VCS Infrastructures and Components

Components in VCS can be classified into three parts, namely the mobile com- munication devices, VCS infrastructures and the VCS authorities. The mobile communication devices are the bottom of the network structure. VCS infrastruc- tures are the basic framework of the VCS. The role of the network manager is played by the VCS authorities which are located on the top of the architecture.

The mobile communication devices refer to the wireless communication mod- ule that has the basic capability of receiving, processing, relaying and transmitting VCS messages, the device is known as the On-Board Unit (OBU). Extra functions are added into OBU in order to satisfy the requirements of ITS applications. The applications contain from traffic management to commercial use cases. Naviga- tion function is an important scenario for traffic management, OBU needs to have satellite signal reception module to receive the satellite broadcast signal, also the electronic maps are necessary to support navigation service. In fact, OBU is al- ready equipped with some vehicles such as GPS modules in vehicle electronic system. Another traffic management use case is the traffic report, OBU collects

the nearby safety messages and generate the traffic conditions in front of the ve- hicle based on the information inside the safety messages. Commercial use cases include entertainment services, Internet access and advertisements.

The compulsory VCS infrastructure is the Road Side Unit (RSU), aiming to fulfill the basic access point and relay functions between the VCS backbone net- work and mobile nodes. In the IEEE 802.11p-based protocol stacks (DSRC, C- ITS and ARIB T109), RSUs are supposed to be built along the road at regular intervals to maintain acceptable coverage. In the system using LTE-V protocol stack, the VCS network coverage is supported by the existing LTE base stations. However, these LTE base stations are still called RSU since they responsible to provide ITS access points for vehicles. Assumptions about RSU in some VCS architectures are: RSUs have powerful computation ability to process the VCS messages by themselves, and they have a direct connection to the VCS cloud net- work which is composited by upper layer network managers and other RSUs [2] [30]. For security purposes, Group Keys (GK) are distributed managed by RSUs in VCS networks. Another important function of RSU is to bridge a route between vehicles and upper layer authorities, allowing vehicles finish the registration or certificate update step upon joining or switching VCS regions. Some other publi- cations assume that RSUs equivalent to the network switch in the traditional net- work, that means RSUs only have limited processing ability and heavy processing tasks are accomplished by upper layer computation infrastructures. The authors in paper [31] proposes a new infrastructure called Security Manager (SM). SM is considered as an infrastructure with powerful computation ability which super- vises multiple RSUs. SMs are connected to each other via secure cable to form an SM-cloud network. Upper layer network authorities are linked to the cloud network. The normal safety messages are still processed by RSUs, while the im- portant messages (e.g. Rekeying messages or secret key handover messages) are forwarded to SM by RSUs to be processed under highly secured algorithms.

VCS authorities are the top layer infrastructures to manage the running of VCS, two aspects are concerned: VCS self-management and application man- agement. VCS self-management involves the identity of communication nodes within VCS, cryptographical materials of vehicles and communication perfor-

mance of VCS. The identity and cryptographical materials are mainly managed by the Public Key Infrastructure (PKI), the parent module of Certificate Authority (CA) and Anonymity Server (AS). Generally speaking, PKI is normally man- aged by governmental organisations which are in charge of the entire ITS and VCS, such as the Department of Transport of each country. Some approach com- bines PKI and CA as a single infrastructure called Central Manager (CM) [31]. The major security functions provided by PKI based on the cooperation with CA and AS. These two infrastructures cooperate with each other to provide security and privacy. The responsibility of CA is to generate certificates which provide the authorised link between private/public key pairs and vehicle node identifier [9]. To protect user privacy, AS generates pseudonyms (this includes pseudonym identities and pseudonym key pairs) and pseudonym mapping which builds link among real identities, pseudonyms and pseudonym certificates. AS also involves the identity-hiding between VCS and third-party applications. Identity-related in- formation sets (e.g. IP address, location information, MAC address and identity) are removed from the messages before forwards messages to the third-party appli- cation service providers [32]. Communication performance of VCS is monitored and controlled by central monitor systems, such as Supervisory Control and Data Acquisition (SCADA), which is maintained and operated by the network service provider.

Application management schedules application messages between the third- party application server and VCS. The job is finished by the third-party applica- tion servers [32]. The third-party application servers are places outside the VCS and under the management of the third-party service provider. Message traffic is controlled by the service provider but not the VCS. VCS is only responsible to hide the privacy-related information which is delivered by AS.