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Directed retry(DR) is a procedure which is used in a call set-up phase when a mobile station is assigned to a traffic channel in a cell other than the serving cell in situations of congestion.
Directed retry procedure is an optional feature.
When the directed retry procedure is initiated, the following two timers control the creation procedure for a handover candidate cell list.
·It is possible to determine the period starting from the assignment request during which the directed retry is not allowed. The BSC can start the target cell evaluation for the DR handover after the time supervision has expired. This period is allowed for the mobile station to decode the base station identity code (BSIC) of the adjacent cells before the target cell evaluation. The time supervision is controlled on a cell-by-cell basis with the parameter MinTimeLimitDR.
·The BSC can continue the target cell evaluation for the DR handover until the maximum time allowed for the start of the DR handover expires. The time supervision is controlled on a cell-by-cell basis with the parameter MaxTimeLimitDR.
When the directed retry procedure is initiated, the directed retry threshold method can be taken into use. The following two parameters control the directed retry threshold method.
·The directed retry threshold method makes it possible to use RX signal level of the adjacent cell in the candidate cell list creation procedure. The directed retry threshold method is controlled on a cell-by-cell basis with the parameter DRMethod.
·The directed retry threshold method determination is based on the predefined minimum threshold value of RX signal level. The directed retry threshold is controlled on a cell-by-cell basis with the parameter DRThreshold.