7.5.6 Conference call (CONF)

29.1633GPPInterworking between the IP Multimedia (IM) Core Network (CN) subsystem and Circuit Switched (CS) networksTS

7.5.6.1 General

The protocol description of the CONF supplementary service is described in 3GPP TS 24.605 [61]. In this clause the interworking from the conference event package in accordance with IETF  RFC 4575 [100] to the messages of the PSTN/ISDN CONF supplementary service is described. Note that an interworking from the PSTN/ISDN to the IMS is out of scope.

7.5.6.2 Subscribing for the conference event package

Based on local policy, the MGCF may subscribe for the conference event package on behalf of the PSTN/ISDN participant after the participant joins or is added to a conference.

When the conference event package option is implemented, and one of the following events occurs at the MGCF:

– a 200 (OK) response is received as a response to an initial INVITE request originated by the MGCF, where the Contact header field contains an "isfocus" parameter; or

– an ACK message is received which acknowledges a 200 (OK) response to the initial INVITE request, and the initial INVITE request is originated by the conferencing AS and contains an "isfocus" parameter in the Contact header field;

then the following steps shall be performed:

1) a SUBSCRIBE request shall be created according to IETF RFC 4575 [100], using the updated procedures from IETF RFC 6665 [138];

2) the Request URI is set to the Contact address of the conferencing AS;

3) the P-Asserted-Identity header field, the From header field and the Privacy header field are set with the same value as:

– the P-Asserted-Identity header field, the From header field and the Privacy header field in the initial INVITE request originated by the MGCF; or

– the P-Asserted-Identity header field, the To header field and the Privacy header field in a 18x or 2xx response sent by the MGCF to the initial INVITE request from the conferencing AS.

7.5.6.3 Interworking the notification

NOTE: There is a need to differentiate between the procedures of interworking for a full and a partial type of notification.

When a full type of notification is received a check is made of the content. If the changes with respect a previous version of the notification have not been sent on to the PSTN/ISDN for this session, the MGCF shall perform an ISUP interaction towards the PSTN/ISDN. If the changes with respect a previous version of the notification have been sent to the PSTN/ISDN for this session, the MGCF shall not perform an ISUP interaction towards the PSTN/ISDN.

When a partial notification is received then it is assumed that a value of a received notification has changed, so the MGCF performs an ISUP interaction towards the PSTN/ISDN, as follows:

– Conference established:

Upon the receipt of a conference information document with the <conference-state-type> element active is set to "true", the MGCF shall send a CPG message to the PSTN/ISDN with a notification "conference established".

– Participant added:

Upon the receipt of a conference information document with the <endpoint-type> and the element status of endpoint‑status-type is set to "connected" and it was not set to "on-hold" before and the Contact URI in the element entity is not the address of the served PSTN/ISDN participant, the MGCF shall send a CPG message to the PSTN/ISDN with a notification "other party added".

– Served PSTN/ISDN participant isolated:

Upon the receipt of a conference information document with the <endpoint-type> and the element status of endpoint‑status-type is set to "on-hold" and it was set to "connected" before and the Contact URI in the element entity is the address of the served PSTN/ISDN participant, the MGCF shall send a CPG message to the PSTN/ISDN with a notification "isolated".

– Other participant isolated:

Upon the receipt of a conference information document with the <endpoint-type> and the element status of endpoint‑status-type is set to "on-hold" and it was set to "connected" before and the Contact URI in the element entity is not the address of the served PSTN/ISDN participant, the MGCF shall send a CPG message to the PSTN/ISDN with a notification "other party isolated".

– Served PSTN/ISDN participant reattached:

Upon the receipt of a conference information document with the <endpoint-type> and the element status of endpoint‑status-type is set to "connected" and it was set to "on-hold" before and the Contact URI in the element entity is the address of the served PSTN/ISDN participant, the MGCF shall send a CPG message to the PSTN/ISDN with a notification "reattached".

– Other participant reattached:

Upon the receipt of a conference information document with the <endpoint-type> and the element status of endpoint‑status-type is set to "connected" and it was set to "on-hold" before and the Contact URI in the element entity is not the address of the served PSTN/ISDN participant, the MGCF shall send a CPG message to the PSTN/ISDN with a notification "other party reattached".

– Other party disconnected:

Upon the receipt of a conference information document with the <endpoint-type> and the element status of endpoint‑status-type is set to "disconnected" and the element joining-method of joining-type is not set to "focus-owner", the MGCF shall send a CPG message to the PSTN/ISDN with a notification "other party disconnected".