Nt (application id: 16777348)

The Nt interface enables communication between the Policy and Charging Rules Function (PCRF) and the Service Capability Exposure Function (SCEF). This interface facilitates the transfer of data transfer policies and is particularly relevant in IoT (Internet of Things) environments where efficient and regulated data communication is essential.

Nt interface workflow:

1. Initiation by SCEF: The SCEF, typically based on a request from an external application or Service Capability Server (SCS), initiates a Background-Data-Transfer-Request (BTR) command to the PCRF. This request includes AVPs (Attribute-Value Pairs) such as Transfer-Request-Type, Application-Service-Provider-Identity, and various data volume parameters.
2. Policy Retrieval by PCRF: Upon receiving the BTR command, the PCRF retrieves existing transfer policies related to the requesting Application Service Provider (ASP) from the Subscriber Profile Repository (SPR).
3. Policy Evaluation and Response: The PCRF evaluates the retrieved policies based on the network's current state, including congestion levels and available resources. It then sends a Background-Data-Transfer-Answer (BTA) command back to the SCEF, containing the selected transfer policies.
4. Policy Notification: If the BTA command includes multiple transfer policies, the SCEF selects the most appropriate one based on its criteria and sends a notification back to the PCRF. The SCEF then begins enforcing the selected policy.
5. Policy Enforcement: The SCEF manages data transfers according to the established policies, ensuring that data from IoT devices is transmitted efficiently and in line with network conditions.
6. Ongoing Policy Management: As network conditions or user requirements change, the PCRF can update the policies and communicate these updates to the SCEF through the Nt interface.

For complete technical specification of Nt interface in Diameter protocol please refer to: [3GPP TS 29.154]