| 摘要 |
A telecommunications system includes an internet protocol multimedia system operable to provide an internet protocol communications service to a mobile terminal. The internet protocol multimedia system is arranged to register the mobile terminal for deploying multimedia communications sessions, the registration including authentication and authorisation of the mobile terminal. The mobile terminal is operable as a calling terminal to communicate a set up request message for requesting a bearer channel via a first mobile access network for communicating user data to and from a correspondent node acting as a called terminal to support a communications session with the correspondent terminal. When the mobile user equipment roams from the first mobile access network to a second mobile access network and requests a communications bearer from the second mobile access network for continuing the communications session via the second mobile access network, the internet protocol multimedia system establishes the communications bearer via the second mobile access network and communicates a confirmation message to the mobile terminal via the second mobile access network to provide the communications bearer via the second mobile access network for continuing the communications session with the correspondent terminal via the second mobile access network. A mobile terminal can handover from a circuit switched access network to a packet switched access network with a reduce delay in which communication of internet protocol packets is not possible. |
