The Transmission Convergence Sublayer (TCS) is defined in the OFDM PHY Layer and the Non-WiMAX SC PHY Layer. The TCS is located between the MAC and PHY Layers. If the TCS is enabled, the TCS converts MAC PDUs of variable size into proper-length FEC blocks, called TC PDU. An illustration of a TC PDU is shown in Figure 6.11. A pointer byte is added at the beginning of each TC PDU, as illustrated in the figure. This pointer indicates the header of the first MAC PDU.
The TCS is an optional mechanism for the OFDM PHY. It can be enabled on a preburst basis for both the uplink and downlink through the burst profile definitions in the uplink and downlink channel descriptor (UCD and DCD) messages respectively. The TCS_ENABLE parameter is coded as a TLV tuple in the DCD and UCD burst profile encodings (see Chapters 8 and 9 for TLV and UCD/DCD). At SS initialisation, the TCS capability is negotiated between the BS and SS through SBC-REQ/SBC-RSP MAC messages as an OFDM PHY specific parameter. The TCS is not included in the OFDMA PHY Layer.