Information Technology Reference
In-Depth Information
Opportunistic dissemination . The idea of opportunistic diffusion is that the
messages are stored in each intermediate node and forwarded to every encountered
node till the destination is reached. Therefore, the delivery ratio is improved.
However, this kind of mechanism is not suitable for applications which are not
delay tolerant.
Geographical dissemination . Due to the fact that end-to-end paths are not con-
stantly present in a VSN, a geographic dissemination is used by sending the mes-
sage to the closest node toward the destination till it reaches it.
Peer-to-peer dissemination . In a P2P solution, the source node stores the data in
its storage device and does not send it in the network till another node asks for it.
This solution is used and proposed for delay tolerant applications.
Cluster-based dissemination . For a better delivery ratio and to avoid or reduce
broadcast storms, a message has to be relayed by a minimum of intermediate nodes
to the destination. In order to do so, nodes are organized in clusters in which one
node (a clusterhead) gathers data in its cluster and sends it after to the next cluster.
The advantage of the cluster-based solutions is the lower propagation delay and
high delivery ratio with bandwidth equity also. Avoiding the broadcast storm prob-
lem can be achieved by using a distributed clustering algorithm to create a virtual
backbone that allows only some nodes to broadcast messages. An example of this
approach is given in [ 27 ].
This section elaborated on some of the most relevant VSNs' basic mechanisms.
These mechanisms provide the cornerstones of the VSNs' operation and manage-
ment and clearly distinguish the VSNs as an intriguing networking paradigm. The
following section will give a greater insight into the VSNs' protocol stack details
and the layering architecture VSNs usually obey.
10.4
VSNs Layering Architecture
The layering architecture that most VSNs employ is shown in Fig. 10.4 . The archi-
tecture differs according to the type of the deployed application, i.e., whether it is
a safety or a non-safety one. Safety applications require a reliable transport proto-
col, suitable for real-time operation, and use the specifically tailored vehicular
network layer, while the non-safety applications use the standard TCP/IP model.
Finally, same physical and data link layers are used for both safety and non-safety
applications. These two layers are based on different DSRC (Dedicated Short
Range Communication) standards [ 13, 28 ].
The DSRC standards are the fundamental part of the V2V communication and,
as such, a vital part of VSNs as well. In VANETs, the DSRC standards include the
physical layer, the data link layer and the application layer where the first two serve
as the foundation for VSNs. Similar standards have been standardized in Europe,
USA, and Japan by different standardizing bodies as shown in Table 10.1 .
Despite the number of different standards, IEEE 802.11p is slowly becoming the de
facto DSRC standard worldwide being the most advanced and most suitable of all other
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