Link layer acknowledgement and retransmission for cellular telecommunications

The mobile telecommunication system comprises a mobile user equipment unit (20); and at least node (24); (32) and a packet-switched data session between the user equipment device and data network via the node. Node and a user equipment unit and used for data packet the sending of groove, and node and other user equipment unit and used for data packet the receiver of partition. The separation of a first output timing is not connected to the received in gap, and clapboard and a second output timing is - output during the gap, wherein the ineffective of timing, a receiver transmission selective confirmed of message (CSACK) is a transmitter, request according reissues first output to the clapboard and second by the clapboard. Authentication system information with simple format, comprising a starting serial number and variable size bitmap field.