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5G N26 Interface – 5G to 4G Interworking

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The N26 interface is a key interface defined in the 3GPP (3rd Generation Partnership Project) specifications for 5G networks. It facilitates interworking between 5G and 4G networks, allowing seamless communication between devices and services across these two generations of mobile networks. Let's delve into the technical details of the 5G N26 interface and its role in 5G to 4G interworking.

1. Interface Purpose:

  • Definition: The N26 interface is specifically designed for interconnecting the 5G Next Generation Core (5G NGC) with the 4G Evolved Packet Core (4G EPC).
  • Purpose: It enables mobility and session continuity when a user equipment (UE) moves between 5G and 4G coverage areas.

2. Mobility and Session Continuity:

  • Handover Support: N26 facilitates the handover of a user's data session from a 5G cell to a 4G cell or vice versa.
  • Session Management: It ensures that ongoing user sessions (e.g., voice calls, video streaming) are maintained without interruption during handovers.

3. Key Components and Functions:

  • User Plane Function (UPF): The UPF is a critical component that plays a central role in the N26 interface. It manages the user's data plane and is responsible for the efficient forwarding of user data between 5G and 4G networks.
  • Session Management: The N26 interface supports the transfer of session context information, allowing the 4G EPC to seamlessly take over ongoing sessions from the 5G NGC and vice versa.

4. Data Forwarding:

  • Packets Forwarding: When a handover occurs, the UPF ensures that the user's data packets are forwarded from the source to the target network seamlessly.
  • QoS (Quality of Service) Preservation: The N26 interface ensures that the QoS parameters established in the 5G network are maintained during the handover to the 4G network.

5. Control Plane Aspects:

  • Interface Messages: The N26 interface involves the exchange of control messages between the 5G NGC and the 4G EPC. These messages include handover commands, acknowledgments, and signaling for session management.
  • Authentication and Authorization: The N26 interface supports the authentication and authorization mechanisms necessary for the user equipment to access services in both 5G and 4G networks.

6. Security Considerations:

  • Security Protocols: The N26 interface incorporates security protocols to protect user data during the handover process.
  • Authentication and Encryption: Mutual authentication and encryption mechanisms are employed to ensure the confidentiality and integrity of user data.

7. Interworking Scenarios:

  • Initial Attach and Registration: When a device attaches to the network or registers for the first time, the N26 interface may be involved in the establishment of initial session context.
  • Handovers: N26 is crucial during handovers between 5G and 4G cells, ensuring a smooth transition for active user sessions.

8. Evolutionary Aspects:

  • Compatibility: The N26 interface allows for a phased deployment where 4G and 5G networks can coexist and support interoperability.
  • Migration Paths: As the transition from 4G to 5G evolves, the N26 interface accommodates different network deployment scenarios and migration paths.

The 5G N26 interface serves as a vital link between the 5G NGC and the 4G EPC, enabling seamless interworking and ensuring a smooth user experience as devices move across different generations of mobile networks.