link traffic, to establish an RRC connection and to indicate a change in system information. A paging message is sent 782 Chapter 6 over the NPDSCH and may contain a list of UEs being paged and the information on whether paging is for connection setup or system information has changed. Each UE which finds its identifier in this list would notify the upper layers in order to initialize the RRC connection setup. If the paging message indicates a change in system information, then the UE acquires SIB1-NB to find out which SIBs have been updated. The UE in the RRC_IDLE state only monitors some of the subframes with respect to paging, the paging occasions (POs) within a subset of radio frames and the paging frames (PFs), as shown in Fig. 6.25. If coverage enhancement repetitions are applied, the PO refers to the first trans- mission within the repetitions. The PFs and POs are determined from the DRX cycle pro- vided in SIB2-NB, and the international mobile subscriber identity (IMSI) provided by the universal subscriber identity module (USIM) card. The DRX is the discontinuous reception of downlink control channel that is used to save the UE battery life. DRX cycles of 128, 256, 512, and 1024 radio frames are supported, corresponding to a time interval between 1.28 and 10.24 seconds. Since the algorithm for determining the PFs and POs also depends on the IMSI, different UEs have different POs, which are uniformly distributed across time. It is sufficient for the UE to monitor one PO within a DRX cycle, if there are several POs therein, the paging is repeated in every one of them. As we stated earlier, the concept of extended DRX may be applied for NB-IoT, as well. If eDRX is supported, then the time interval in which the UE does not monitor the paging messages may be considerably extended up to almost 3 hours. Correspondingly, the UE must know on which HFN and on which time interval within this HFN, that is, the paging transmission window (PTW), it has to monitor the paging. The PTW is defined by a start and stop SFN. 