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making the network
scalability
another challenging problem. It is usually met by
using mesh networking (in high traffic density situations) and long ranged
transmissions (in low-density situations). In addition to scalability,
routing,
and
maintaining
end-to-end connectivity
are additional requirements of a functional
VSN, the latter being especially important for sparsely populated VSNs where
vehicles form isolated clusters as a result of the dynamic network topology.
Possible solutions include the use of specific roadside gateways used for proper
data propagation and message relay boxes for storing messages [
2
]. Since the
VSNs' main applications are safety applications,
reliability
and
promptness
are
crucial to the feasibility of these applications. This is a serious challenge that
needs to be resolved for every specific application. Last but not least, the inclu-
sion of
Quality-of-Service
(
QoS
) in VSNs is challenging, considering the high
mobility of the VSN nodes.
The importance and the rising popularity of VSNs lead to numerous interna-
tional research projects lately. The main interests of the majority of VSNs-related
projects lie in the design of a cooperative vehicular environment enabling a
plethora of cooperative services for its participants and design of efficient
addressing schemes. For example, the CVIS project [
3
] aims to create a unified
technical solution for cooperative VSNs that addresses issues such as user accep-
tance, data privacy and security, system openness and interoperability, risk and
liability, public policy needs, business models etc. The SafeSpot project [
4
]
targets an integration among vehicle-isolated, telematic, technologies into a
single cooperative solution that enables development of reliable and extended
driving support systems for road safety. Both projects also focus on dynamic
creation of road maps, a feature that may be extensively used for intelligent trans-
portation applications. The Mobile Millenium project [
5
] focuses on the reliabil-
ity aspect of VSNs and exploits a centralized packet delivery solution for
supporting safety-critical applications. The GeoNet project [
6
] implements and
formally tests a networking mechanism as a stand-alone software module for
cooperative systems. It relies on geographical addressing scheme that enables a
multi-hop communication among vehicles and the infrastructure. This project
fills the implementation gap among many finished and ongoing VSNs-related
projects. Its prominent work inspired the latest spatiotemporal addressing [
7
], a
natural extension of the geographical addressing.
This chapter elaborates the general aspects and the system implementation
issues of VSNs. It provides a VSN classification framework, briefly discusses the
basic mechanisms deployed in VSNs, introduces a layering architecture for
VSNs, discusses the practical implementation of sensors in vehicular environ-
ments, introduces the RFID technology as an evolutionary step in VSNs' design
and classifies and elaborates on the most popular applications of VSNs today.
The chapter's aim is to serve as an introductory text in the field, tackling the
specifics of the vehicular environment that distinguishes the VSNs within the
wireless sensor networking paradigm in general. More details on this vibrant
research area and the relevant entities that drive the VSNs' related research can
be found in [
8, 9
].
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