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Diameter Session Initiation Protocol (SIP) Application (application id: 6)

The Diameter Session Initiation Protocol (SIP) application designed to support SIP-based IP multimedia services. The primary purpose of this application is to facilitate the authentication, authorization, and accounting (AAA) of SIP sessions, ensuring that only authorized users can initiate or receive SIP-based communications, such as VoIP calls or video conferences. The SIP application in Diameter allows a SIP server to request authentication and authorization information from a Diameter server, which helps in securing the SIP sessions.

In a typical deployment, the Diameter SIP application operates within an environment where the SIP server (e.g., SIP proxy server, registrar, or redirect server) and the Diameter client are co-located on the same node. This setup allows the SIP server to directly interact with the Diameter client to handle SIP requests and responses. The Diameter SIP application enables the SIP server to rely on the AAA infrastructure for validating SIP requests and authorizing the use of SIP services.
One of the key functionalities of the Diameter SIP application is its ability to download or receive updated user profiles and provide rudimentary routing functions, which can help a SIP server in locating another SIP server assigned to a particular user. This is especially important in large-scale SIP deployments where users might need to be routed through different servers based on their location or service requirements.
The Diameter SIP application also provides limited support for accounting services. The Diameter server can provide the addresses of accounting servers to the Diameter client, which is crucial for tracking and billing the usage of SIP services.

Diameter SIP Application interface workflow:

  1. User Registration and SIP Session Initiation:
    • A SIP User Agent (UA) initiates a SIP request (e.g., REGISTER, INVITE) to the SIP server.
    • The SIP server, implementing the Diameter client, sends an authentication and authorization request to the Diameter server using the appropriate Diameter commands (e.g., User-Authorization-Request/Answer [UAR/UAA], Server-Assignment-Request/Answer [SAR/SAA]).
    • The Diameter server processes the request, authenticates the user, and provides the necessary authorization for the SIP session.
  2. SIP Message Exchange:
    • During the SIP session, the SIP server might need to update or retrieve user profiles or route requests to other SIP servers. The Diameter SIP application allows the SIP server to make these requests to the Diameter server, which provides the necessary information or routing functions.
  3. Session Maintenance and Termination:
    • Throughout the SIP session, the Diameter server maintains the session state (if applicable) and ensures that the user remains authenticated and authorized for the duration of the session.
    • Upon session termination, the Diameter SIP application ensures that all related accounting data is properly recorded and forwarded to the appropriate accounting servers.
  4. Subscriber Locator (SL) Functionality:
    • The Diameter Subscriber Locator (SL) serves to locate the Diameter server that holds the user-related data within the AAA architecture. This function is particularly useful in scenarios where the user might be associated with different SIP servers over time.

For complete technical specification of Diameter Mobile IPv4 Application interface in Diameter protocol please refer to: [RFC4740]

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