# Advancing C-V2X for Level 5 Autonomous Driving from the Perspective of 3 GPP Standards
## 4 4G and NSA-Based 5G V2X Services
### System Support
#### 4.1.3 Application Layer Support
For information flows, the entities and actors perform various operations. We list some of the important procedures i.e., UE registration, location tracking, message delivery, file distribution, network monitoring, switching modes of operations, service delivery, resource management, QoS monitoring, etc. To avail the full use of these operations, the specification _(TS 23.286 Rel-16)_ provides details over VAE layer Application Programming Interfaces (APIs) focusing on server APIs. The V2X application layer architecture, discussed above, assisted in addressing the utilization and deployment of services through the VAE functional model. Since these services were produced in _Rel-16_ of the specification (_TS 23.286_), there exists a need for enhancing the architecture for future releases. In this regard, the technical document (_TR 23.764_) in _Rel-17_ reported and identified the enhancements to application layer support for V2X services. Moreover, the report includes key issues (16), solutions (18), architectural requirements, and an analysis of V2X standards. Some of the important key issues are eV2X application QoS requirements for V2X communication over PC5 and Uu, V2X control and message distribution over Uu, UE-to-UE application layer relay, and V2X UE measurement reporting to the VAE server. Whereas some key issues only highlight the demand for various supports, i.e., network slicing, teleoperated driving, communication modes, switching modes for communication types, service providers, and dynamic information for high-definition (HD) maps. Some of the important requirements i.e., reliability, data rate, transmission rate, maximum latency, communication range, etc., can be found in the detailed descriptions of these key issues. Apart from the requirements listed for key issues, the 3 GPP reported architectural requirements for V2X message distribution, eV2X QoS monitoring & control by the application layer, and coordination based on EPS and 5 GS connectivity in _(TR 23.764 Rel-16)_ for addressing the key issues. In addition, the important solutions for key issues are NR-PC5 QoS monitoring and control, monitoring and control of QoS for eV2X communications, UE-to-UE broadcast configuration and delivery by VAE layer, UE-initiated session-oriented service establishment support, communication configuration for switching modes, etc. The discussed enhancements report also provides an analysis of the impactful functions of the V2X application layer and declares two internal reference points (interfaces), i.e., V1 and V5 as out of scope of technical specification (_TS 23.287 Rel-16_), which is discussed in Section 5. It goes without saying that these key issues and their corresponding solutions hold importance in addressing future challenges related to V2X services. Hopefully, the research community working with V2X services and applications will witness huge support in enhancing and advancing the V2X application layer architecture in the announced future release i.e., _Rel-18_.