Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf
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Routing Protocolsfor Ad Hoc Networks<br />
Chapter 2<br />
protocols (AODV and DSR) were superior to the proactive protocol (DSDV) in all<br />
event scenarios simulated because of the failure of DSDV to convergence when<br />
mobility was introduced.<br />
2.2.3. Routing Based on Network Stability<br />
Associativity Based Routing (ABR) [Toh96], [Toh99] and Signal Stability Based<br />
Adaptive Routing (SSR) [Dube97] are two reactive protocols that have unique<br />
metrics for determining which route is optimal based on notions of network stability.<br />
2.2.3.1. ABR<br />
ABR is an on-demand routing protocol that uses a unique metric known as the<br />
"degree of association stability". Each node maintains an associativity table that<br />
contains "ticks" for every other node in the network. The nodes periodically generate<br />
beacons which when received by a neighbouring node causes the neighbouring node<br />
to update its associativity table with respect to the beaconing node by incrementing<br />
the number of ticks associated with the beaconing node. A node is considered more<br />
stable if there are many ticks associated with it. Nodes are therefore more likely to<br />
use routes through neighbours that have displayed a high degree of association<br />
stability. A low degree of association stability indicates a high state of node mobility<br />
while a high degree of association stability indicates a low state of node mobility.<br />
The associativity ticks for a neighbouring node are reset when the neighbouring node<br />
moves out of proximity. The objective of ABR is to utilise stable routes.<br />
ABR consists of three phases: route discovery, route reconstruction (RRC) and route<br />
maintenance. When a node requires a route to a destination, a broadcast query (BQ)<br />
is broadcast to its neighbours. When a node receives a BQ, it appends to the BQ its<br />
ticks associated with the neighbour it has just received the BQ from, together with its<br />
address and current load information. In this way, each BQ arriving at the destination<br />
will contain associativity ticks of the nodes along the route to the destination on<br />
which the BQ has travelled. The destination then selects the best route by examining<br />
each of the BQs. When multiple paths have the same degree of association stability,<br />
the route with the minimum number of hops is selected. A REPLY is then<br />
2-14
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