does not share a current and valid security context with the MS, or in the event that the BS has opted to instruct the MS to use Unsecure Location Update, the MS initiates network re-entry from the Idle State. CHAPTER 4 IEEE 802. 16m System Operation and State Diagrams On completion of network re-entry, the target BS (now the new serving BS) provides the MS with uplink allocation for transmission of Sequence Number Report signaling header containing the least significant bits of the sequence number of ARQ block or virtual MAC SDU number for continuation of the interrupted data transmission due to handover. After reception of this signaling header, the BS resumes transmission of the data of the corresponding downlink service flow starting from MAC SDUs pointed by the sequence number [1]. 4.2.2 Fast Network Re-Entry Fast network re-entry is a process used to accelerate the transition from the Idle State to the Connected State. As mentioned earlier, some of the Access State procedures may be skipped or simplified if the MS context has not been revoked or expired, and the BS can obtain this information from the previous serving BS. Note that the IEEE 802.16 standard does not support Idle State handover (i.e., the MS cannot perform or be instructed to perform a handover during an idle period). Therefore, when the MS moves from the coverage area of the previous serving BS (i.e., the BS which was serving the MS prior to transition to the Idle State) to the coverage area of a new BS while in Idle State, the MS must perform the network re-entry process. For the purpose of expediting network re-entry of the MS with the target BS, the serving BS may negotiate with the target BS allocation of a non-contention-based ranging opportunity for the MS, i.e., an unsolicited uplink allocation for transmission of ranging request message. The agreed time takes into account the Handover Indication Readiness Timer (i.e., the minimum time that the MS may require to process handover request or handover response messages from the BS) and t