Call Process : SA Initial Attach

The "SA Initial Attach" process is a technical term related to 5G (Fifth Generation) mobile networks. SA stands for Standalone, indicating that the 5G network operates independently without relying on any legacy 4G or 3G networks. An "Initial Attach" is the process by which a user device (UE - User Equipment) establishes a connection with the 5G network for the first time.

Let's break down the technical details of the SA Initial Attach process:

1. Radio Link Establishment (RRC Connection Establishment):
   • The UE initiates the connection by establishing a Radio Resource Control (RRC) connection with the 5G gNB (gNodeB - Next Generation NodeB), which is the radio access node in the 5G network.
2. Random Access Procedure:
   • The UE performs a Random Access procedure to request resources for communication with the gNB. This involves transmitting a Random Access Preamble.
3. Random Access Response:
   • The gNB responds with a Random Access Response, assigning resources to the UE.
4. RRC Setup:
   • Once the random access procedure is successful, the RRC connection is set up between the UE and the gNB. This involves exchanging necessary parameters and capabilities.
5. Registration and Authentication:
   • The UE performs registration and authentication procedures to securely establish its identity and ensure that it is allowed to access the 5G network.
6. N1 Initial Registration:
   • The UE sends an N1 Initial Registration message to the gNB. This message includes information about the UE's capabilities and initial registration request.
7. Security Mode Command:
   • The gNB sends a Security Mode Command to the UE, instructing it to establish secure communication. This involves setting up encryption algorithms and keys.
8. Security Mode Complete:
   • The UE responds with a Security Mode Complete message, indicating that it has successfully established secure communication.
9. AMF Registration Update Request:
   • The UE sends an Access and Mobility Management Function (AMF) Registration Update Request to the gNB. The AMF is responsible for managing mobility and access in the 5G network.
10. AMF Registration Update Accept:
    • The gNB responds with an AMF Registration Update Accept, indicating that the UE's registration has been accepted.
11. Initial Context Setup:
    • The gNB sets up the initial context for the UE, including the establishment of bearers for data communication.
12. UE Capability Information:
    • The UE provides information about its capabilities to the gNB, including supported features and protocols.
13. Service Request:
    • The UE sends a Service Request to request specific services from the network.
14. Service Accept:
    • The gNB responds with a Service Accept message, indicating that the requested services are granted.
15. Bearer Setup:
    • The gNB sets up the bearers for user data transfer. This involves establishing data paths and configuring Quality of Service (QoS) parameters.
16. Attach Complete:
    • The UE sends an Attach Complete message to the gNB, indicating that the SA Initial Attach process is complete, and the UE is ready to use 5G services.

This process ensures that the UE is successfully attached to the 5G network, and both the UE and the network are configured for secure and efficient communication.