# Survey on Routing Protocols for Vehicular Ad Hoc Networks Based on Multimetrics
## 2 VANET Characteristics  
In VANETs, vehicles equipped with data wireless devices act as mobile hosts and routers for other nodes. Even though VANETs share characteristics with classical mobile ad hoc networks, such as a short transmission range, self-organization and self-management, and low bandwidth, vehicular ad hoc networks have special characteristics that distinguish them from other types of mobile ad hoc networks as follows [7; 22]:  
* Ability to provide continuous power: the node (vehicle) itself can, via a long-life battery, provide continuous power for computing and communication devices compared to the capabilities of typical MANET nodes.
* High computational capability: operating vehicles can use significantly higher computing, communication, and sensing capabilities compared to other mobile nodes (such as smartphones).
* Predictable mobility: vehicles have more predictable movements than typical MANET nodes. Vehicles only move over roads. Roadway information is available from positioning systems and map-based technologies. The future position of a vehicle could be estimated as a function of speed and road trajectory. The hour of the day or the specific day of the week is also a determinant parameter to predict vehicle mobility.
* Large scale: vehicular networks could cover an entire road network including many participants. Its coverage area can range from a neighborhood to an entire city. In highways, a VANET can easily reach tens of kilometers.  
* High mobility: the topology created by vehicles in a VANET is extremely dynamic and includes different configurations. For instance, topology information of a vehicle that leaves an avenue to go to a residential area can dramatically change. In this regard, the density of nodes plays a very important role. If the density of vehicles is very high, as in, during rush hour, topology changes can be minimal. On the other hand, very low vehicle density, such as during week nights, leads to more changes in topology due to high mobility.
* Partitioned network: vehicular networks are frequently partitioned because of the nature of traffic. In residential and rural areas, there are intervehicle gaps because these are sparsely populated scenarios. This forms several isolated clusters of nodes.
* Various communication environments: very related to the mobility and partition ratio of VANETs are the communications environments in which they are typically operated. These scenarios can be, most of the time, highways or urban areas; the former are relatively simple and straightforward, while cities include more signal perturbations because of different types of obstacles, such as buildings, houses, and trees.
* Interaction with on-board sensors: Currently, vehicles are equipped with a good number of on-board sensors that provide information on the vehicle that can be used to make routing decisions (speed, direction) or to monitor surroundings (temperature, wind, humidity, etc.).  
All these characteristics should be taken into account when designing a routing protocol or application dedicated to a vehicular network.