In EUTRAN, there are four processes in the idle mode, as schematized in Figure 11.1.
The following describes these processes in detail.
PLMN selection is made by the UE's NAS through relaying the identifier of the selected PLMN. To do so, the UE requires knowledge of identified PLMNs and supporting measurements from the AS. This relay of identified PLMNs requires the UE's synchronization to a broadcast channel, and can be either on request or autonomously. PLMN selection can be done either automatically (without user interruption) or manually. The AS, in its search and measurements, identifies to the NAS PLMNs with both high and low quality signals. An optimization for PLMN search can be made through using stored information, such as carrier frequencies. At any instant, the search may be stopped on request from the NAS. Once completed, the UE proceeds to the cell selection process.
If a CSG ID is passed along to the NAS during the PLMN search process, the UE must consider either an acceptable or a suitable cell belonging to the provided CSG ID to camp on. The AS will inform the NAS if the UE is no longer camped on a cell with the provided ...