ossible a where an SHO is not possible. Usually intrafrequency handover is used as a 'last chance' in a case where an SHO is not possible. An intrafrequency hard handover is used, for example, when an inter-RNC SHO is not possible. This occurs if the Iur interface is not implemented. The decision to make an intrafrequency hard handover is made by the RNC. There is a threshold margin defined for a neighbouring cell. The neighbouring cell Ec/10 must be better than the serving cell Ec/10, with at least the amount of threshold margin to perform an intrafrequency hard handover. The margin is used to avoid the 'ping-pong' effect, where the UE selects back and forth between the two cells. Also the threshold margin has been defined such that the UE first tries to make an SHO. The intrafrequency hard handover causes a temporary disconnection of the RT RAB. In the case of NRT RABs the disconnection is transparent to the user. Interfrequency Handover and Intersystem Handover WCDMA All the interfrequency and intersystem (or inter-RAT) handovers are hard handovers. The interfrequency and intersystem handover mechanisms follow a similar pattern. The decision to start interfrequency/RAT handover measurements is done by the network. Both of these hard handovers follow a similar network evaluated handover (NEHO) procedure. The network evaluated handover procedure consists of three steps: measurement triggering criteria define when interfrequency/RAT measurements start; the RNC sends measurement parameters to the UE to command how measurements are done; the UE then performs measurements and reports according to measurement reporting criteria. Finally, the RNC commands handover when the handover criteria are fulfilled. Measurement Triggering Implementation of different measurement triggering criteria in the network is vendor specific. Possible measurement triggering criteria include: Best active set cell RSCP (UE measurement report) Best active set cell Ec/N (UE measurement report) Uplink DCH quality (RNC measurement) Downlink DCH 