Method of controlling a channel between a radio terminal and a cellular radiocommunication infrastructure, and access network implementing such a method

DETAILED DESCRIPTION The invention thus proposes a method of controlling a circuit mode communication logical channel between a radio terminal and a cellular radiocommunication infrastructure.
The infrastructure comprises 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 comprises the following steps: 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.
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 is performed as a function of parameters comprising a secret key and a ciphering sequence number combined with said key.
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.
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