equent to the PDU indicated by upper layers for the downlink and uplink transmissions. As the RRC message which activates the integrity protection function is itself integrity protected with the configuration included in that RRC message, the message must be decoded by RRC before the integrity protection verification could be performed for the PDU in which the message was received. The parameters that are required by PDCP for integrity protection are defined in reference [23] and are input to the integrity protection algorithm. The required inputs to the integrity protection function include the COUNT value and DIRECTION (direction of the trans- mission). The parameters required by PDCP which are provided by upper layers are BEARER (defined as the radio bearer identifier) and the KEY. During transmission, the UE computes the value of the MAC-I field and, at reception, it verifies the integrity of the PDCP PDU by calculating the X-MAC, i.e., Computed MAC-I, based on the input parameters. If the calculated X-MAC corresponds to the received MAC-I, integrity protection is verified successfully. When a PDCP entity receives a PDCP PDU that contains reserved or invalid values, the PDCP entity discards the received PDU. The PDCP Data PDU is used to transport PDCP SDU SN and user-plane data containing an uncompressed PDCP SDU, user-plane data containing a compressed PDCP SDU, or control-plane data as well as MAC-I field for SRBs. 5.5 The 3GPP LTE packet data convergence protocol The PDCP Control PDU is used to convey the PDCP status report identifying missing PDCP SDUs following PDCP re-establishment and header compression control information, e.g., ROHC feedback. References [1] IEEE Std 802.16-2009, IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems, May 2009. [2] IETF RFC 2507, M. Degermark, et al., "IP Header Compression," February 1999. <http://www.rfc-editor. org/rfc/rfc2507.txt>. [3] IEFT RFC 791, Internet Protocol, September 1981. <http://www.