# 5G V2X System-Level Architecture of 5 GCAR Project
## 4 Detailed Analysis of Selected Features
### V2X Service Negotiation  
The feature of adapting the behaviour of a service according to network capabilities has been studied from different angles, but with the main focus on rate adaptation. The first approach has focused on adapting transmission rate on an end-to-end basis as for instance considered in [18; 19], where both the sender and receiver perform some kind of measurement and the receiver transmit feedback to the sender to adapt the end-to-end data rate. Rate adaptation with network support has been also considered by 3 GPP in [20], which defines progressive download and dynamic adaptive streaming over HTTP (3 GP-DASH) for continuous media delivery. Within 3 GP-DASH, server and network-assisted DASH (SAND) introduces messages between DASH clients and DASH-aware network element (DANE) or between various network elements for the purpose to improve the efficiency of streaming sessions by providing information about real-time operational characteristics of networks, servers, proxies, caches as well as DASH client's performance and status. The above-listed approaches, although enabling network-application interaction, only focus on a reduced set of adaptation capabilities (i.e., rate) that might be too limited for V2X use cases. Furthermore, such approaches do not consider the availability of additional information regarding the service at the network as they only focus on the network providing information for rate adaptation. The aspect of interaction between the application and the network has been enhanced by 5 GCAR as follows. The V2X service negotiation represents a network procedure introduced within 5 GCAR with the scope to enhance the network awareness about service requirements, which is usually referred to QoS only. Examples of such additional requirements are spatial/time information associated with the service (i.e., the location where the service is expected to run and for how long), information about receiver (i.e., vehicle) status, such as its location, speed, intended trajectory, etc. This set of information enhances network knowledge about the service and can be then exploited by the network to optimize service delivery. In a similar way, the service might also benefit from additional network information, e.g., network capability in fulfilling QoS in a certain area/time or in transferring a message within a certain deadline. As an example, the service can select the most appropriate vehicle driving status (e.g., speed, route, and level of automation) thanks to its increased network awareness. In summary, the benefits introduced by the V2X service negotiation are in terms of: (i) Supporting a more dynamic network-service negotiation with additional information exchanged compared to current QoS-based negotiation procedures; (ii) increasing network awareness on V2X service features which can be used e.g., to optimize the service delivery; (iii) increasing service awareness on network capabilities, e.g., network capabilities on delivering a certain service; and (iv) facilitating the introduction of V2X-specific network features, e.g., the V2X service negotiation gathers and provides service-specific information to other network functions. An example of an interaction between a V2X service and the V2X service negotiation is depicted in Figure 6. Considering a 5G system, the V2X service can be an AF interacting with a 5G core network, while the V2X Service negotiation can be an enhanced network functionality of e.g., a NEF or of a PCF. From Figure 6, the V2X service provides the network with the V2X service descriptor, which contains the following information:  
* Application information, which could be e.g.,: \(\odot\) Application type (video, voice, remote control, etc.). \(\odot\) QoS, which might the desired QoS by the application (e.g., a certain 3 GPP QoS Profile) or a request by the service towards the network receiving information about the QoS the network is expected to support in a certain location. Message size, for file-transfer services such as HD map acquisition, software updates, etc.