e links. In the case of a relay station, the scheduling of the resources is within the radio resources assigned by the BS. The BS notifies the relay and mobile stations of the frame structure configuration. The radio frame is divided into access and relay zones. In the access zone, the BS and the RS transmit to, or receive from, the mobile stations. In the relay zone, the BS transmits to the relay and the mobile stations, or receives from the relay and mobile stations. The start times of the frame structures of the BS and relay stations are aligned in time. The BS and relay stations transmit synchronization channels, system information, and the control channels to the mobile stations at the same time. The MAC layer of a relay station includes signaling extensions to support functions such as network entry of an RS and of an MS through an RS, bandwidth request, forwarding of PDUs, connection management, and handover. Two different security modes are defined in the IEEE 802.16j- 2009 standard: (1) a centralized security mode that is based on key management between the BS and an MS; and (2) a distributed security mode which incorporates authentication and key management between the BS and a non-transparent access RS, and between the access-RS and an MS. An RS may be configured to operate either in normal CID allocation mode, where the primary management, secondary, and basic CIDs are allocated by the BS, or in local CID allocation mode where the primary management and basic CID are allocated by the RS. The IEEE 802.16m RS uses the same security architecture and procedures as an MS to establish privacy, authentication, and confidentiality between itself and the BS on the relay link. The IEEE 802.16m relay stations use a distributed security model. The security association is established between an MS and an RS during the key exchange similar to a macro BS. The RS uses a set of active keys shared with the MS to perform encryption/decryption and integrity protection on the access link. The RS runs a secure encapsulatio