Sign in Subscribe

How does 5G handle the RRC connection setup procedure?

Last updated on 


The Radio Resource Control (RRC) connection setup procedure in 5G is a critical step that enables the establishment of a connection between a user equipment (UE) and the network. It involves several steps and messages exchanged between the UE and the base station (gNB - gNodeB). Here's a detailed technical explanation of how 5G handles the RRC connection setup procedure:

Random Access Preamble:

  • The UE initiates the RRC connection setup procedure by sending a Random Access Preamble on the Random Access Channel (RACH) to request access to the network.
  • The preamble carries information about the UE's synchronization status and timing.

Contention Resolution:

  • The gNB acknowledges the Random Access Preamble by sending a Contention Resolution message.
  • If multiple UEs transmit the same preamble, a contention resolution process determines the UE that can proceed to the next step.

Random Access Response (RAR):

  • The gNB responds to the UE with a Random Access Response (RAR) message.
  • The RAR includes information like the selected preamble identifier, temporary identifier (C-RNTI), and scheduling request information.

Scheduling Request (SR) and Connection Setup Request:

  • If needed, the UE sends a Scheduling Request (SR) message to request uplink resources for data transmission.
  • The UE may also send a Connection Setup Request if it has data to send during the connection establishment.

RRC Connection Request:

  • The UE sends an RRC Connection Request message to request the establishment of an RRC connection.
  • This message includes information about the establishment cause and UE capabilities.

RRC Connection Setup:

  • The gNB responds with an RRC Connection Setup message.
  • This message contains important parameters such as establishment cause, RRC configuration, and initial downlink radio resource configuration.

RRC Configuration Complete:

  • The UE acknowledges the RRC Connection Setup message by sending an RRC Configuration Complete message to the gNB.
  • This message indicates that the UE has successfully configured the provided RRC parameters.

Security Setup (Optional):

  • If security is required for the connection, the gNB initiates a security setup procedure.
  • This involves the exchange of security-related information like encryption algorithms, keys, and authentication.

RRC Connection Reconfiguration:

  • The gNB may initiate an RRC Connection Reconfiguration to update or modify the existing RRC configuration based on the negotiated capabilities or changing network conditions.
  • This message may include changes to the security configuration, mobility-related parameters, or addition of radio bearers.

RRC Connection Complete:

  • The UE responds with an RRC Connection Complete message after processing the RRC Connection Reconfiguration.
  • This message confirms the successful reconfiguration and establishment of the RRC connection.

After completing these steps, the RRC connection is established between the UE and the network, allowing for the exchange of data and control information for ongoing communication. The procedure ensures efficient setup and configuration of the radio resources and security measures necessary for a reliable connection in the 5G network.