Sequence number synchronization for ciphering

1. A method comprising:

generating, by a processor, sequence numbers for data packets to be transmitted using bearers having bearer identifiers in a communications system, wherein the sequence numbers are generated independently for each of the bearers used to transmit the data packets; and

storing and holding, by a memory, last generated sequence numbers for each of the bearer identifiers,

wherein when a starting sequence number for data packets to be transmitted using a bearer out of the bearers which has been used before with a current ciphering key is to be generated, a last generated sequence number for the bearer is determined, where the bearer has a previously used bearer identifier, and the starting sequence number for the data packets is generated in accordance therewith.

2. The method of claim 1 , comprising: providing the starting sequence number to a receiver, which is to receive the data packets, during establishment of the bearer.

3. The method of claim 1 , wherein a last generated sequence number for the bearer is stored in the memory when the bearer terminates.

4. The method of claim 1 , wherein the data packets are user plane data packets or control plane packets.

5. The method of claim 1 , wherein the bearer identifier is five bits long.

6. An apparatus, comprising:

a processor; and

a memory including computer program code,

the memory and the computer program code configured to, with the processor, cause the apparatus at least to:

generate sequence numbers for data packets to be transmitted using bearers having bearer identifiers in a communications system, wherein the sequence numbers are generated independently for each of the bearers used to transmit the data packets; and

store and hold last generated sequence numbers for each of the bearer identifiers in the memory,

wherein when a starting sequence number for data packets to be transmitted using a bearer out of the bearers which has been used before with a current ciphering key is to be generated, a last generated sequence number for the bearer is determined, where the bearer has a previously used bearer identifier, and the starting sequence number for the data packets is generated in accordance therewith.

7. The apparatus of claim 6

wherein the starting sequence number for the data packets is generated in accordance with a check result provided by the memory.

8. The apparatus of claim 6 , wherein the memory and the computer program code are configured to, with the processor, cause the apparatus at least to provide the starting sequence number to a receiver, which is to receive the data packets, during establishment of the bearer.

9. The apparatus of claim 6 , wherein the memory and the computer program code are configured to, with the processor, cause the apparatus at least to store a last generated sequence number for a bearer in the memory when the bearer terminates.

10. The apparatus of claim 6 , comprising at least one of a user plane entity, a mobility management entity, a user equipment and a base station.

11. The apparatus of claim 6 , wherein the apparatus is caused at least to generate the sequence of numbers independently for each of the bearers used to transmit user plane data packets or control plane packets.

12. The apparatus of claim 6 , wherein the data packets are user plane data packets or control plane packets.

13. A non-transitory computer-readable medium encoded with instructions configured to control a processor to perform a process, the process comprising:

generating sequence numbers for data packets to be transmitted using bearers having bearer identifiers in a communications system, wherein the sequence numbers are generated independently for each of the bearers used to transmit the data packets; and

storing and holding last generated sequence numbers for each of the bearer identifiers in a memory, wherein when a starting sequence number for data packets to be transmitted using a bearer out of the bearers which has been used before with a current ciphering key is to be generated, a last generated sequence number for the bearer is determined, where the bearer has a previously used bearer identifier, and the starting sequence number for the data packets is generated in accordance therewith.

14. The non-transitory computer-readable storage memory according to claim 13 , wherein a last generated sequence number for a bearer is stored in the memory when the bearer terminates, and wherein the transmitted data packets are user plane data packets or control plane packets.

15. The non-transitory computer-readable medium according to claim 13 , wherein the instructions are directly loadable into an internal memory of the processor.

16. An apparatus, comprising:

generating means for generating sequence numbers for data packets to be transmitted using bearers having bearer identifiers in a communications system, wherein the generating means are configured to generate the sequence numbers independently for each of the bearers used for transmitting the data packets; and

storing means for storing and holding last generated sequence numbers for each of the bearers identifiers in a memory,

wherein when a starting sequence number for a data packets to be transmitted using a bearer out of the bearers which has been used before with a current ciphering key is to be generated by the generating means, the storing means are configured to determine a last generated sequence number for the bearer, where the bearer has a previously used bearer identifier and the generating means are configured to generate the starting sequence number for the data packets in accordance with a check result provided by the storing means.

17. A method comprising:

determining, by a processor, whether a bearer identifier for a new bearer transmission has been used previously with a current ciphering key in a previous bearer transmission;

in response to determining that the bearer identifier has been used previously with a current ciphering key, retrieving, from a memory, a last used sequence number for the previous bearer transmission; and

assigning, by a processor, a starting sequence number for the new bearer transmission in accordance with the last used sequence number for the previous bearer transmission.

18. The method of claim 17 , further comprising replacing, in the memory, the last used sequence number with the new sequence number.

19. The method of claim 17 , further comprising transmitting the starting sequence number.