Patent ID: 8369315

Claim:
A method of informing a call connection failure in an IP multimedia subsystem (IMS), comprising: receiving, by an entrance network element (NE) of a called network, a session request carrying called user identification (ID) information from a calling network; determining, by the entrance NE of the called network, whether the called user ID information is complete; and if it is determined that the called user ID information is incomplete, sending by the entrance NE of the called network, a response message indicating that the called user ID information is incomplete to the calling network to inform the calling network of a call connection failure; wherein the session request carries a called user ID information requirement indication which is used to determine whether to return required information for the called user ID information; if it is determined to return the required information according to the called user ID information requirement indication, carrying in the response message the required information from the called network, wherein the response message is sent by the entrance NE of the called network, to the calling network.