Method, network and network entity for establishing a communication session to a user equipment roaming in IMS

A communications network, including a calling subscriber user equipment residing in a first Visited Internet Protocol Multimedia Subsystem, IMS, network;

• and
• a called subscriber user equipment roaming in a second Visited IMS network and having associated therewith a Home IMS network of the called subscriber,
• wherein the first Visited IMS network is arranged for routing a first Invite request having a media path for the communication session from the first Visited IMS network via the Home IMS network of the called subscriber to the second Visited IMS network;
• wherein the first Visited IMS network is arranged for routing the first Invite request having a control path for the communication session from the first Visited IMS network via the Home IMS network of the called subscriber to the second Visited IMS network;
• wherein the called subscriber user equipment is arranged for establishing the communication session;
• wherein the second Visited IMS network is arranged for next inserting an additional IMS network entity in the part of the media path of the communication session from the first Visited IMS network to the Home IMS network of the called subscriber;
• wherein the second Visited IMS network is arranged for next inserting an additional IMS network entity in the part of the control path of the communication session from the first Visited IMS network to the Home IMS network of the called subscriber;
• and
• wherein the Home IMS network of the called subscriber is arranged for removing the Home IMS network of the called subscriber from the media path.

A Proxy Call Session Control Function, P-CSCF entity, associated with a called subscriber residing in a Visited IMS network, including:

• a receiver arranged for receiving an Invite request for establishing a communication session from an IMS network associated with a calling subscriber including an indication that optimization of a media path of the communication session is supported,
• a processing unit arranged for generating a first instruction to reroute the communication session via an additional network entity in the Visited IMS network of the called subscriber, the additional network entity anchoring the media path and the control path,
• a transmitter arranged for transmitting the instruction towards the IMS network associated with the calling subscriber,
• the receiver further being arranged for receiving an indication that the additional network entity of the Visited IMS network of the called subscriber is capable of forwarding media to the P-CSCF without traversing a Home IMS network of the called subscriber, and
• the processing unit further being arranged for generating a second instruction for the Home IMS network of the called subscriber to release anchoring of the media path so that the media does not traverse the Home IMS network,
• the transmitter further being arranged for transmitting the second instruction to the Home IMS network of the called subscriber, said instruction being forwarded to the additional IMS network entity.