Patent ID: 8379855

Claim:
A method comprising: 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; determining to transfer 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 determining to transmit the link layer protocol data unit and information relating to the discarding for a peer link layer, wherein one or more of: the information relating to the discarding contains initiation data of a convergence layer sequence number synchronization procedure for synchronizing ciphering configuration timing; and a data part of the convergence layer protocol data unit is ciphered and the ciphered data part of the convergence layer protocol data unit is a convergence layer sequence number protocol data unit excluding a first three octets of the convergence layer sequence number protocol data unit.