8.4.3.7).

My apologies for not making this more clear in the originally supplied text.

glenn

Glenn Stewart

gstewart@sonusnet.com
Sonus Networks

PS: Gary - I'm not sure if your still editing H.323, but I thought the editor should have a copy of this. Can you please forward this as appropriate?

...

-----Original Message----- From: Chris Purvis WVdevmt-WS [mailto:cpurvis@MADGE.COM] Sent: Thursday, June 18, 1998 1:07 PM To: ITU-SG16@MAILBAG.INTEL.COM Subject: conferenceListChoice

All,

H.323 version 2 states in 8.4.3.1 A2d) and 8.4.3.4 that an

MCU can use

...

conferenceListChoice to give a version 2 endpoint the choice between a number of possible conferences of which one it would like to create(!). I have two points with regard to this:

1. Surely it would also be sensible to have a similar method

for joining extant conferences (rather than just sending ReleaseComplete when CIDs don't match)? Would'nt this be an easy (no extra ASN.1!) and useful addition? 2. (more serious) I can't see how an endpoint tells the MCU which conference from the list it has chosen! Is it up to the endpoint to release the call and send a new setup message with the appropriate conference alias in, or does it send back a similar facility message to the one it was sent, with a single ConferenceList in rather than a sequence of same?

Chris

Dr Chris Purvis - Senior Development Engineer, WAVE CC Software Madge Networks Ltd, Wexham Springs, Framewood Road, Wexham, Berks. Phone:+44 1753 661359 email: cpurvis@madge.com