Ciphering in a packet-switched telecommunications system

A method comprising:

• receiving a link layer protocol data unit and information relating to discarding of at least one ciphered convergence layer protocol data unit at a peer link layer in a packet-switched telecommunications system;
• generating a ciphered convergence layer protocol data unit from the received link layer data unit when transferred to a convergence layer;
• defining a deciphering sequence number based on the information relating to the discarding;
• and
• deciphering the ciphered convergence layer protocol data unit using the deciphering sequence number.

An apparatus comprising:

• at least one processor;
• at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:
• generate a plurality of convergence layer protocol data units in a packet-switched telecommunications system protocol stack;
• cipher said plurality of convergence layer protocol data units using a ciphering sequence number;
• transfer said plurality of ciphered convergence layer protocol data units to a link layer of the packet-switched telecommunications system;
• discard at least one ciphered convergence layer protocol data unit at the link layer and generate a link layer protocol data unit from at least one of the ciphered convergence layer protocol data units that has not been discarded;
• and
• transmit the link layer protocol data unit and information relating to the discarding for a peer link layer.

An apparatus comprising:

• at least one processor;
• at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:
• receive a link layer protocol data unit and information relating to discarding of at least one ciphered protocol data unit at a peer link layer in a packet-switched telecommunications system;
• generate a ciphered convergence layer protocol data unit from the received link layer protocol data unit in a packet-switched telecommunications system protocol stack;
• define a deciphering sequence number based on the information relating to the discarding;
• and
• decipher the ciphered convergence layer protocol data unit using the deciphering sequence number.

A computer program embodied on a computer readable medium comprising computer executable program code which, when executed by at least one processor of an apparatus, causes the apparatus to perform:

• generating a plurality of convergence layer protocol data units in a packet-switched telecommunications system protocol stack;
• ciphering said plurality of convergence layer protocol data units using a ciphering sequence number;
• transferring said plurality of ciphered convergence layer protocol data units to a link layer of the packet-switched telecommunications system;
• discarding at least one ciphered convergence layer protocol data unit at the link layer and generating a link layer protocol data unit from at least one of the ciphered convergence layer protocol data units that has not been discarded;
• and
• transmitting the link layer protocol data unit and information relating to the discarding for a peer link layer.

A computer program embodied on a computer readable medium comprising computer executable program code which, when executed by at least one processor of an apparatus, causes the apparatus to perform:

• receiving a link layer protocol data unit and information relating to discarding of at least one ciphered convergence layer protocol data unit at a peer link layer in a packet-switched telecommunications system;
• generating a ciphered convergence layer protocol data unit from the received link layer data unit when transferred to a convergence layer;
• defining a deciphering sequence number based on the information relating to the discarding;
• and
• deciphering the ciphered convergence layer protocol data unit using the deciphering sequence number.