for downlink traffic will perform ciphering on the initial pdus created by the rlc and will also perform ciphering on the sub pdus or pdus that are retransmitted by the rlc according to the architecture the transmitting node txn i e the wtru in case of uplink traffic direction and the enb in case of downlink traffic direction will perform the following procedure first the txn may perform segmentation and concatenation 710 on one or more of the rlc sdu s and create an initial rlc pdu the txn will store a copy of the non ciphered initial rlc pdu in the retx buffer 720 to support future retransmission if needed the txn will cipher the payload of the initial rlc pdu u201c initial u201d here refers to the first level of segmentation concatenation operation as opposed to further levels the txn will transmit the ciphered initial rlc pdu in case arq retransmission is required the txn will use the non ciphered initial rlc pdu stored in the retx buffer 720 the txn may re segment the stored pdu 730 and create one or more sub pdus 740 the txn will cipher the payload of the created pdus or sub pdus 750 as shown in fig1 according to this architecture the receiving node rxn i e the ue in case of downlink traffic direction and the enb in case of uplink traffic direction will perform the following procedure first the rxn will decipher the payload of the initial rlc pdus or sub pdus it receives 1710 the rxn reassemble an initial rlc pdu from multiple sub pdus or from a single pdu in case no re segmentation was done 1720 the rxn will reassemble the rlc sdu.