The IEEE 802.16 set of standards lays down the specifications for wireless broadband technology. It has been commercialized as Worldwide Interoperability for Microwave Access (WiMAX) that is responsible for the delivery of last-mile wireless broadband access.
The IEEE 802.16 MAC sublayer is the most important sublayer and concerned with channel management. It has been designed for connection-oriented channel management for point-to-multipoint (PMP) broadband services.
The frame format of a generic MAC frame is shown below −
The fields are −
EC − A single-bit field indicating whether the payload is encrypted.
Type − A 6-bit field identifying frame type.
CI − A single-bit field denoting the presence or absence of a final checksum.
EK − A 2-bit field mentioning the encryption key or the absence of it.
Length − An 11-bit field containing the total length of frame inclusive of the header.
Connection ID − A 16-bit identifier mentioning the connection to which the frame belongs to.
Header CRC − A 8-bit checksum over the header, using the polynomial − 𝑥8 + 𝑥2 + 𝑥 + 1
Data − A variable-length field containing payload from the upper layers.
CRC − A 4-bit checksum over the payload.
There may be a number of types of MAC frames. One of the common variations is the bandwidth – request frame. The following diagram shows the frame format −
The identifying features of this frame are −
It starts with a 1 bit instead of a 0 bit of the generic frame.
The second and the third byte form a field that mentions the bandwidth needed for further transmission.