Gugrajah_Yuvaan_ Ramesh_2003.pdf

Routing Protocols for Ad Hoc Networks
2.2.4.3. Comparison of LAR and DREAM
Chapter 2
[Camp02] presents a simulation comparison of DSR, LAR, DREAM and a pure
flooding algorithm. With zero average node speed the data packet delivery ratio of
the DSR and LAR protocols is 100 % while that of DREAM and flooding is
approximately 68% since there is much congestion in the network with the flooding
algorithm and DREAM. When average speed is increased, LAR performs better than
DSR. This is because LAR's use of location information to find a new route is more
efficient than DSR's route discovery method. The promiscuous mode of DSR was
found to significantly aid nodes in finding routes. DREAM had the highest average
end-to-end delay of all protocols simulated. This is because the DREAM recovery
procedure is used approximately 40 % of the time at low mobility and almost all the
time at high speeds since the ACK is not received within the timeout. [Camp02]
concluded that the added location capability of DREAM did not provide benefits
over simple flooding algorithms. The location information used in the LAR protocols
however was found to be significantly more beneficial than using the route request
procedure of DSR. The LAR protocols were found to be considerably more efficient
than DREAM in terms of packet delivery ratio and throughput.
2.2.5. Routing with a Backbone
Sivakumar et al [Siva98] describe a self organizing network structure ,called a spine
which functions as a virtual backbone to facilitate routing in ad hoc networks. The
spine is chosen to be a small and relatively stable sub-network of the ad hoc network
whose primary role is to compute and maintain routes as opposed to carrying data
packets. Every node in the network is either in the spine or is a neighbour of a node
in the spine. The spine nodes maintain local copies of the global topology of the
network and .collectively compute routes between any pair of nodes in the network.
They are thus able to minimize the access overhead for routing information. Besides
computing routes and tracking topology changes, the spine nodes also provide
temporary backup routes for fault tolerance. The spine of an ad hoc network is
depicted in Figure 2-6.
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