Traffic control within an IP multimedia subsystem

An apparatus comprising a first Serving Call Session Control Function (S-CSCF) and a Proxy Call Session Control Function (P-CSCF) within an IP Multimedia Subsystem (IMS) network, the apparatus comprising:

• a transmitter;
• and
• one or more processor coupled to the transmitter, wherein the apparatus is configured to:
• register users of the IMS network to allow the provision of IMS services to the registered users;
• make a decision or receive an instruction to transfer a registered user to an alternative S-CSCF within the IMS network;
• and
• employ the transmitter to send to the P-CSCF a notification comprising an identification of said first S-CSCF a request to select an alternative S-CSCF as a result of making the decision or receiving the instruction to transfer said registered user to an alternative S-CSCF, wherein
• the P-CSCF is configured such that, in response to receiving the notification, the P-CSCF sends to an Interrogating Call Session Control Function (I-CSCF) of the IMS network an S-CSCF reselection request comprising said identification together with an explicit instruction to select an alternative, second S-CSCF.

An apparatus configured to operate as a Call Session Control Function (CSCF) within an IP Multimedia Subsystem (IMS) network, the apparatus comprising:

• a receiver for receiving from a first Serving Call Session Control Function (S-CSCF) with which an IMS user is currently registered, a notification to select an alternative, second S-CSCF, said notification comprising an identification of said first S-CSCF;
• and
• a registration initiation entity for sending a registration initiation request to a further IMS node, said request including an explicit instruction to select an alternative second S-CSCF and said identification of said first S-CSCF, wherein
• said registration initiation entity is configured to include within said registration initiation request, an identification of said first S-CSCF from which said notification is received.