Patent ID: 8359015

Claim:
A method of providing a call completion service to a not registered or not available user, the service being referred to as CCNReg, the call originating from a first user and terminating at a second user that are both in an IP Multimedia Subsystem (IMS) telecommunication network comprising: a Proxy-Call Session Control Function P-CSCF; an originating Interrogating-Call Session Control Function (I-CSCF), for a first user who is originating a call to a second user; a terminating I-CSCF, for the second user; an originating Serving-Call Session Control Function (S-CSCF), for the first user; a terminating S-CSCF, for the second user; an originating application server, for the first user; a terminating application server, for the second user; and a Home Subscriber Server (HSS); the method comprising: detecting that the second user is not registered or not available; and monitoring the status of the second user; wherein, for monitoring the status of the second user, the method comprises: sending a first SUBSCRIBE message, from the originating application server to the terminating I-CSCF, via the originating S-CSCF, the first SUBSCRIBE message comprising indications to inform the terminating I-CSCF of the initiation of the CCNReg service for completion of the communication attempt between the first user and the second user; on determining that the first SUBSCRIBE message is for CCNReg by finding the indications mentioned above, sending a Location Information Request (LIR), from the terminating I-CSCF towards the HSS, requesting information about the terminating S-CSCF; sending a Location Info Answer (LIA) comprising S-CSCF capabilities or/and name, from the HSS to the terminating I-CSCF; on receiving S-CSCF capabilities or/and name in the terminating I-CSCF, assigning the terminating S-CSCF, and forwarding the SUBSCRIBE message to the terminating S-CSCF; sending a Server Assignment Request (SAR) from the terminating S-CSCF to the HSS; sending a Server Assignment Answer (SAA) comprising second user's profile info, from the HSS to the terminating S-CSCF; forwarding the first SUBSCRIBE message, from the terminating S-CSCF to the terminating application server, for requiring to handle the CCNReg service functions for the second user; sending a first NOTIFY message from the terminating application server to the originating application server with the indication that the CCNReg subscription to the CCNReg service is active, and that the CCNReg request for the first user to communicate with the second user has been queued; and when the second user becomes registered/available again, and becomes ready for completion for the CCNReg call, and the first user becomes the first entry in the call completion queue, sending a second NOTIFY message from the terminating application server to the originating application server with the indication that the CCNReg subscription to the CCNReg service is active, and that the second user is now registered/available and ready for call completion to the first user.