 Set. When mean CINR of a neighbor BS is higher than a certain threshold, the MS may send a MOB_MSHO-REQ message to request adding this neighbor BS to the diversity set. In each case, the Anchor BS responds with a MOB_BSHO- RSP message with an updated Diversity Set [1]. This is the offset, measured in units of frame duration, when the BS is expected to provide a non-contention-based ranging opportunity for the MS. The offset is calculated from the frame where the RNG-RSP message is transmitted. The BS is expected to provide the non-contention-based ranging opportunity at the frame specified by the rendezvous time parameter [1]. CHAPTER 6 The IEEE 802. 16m MAC CPS (Part I) Anchor BS Target BS MOB_NBR-ADV Receive Neighbor B$ Parameters and Compare Measured CINRs to Thresholds MOB_SCN-REQ MOB_SCN-RSP CDMA Code Anonymous RNG-RSP RNG-REQ RNG-RSP MOB_MSHO-REQ MOB_BSHO-RSP Compare Measured CINRs to Thresholds and MOB_MSHO-REQ Update Diversity Set MOB_BSHO-RSP Update Anchor BS MOB_MSHO-IND to Target BS FIGURE 6-12 Fast base station switching call flow with association level 0 [1,9] After the MS completes the initial network entry/re-entry or handover procedure, the BS automatically becomes an Anchor BS. Furthermore, the Diversity Set is initialized and the TEMP_BS-ID parameter of the Anchor BS is set to zero. However, the TEMP_BS-ID parameter and Diversity Set are maintained when Anchor BS switching occurs. As shown in Figure 6-12, the process of Anchor BS update may begin with a MOB_MSHO-REQ message from MS or a MOB_BSHO-REQ from the Anchor BS. The acknowledgement of MOB_MSHO- REQ with MOB_BSHO-RSP is required. After MS transmits MOB_MSHO-REQ, the MS does not transmit the MOB_MSHO-REQ message prior to expiration of internal timer MS_handover_retransmission_timer. The MS deactivates this timer on transmission of the MOB_HO-IND message or on MS receipt of a MOB_BSHO-RSP message. The process of Anchor BS update may also begin with anchor switching indication via fast-feedback channel. 6.4 Mobility management and handover I