Patent ID: 6909887

Claim:
Method of controlling a circuit mode communication logical channel between a radio terminal and a cellular radiocommunication infrastructure, the infrastructure comprising at least one core network, radio network controllers linked to the core network and comprising first and second controllers, and base stations provided with radio interfaces and each linked to one of the radio network controllers, the method comprising the steps of: establishing at least one first communication path between the core network and the terminal, passing through one of the base stations and through the first controller constituting a master controller for said first path; transmitting information pertaining to the logical channel along the first communication path; establishing at least one second communication path between the core network and the terminal, passing through one of the base stations and through the second controller constituting a master controller for said second path; and transmitting information pertaining to the logical channel along the second communication path, wherein the information transmitted along each communication path is ciphered in a portion of said path going from the master controller to the radio terminal, the ciphering being performed as a function of parameters comprising a secret key and a ciphering sequence number combined with said key, whereby the master controller and the terminal jointly increment the ciphering sequence number at the rate of frames of determined duration, so as to have the same ciphering parameters to allow deciphering of the information, and wherein the second path is established in a transfer procedure which comprises transmitting adjustment data from the first controller to the second controller and suppressing each first path, the adjustment data being representative of a current value of the ciphering sequence number and of an offset between the ciphering sequence number and a time reference available to the second controller.