 scheduling, and schedules the transmission of MAC PDUs. The ARQ block assists MAC ARQ functions between the BS and RS over the relay link and between MS and RS over the access link. The MAC SDUs may be fragmented or augmented depending on the size of the payloads. The fragmentation/packing block in the RS side includes the unpacking and repacking of data fragments that have been received for relaying, in order to adapt the size of MAC PDUs to the estimated channel quality of the outbound link. The MAC PDU formation block constructs MAC PDUs which contain user traffic or management messages. User traffic is assumed to have originated at either the BS or MS. The MAC PDU construction block may add or modify MAC PDU control information (e.g., MAC header). The data forwarding block performs routing functions on the link between the BS and the RS or MS. The data forwarding block may work in conjunction with other blocks such as scheduling and resource mul- tiplexing and MAC PDU formation. The interference management block at the RS performs inter-cell and inter-RS interference management. This function includes reception of interference level measurements and selection of transmission format used for the mobile stations attached to the RS. The control functions can be divided among the serving BS and the relay stations using a centralized model or a distributed model. In a centralized model, the serving BS generates control signals, and the relay stations communicate the control information between the BS and MS. In a distributed model, the RS generates control signals for the subordinate mobile stations and makes the BS aware of that control information. The determination of whether a particular control function should be centralized or distributed is made independently for each control function. Convergence Sublayer Convergence Sublayer MAC CPS MAC CPS MAC CPS Security Sublayer Security Sublayer Security Sublayer Physical Layer Physical Layer Physical Layer FIGURE 3-17 Protocol termination in a relay-enabled network