Apparatus and method of ciphering in wireless communications user equipment operative with a plurality of radio access networks

1. A method in a wireless telecommunications device operative with a plurality of radio access networks, the method comprising:

establishing a call with a non-UMTS radio access network;

reading the value of a UMTS variable START from the device;

when the value of START in the device is equal to a value THRESHOLD, sending a substitute value for START to the network;

otherwise, sending the value of START in the device to the network; and

writing the value of THRESHOLD into the variable for START after substitute value of START is sent to the network.

2. A method as claimed in claim 1 wherein the substitute value for START is a constant.

3. A method according to claim 1 wherein the substitute value for START is calculated according to the formula THRESHOLD minus y, where y is one of a randomly generated number comprising a positive integer in the range 1 to (THRESHOLD−1) and a pseudo randomly generated number comprising a positive integer in the range 1 to (THRESHOLD−1).

4. A method as claimed in claim 1 wherein the substitute value for START is 0000 0000 0000 0000 0010 in binary.

5. A method as claimed in claim 1 wherein the first radio access network is one of a GSM network, a Wifi network, a cdma2000 network, a GPRS network and an EDGE network.

6. A computer-readable storage medium having stored thereon instructions which can be executed by a device to carry out the actions of claim 1 .

7. A wireless communications device operative with a plurality of radio access networks, the device comprising:

a transceiver for transmitting and receiving radio signals;

a processor; and

a memory having stored therein: one or more routines executable by the processor, the one or more routines being adapted to:

when in connected mode with a non-UMTS radio access network, read the value of a UMTS variable START from the device;

when the value of START from the device is equal to a value THRESHOLD, sending a substitute value for START to the network; otherwise, sending the value of START from the device to the network; and

write the value of THRESHOLD into the variable for START after substitute value of START is sent to the network.

8. A device as claimed in claim 7 wherein the substitute value for START is a constant.

9. A device as claimed in claim 7 wherein the substitute value for START is calculated according to the formula THRESHOLD minus y, where y is one of a randomly generated number comprising a positive integer in the range 1 to (THRESHOLD−1) and a pseudo randomly generated number comprising a positive interger in the range 1 to (THRESHOLD−1).

10. A device as claimed in claim 7 wherein the substitute value for START is 0000 0000 0000 0000 0010 in binary.

11. A device as claimed in claim 7 wherein the first radio access network is one of a GSM network, a Wifi network, a cdma2000 network, a GPRS network and an EDGE network.

12. A method in a wireless telecommunications device operative with a plurality of radio access networks, the method comprising:

when operating with a first radio access network reading at least one ciphering variable applicable in the second radio access network;

when at least one ciphering variable applicable in the second radio access network renders ciphering in the second radio access network infeasible without further authentication, using a substitute value for the ciphering parameter when establishing a connection with the second radio access network;

when in connected mode with a non-UMTS radio access network reading the value of a UMTS variable START from the device;

when the value of START is equal to a value THRESHOLD, using a substitute value for START and sending the substitute value for START to the network; and

writing the value of THRESHOLD into the variable for START after substitute value of START is sent to the network.