Subject: [cuss] Open issue in draft-ietf-cuss-sip-uui-isdn-01

From: "DRAGE, Keith (Keith)" <[email-masked]>
Date: Sun, 26 Feb 2012 00:46:51 +0100

Currently we have the following text in the draft:

"ISDN conferencing allows the user to still exchange user-to-user data after the conference is created. As far as UUS1 is concerned, this means that when an individual party clears, those clearing messages can still contain user-to-user data. As a conferee this is sent to the conference controller. As the conference controller, as this effectively clears the conference, it can be broadcast to all conferees, or sent to individual conferees [OPEN ISSUE - CHECK THIS IN THE PROTOCOL - DOES IT REQUIRE EXPLICIT]."

"The ISDN three-party supplementary service is similar in many ways to conferencing, but is signalled using a different mechanism. This means that on clearing, the controller using UUS1 implicit does have the choice of sending data to either or both remote users."

Investigation of the ISDN service description in ITU-T Recommendation I.257.1 reveals:

"6.7	Conference services
6.7.1	Conference Calling (CONF)
For a conference, only service 3 shall be available.
NOTE 1 - However, on calls which are set up to potential conferees outside the conference, service 1 and/or service 2 may be available.
In the following paragraphs, references to the UUS supplementary service refer only to service 3.
The UUS supplementary service cannot be activated by the conference controller, nor by a conferee, for communication between the participants in the conference.
When a user is added to the conference and the UUS supplementary service has been activated on the call between the conference controller and that user, the UUS supplementary service shall remain activated for communication between the conference controller and that conferee.
If the UUS supplementary service has been activated for communication between the conference controller and a conferee, then when a private communication is created with that party, the UUS supplementary service shall remain activated for the private communication.
NOTE 2 - Once this private communication is created, it is considered as a separate call and therefore the normal procedures for the UUS supplementary service apply.
UUI can be sent by the conference controller to conferees individually, or broadcast to all conferees. UUI can be received by the conference controller from any of the conferees. The network shall identify the conferee sending the UUI to the conference controller.
The same limitations on the amount of UUI which can be transferred between two users shall apply to communications between the conference controller and the conference.
Conferees can send UUI to and receive UUI from the conference controller. UUI shall not be transferred between the conferees in association with the conference.
6.7.2	Three-Party (3PTY)
During the three-way conversation, the served user of the three party supplementary service can send UUI separately to each remote party of the three party supplementary service, and the served user of the three party supplementary service can receive UUI separately from each remote party of the three party supplementary service. UUI shall not be transferred between the remote parties of the three party supplementary service."

Thus for the normal ISDN conference service there is no UUS1 service and therefore no UUS1 implicit service.

Operation in the ISDN three party service is dependent on being able to distinguish two independent signalling relationships at the conferencing user. This is not possible in SIP, no real direct equivalent of the ISDN three party service exists in SIP (unless the conferencing is performed in the served user's UE).

It is therefore proposed to rewrite the text as follows:

"ISDN conferencing allows the user to still exchange user-to-user data after the conference is created. As far as UUS1 is concerned, it is not permitted."

"The ISDN three-party supplementary service is similar in many ways to conferencing, but is signalled using a different mechanism. This means that on clearing, the controller using UUS1 implicit does have the choice of sending data to either or both remote users. Because SIP conferencing cannot completely emulate the ISDN three-party supplementary service at the served user, UUS1 implicit is not possible."