d in the PDCP sub-layer. Note that, unlike IEEE 802.16m where the CS PDUs are not encrypted and the encryption is performed on MAC PDUs, in 3GPP LTE the RLC SDUs are ciphered. For the control- plane, the data unit that is ciphered is the data part of the PDCP PDU and the Message Authen- tication Code for Integrity (MAC-I), i.e., a 32-bit field that carries message authentication code. For the user-plane, the data unit that is ciphered is the data part of the PDCP PDU; ciphering is not applicable to PDCP control PDUs. The ciphering algorithm and key to be used by the PDCP entity are configured by upper layers, and the ciphering method is applied according to Security Archi- tecture of 3GPP System Architecture Evolution [23]. The ciphering function is activated by upper layers. After security activation, the ciphering function is applied to all PDCP PDUs indicated by upper layers for the downlink and uplink transmissions. The parameters that are required by PDCP for ciphering are defined in reference [23] and are input to the ciphering algorithm. The required inputs to the ciphering function include the COUNT value and DIRECTION (direction of the transmission). The parameters required by PDCP which are provided by upper layers are BEARER (defined as the radio bearer identifier) and KEY (the ciphering keys for the control-plane and for the user-plane) [21]. The integrity protection function includes both integrity protection and integrity verification, and is performed in PDCP for PDCP entities associated with SRBs. The data unit that is integrity protected is the PDU header and the data part of the PDU prior to ciphering. The integrity protection algorithm and key to be used by the PDCP entity are configured by upper layers and the integrity protection method is applied according to Security Architecture of 3GPP System Architecture Evolution [23]. The integrity protection function is activated by upper layers. Following security activation, the integrity protection function is applied to all PDUs including and subs