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These mobility models are only a fraction of the possible VSN applicable ones.
Being a vibrant research area, the quest for more realistic VSN mobility model
continues.
10.3.3
Routing in VSNs
As it has been previously discussed, VSNs are ad hoc networks in a vehicular envi-
ronment used for transmission of “sensed” data. Therefore, routing, which is a
major issue in ad hoc networking in general, is also a serious challenge in VSNs as
well. Many routing protocols and strategies for ad hoc networks have been pro-
posed in recent years, including those specific for VANETs and VSNs. These
protocols can be used for sensor data with the additional aspects on QoS due to the
nature of applications that are mostly associated with VSNs.
In general, VSN routing techniques can be broadly distinguished into two main
classes:
•
Topology based
[
24
]
•
Geo-position based
[
25
]
The first step in topology-based routing is recognizing the topology of the network.
Then, distance vector and link state algorithms can be used for the maintenance of
the routing tables in each node. Additionally, topology-based routing protocols may
be divided into
proactive
and
reactive
ones. Proactive topology-based routing
protocols periodically distribute their routing tables throughout the network so that
the changes in the topology can be updated continuously, while reactive ones are
event driven and routes are discovered only when they are needed. Proactive rout-
ing produces smaller delays for propagating the data through the network due to the
already established routes. However, it uses large amounts of data for routing table
maintenance and reacts slowly on topology restructurings or failures. Good exam-
ple for proactive topology-based routing is FSR (Fisheye State Routing). On the
other hand, reactive topology-based routing uses less data for routing table mainte-
nance, which makes it more suitable for highly dynamic topologies such as the
VSNs' type of scenarios. But, this type of routing can lead to higher latency and
network congestions since it floods the network during route discovery. Reactive
topology-based routing is represented by AODV (Ad-hoc On demand Distance
Vector) and DSR (Dynamic Source Routing). Considering all the pros and cons of
both topology-based routing protocols, it is evident that they do not meet all the
demands that the VSNs may impose.
Geo-position-based routing is a better choice in a vehicular environment accord-
ing to a number of studies. This routing technique is based on sending the informa-
tion to physical locations instead of logical addresses. Each node possesses a
unique identifier, which contains information of the geographical position of the
node. The geographical location can be obtained either by GPS or specific distance
sensors. GPS devices are expensive and impractical to use, which leads to the idea
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