Gugrajah_Yuvaan_ Ramesh_2003.pdf

Routing Protocols for Ad Hoc Networks
Chapter 2
speed in the network was increased DSR uses shortest hop routes, while ABR uses
routes that are more likely to last longer. DBF performs poorly because more event­
triggered updates are generated when mobility increases. The delay results showed
that ABR performed better in this regard as well. This can be attributed to the fact
that beaconing provides a method of faster convergence when finding suitable routes.
It is admitted [Gerla99] that power consumption is a problem with ABR, especially
since nodes use portable power supplies. Another possible problem is the
interception of beacons by unintended receivers, such as the enemy in a battlefield
scenario, which would reveal a nodes location.
2.2.3.2. SSR
Signal Stability Based Adaptive Routing [Dube97] is another on-demand routing
protocol that selects routes based on network stability metrics. In SSR a route is
selected based on the signal strength between nodes and a node's location stability.
Periodic beacons are broadcast which allow neighbouring nodes to determine signal
quality, which ·is recorded as either "weak" or "strong" in a Signal Stability Table
(SST). A route search process is initiated if a valid route is not contained in the
Routing Table (RT). Route requests are broadcast throughout the network but are
only forwarded to the next hop if they are received over strong channels and have not
been processed before. Once the destination receives a route request it ignores later
copies that have taken different routes because it is assumed that the first route
request arriving has arrived over the shortest path with the least congestion. The
destination then replies using the same route along which the first route request
arrived because it is assumed to be the route with the best signal quality. Route
requests are dropped if the channel was recorded as weak. If the source does not
receive a route reply within a specified timeout period, the source specifies in the
header of the next route request that weaker links may be used since they may be the
only links available.
Erase messages are sent by the source node once it is informed of failed links by an
intermediate node along a route. The erase message is sent to notify all nodes of the
broken link. The source then reinitiates a route-search process.
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