T6a (application id: 16777346)

The T6a interface is a critical reference point in the 3GPP architecture that connects the Mobility Management Entity (MME) or Serving GPRS Support Node (SGSN) with the Service Capability Exposure Function (SCEF). This interface is designed to facilitate communications between network elements, particularly for supporting Machine-Type Communication (MTC) and Internet of Things (IoT) services. 

The T6a interface serves several key functions within the 3GPP system, particularly in the context of IoT and MTC services:

• Monitoring Event Reporting: The T6a interface allows the MME/SGSN to report various monitoring events to the SCEF. These events can include changes in the UE’s connectivity status, reachability, location, communication failures, and idle status indications.
• Configuration of Monitoring Events: The SCEF uses the T6a interface to configure specific monitoring events within the MME/SGSN. This configuration can include setting up events that are not directly related to user equipment in non-roaming scenarios.
• Connection Management: The T6a interface supports the management of connections between the MME/SGSN and the SCEF, ensuring continuous communication and data exchange between these network elements.
• Data Exchange: The T6a interface is used to transfer Mobile Terminated (MT) data and receive Mobile Originated (MO) data, enabling effective communication between the MME/SGSN and the SCEF.

T6a interface workflow:

1. Event Configuration: The SCEF initiates the process by sending a command to the MME/SGSN to configure specific monitoring events. These configurations are crucial for tracking and reporting on various network conditions and user equipment statuses.
2. Monitoring and Reporting: Once the monitoring events are configured, the MME/SGSN actively monitors the network and user equipment based on the defined events. If a specific event occurs, such as the loss of connectivity or a change in location, the MME/SGSN reports this information to the SCEF via the T6a interface.
3. Data Transfer: In addition to event reporting, the T6a interface facilitates the transfer of MT data from the SCEF to the MME/SGSN. Conversely, MO data can be sent from the MME/SGSN to the SCEF, ensuring a bidirectional flow of data critical for IoT and MTC operations.
4. Connection Management: Throughout the communication process, the T6a interface manages the connection between the MME/SGSN and the SCEF. This management includes handling the setup, maintenance, and termination of connections as necessary to support ongoing data exchange and event reporting.
5. Filtering and Forwarding: The SCEF may also apply filtering to the received monitoring event reports and forward only the relevant information to other network components or external applications, as required by the service or operational context.

For complete technical specification of T6a interface in Diameter protocol please refer to: [3GPP TS 29.128]