Application Layer ID

Description

The Application Layer ID is a newly introduced identifier in 3GPP Release 19, defined in the context of Aerial Vehicle-to-Everything (A2X) services. It identifies an entity, such as an Unmanned Aerial Vehicle (UAV) or a UAV Controller (UAV-C), within the scope of a specific A2X application. This identifier is used for Direct C2 (Command and Control) Communication and for Direct Detect And Avoid (DAA) procedures. The Application Layer ID is an application-level identifier, meaning it is not tied to the 3GPP network layer (e.g., IP address or IMSI). Its format is outside the scope of 3GPP, allowing application providers to define their own naming schemes. The 3GPP specifications (TS 23.256 and TS 23.287) define how this identifier is used within the 3GPP system, particularly for establishing and managing direct communication links between UAVs and UAV-Cs.

In the A2X architecture, the Application Layer ID enables direct communication between UAVs and UAV-Cs without relying on network infrastructure. This is particularly important for beyond-visual-line-of-sight (BVLOS) operations, where reliable command and control links are critical. The Application Layer ID is used to authenticate and authorize entities for direct communication. When a UAV or UAV-C wants to establish a direct C2 link, it uses the Application Layer ID to identify itself and the peer. The 3GPP network, specifically the 5G system, assists in the discovery and establishment of these direct links by mapping the Application Layer ID to network-level identifiers (e.g., a PC5 link identifier). The Application Layer ID is also used for Direct Detect And Avoid, where UAVs exchange position and trajectory information to avoid collisions. This identifier ensures that the DAA messages are correctly attributed to the sending entity.

The Application Layer ID is provisioned to the UAV and UAV-C by the A2X application provider. It is typically a string or a numeric value that is unique within the A2X application's namespace. The 3GPP network does not interpret the content of the Application Layer ID; it only uses it as an opaque identifier for routing and authorization. The network may store a mapping between the Application Layer ID and the 3GPP subscription identifier (e.g., GPSI) to enable policy enforcement and charging. The Application Layer ID is used in various procedures, including direct communication establishment, link maintenance, and release. It is also used in the A2X service authorization procedure, where the network verifies that the UAV/UAV-C is authorized to use the A2X service and to communicate with specific peers.

In terms of architecture, the Application Layer ID is used by the UAV, UAV-C, and the A2X application server. The 5G system provides the underlying connectivity, which can be direct (PC5) or indirect (Uu). For direct communication, the Application Layer ID is used in the PC5 signaling to identify the endpoints. The 3GPP network functions, such as the PCF and UDM, may store the Application Layer ID as part of the subscription data to enforce policies. The Application Layer ID is also used in the A2X service authorization and revocation procedures. The identifier is crucial for ensuring that only authorized entities can participate in direct C2 and DAA, enhancing safety and security in UAV operations.

The introduction of the Application Layer ID in Release 19 reflects the growing importance of UAVs and the need for standardized support in 3GPP networks. It enables seamless integration of UAV operations with cellular networks, allowing for beyond-line-of-sight control and autonomous flight. The Application Layer ID is a key enabler for advanced A2X use cases, such as cooperative collision avoidance, formation flying, and remote identification. As UAVs become more prevalent, the Application Layer ID will play a vital role in ensuring safe and efficient airspace management.

Purpose & Motivation

The Application Layer ID was created to address the need for a standardized way to identify entities in A2X applications, particularly for direct communication and detect-and-avoid procedures. Before its introduction, A2X applications relied on proprietary identifiers, which hindered interoperability and network integration. The Application Layer ID provides a common identifier that can be used across different UAVs and UAV-Cs, regardless of the manufacturer or application provider. It enables the 3GPP network to assist in establishing direct links and enforcing policies without needing to understand the application-specific semantics. This identifier is essential for safety-critical operations, such as collision avoidance, where unambiguous identification of the communicating parties is paramount. The Application Layer ID also facilitates regulatory compliance, as authorities can require UAVs to broadcast their identity for remote identification. By defining this identifier in Release 19, 3GPP ensures that A2X services can leverage the advanced capabilities of 5G networks, including low-latency and high-reliability communication, while maintaining flexibility for application providers to define their own identifier formats.