5G Interfaces N1 N2 N3 N4

Article by Abhijeet Kumar

As the telecommunications industry transitions from 4G LTE to 5G, one of the key enablers of this new technology is the redesigned core network architecture, known as the 5G Core (5GC). 5G introduces new network interfaces, many of which were not present in previous generations, to handle advanced capabilities, such as ultra-low latency, massive IoT support, and enhanced mobile broadband. These interfaces facilitate communication between different network functions within the 5G architecture, ensuring seamless data flow and network resource management. This article explores the primary 5G interfaces, detailing their functions, key messages, and 3GPP specifications.

N1 Interface

• Between: User Equipment (UE) and Access and Mobility Management Function (AMF)
• 3GPP Specification: 3GPP TS 23.501
• Function: The N1 interface is the NAS (Non-Access Stratum) signaling interface between the UE and AMF. It is responsible for critical signaling messages related to registration, authentication, session management, and mobility management.
• Key Messages:
• Registration Request: The UE initiates the registration process with the AMF, providing essential identity and security information.
• Authentication Request/Response: The AMF authenticates the UE to ensure that it is a legitimate subscriber.
• Deregistration Request/Accept: Used for deregistering the UE from the 5G network.
• Service Request: Enables the UE to request specific services from the network, like data access or voice services.

N2 Interface

• Between: Radio Access Network (RAN) and AMF
• 3GPP Specification: 3GPP TS 38.413
• Function: The N2 interface facilitates control plane communication between the RAN and the AMF, allowing for signaling related to mobility and session management. It enables the AMF to control the UE’s connectivity status, handover processes, and network slice selection.
• Key Messages:
• Initial UE Message: Sent from RAN to AMF to notify that a UE has connected to the RAN and requires network services.
• Handover Request: Used during mobility events, enabling handover of active sessions between cells or base stations.
• UE Context Release: Sent when a UE moves out of a particular RAN node's area, prompting release of resources in the current cell.

N3 Interface

• Between: RAN and User Plane Function (UPF)
• 3GPP Specification: 3GPP TS 29.281
• Function: The N3 interface is a user plane interface that carries data packets between the RAN and the UPF. This interface enables data sessions for user traffic, providing the actual data path for user data transmission.
• Key Information:
• GTP-U (GPRS Tunneling Protocol - User Plane): Used for encapsulating user data and forwarding it between the RAN and
• UPF.Data Session Setup: Sets up the data tunnel for each active session, allowing user data to flow from the UE through the network to the data network.

N4 Interface

• Between: Session Management Function (SMF) and UPF
• 3GPP Specification: 3GPP TS 29.244
• Function: The N4 interface is used for control plane communication between the SMF and UPF. It is responsible for the establishment, modification, and deletion of user sessions and bearers, allowing the SMF to manage data paths through the UPF.
• Key Messages:Session Establishment: Establishes a new session with appropriate QoS and traffic policies.
• Session Modification: Adjusts session parameters, such as QoS or traffic handling, in response to network conditions or policy changes.
• Session Deletion: Removes a session and releases the associated resources when a data session ends.

N11 Interface

• Between: AMF and SMF
• 3GPP Specification: 3GPP TS 29.518
• Function: The N11 interface is responsible for session management and mobility management coordination between AMF and SMF. It enables seamless transition of user sessions, especially during handover between cells.
• Key Messages:Session Establishment Request: Initiated by the AMF to request session setup from the SMF.
• Session Modification Request: Allows the AMF to modify session parameters in coordination with SMF.
• Session Release: Sent by AMF to terminate a session managed by the SMF.

N12 Interface

• Between: AMF and AUSF (Authentication Server Function)
• 3GPP Specification: 3GPP TS 29.509
• Function: The N12 interface is used for authentication purposes, allowing the AMF to request authentication vector information from the AUSF for validating user credentials.
• Key Information:
• Authentication Vectors: Provides cryptographic keys and vectors to authenticate the UE.
• Authentication Response: Confirms successful or failed authentication based on user credentials.

Thanks for reading the Article.

icle by Abhijeet Kumar

As the telecommunications industry transitions from 4G LTE to 5G, one of the key enablers of this new technology is the redesigned core network architecture, known as the 5G Core (5GC). 5G introduces new network interfaces, many of which were not present in previous generations, to handle advanced capabilities, such as ultra-low latency, massive IoT support, and enhanced mobile broadband. These interfaces facilitate communication between different network functions within the 5G architecture, ensuring seamless data flow and network resource management. This article explores the primary 5G interfaces, detailing their functions, key messages, and 3GPP specifications.

N1 Interface

• Between: User Equipment (UE) and Access and Mobility Management Function (AMF)
• 3GPP Specification: 3GPP TS 23.501
• Function: The N1 interface is the NAS (Non-Access Stratum) signaling interface between the UE and AMF. It is responsible for critical signaling messages related to registration, authentication, session management, and mobility management.
• Key Messages:
• Registration Request: The UE initiates the registration process with the AMF, providing essential identity and security information.
• Authentication Request/Response: The AMF authenticates the UE to ensure that it is a legitimate subscriber.
• Deregistration Request/Accept: Used for deregistering the UE from the 5G network.
• Service Request: Enables the UE to request specific services from the network, like data access or voice services.

N2 Interface

• Between: Radio Access Network (RAN) and AMF
• 3GPP Specification: 3GPP TS 38.413
• Function: The N2 interface facilitates control plane communication between the RAN and the AMF, allowing for signaling related to mobility and session management. It enables the AMF to control the UE’s connectivity status, handover processes, and network slice selection.
• Key Messages:
• Initial UE Message: Sent from RAN to AMF to notify that a UE has connected to the RAN and requires network services.
• Handover Request: Used during mobility events, enabling handover of active sessions between cells or base stations.
• UE Context Release: Sent when a UE moves out of a particular RAN node's area, prompting release of resources in the current cell.

N3 Interface

• Between: RAN and User Plane Function (UPF)
• 3GPP Specification: 3GPP TS 29.281
• Function: The N3 interface is a user plane interface that carries data packets between the RAN and the UPF. This interface enables data sessions for user traffic, providing the actual data path for user data transmission.
• Key Information:
• GTP-U (GPRS Tunneling Protocol - User Plane): Used for encapsulating user data and forwarding it between the RAN and
• UPF.Data Session Setup: Sets up the data tunnel for each active session, allowing user data to flow from the UE through the network to the data network.

N4 Interface

• Between: Session Management Function (SMF) and UPF
• 3GPP Specification: 3GPP TS 29.244
• Function: The N4 interface is used for control plane communication between the SMF and UPF. It is responsible for the establishment, modification, and deletion of user sessions and bearers, allowing the SMF to manage data paths through the UPF.
• Key Messages:Session Establishment: Establishes a new session with appropriate QoS and traffic policies.
• Session Modification: Adjusts session parameters, such as QoS or traffic handling, in response to network conditions or policy changes.
• Session Deletion: Removes a session and releases the associated resources when a data session ends.

N11 Interface

• Between: AMF and SMF
• 3GPP Specification: 3GPP TS 29.518
• Function: The N11 interface is responsible for session management and mobility management coordination between AMF and SMF. It enables seamless transition of user sessions, especially during handover between cells.
• Key Messages:Session Establishment Request: Initiated by the AMF to request session setup from the SMF.
• Session Modification Request: Allows the AMF to modify session parameters in coordination with SMF.
• Session Release: Sent by AMF to terminate a session managed by the SMF.

N12 Interface

• Between: AMF and AUSF (Authentication Server Function)
• 3GPP Specification: 3GPP TS 29.509
• Function: The N12 interface is used for authentication purposes, allowing the AMF to request authentication vector information from the AUSF for validating user credentials.
• Key Information:
• Authentication Vectors: Provides cryptographic keys and vectors to authenticate the UE.
• Authentication Response: Confirms successful or failed authentication based on user credentials.

Thanks for reading the Article.