andover initiation message by sending a handover command to the MS. In the case of BS-initiated handover, the serving BS sends a handover command to the MS. In both cases, i.e., MS or BS initiated handover; the handover command includes one or more target base stations. If the handover command includes only one target BS, the MS will execute the handover as directed by the BS. An MS may send a handover indication message to the serving BS before the expiration of disconnect timer. The serving BS stops sending DL data and providing UL allocations to the MS after expiration of the disconnect timer or after receiving a HO-IND message. If the handover command includes more than one target base station, the MS selects one of those target base stations and informs the serving BS of its choice by sending a handover indication message before the expi- ration of disconnect timer. The network re-entry procedures with the target BS may be optimized by providing the target BS with the MS context. The MS may also maintain communication with the serving BS while performing network re-entry process with the target BS, as shown in Figure 6-15. The serving BS defines the conditions based on which the MS may decide when a target BS among those that are included in the handover command is unreachable. If all target base stations that were Serving BS Target BS HO-REQ HO-RSP BS Initiated HO HO-CMD HO-REQ HO-REQ MS Initiated HO HO-RSP HO-CMD HO-IND Network Re-entry with Target BS Data Communication with Serving BS during Network Re-entry HO-COMPLT Data Plane Re-established FIGURE 6-15 General handover call flow [2,5] 6.4 Mobility management and handover included in the handover command are unreachable for the MS, the MS may find a new target BS and inform the serving BS by sending a handover indication message before expiration of disconnect timer, and the MS may proceed with network re-entry with the new target BS. The MS also indicates the identity of previous serving BS to the new target BS during network re-entry. The handover pro