2.2 IEEE 802.16 Protocol Layers
The IEEE 802.16 standard is structured in the form of a protocol stack with well defined interfaces. As shown in Figure 2.1, the MAC layer is formed with three sublayers:
Service Specific Convergence Sublayer (CS) MAC Common Part Sublayer (CPS) and Privacy Sublayer.
The MAC CS receives higher level data through CS Service Access Point (SAP) and provides transformation and mapping into MAC Service Data Unit (SDU).MAC SDUs are then received by MAC CPS through MAC SAP. The specification targeted two types of traffic transported through IEEE 802.16 networks: Asynchronous Transfer Mode (ATM) and Packets. Thus, Multiple CS specifications are available for interfacing with various protocols.
The MAC CPS is the core part of the MAC layer, defining medium access method. The CPS provides functions related to duplexing and channelization, channel access, PDU framing, network entry and initialization. This provides the rules and mechanism for system access, bandwidth allocation and connection maintenance. QoS decisions for transmission scheduling are also performed within the MAC CPS.
The Privacy layer lies between the MAC CPS and the PHY layer. Security is a major issue for public networks. This sub layer provides the mechanism for encryption and decryption of data transferring to and from PHY layer and is also used for authentication and secure key exchange. Data, PHY control, statistics are transferred between the MAC CPS and the PHY through the PHY SAP.