# 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)  
RSUs provide support to the vehicles circulating on the road and are typically stationed close to it. They act as a bridge between the local vehicular network and the road managers responsible for managing and monitoring the roads. They can disseminate and retransmit important vehicular data and events for improved information dissemination. For the devised architecture, a roadside unit (Figure 2), was developed in partnership between A-to-Be Mobility Technology S.A. and Instituto de Telecomunicacoes, comprised of a Single Board Computer (SBC) connected to a VERA V2X series ITS-G5 board from u-blox [24]. A Global Navigation Satellite System (GNSS) receiver for positioning and time synchronization is included. In addition, an embedded LTE module or optical fiber-based link provides connectivity to the Internet and, by extent, to the cloud infrastructure from which the road manager can manage the RSUs. The road operator interacts with the RSUs either through a Secure Shell Protocol (SSH) connection used for RSU setup, configuration and maintenance, or through an MQTT-based approach specifically for vehicular data exchange, which is detailed in the following subsection. Figure 2: A deployed RSU. It is pictured: the front of the RSU (**top left**) with frontal power switch and USB, Ethernet and HDMI ports; the back of the RSU (**bottom left**) with back power switch, power socket and GSM/LTE, DSRC (ITS-G5) and GNSS antenna connectors; and the housing of the RSU adjacent to a motorway (**right**). A multilayered Open Systems Interconnection (OSI)-like architecture characterizes the current software implementation of the ITS-G5 RSUs. Five vertical services and two parallel services compose the architecture. Each layer is associated with a running service (C program) where Interprocess Communications (IPC) are established through the ZeroMQ networking library. Figure 3 represents the implemented ETSI ITS-G5 protocol stack. * The Access service, is responsible for managing the access technologies and encapsulating and decapsulating the packets' Ethernet protocol headers, namely the Media Access Control (MAC) [25], and Logical Link Control (LLC) [26; 27] headers. This service serves as the bridge between the physical layer and the rest of the upper stack, handling the transmission and receiving of packets;
* The Networking service, which mainly implements the GeoNetworking (GN) [28] protocol, is a geographical addressing and packet forwarding system for point-to-point and point-to-multipoint communications. This service also implements the IPv6 protocol [29], and the GN/IPv6 adaptation sublayer (GNoASL) [30] to combine IPv6 and GN routing features. GeoNetworking and IPv6 packet header encapsulation procedures are handled here;
* The Transport service, which implements the Basic Transport Protocol (BTP) [31], a transport layer protocol similar to User Datagram Protocol (UDP) [32], and the Transmission Control Protocol (TCP) protocol [33]. BTP provides port numbers to address upper-layer sub-services and is similar to UDP in that it does not provide a reliable connection between devices like TCP. The Transport service is responsible for processing the BTP and TCP headers. * The Facilities service supports various ETSI ITS standard-defined sub-services. The current implementation provides support for the processing of beacon-like CAMs [34] through the Cooperative Awareness (CA) subservice, event-focused DENMs [35] through the Decentralized Environmental Notification (DEN) subservice, IVIMs [36] through the V2I oriented Infrastructure to Vehicle (IVI) subservice, radar-based CPMs [37] through the Collective Perception (CP) subservice, and non-safety Services  
Figure 3: Implemented ETSI ITS-G5 protocol stack. Announcement Essential Messages (SAEMs) [38] through the Services Announcement (SA) subservice;
* The Security service aims to provide and verify the authenticity in the vehicular network and manage the trust among ITS-Ss.