SWx (application id: 16777265)

The SWx interface is a critical component in the Diameter protocol, defined between the 3GPP AAA Server and the Home Subscriber Server (HSS). It is primarily used for transporting authentication, subscription, and PDN (Packet Data Network) connection-related data, playing a vital role in scenarios where users access the network through non-3GPP IP-based networks, such as Wi-Fi or other trusted and untrusted IP access networks.

Functionality

• User Authentication and Authorization: The SWx interface is utilized by the 3GPP AAA Server to authenticate and authorize User Equipment (UE) when accessing the network via non-3GPP IP access points. The interface ensures that the UE is properly authenticated, and its access to network resources is authorized based on the user’s subscription profile stored in the HSS.
• Mobility Management: The SWx interface supports the transfer of mobility-related parameters, particularly when Network-Based Mobility (NBM) is employed. It updates the HSS with the PDN Gateway (PDN-GW) address information, which is necessary for establishing and maintaining connectivity to the Evolved Packet Core (EPC).
• Location Management: The SWx interface is responsible for updating the HSS with the current AAA Server address each time a UE connects to a non-3GPP access network. This ensures that the HSS has the most recent information, enabling accurate routing of user sessions and services.
• Additionally, it handles the retrieval of charging-related information and subscriber profiles from the HSS, which is essential for service provisioning and billing.
• De-registration and Session Management: When a UE disconnects from the network or moves between different access points, the SWx interface manages the de-registration process. It ensures that any session-related data is purged from the HSS, preventing stale or outdated information from affecting future network operations.

SWx interface workflow:

1. Initial Authentication and Authorization: When a UE connects to the network via a non-3GPP access point, the 3GPP AAA Server sends an authentication request to the HSS over the SWx interface. The HSS responds with the necessary authentication vectors and subscription data. The 3GPP AAA Server uses this information to authenticate and authorize the UE’s access to the network.
2. Mobility Management: As the UE moves between different access points, the SWx interface is used to update the HSS with the new AAA Server address and PDN-GW information. This ensures that ongoing sessions are maintained seamlessly, and the UE remains connected to the correct network resources.
3. Location Management: The SWx interface registers the current AAA Server address with the HSS whenever the UE connects to a new access point. This registration process ensures that the HSS can accurately route user data and manage services effectively.
4. The SWx interface also facilitates the retrieval of the UE’s profile and charging information from the HSS, enabling precise billing and service management.
5. Session Termination and De-registration: Upon session termination or when the UE disconnects, the SWx interface is used to de-register the UE from the HSS, ensuring that all session data is cleared. This step is crucial for maintaining network efficiency and preventing resource conflicts.

For complete technical specification of SWx interface in Diameter protocol please refer to: [3GPP TS 29.273], [3GPP TS 23.402]