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Selecting an appropriate backup route can be done by considering two points; the
primary and the backup routes must have the minimum common nodes, the backup
route should have a low probability of having nodes that may leave the radio range of
their previous hop node. Experimental results in [ 13 ] showed that by using LARWB,
the number of nodes which participate in routing operation, the average number of
exchanged messages in route discovery process and also the average time of route
discovery are reduced considerably.
Multipath Location Aided Routing (MLAR) [ 14 ] is a multipath routing version of
LAR that works efficiently in both 2-Dimensional (2D) and 3-Dimensional (3D)
networks. By multipath they meant caching of alternate paths to be used on failure of
the primary path and not the use of multiple simultaneous paths which can lead to
out-of-order packet delivery problems. They cached the two most recently received
routes even if they are longer. They believe that the most recently received path (even
if it is longer) is the path most likely to succeed since mobility is more likely to break
an older path. However, a routing protocol with longer average hop counts may have
lower packet delivery rate. This is because the probability of a packet being dropped
is higher when packets traverse longer paths than shorter paths. If the second path also
failed a new route request cycle is initiated. Since the packet header contains the
entire source route, all paths are checked easily as being loop-free at each node that
stores routes.
In order to be able to compare MLAR to other existing protocols, the authors have
extended ns-2 to support 3D mobility models and routing protocols. The simulation
results demonstrated the performance benefits of their multipath position-based
algorithm over a multipath non-position-based algorithm, Ad Hoc On-demand
Multipath Distance Vector routing (AOMDV) [ 27 ], as well as with both their single
path versions (LAR and AODV) in both 2D and 3D. Only AOMDV consistently
performs better than MLAR in terms of overall packet delivery, but does so at the
cost of more frequent flooding of control packets and thus uses significantly more
bandwidth. Hence, MLAR has lower bandwidth and energy usage than non-position-
based algorithms and is more scalable and efficient. Moreover, MLAR performs
consistently better than LAR in terms of packet delivery ratio by as much as 30% in
some cases.
The two main strategies used to combine nodes location and hierarchical network
structures are the zone-based routing and the dominating set routing [ 24 ]. In GRID
algorithm [ 15 ] the dominating set concept is applied. A set is dominating if all the
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