eselection, radio connection release with redirect or handover. The latter two can be either blind or based on measurements. Throughout the section it is assumed that LTE has higher priority than the 2G or 3G RAT where the CS call is released. Inter-RAT Cell Reselection from 3G to LTE UE inter-RAT reselection measurement scheduling from 3G to a higher priority LTE layer depends on the DRX cycle and priority search thresholds Sprioritysearch1 and Spriority- search2 which are broadcast in SIB19 In line with the design of the priority-based reselection, if the UE is considered to be in good RF conditions - 'good' defined by the priority search parameters - higher priority layer cell search can be performed at the interval of 60 sec- onds times the number of higher priority layers broadcast on SIB19. Otherwise the search VoLTE Optimization Ec/NOServingCell Inside this region UE must search for higher priority layers at least once every 60 seconds Outside this region, the requirement depends on idle mode DRX cycle as specified in 3GPP TS 25.133 Sprioritysearch1 prioritysearch2 qRxQualMin RSCPServingCell qRxLevMin Figure 14.6 Dependence of 3G to LTE reselection measurements on priority search parameters requirements are considerably stricter. This principle is illustrated in Figure 14.6 from where it is seen that if either Sprioritysearch1 or Sprioritysearch2, or both, are set to a high value the UE will search for LTE cells more frequently. The search requirement is per layer, SO for two LTE layers the search requirement in good radio conditions would be 2 X 60 = 120 seconds. When the received RSCP level and quality are outside the region shown in Figure 14.6, the UE cell search and measurement minimum requirements are given in Table 14.2. The DRX cycle length given in the table may be different in CELL_PCH and idle mode. The detection time in the second column is defined as the maximum time from cell search to cell reselection decision, that is, it includes cell measurements. The requirements apply only to LTE cells 