e handover ranging is a process similar to the initial ranging except that in the CDMA handover ranging process, random selection is used instead of random backoff and the CDMA handover ranging code is used instead of the initial ranging code. Furthermore, if the BS is notified of an upcoming handover, it may provide bandwidth allocation information using Fast Ranging IE SO that the MS can send a RNG-REQ message [1]. Serving BS Target BS Serving BS Target BS AAI_HO-REQ AAI_HO-REQ AAI_HO-CMD AAI_HO-CMD AAI_HO-IND AAI_HO-IND (Dedicated) CDMA Ranging Code (Dedicated)- -GDMA Ranging Code AAI_RNG-ACK AAI RNG-ACK Maintain Data Communication Unicast Encrypted DL Data/UL Grant with the Serving BS during Network Re-entry -Unicast Encrypted UL Data/Bandwidth Request -AAI_RNG-REQ (CMAC) AAI_RNG REQ (CMAC) AAI_RNG-RSP (CMAC) AAI_RNG RSP (CMAC) Completion of Network Re-entry and HO Completion of Network Re-entry and HO Network Re-entry Procedures when Entry-Before-Break Disabled Network Re-entry Procedures when Entry-Before-Break Enabled FIGURE 6-17 Handover network re-entry call flow [2] 6.4 Mobility management and handover Ranging Initiation Deadline parameter, it assumes the handover has failed and stops allocating bandwidth to the MS. If the MS transmits AAI_RNG-REQ prior to the deadline, the handover may still fail, if the MS does not receive an AAI_RNG-RSP within the permissible time. If data packets are exchanged between the MS and the target BS before the AAI_RNG-REQ/RSP messaging is complete, the recipient (MS or target BS) stores the received data packets, but will not deliver them to the upper layers until the sender is authenticated. If the data packets belong to a service flow associated with a trusted entity that supports data authentication, as indicated by the data authen- tication algorithm identifier in the cryptographic suite of the IEEE 802.16m security, the receiver can authenticate the sender by verifying the cipher text authentication code included in each data packet. On the other hand, if the data pac