WHAT ARE THE POSSIBLE RRC STATES?

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RRC has two possible states

  1. RRC IDLE
  2. RRC CONNECTED.

A UE in EPS Mobility Management (EMM) – IDLE is RRC IDLE

A UE in EPS Mobility Management (EMM) – CONNECTED is RRC CONNECTED.

RRC IDLE

  • Support for Discontinous Reception (DRX) configured by NAS
  • UE has no RRC connection
  • UE listens to paging and broadcast system information
  • UE has an identity , which uniquely identifies the UE in a tracking area level only not at cell level
  • For mobility purpose Cell re-selection is performed (by the UE)
  • No RRC context in the eNode B for the UE

RRC CONNECTED

  • UE has an RRC connection
  • Network can transmit and/or receive data from UE with very limited access delay
  • UE has context in eNodeB
  • Mobility is Network controlled and is triggered by Measurement reporting and executed as handover
  • UE performs neighboring cell measurements
  • UE specific DRX/DTX for UE power saving and resource preservation exists in RRC Connected mode. These functions are controlled by an eNodeB using RRC protocol
  • Channel quality monitoring reported by the UE in MAC layer
  • MAC control plane related procedures such as Discontinuous Transmission (DTX), UL synchronization, channel estimate etc. take place in connected mode.
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