Gugrajah_Yuvaan_ Ramesh_2003.pdf

Routing Protocolsfor Ad Hoc Networks Chapter 2
transmitted back to the source along the best route selected. Each node along the
route that receives the REPLY marks their routes as valid.
RRC consists of a localized search for a valid route when a link along the chosen
route fails. If the source node moves, a broadcast query and reply (BQ-REPLY)
cycle is reinitiated. If the destination node moves the predecessor on the route
attempts a localized query (LQ). The LQ determines whether the destination is still
reachable via a minimum number of hops. The hop count is incremented if the
destination is still not found and the process backtracks to the next upstream
neighbour, who again initiates a LQ. If the destination is reached the destination
transmits a REPLY to the source using the new partial route and the remainder of the
original route. If the destination node is not reached, the process continues
backtracking upstream until it reaches the node that was originally halfway along the
route. This node then informs the source of the error and the source reinitiates a BQ­
REPLY cycle. The movement of intermediate nodes invokes the same backtracking
process.
A route delete (RD) is propagated by a full broadcast when the source node no longer
requires a route that has been discovered. A direct unicast is not used because the
source may not be aware of any changes that have been made during RRC.
Although the route selected is not necessarily the shortest, it will tend to be longer
lived resulting in fewer RRCs. Also, since only the selected route is marked as valid,
ABR is free of packet duplicates being transmitted through the network. However,
periodic beaconing is a potential problem and may result in additional power
consumption. In [Gerla99], ABR is compared to the Distributed Bellman-Ford
(DBF) algorithm and DSR. Both ABR and DSR had significantly lower control
message overhead (up to 76.56% less control message overhead) than DBF, which is
a proactive protocol. It was found that when the node speed was low, ABR had more
control message overhead than DSR because of the beaconing but as speed was
increased, ABR became more efficient due to ABR's local route recovery feature.
DSR propagates the route error message all the way back to the source. It was also
found that ABR has higher throughput than DSR because when the average node
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