How to understand 5G test signaling

UE needs to register with 5GS before being authorized to receive service and establish user context in 5GS. The UE can only perform connection management and session management after registration.

The registration behavior of UE can be divided into three types:

Initial registration

Mobile update registration: Once the UE moves to a new TA cell, the new TA no longer belongs to the registration area of the UE, so it is necessary to start mobile update registration.

Periodic registration: When the periodic registration timer expires, it will trigger periodic registration, which is similar to heartbeat mechanism, that is, let the network know that the terminal is still in the power-on state in the service area.

Signaling flow

Explain the initial registration process for first-time users:

signal analysis

PART 1 has started registration.

The UE establishes RRC connection with gNB, and initiates a Register request of type InitialRegistration, which carries information such as SUPI, NSSAI and security parameters.

After receiving the registration request of the UE, gNB selects the corresponding AMF according to the NSSAI provided by the UE or according to the configuration, and sends the NAS information of the UE to the AMF, carrying N2 interface parameters such as gNB's own location information and cell ID.

Note: SUPI in 5G is equivalent to IMSI in LTE, but different from IMSI, SUCI is used instead of IMSI in previous occasions (such as initial registration and identification process). ), in which the user's permanent identity information will never appear. SUCI is an encrypted version of SUPI, which can ensure that SUPI will not be leaked, and can also ensure the normal authentication between UE and network.

Part 2 Authentication and Security

AMF received gN.

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