ing on the current operational state of the mobile station, the network entry procedures can be different. A mobile station which is just powered on must perform an initial network entry which, as described earlier, includes successful completion of the Initialization and Access State procedures to establish data- and control-planes and to enable any data transfer in the downlink or uplink. The initial network entry procedures in the mobile station and base station are illustrated in Figures 4-12 and 4-13. There are other access- and core-network entities such as ASN-GW/Authenticator and Home AAA Server involved in the initial network entry process which are not shown in the figures. Those network entities are involved in authentication, authorization, and key exchange, as well as in the registration procedures with the BS [5]. The MAC management messages in IEEE 802. 16m are distinguished from their legacy counterparts by an "AAI" prefix denoting "Advanced Air Interface" messaging. There are some timers associated with execution of each procedure that are denoted by Ti. These timers are used to control the amount of permissible time to enact or execute a specific procedure that once expired, forces the restart of the same or a different procedure. The MAC management messages that are shown in Figures 4-12 and 4-13 will be introduced and discussed in Chapter 6. However, the procedures such as initial ranging (AAI_RNG- REQ/RSP), basic capability negotiation (AAI_SBC-REQ/RSP), and registration with the BS (AAI_REG-REQ/RSP) have already been discussed in the description of IEEE 802.16 states. Network re-entry is a sequence of procedures similar to network entry, where the MS attempts to transition from the Idle State to the Connected State or during handover and prior to establishment of data-plane with the target BS. The MS may exit the Idle State and re-enter the network either in response to a page by the BS (i.e., network-initiated), or to start communication with the BS (i.e., MS- initiated). The network re-ent