At this time, the UE is in EMM-Deregistered, ECM-Idle, and RRC-Idle state. Then, the user can communicate with the eNB. So, the UE selects an eNB (cell) through PLMN selection and cell search procedures, and has the radio link synchronized (PLMN selection and cell search procedures are out of the scope of this document, and thus will not be covered here). In order for a UE to request initial attach to a network, communication with an eNB is essential. ❶ Initial State after Radio Link Synchronization The ECM connection establishment phase can be further divided into two sub-phases: (1) RRC connection establishment, and (2) S1 signaling connection establishment. For the purpose of explanation, this step can be further divided into two sub-steps: ❶ the UE stays in the initial state after radio link synchronization, and ❷ the UE establishes ECM connection for delivering an Attach Request message to the MME. The UE attempts to initially attach to the network by sending an Attach Request message, with its IMSI in it, and the MME obtains the IMSI from the message. By the end of this first step, the MME obtains an IMSI from the UE. Figure 1 illustrates initial attach procedures in EMM Case 1, along with function blocks required in each procedure, as defined in Part 1.įigure 1. Summary of Initial Attach Proceduresįigure 2 shows the first step in the procedures.
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