## 2 Related Work  
### Technological Background for V2V and V2I Applications  
Since the proposal of ITS in the decades of the 80's and 90's, these systems offer new ways to address the negative effects of the vehicular congestion problem in urban environments [12]. The work in ITS is based on the effective communication between different elements of the vehicular domain through new technologies. The European Telecommunication Standards Institute (ETSI) has defined an architecture standard for ITS communications (ITSC) [13]. The reference architecture follows the principle of the OSI model [14] defining an extension of the OSI layers to support ITS communication. As Figure 3 shows, three main layers are defined: _Access_, _Networking_ and _Facilities_. In addition the _Applications_, _Management_ and _Security_ layers exist. The general architecture and example elements are shown below. Figure 3: Main components in ITS systems architecture. Three are the functional elements defined for ITSC: gateways, hosts and routers. This elements are present in several ITS subsystems: personal ITS subsystem (Figure 4a), vehicle ITS subsystems (Figure 4b), roadside ITS subsystems (Figure 4c), and central ITS subsystems (Figure 4d). The Internet of Things paradigm emerges as an enabler for ITS applications. IoT is totally based in the fact that objects in the real world can be integrated to traditional communications, serving as active components that are capable of modifying the context in which they locate, according to the needs of new specific services. The cornerstone in the IoT are the sensors and actuators available in the target objects which are incorporated to the communication architectures. Figure 5 shows the relationship between sensor networks and Internet of Things components [15]. Specific cases where sensor/actuators are used in combination with other network elements are Vehicle-to-Infrastructure and Vehicle-to-Vehicle communication. V2V and V2I are two subsets of Vehicular Ad-hoc Networks (VANETs), which are architectures for communication between two or more vehicles and between vehicles and road infrastructure, in which those who are equipped with processing capabilities and wireless communication capabilities can form networks as they move along the roads [16]. In the specification of the architecture for VANETs, some protocols are defined to achieving effective communication between elements in the network. Figure 4: Existing ITS subsystems. (**a**) Personal ITS Subsystem; (**b**) Vehicle ITS subsystem; (**c**) Roadside ITS subsystem; (**d**) Central ITS Subsystem. In [16] is done a review of protocols in physical, MAC, network, transport and application. In the physical layer, Dedicated Short-Range Communication (DSRC) has been lately defined by different standardization entities to establish a short-range communication mechanism in moving vehicles (200 km/h and ranges from 300 to 1000 m). IEEE 802.11 technical committee have defined DSRC as 802.11p Wireless Access in Vehicular Environments (WAVE) [17]. Some researchers have focused in studying the performance of 802.11p in urban traffic environments [18; 19; 20]. On the other hand, 3 GPP standards are used in other communication solutions proposed for V2V and V2I [21; 22]. The comparison between these two technologies shows that the general performance of the communication between nodes where 802.11p is used is better than the performance obtained when the mechanism is based on 3 GPP technologies (LTE for example) [23; 24]. However the main advantage in the use of 3 GPP technologies for vehicular communications relies in (1) the penetration rate in the market of devices that implement this technologies and (2) the existing deployed infrastructure.