E4 (application id: 16777231)

The E4 interface is a component within the Resource and Admission Control Subsystem (RACS) architecture, used to facilitate the exchange of IP-connectivity session data between the Network Attachment Subsystem (NASS) and RACS. This exchange ensures efficient resource allocation and admission control for IP-based services.

E4 interafce workflow

1. Session Initiation:
   • The UE initiates a session and connects to the network through the Access Node.
   • The Access Node communicates with the NASS over the Ra interface to authenticate the user and allocate an IP address.
2. Session Data Exchange:
   • After authentication and IP address allocation, the NASS sends session data to the A-RACF via the e4 interface.
   • This data includes details such as the user’s IP address, identity, and QoS requirements.
3. Resource and Admission Control:
   • The A-RACF processes the session data received via the e4 interface to make resource and admission control decisions based on available network resources and the QoS requirements of the session.
   • The A-RACF then communicates with the RCEF at the IP Edge over the Re interface to enforce these decisions.
4. Policy Enforcement:
   • The RCEF enforces resource control policies as directed by the A-RACF.
   • For additional policy decisions, the A-RACF interacts with the SPDF, which communicates with the Application Function (AF) over the Gq interface.
5. Session Management:
   • Throughout the session, the e4 interface ensures ongoing communication between the NASS and A-RACF, managing any changes in session parameters.

For complete technical specification of E4 interface in Diameter protocol please refer to: [ETSI ES 283 034]