Vehicular Sensor Networks: General Aspects and Implementation Issues - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 210

of acquiring the location of nodes through appropriate sensors. An intermediate
node in geo-positional routing only needs to be aware of its own location and the
geographical location of its one-hop neighbors, while the source node additionally
needs to be aware of the destinations' geographic location.
Three main strategies in geo-positional routing can be distinguished, i.e.,
flooding , single path, and multipath [ 26 ]. When a flooding strategy is used, the
network is being flooded starting from the source to its one-hop neighbors. When
using a multipath strategy, multiple paths from source to destination are used in
order to forward the information. When using a single-path strategy, a single path
from the source to the destination is being established. The single-path strategy
can be implemented in two ways, i.e., greedy forwarding and face forwarding .
Greedy forwarding sends the information to the next nearest one-hop neighbor of
the previous node or the next nearest one-hop neighbor in the direction to the
destination node ( compass forwarding ). The face forwarding strategy recognizes
the topology and by measuring the angles of the nearest one-hop neighbors,
compared to the direction of the destination, sends the information through the
interior of the network.
The advantages of geo-positional routing, compared to topology-based routing,
are in the no route set up and route maintenance need, which leads to a reduction
in latency. On the other hand, position-based routing requires complex data dis-
semination and harvesting mechanisms for successful management of position
information so that communicating nodes can learn their respective locations.

10.3.4 Basic Dissemination Mechanisms in VSNs

Data dissemination in VSNs refers to a way of distributing the data collected from
the vehicles' sensors among the vehicles and to the RSUs. It resides on top of the
routing mechanisms and uses them to enable efficient transportation of data to the
intended recipients while satisfying certain requirements such as delay, reliability,
etc. These requirements vary depending upon the data being disseminated (safety
or user applications).
Data dissemination in VSNs is a complex subject that is linked to the MAC and
routing issues and brings additional possibilities such as the use of the infrastruc-
ture support and the possibility of aggregating the data. Different approaches of
data dissemination in VSNs are found in the literature. Each of them has its own
advantages and disadvantages. Depending on the architecture of the VSN (whether
it is a V2I/I2V or V2V communication), four basic ways of data dissemination are
known. For V2I/I2V, there are the push-based and pull-based mechanisms, whereas
for V2V, there are the flooding and relaying (next hop) mechanisms.
The idea of push-based dissemination is useful for distributing so called popular
data like traffic alerts, weather alerts, etc. The vehicle that wants to disseminate sensed
data pushes it out to everyone. As there is no cross traffic, this approach is characterized
with low contention. However, the drawback is that everyone might not be interested