ed in the previous sections. Therefore, it can be concluded that the data trans- mission to and from an MS initiating handover (or being instructed to handover) will be interrupted for a period of time starting from a handover indication message transmission till re-establishment of the data-plane with the target BS. During handover interruption time, the MS may exit the Connected State and perform (normal or fast) network re-entry procedures with the target BS. The MS will transition to the Active Mode once the data-plane is established with the target BS (see Figure 4-15). 4.4 STATE TRANSITIONS IN RELAY STATIONS Optional multi-hop relay architecture may be used to provide extended coverage or performance improvement in a radio access network [10-12]. In multi-hop relay networks, the BS may be replaced viii "An MS that wishes to perform handover ranging follows a process similar to that defined for initial ranging, except that random selection is used instead of random backoff, and the handover ranging code is used instead of the initial ranging code. Note that the set of physical codes for the ranging process are divided into three subsets: handover ranging; initial ranging; and periodic ranging. Alternatively, if the target BS is notified in advance of the MS handover, it may provide bandwidth allocation information to the MS using a fast ranging information element to send a ranging request message (i.e., non-contention-based ranging) [1,2]. 4.4 State transitions in relay stations Cell Search and Cell Selection Initial Network Entry Cell Reselection, Scanning Intervals for Normal Operation Detecting and Evaluating Neighbor BS HO Decision Select Alternate Target Synchronize with New BS and Obtain System Information Cell Rejected Obtain Uplink Parameters Cell Rejected HO Ranging and UL Parameter Adjustment Cell Rejected MS Reauthorization MS Re-registration and Service Flows Re-establishment Re-establish IP Normal Operation Connectivity FIGURE 4-15 The handover process and network re-entry [1] by a relay-enable