RRC Connection Release procedure is used to release an RRC Connection.
Here eNB initiates the RRC connection release procedure to the UE.
Then the UE will go from RRC_Connected to RRC_Idle state.
There is no ACK in RRC Connection Release
Signalling Radio Bearer: SRB1
RLC Mode: AM
Logical Channel: DCCH
Transport Channel: DL-SCH
Reasons for eNB initiating RRC Connection Release Procedure
1. RRC Connection release with redirection information can be used for CS-Fallback to GERAN or UTRAN.
2. It can be also used to MME load balancing.
3. eNB can also give cell re-selection priority for each frequency in RRC Connection Release procedure.
Information Elements IEs present in RRC Connection Release:
ReleaseCause: LoadBalancingTAUrequired, cs-FallbackHighPriority, redirection or other
RedirectionCarrierInfo: It has a carrier frequency which is used to redirect the UE to an E-UTRA o
IdleModeMobilityControlInfo: It provides dedicated cell reselection priorities.
SystemInformation: Container for system information of the GERAN cell.
cellInfoList: It is used to provide system information of one or more cells on the redirected inter-RAT carrier.
ultra-BCCH-Container: Has System Information Container message defined in TS 25.331
Reference: 3GPP TS 36.331