s the MIC one block at a time. If the last block is not exactly 128-bits, it is padded with zeros. The final output is one 128-bit block, but the CCM requires only a 64-bit MIC, SO the low order 64-bit final output is discarded. The encryption process uses the AES CBC-MAC core to generate the MIC and the AES Counter core for the encryption of data. CHAPTER 7 The IEEE 802. 16m MAC CPS (Part II) UL Burst N UL Burst N+1 UL Burst N+2 Bandwidth Bandwidth User MAC PDU User MAC PDU User MAC PDU User MAC PDU Request Management Request connections) (Two connections of (Two connections of (one connection) MAC PDU MAC PDU Flow ID 0x5 FlowID 0x1 Flow ID 0x1 Flow ID = 0x8 Flow ID = 0x6, 0x4 Flow ID 0x6, 0x4 Flow ID 0x8, 0x9 SA1: Security Association 1 (AES CCM) SA2: Security Association 2 (No Protection) FIGURE 7-14 An example MAC PDU concatenation [2] Figure 7-14 illustrates the concatenation concept for a UL burst transmission. Since the MAC SDUs in a MAC PDU are identified by a Flow ID in the AGMH and MEH, the receiving MAC entity is able to present the MAC SDU (after reassembling the MAC SDU from one or more MAC PDUs) to the correct instance of the MAC SAP. The MAC PDUs containing control messages, user data, and bandwidth request may be concatenated into the same transmission. Fragmentation is a process by which a MAC SDU (or MAC control message) is divided into two or more MAC PDUs. The capabilities of fragmentation and reassembly are mandatory for IEEE 802.16m entities. For transport connections, the FPEH or MEH header in the MAC PDU provides information about the SDU fragment. The FPEH or MEH header is always present in a MAC PDU for transport connections. The SN in FPEH or MEH header is used for sequencing the SDU fragments and the fragmentation control bits in FPEH or MEH header are used to tag the SDU fragments with respect to their position in the parent SDU. For non-ARQ transport connections, the fragments are transmitted once. The sequence number assigned to each connection PDU carrying SDU fragment allows the r