The service-specific Convergence Sublayer (CS), often simply known as the CS, is just above the MAC CPS sublayer (see Figure 3.2). The CS uses the services provided by the MAC CPS, via the MAC Service Access Point (SAP). The CS performs the following functions:
Accepting higher-layer PDUs from the higher layers. In the present version of the standard , CS specifications for two types of higher layers are provided: the asynchronous transfer mode (ATM) CS and the packet CS. For the packet CS, the higher-layer protocols may be IP v4 (version 4) or v6 (version 6).
Classifying and mapping the MSDUs into appropriate CIDs (Connection IDentifier). This is a basic function of the Quality of Service (QoS) management mechanism of 802.16 BWA.
Processing (if required) the higher-layer PDUs based on the classification.
An optional function of the CS is PHS (Payload Header Suppression), the process of suppressing repetitive parts of payload headers at the sender and restoring these headers at the receiver.
Delivering CS PDUs to the appropriate MAC SAP and receiving CS PDUs from the peer entity.
CS procedures and operations are detailed in Chapter 7.