RRC Connection Setup
RRC Connection Setup
RRC connection establishment involves the establishment of SRB 1. The E-UTRAN completes RRC connection establishment prior to completing the establishment of the S1 connection (i.e., prior to receiving the UE context information from the EPC).
Consequently, AS security is not activated during the initial phase of the RRC connection. During this initial phase of the RRC connection, the E-UTRAN may configure the UE to perform measurement reporting.
When the UE sends an RRC Connection Request to the eNB, this message is sent using the RLC-TM, and includes the UE identity, and the establishment cause (Emergency, High Priority Access, Mobile-Terminated Access, Mobile-originated Signaling, Mobile-Originated Data).
Once the eNB receives this message, this typically pegs an RRC connection attempt counter that is normally used for the accessibility formulas. Then, the eNB answers with RRC Connection Setup. This message is used to establish SRBs and includes the RRC Transaction ID.
This message is sent using the RLC-TM. The UE is now identified by a CRNTI. The details of the Signaling Radio Bearer (SRB 1) are provided to the UE by the eNB in the RRC Connection Setup message.
The RRC connection set up ends with the RRC connection setup complete sent by the UE using the just-allocated SRB1 to confirm the successful completion of an RRC connection establishment.
It includes the selected PLMN identity from the PLMN-Identity list provided in the SIB 1, the registered MME (GUMMEI, if known), and also the initial NAS-dedicated information message. This message is sent using the RLC-AM.
The NAS information is the Attach Request that is being sent to the eNB to be forwarded to the MME. The RRC connection success counter is pegged as soon as the eNB receives this message. RRC connection attempts along with the number of RRC connection setup complete messages are used to calculate the success rate in establishing an RRC connection.
On the successful completion of the RRC Connection establishment procedure, the UE is in the RRC Connected state and is provided periodic Time Alignment commands by the eNB, is providing channel quality feedback, and is making neighboring cell measurements.