4G Layer-3 (RRC)

4G Layer-3 (RRC)

Radio resource control (RRC) protocol exists at IP level (layer 3) between UE and eNB.

The major functions of the RRC protocol include connection establishment/release functions, broadcast of system information, radio bearer establishment, reconfiguration/release, RRC connection mobility procedures, paging notification and outer loop power control.

The operation of the RRC is guided by a state machine which defines certain specific states that a UE may be present in. The different states in this state machine have different amounts of radio resources associated with them and these are the resources that the UE may use when it is present in each specific state -

RRC_IDLE:
• PLMN selection
• Broadcast of system information
• Cell re-selection mobility
• Paging for mobile terminated data is initiated by EPC
• DRX for CN paging configured by NAS
• UE controlled mobility

RRC_CONNECTED:
• EPC – RAN connection (both C/U-planes) is established for UE
• UE AS context is stored in RAN and the UE
• Network knows the cell which the UE belongs to
• Transfer of unicast data to/from the UE
• Network controlled mobility including measurements

Number of these RRC connected users are analyzed sometimes to estimate the impact on the capacity/load of a cell.

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