kets belong to a service flow associated with a trusted entity that does not support data authentication, the receiver can authenticate the sender when the AAI_RNG-REQ/RSP messaging is successfully completed. In all cases, if the sender is authenticated, the decrypted data packets will be delivered to the upper layer in the receiving end; otherwise, the data packets are discarded. Alternatively, the sender can authenticate the receiver when the AAI_RNG-REQ/RSP messaging is successfully completed. In all cases, if the sender fails to authenticate the other end, all previously transmitted packets will be re-transmitted to the BS (or the MS) when a new connection is established. The handover network re-entry call flow is shown in Figure 6-17. The MS initiates the AAI_RN- G_REQ/RSP messaging by transmitting the AAI_RNG-REQ message to the target BS before the expiration of the HO Ranging Initiation Deadline time contained in the AAI_HO-CMD message. The MS MAC address or the previous serving BS-ID are not communicated over the air interface once the initial entry is completed, instead temporary and permanent station identifiers are assigned to the MS during network entry to identify the MS throughout the active session. The exclusion of the MAC address in the MAC messages was meant to improve network security. When the BS receives the AAI_RNG- REQ message including a valid CMAC tuple, the BS responds by transmitting an encrypted AAI_RNG- RSP message. The AAI_RNG-RSP message uses the STID assigned to the MS. On completion of the network re-entry with the target BS, the target BS becomes the new serving BS for the MS. In the case of an uncontrolled handover, the AAI_RNG-REQ message includes the former serving BS-ID and previously used STID, if the Resource Retain Timer has not expired. When the BS receives *There are two types of handover, i.e., controlled and uncontrolled, from a QoS point of view. A controlled handover considers the following conditions [22,23]: If the handover is MS initiated, the MS must send the BS 