Patent ID: 8515053

Claim:
A method for changing IP multimedia sub-system (IMS) centralized service (ICS) session media, comprising: controlling a media negotiation between a terminal equipment and a second party via an established IMS circuit-switched (CS) control channel (ICCC); establishing a CS call leg based on a negotiated media type between an IMS CS control function (ICCF) and the terminal equipment; establishing a second call leg based on the negotiated media type between the ICCF and the second party; binding the CS call leg established with the terminal equipment and the second call leg established with the second party, and establishing a call connection between the terminal equipment and the second party; wherein the step of controlling the media negotiation between the terminal equipment and the second party via the established ICCC comprises: establishing, by the terminal equipment, the ICCC with the ICCF; sending, by the terminal equipment, an identity of the second party and a media type of a request to establish the call connection with the second party to the ICCF via the ICCC; sending, by the ICCF, a session invitation message comprising the media type to the second party through the identity of the second party; returning, by the second party, a media type change request comprising a new media type to the ICCF; returning, by the ICCF, the new media type to the terminal equipment via the ICCC; returning, by the terminal equipment, an acknowledgement message to the ICCF via the ICCC, wherein the acknowledgement message indicates an acceptance of the new media type; and determining, by the ICCF, whether a CS network in which the terminal equipment is located supports a service change and unrestricted digital information (UDI) fallback (SCUDIF), and if the CS network in which the terminal equipment is located does not support the SCUDIF, performing, by the ICCF, the step of releasing the CS call leg based on the media type established with the terminal equipment; if the CS network in which the terminal equipment is located supports the SCUDIF, modifying, by the ICCF, the CS call leg based on the media type into the CS call leg based on the new media type by using SCUDIF; returning, by the ICCF, an acknowledgement message of the media type change request to the second party to acknowledge that the terminal equipment accepts the new media type.