A variety of applications is provided by the VANETs

A
variety of applications is provided by the VANETs (Bali et al., 2009).   There can be three major sections for these
applications: commercial, non-safety, and safety applications.  The main objective of the Vehicle Safety
Communication Consortium (VSCC) is the safety applications. An effective and new class of
communication applications is enabled by the DSRC.  The safety of the road is improved by these
applications. 

Traffic information distribution is a unique problem in
VANET.  In most of the applications in
VANET and safety applications in particular, there are no specific destination
for the exchanged messages.  In fact, the
Region of Interest (RoI) for these messages is all of the surrounding vehicles
and these vehicles are the targeted destinations.  In other words, the public interest is the
aim of these applications and instead of a particular individual; a group of
users are the beneficiaries of them.  As
a result, instead of using a unicast routing scheme to distribute the traffic
information, the application of a broadcasting scheme is more appropriate.  However, the blind broadcasting of the
packets can initiate and cause conflict in the transmissions that take place
between the neighboring vehicles.  This
is a problem that has been referred to as the broadcast storm problem (Williams
and Camp, 2002).  During the rush hour traffic, it is more likely for VANETs
to be formed a highly dense network in urban areas or freeways.

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Until now, the focus of the most of the broadcasting
research in VANET has been on the analyzing the protocols in order to deal with
the problem of the broadcast storm in a network with high density under an over
simplified assumption, a typical VANET is a connected network in nature (Tonguz
et al., 2007).  However frequent network fragmentation is expected to be
experienced by the VANETs during the late night hours or in the rural freeways
of sparsely populated areas. In addition to research carried out on
dense networks, there is an increasing demand for investigation on the
fragmentation problem in sparse VANETs, in which the nodes are positioned
sparsely, and in these conditions, generally there cannot be found paths from
source to destinations (Rodrigues et al., 2011).  Various routing protocols have been proposed
specifically to solve the routing problem within the fragmented networks, for
example store carry forward (Sahin and Chindapol, 2007), Mobyspace (Santa et
al., 2009), Spray and Wait (Huang et al., 2011).