3UNIVERSIDAD TCNICA PARTICULAR DE LOJA. Barros, Ramrez, Sanmartn. PRM1.

I. Networking features VANET

The nodes of a VANET network have a characteristic mobility which is influenced by aspects such as achieved route, maintenance a topology, reconstruction of roads, etc. One can say that in every moment you have a totally different network with other features in which coexist mobile elements (vehicles that move through the highways, roads, etc.). And static elements (antennas provide connectivity to these vehicles). Considering the above, this type of networks should have the following characteristics:

Dynamic Topologies: The VANET networks are constituted by mobile nodes, causing which the network topology change continuously, building and destroying links between nodes.Network Connectivity: The degree of connectivity to network, depends heavily on the range of wireless connections and the number of participating vehicles, namely not all vehicles on the road; could be equipped with wireless interfaces of communication (OBUs).Limited bandwidth: The available bandwidth in a wireless infrastructure is lower than in a wired infrastructure additionally is underutilized due to attenuation and interference of electromagnetic signals. However, users will want to have the same applications available on a wired medium.Unlimited Power: The drawbacks of power in mobile devices not constitute a major limitation for vehicular networks, since the node itself (vehicle); can provide continuous power to the computer and communication devices.Greater capacity computational: Indeed, vehicular networks often require providing greater detection capabilities, communication and computing, so vehicles and stations should have very good computer equipment.

Predictable Mobility: Usually vehicles tend to have movements easy prediction, since they are limited by the design of the roads. With GPS technology, it is possible to know the exact position of the vehicle, with this information and knowing also the trajectory and speed of movement thereof, can predict its future position.

Scale potentially large: The vehicular networks extend over the entire road network, thereby increasing the size of the network; this would involve the participation of a large number of nodes, which require high power levels to expand their range of coverage and maintain the communications.

High Mobility: Vehicular networks operate on a highly dynamic environment. The topology of the network tends to change of form randomly and rapidly at all times, preventing the establishment of network connectivity, which must be maintained stable for which communication services can operate smoothly. In this case the routing protocol should be changed or adjusted. Vehicles on the road traveling at very high speeds (relatively 100 km/h on motorways and 60 km/h in the city) which leads to predict that the period of inter-vehicular communication can be short.The increases of speed occur when the traffic density is low and when it increases (especially in peak hours), the speed decreases accordingly.Network Partition: Due to the dynamic nature of traffic, the vehicular networks frequently are partitioned. For example, in scenarios of low population density (rural areas), traffic can become so scarce and therefore be several clusters of isolated nodes.Autonomy: Each terminal is an autonomous node with capacity of to process and route the information from other nodes in the same network.

Control Distributed of Network: The control is done at each node, since there is no infrastructure to do.

Routing: It is necessary that each node by separately and all together provide a dynamic routing mechanism. The classical protocols of routing are not applicable to this type of networks because they are not prepared for the changes of topology that present the VANETs. Currently, they are developing routing algorithms to address this problem.Given these characteristics also have to take into account some factors when implementing a protocol for VANET infrastructure with in order to obtain high yields of the network and try to mitigate the possible adverse obstacles that can be found in such architectures. Among these factors have:

Security: This type of networks used the wireless medium of transport, which means that anyone can have access. Should be maintained the confidentiality of information for that are not received by third parties not involved. The impersonation of nodes and DoS (Denial of Service) are some of the simplest attacks that can suffer the environment in which this architecture moves.Position the streets: In a population, existing streets delimit the paths which can carry the vehicles. This restriction of mobility implies the relevance of factors such as the spatial distribution of the nodes and network connectivity. This spatial distribution of the nodes can lead to scenarios where exist roads with one or more lanes, with one direction or two directions, to nodes in parallel streets, etc.

Size of population sectors: The urban areas are made up of a cluster of buildings, houses, parks of different sizes and other heterogeneous elements that make up the different urban areas: towns, cities, etc. The size of these areas will help to determine the traffic density that may occur in a given time.

Mechanisms traffic control: Road signs intended to control traffic in an urban area, located at the intersections, cause intermittent stops on vehicles. And traffic density, the formation of jams, decreases their mobility and directly affects the rate of changes in the network topology.

II. ArchitectureWireless networks are not based on a fixed infrastructure of information broadcast. The VANET networks follow the same principle established that the infrastructure ad-hoc being able to define three main types of architectures for the broadcast of messages. These architectures are: architecture with infrastructure, Architecture without infrastructure, and finally hybrid architecture between the two previous.

Architecture with infrastructure: Also known by the name of centralized networks, where there is an access point (base station), which provides communication between the different vehicles in the network. The central node has a coverage range in which vehicles can move freely, provided you do not get out of this node, because all communications pass through this access point.

Architecture without infrastructure: Also known as the distributed network. This architecture consists of vehicles that can be interconnected arbitrarily, without the existence of any fixed element in the network topology and can take many forms. In such networks, communication between two vehicles can be carried out through other intermediate vehicles that play the role of routers (routers) and perform the forwarding of message since the origin node of communication to the destination node, it can even be involved in the discovery and maintenance of new routes.Hybrid Architecture: Combines the functionality of the architectures described above. Therefore vehicle can establish communication directly with a base station, or can perform the same communication through a neighbor vehicle that allows it to reach the same base station, playing the role router.

The Architecture VANET of reference given by the Car-to-Car Communication Consortium (C2C-CC) which is shown in the figure below; distinguishes three domains of communication in vehicular networks: Vehicle Domain, Domain Ad-Hoc, and Domain in Infrastructure .

Reference Architecture for Vehicular Networks C2C-CCDomain Vehicle: It has to do with a local network in each vehicle, evidently composed of two types of units as:

On-Board Unit (OBU): An OBU is a device in the vehicle, which has capabilities of wireless or wired communication.

Board unit (OBU)AU: A device that is running one or multiple applications; while using the communication capabilities of the OBU. The AU can be laptops, PDAs, smartphones, connecting dynamically to OBU.

Application unit (AU)Domain Ad-Hoc: It is a communication of vehicle to vehicle (V2V) unsupported of network of infrastructure. Here the network is composed of vehicles equipped with OBUs and RSUs that are set along the road to improve road safety; by running special applications or sending, receiving and relaying data to vehicle units.

Vehicle to vehicle communication (V2V).Domain Infrastructure: as the name implies; is the vehicular communication, with support of network infrastructure. Access to it can be through the RSUs and public, commercial or private Hotspots; or also taking advantage of the communication capabilities of cellular networks and radio technologies (GSM, GPRS, UMTS, and WIMAX) integrated as part of the equipment OBU of the vehicle units, if the RSUs and Hotspots terminals are insufficient.

Vehicle communication.

III. Conclusions and RecommendationsREFERENCES[1] Marcelo R. Mazzaro, Tesis de Post-Grado Modelizacin de canal RF para las frecuencias de 850 y 1900 MHz. Instituto Tecnolgico de Buenos Aires. 2005.

[2] Alberto Escudero Pascual, Tutorial Radio Mobile Inicindose con el Radio Mobile. En lnea. Disponible en: www.wilac.net/tricalcar[3] Antenas VHF de altas. En lnea. Disponible en: prestaciones:www.msmcomunicaciones.com/index.htm.[4] Radio Mobile. Materiales de apoyo para entrenadores en redes inalmbricas. En lnea. Disponible en: http://www.eslared.org.ve/walcs/walc2011/material/track1/08-Radio_Mobile-es-v1.2-notes.pdf.