S6b (application id: 16777272)

The S6b interface is a key component in the architecture of the Diameter protocol, specifically designed to facilitate communication between the 3GPP AAA Server and the Packet Data Network Gateway (PDN-GW) within the Evolved Packet Core (EPC) of a mobile network. The primary purpose of the S6b interface is to support the authentication, authorization, and mobility management of User Equipment (UE) accessing the network via non-3GPP access technologies such as Wi-Fi.

The S6b plays a vital role in the following areas:

• Authentication and Authorization: The S6b interface ensures that the UE is properly authenticated and authorized when it attempts to attach to the EPC. This is critical for maintaining the security of the network and ensuring that only authorized users can access network resources.
• Authentication typically involves the use of the Extensible Authentication Protocol (EAP), specifically EAP-AKA (Authentication and Key Agreement) over the IKEv2 protocol, which is common in scenarios involving Proxy Mobile IPv6 (PMIPv6).
• Mobility Management: The interface supports the dynamic management of mobility-related parameters. When a UE moves between different non-3GPP access points or networks, the S6b interface is used to update the PDN-GW with the UE’s current location, IP address, and other session-related information.
• Quality of Service (QoS) Management: The S6b interface allows for the provisioning, modification, and removal of QoS rules. This ensures that the network can dynamically allocate resources based on the current requirements of the UE, maintaining a high quality of service for ongoing sessions.
• Accounting: The interface supports accounting functionalities, enabling the accurate recording and reporting of data usage for billing purposes. This is critical for service providers to manage and monetize the data services they offer.

S6b interface workflow:

1. UE Attachment:
   • When a UE connects to the EPC via a non-3GPP access network (e.g., using the S2a or S2b reference point), it initiates a connection request. This request is forwarded by the PDN-GW to the 3GPP AAA Server over the S6b interface for authentication and authorization.
2. Authentication and Authorization:
   • The 3GPP AAA Server authenticates the UE using protocols such as EAP-AKA over IKEv2. Once the UE is successfully authenticated, the AAA Server authorizes the session, allowing the UE to access network resources.
3. Session Management:
   • Upon successful authentication, the PDN-GW updates its session information to reflect the UE’s current status, IP address, and other relevant data. The S6b interface facilitates this information exchange, ensuring that the PDN-GW has the latest data to manage the UE’s session effectively.
4. Mobility Handling:
   • As the UE moves between different access points or networks, the S6b interface is used to update the PDN-GW with new location and session parameters. This ensures that the UE can maintain an ongoing session without interruption, even as it changes its point of attachment to the network.
5. QoS and Resource Management:
   • Throughout the session, the S6b interface is used to dynamically adjust QoS parameters based on the UE’s needs and network conditions. This allows the network to provide the best possible service to the UE while managing overall network resources efficiently.
6. Accounting and Reporting:
   • The S6b interface ensures that all relevant data usage is accurately recorded and reported to the service provider’s billing systems. This is essential for accurate billing and for providing users with detailed information about their data usage.
7. Session Termination:
   • When the UE disconnects or the session is otherwise terminated, the S6b interface is used to properly close the session, releasing any resources that were allocated to the UE.

For complete technical specification of S6b interface in Diameter protocol please refer to: [3GPP TS 29.273]