# A Roadside and Cloud-Based Vehicular Communications Framework for the Provision of C-ITS Services
## 3 Roadside and Cloud Architecture
### Roadside Architecture
#### 3.1.1 Roadside Unit (RSU)
It is responsible for creating signatures and verifying them carried on the packet's GeoNetworking Secured Header and triggering identity change across layers for privacy purposes. The identity change is a process where services simultaneously change identifiable information, such as GeoNetworking address, a certificate in use, and station ID. The goal is to increase user privacy through rotational pseudonymity, making the tracking of the vehicle by onlookers more difficult. * The Management service provides several kinds of information for the remainder of the protocol stack. It provides the ITS-S with time and position, and record packets sent back and forth between layers for applicational purposes. It can also simulate both time and position depending on how it is configured; for example, in OBU mode, the ITS-S can simulate its position to follow a specified route;
* The Applications service is a standard agnostic implementation supporting specific applications and ITS-S interactions. Employed applications include forwarding ITS messages from the ITS-G5 environment to the cloud system, vice-versa, and a heartbeat system, both implemented using an MQTT approach. In the IPC implemented among the services, Service Data Units (SDUs) are exchanged through ZeroMQ. The format of these SDUs follows defined structures using the Abstract Syntax Notation One (ASN.1) description language, which aims at providing future service interoperability and ease of code development. Exchanged SDUs are encoded following the Octet Encoding Rules (OER). By using ZeroMQ, the protocol stack can run and easily switch between different distributed modes. For example, each service can run on a different machine over ZeroMQ's TCP. This can prove to be helpful as the ITS-S can outsource to a higher performing machine any service except the Access service, e.g., outsource the Facilities service where radar data for CPM generation may need to be processed constantly, or outsource the Security service to a more central and secure server for key and credential storage. However, one must consider the additional latency associated with this scheme, as interprocess communications are typically faster than communications over a network. Broadcasted messages are signed and verified at the Networking layer using requests to the Security service, which specializes in key and certificate management. Security is implemented as defined per the standards ETSI TS 103 097 [39], and ETSI TS 102 941 [40], where the former is based on the IEEE WAVE 1609.2 security standard [41]. Signatures are based on the Elliptic Curve Digital Signature Algorithm (ECDSA) and are either 256-bit or 384-bit. These signatures are created using private keys, whose corresponding public keys are included in temporary certificates known as Authorization Tickets (ATs) that are shared between the ITS-Ss. Tickets are issued by an Authorization Authority, which is included in the Portuguese C-ITS PKI and, by extension, included in the European C-ITS PKI. An RSU can also be equipped with traffic radars and cameras, which can significantly increase its perception. Some radars can discretely identify road objects (vehicles, VRUs) and classify them according to their volume, lessening the computational load on the RSU by feeding it this already processed information. Data from these types of sensors can be processed locally by the RSU and then disseminated in the form of CPMs, which contain information about the sensed objects' dimensions, position, and speed. Disseminated CPMs provide valuable information to connected vehicles about legacy vehicles and other road users without V2X capability. Moreover, CPMs containing information about connected vehicles are also valuable to other connected vehicles, as factors such as range limitations, environmental obstacles, or packet loss issues can reduce perception among them (mainly provided through CAM dissemination). Connected vehicles with these sensors can also share their collected data through CPMs.