s that an extended header will follow this header. The Length field indicates the total size of the MAC PDU in bytes including the short-packet MAC header and the extended header (if any). The Sequence Number denotes the MAC Extended Flow ID (4 bits) Header Length (3 bits) (1 bit) Length (8 bits) FIGURE 6-4 IEEE 802. 16m advanced generic MAC header structure [2] CHAPTER 6 The IEEE 802.16m MAC CPS (Part I) Extended Flow ID (4 bits) Header Length (3 bits) (1 bit) Length (4 bits) Sequence Number (4 bits) FIGURE 6-5 Structure of the short-packet MAC header [2] MAC PDU Length Extension Length Extended Header Group Length (4 bits) (3 bits) (1 bit) Extended Header Content 1 Extended Header Type 1 (4 bits) (Variable Length) Extended Header Content 1 (Variable Length) Extended Header Content 2 Extended Header Type 2 (4 bits) (Variable Length:) Extended Header Content 2 (Variable Length) Extended Header Content N Extended Header Type N (4 bits) (Variable Length) Extended Header Content N (Variable Length) FIGURE 6-6 Structure of an extended header group [2] PDU sequence number. The SPMH is identified by the specific FID that is provisioned statically or created dynamically using AAI_DSA-REQ/RSP messages. The AGMH and SPMH header can be extended to include additional information fields depending on the use case and MAC PDU contents. The use of extended header is indicated by the EH flag in the MAC header. The extended header structure is illustrated in Figure 6-6. The description of the extended header fields is as follows: 6.2 MAC PDU headers MAC PDU length extension (3 bits): These bits are appended as the most significant bits to the 11-bit Length field in AGMH to create a 14-bit Length field. Extended header Group Length (4/12 bits): the extended header group length field indicates the total length in bytes of the extended header group as shown in Figure 6-6. Extended Header Type (4 bits): this field indicates the type of extended header. There are some predefined types such as MAC SDU fragmentation or packing, MAC cont