**2. Challenges of vehicular networks**

In comparison to other communication networks, vehicular communication networks come with some unique attractive features: unlimited transmission power, predictable mobility and plethora of potential applications. However, vehicular networks have to cope with some important challenges that include: 1) extreme heterogeneity, 2) rapidly changing topology subject to frequent fragmentations and congestion, 3) the stringent application requirements on real-time and robust message delivery, 4) security of the information and users. In this section of the chapter we analyse some of these challenges that the vehicular networks face.

Emerging Technologies for Urban Traffic Management 63

Mobility is to be considered especially as the path becomes sparser. Regarding operability heterogeneous protocols are also to be considered. For instance in pocket switch network the capabilities and behaviour of the sensors vary largely. Two standards are described in

 **Dedicated Short Range Communication (DSRC)** short to medium range service for vehicle-to-vehicle and –roadside communications. It provides high data transfers and

 **Wireless Access in Vehicular Environments (WAVE)** a universal standard as the DSRC effort of the ASTM E2213 working group migrated to the IEEE 802.11 standard group. It works at the media access control and physical layers and enables

In (Ma et al., 2009) some additional evaluations procedures are presented as alternatives for

Covering the whole requirements for vehicular networks and their applications is imperative for carrying out in an efficient and effective way their functions. As new advances in hardware and software communication technology emerge, new applications

Vehicular software applications may be categorized into four groups (Popescu-Zeletin et al.,

 *Safety* related to the different kinds of collisions that most frequently occur between vehicles and other objects such as animals, trees, and pedestrians. This kind of real-time proactive application usually is vehicle-to-vehicle. They use beacon messages, a singlehop position based or fast-bidirectional communication regime, their latency cannot be

higher than 100ms, whereas the packet delivery ratio cannot be lower than 99%. *Assistance* provides features such as repair notifications, remote diagnostics, context information, navigation facts, and alerts. This type of time-to-live provider application usually is vehicle-to-backoffice or vehicle-to-roadside. They use normal messages, bidirectional communications; their latency cannot be higher than 400ms, whereas the

 *Resource* captures domain issues such as traffic bottlenecks and fuel consumption amongst other, including environmental issues. This type of time-to-live traffic application usually is vehicle-to-backoffice or vehicle-to-roadside. They may use beacons or alerts, a multihop position based communication regime, and their latency cannot be higher than

 *Infotainment* also known as in-car comfort entertainment, usually do not use intervehicular communications. This kind of time-to-live ad-hoc application usually takes place in-car or vehicle-to-roadside. They use alerts, a multi-hop position based communication regime, and their latency cannot be higher than 400ms, whereas the

400ms, whereas the packet delivery ratio cannot be lower than 95%.

turn (Zeadally et al., 2010; Spyropoulos et al., 2010):

analyzing vehicular traffic.

2010):

**2.2 Application requirements for VANET** 

**2.2.1 Classification of applications for VANET** 

packet delivery ratio cannot be lower than 95%.

packet delivery ratio cannot be lower than 95%.

low communication latency in small communication zones.

are enabled in different contexts including vehicular networks.

communications even for vehicles coming from opposite directions.

### **2.1 Extreme heterogeneity**

VANETs are an important component of any Intelligent Transportation System (ITS) and a promising environment to support a number of safety, driving and entertainment applications. However, to support such applications important heterogeneity challenges need to be overcome:


#### **2.1.1 Standards**

VANETs standards are important for applications as they guarantee interconnectivity and interoperability. Connectivity is an important characteristic of wireless networks. In the Internet model paths between two nodes are always there. In VANETs is not the case.

<sup>1</sup> http://www.telargo.com/overview/technology/on\_boardequipment/obu.aspx

<sup>2</sup> http://www.kapsch.net/cl/en/ktc/portfolio/products\_components/Pages/on-board\_units.aspx

<sup>3</sup> http://www.efkon.com/en/products-solutions/ITS/gnss-onboard-unit.php

VANETs are an important component of any Intelligent Transportation System (ITS) and a promising environment to support a number of safety, driving and entertainment applications. However, to support such applications important heterogeneity challenges

 *Wireless technologies.* Existing network technologies are different in terms of geographical coverage, data transfer rate, transmission range and supported content types. Thus, a vehicle using one network technology may not be able to communicate with a vehicle using a different technology. Even tough most on-board devices utilize the 802.11p standard; VANET applications would require to interact with nodes or networks utilizing a different technology. For example, a VANET application may require interacting with a wireless sensor network dedicated to manage traffic lights using the Zigbee technology or to gather data from on-board sensors or devices using

 *Routing protocols.* Recently, many VANET routing protocols have been proposed (Li & Wang, 2007), these protocols have important differences in the mechanims they utilize as many of them target at different VANET environments. For example, some of them consider highly populated environments whereas others are optimized to operate in sparse networks. These differences mean that additional mechanisms are necessary to enable interoperability among heterogeneous routing protocols. The research community has already identified this problem and possible solutions have been

 *Sensors*. In future VANET scenarios different on-board and roadside sensor will be available. On-board sensors will be utilized to capture different vehicle, driver or surrounding parameters whereas roadside sensors will help gather road conditions affecting driving safety (e.g. big holes, thick ice, malfunctioning cars). All this information is important not only for driver in the vehicle but also for neighbouring drivers. However, sensors accuracy, measurement units, among others may vary from one manufacturer or model to another. Thus it is necessary to further investigate

 *On-Board Units (OBU).* Some manufacturers have started to release to the market different on-Board units. Telargo1, Kapsch2 and Efcon3 are examples of such manufacturers. These units offer different capabilities (e.g. positioning, communication, I/O features, sensors) and use different software platforms. This heterogeneity is a clear concern for developers as developing an application that can be deployed on different

VANETs standards are important for applications as they guarantee interconnectivity and interoperability. Connectivity is an important characteristic of wireless networks. In the Internet model paths between two nodes are always there. In VANETs is not the case.

2 http://www.kapsch.net/cl/en/ktc/portfolio/products\_components/Pages/on-board\_units.aspx

mechanisms that allow to correctly exchanging sensed data.

on-Board-units may be too difficult or in some cases not possible.

1 http://www.telargo.com/overview/technology/on\_boardequipment/obu.aspx

3 http://www.efkon.com/en/products-solutions/ITS/gnss-onboard-unit.php

**2.1 Extreme heterogeneity** 

need to be overcome:

Bluetooth.

**2.1.1 Standards** 

investigated (Nundloll et al., 2009).

Mobility is to be considered especially as the path becomes sparser. Regarding operability heterogeneous protocols are also to be considered. For instance in pocket switch network the capabilities and behaviour of the sensors vary largely. Two standards are described in turn (Zeadally et al., 2010; Spyropoulos et al., 2010):


In (Ma et al., 2009) some additional evaluations procedures are presented as alternatives for analyzing vehicular traffic.
