Patent ID: 6768903
Filing Date: 2004-07-27
Classification: H04L,H04W

Abstract:
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 using a first radio access resource 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 using a second radio access resource, different from the first resource, 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, wherein the second path is established in a transfer procedure comprising transmitting adjustment data from the first controller to the second controller, a phase of simultaneous transmission of radio signals on the first and second access resources by the respective base stations of the first and second paths, then suppressing the first path, wherein the radio signals transmitted on the first and second access resources in the phase of simultaneous transmission transport the same information, said information being ciphered by the second controller with a ciphering sequence number which is offset in advance with respect to that used by the first controller to encipher the information transmitted along the first path, and wherein the radio terminal switches over from the first access resource to the second access resource in the phase of simultaneous transmission, by advancing the ciphering sequence number so as to align it with the offset number used by the second controller.