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Request zone
Expected zone
D
S
Fig. 4.7 Example of request and expected zones in scheme 1 of LAR
based on the available position information (e.g., from a route that was established
earlier) [ 6, 23 ]. A request zone is defined as the set of nodes that should forward the
route discovery packet. The request zone typically includes the expected zone. Two
request zone schemes have been proposed in [ 12 ]. The first scheme is a rectangular
geographic region. In this case, nodes will forward the route discovery packet only if
they are within that specific region. This type of request zone is shown in Fig. 4.7 .
In LAR scheme 2, the source or an intermediate node will forward the message to all
nodes that are closer to the destination than itself. Thus, the node that receives the route
request message will check if it is closer to the destination than the previous hop and it
will retransmit the route request message; otherwise, it will drop the message [ 11, 12 ].
In order to find the shortest path in the network level, instead of selecting a
single node as the next hop, several nodes are selected for managing the route
request message and each of them will put its IP address in the header of the request
packet. Therefore, the route through which the route request message is passed will
be saved in the header of the message [ 13 ]; message size grows as it goes far from
the source and the routing overhead will be increased. In LAR, if the discovered
route breaks for any reason, route discovery process is started again.
4.3.7
LARWB
Routes in LAR are often broken due to mobility [ 14 ]. New routes must be rediscov-
ered to continue routing of packets in the queue. This problem was solved by
Location-Aided Routing With Backup (LARWB) [ 13 ] since another route is selected
as a backup route which is used when a breakage appears in the primary route.
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