Method for shortening signaling delay of ISC session transfer, network element and system

An apparatus for controlling IMS service continuity ISC session transfer, said apparatus comprising:

• a network element configured to:
• decide if a condition for anchoring a media path in a media anchor point is met upon reception of a session setup request message, and if yes, then instruct said media anchor point to assign respective media endpoints for a local terminal and a remote terminal;
• upon reception of a first response message with session description protocol information of said media endpoints from said media anchor point, terminate a sub-session with said local terminal according to said session description protocol information and initiate creation of a sub-session with said remote terminal;
• after said remote terminal having acknowledged, send to said local terminal a second response message with session description protocol information of the media endpoint of said local terminal;
• and
• upon reception of a transfer request message, send to said media anchor point a first message with session description protocol information of a target transfer-in access leg.

A network element for anchoring a media path in IMS service continuity ISC session transfer, said network element being configured to:

• upon reception of an instruction from another network element, assign respective media endpoints for a local terminal and a remote terminal and connect said media endpoints together;
• send to said another network element a response message with session description protocol information of said media endpoints (200 OK);
• and
• replace a source transfer-out access leg by a target transfer-in access leg.

A communication system, comprising:

• at least two terminals;
• a first network element configured to:
• decide if a condition for anchoring a media path in a media anchor point is met upon reception of a session setup request message, and if yes, then instruct said media anchor point to assign respective media endpoints for a local terminal and a remote terminal;
• upon reception of a first response message with session description protocol information of said media endpoints from said media anchor point, terminate a sub-session with said local terminal according to said session description protocol information and initiate creation of a sub-session with said remote terminal;
• after said remote terminal having acknowledged, send to said local terminal a second response message with session description protocol information of the media endpoint of said local terminal;
• and
• upon reception of a transfer request message, send to said media anchor point a first message with session description protocol information of a target transfer-in access leg;
• and
• a second network element configured to:
• upon reception of an instruction from a third network element, assign respective media endpoints for a local terminal and a remote terminal and connect said media endpoints together,
• send to said third network element a response message with session description protocol information of said media endpoints, and
• replace a source transfer-out access leg by a target transfer-in access leg.