SWd (application id: –)

The SWd interface is an essential reference point within the 3GPP architecture, specifically designed to facilitate communication between the 3GPP AAA Proxy and the 3GPP AAA Server. It operates based on the Diameter protocol, which ensures secure and efficient authentication, authorization, and accounting (AAA) processes within mobile networks.
The primary function of the SWd interface is to transport AAA-related signaling messages between the AAA Proxy and AAA Server. These messages are crucial for maintaining the security, integrity, and proper management of user sessions across the network. The SWd interface plays a vital role in handling multiple operational aspects, including user authentication, session authorization, charging information, and key management for encryption and integrity protection.

Functional Capabilities

• Authentication Signaling: The SWd interface carries data necessary for the authentication of users. This data exchange between the AAA Proxy and AAA Server ensures that users are properly authenticated before they can access network services.
• Authorization Signaling: In addition to authentication, the SWd interface is responsible for carrying authorization information. This data determines whether a user has the appropriate permissions to access specific network resources or services.
• Charging Information: The SWd interface transmits charging data per user, which is essential for accurate billing and accounting purposes within the network.
• Key Management: The interface facilitates the transfer of keying data required for radio interface integrity protection and encryption, securing communications across the network.
• Tunnel Establishment and Data Encryption: For scenarios involving the ePDG (evolved Packet Data Gateway) in the Visited Public Land Mobile Network (VPLMN), the SWd interface carries the necessary authentication and keying data to establish secure tunnels, authenticate data, and ensure encryption.
• User Identifier Mapping: The SWd interface is responsible for mapping user identifiers to tunnel identifiers, which is crucial for session management within the network.
• Session Purging: The interface supports the purging of user sessions from the network when immediate service termination is required.
• Operator Network Identification: The SWd interface allows for the identification of operator networks involved in roaming scenarios, ensuring that users are correctly connected to the appropriate network during roaming.
• Quality of Service (QoS) Management: The interface carries data related to AN QoS capabilities and policies, ensuring that the appropriate QoS mechanisms are applied during authentication requests.
• IP Mobility Capabilities: The SWd interface also carries information related to IP Mobility Capabilities between the AAA Proxy and AAA Server, enabling seamless session continuity across different IP networks.

SWd interface workflow:

1. Session Initialization: When a user initiates a session, the 3GPP AAA Proxy interacts with the 3GPP AAA Server over the SWd interface to authenticate and authorize the user. This involves the exchange of authentication and authorization requests and responses.
2. Key Management: During session establishment, the SWd interface facilitates the exchange of keying materials necessary for securing the session. This includes keys for encryption and integrity protection at the radio interface level.
3. Session Maintenance: Throughout the session, the SWd interface supports ongoing communication between the AAA Proxy and AAA Server, ensuring that the session remains authenticated, authorized, and secure.
4. Charging and Accounting: The interface continuously transmits charging-related data to ensure accurate billing based on the user’s network usage.
5. Session Termination: Upon session completion or termination, the SWd interface transmits any final accounting data and facilitates the purging of the user's session from the network, ensuring that network resources are properly released.

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