Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

246 ApplicationsTransmit, Tx-CSHigher IP layer (e.g., bridge, router)Receive Rx-CSHigher IP layer (e.g., bridge, router)CS SAPCS-PDUCS-SAPCS-PDUClassifierCID 1CID 2CID nReconstructionMAC SAPTx MACMAC-PDUMAC SAPRx MAC6 BytesMAC-HeaderCIDTypeEncrypt.(Management)ReservedMAC PayloadvariableCRCOptionalFigure 5-24IEEE 802.16 packet convergence sub-layer– classification of the PDUs according to their traffic content and assignment to theappropriate virtual channel connections (CID, connection identification);– packet header compression/suppression (optional);– forwarding and reception of the PDUs to/from the MAC service access point (MAC-SAP);– reception of the PDUs from the peer MAC SAP; and– re-building of any suppressed payload header information (optional).Its exact functionality depends strongly on the convergence sub-layer type: IP, Ethernet,or ATM. The IP CS supports both IPv4 and IPv6.In Figure 5-24 the IEEE 802.16 packet-based CS is illustrated. The packet CS is usedfor transport of all packet-based protocols such as the Internet Protocol (IP), Point-to-Point Protocol (PPP), and IEEE 802.3 (Ethernet). Note that the MAC PDU has a 6 bytesheader and variable length payload field and an optional CRC-byte field (see Figure 5-24).The MAC header transports the following information: CID, PDU-type, MAC-PDUlength, encryption information, etc.5.3.4.3 Common MAC Sub-LayerIn addition to the convergence sub-layer as described above, the main classical functionsof the IEEE 802.16 MAC control plane are depicted in Figure 5-25, where each functionis briefly described [23] in the following: