Gugrajah_Yuvaan_ Ramesh_2003.pdf

Routing Protocols for Ad Hoc Networks
Chapter 2
from the node's route cache and all routes containing the hop are truncated at that
point.
DSR has proposed modifications for optimisation such as a "promiscuous mode", in
which a node listens to route requests, route replies and route errors not intended for
itself and updates its route cache correspondingly. Another DSR feature is the
expanding ring search procedure, in which the route request packets are first sent
with a limited hop count, which can be increased if the destination is not found
within the hop count limit.
2.2.2.2. }\()D"
}\d Hoc ()n-Demand Distance 'lector (}\()D") routing [Perkins99] incorporates the
destination sequence number technique of DSD" into an on-demand protocol while
minimizing the number of required broadcasts by creating routes on a demand basis.
Each node keeps a next-hop routing table containing the destinations to which it
currently has a" route. )\ route expires if it is not used or reactivated for a threshold
amount of time. Like DSR, }\()D" initiates a route discovery process by
broadcasting a route request (RREQ) to neighbours when a route is required. The
neighbours forward the RREQ to their neighbours until the destination receives the
RREQ or an intermediate node with a valid route receives the RREQ. Destination
sequence numbers are utilized to ensure all routes are loop free and contain the most
recent route information. RREQs contain the source's own sequence number and
unique RREQ broadcast identification number together with the latest known
sequence number for the destination. )\ RREQ is therefore uniquely identified. Ifthe
same RREQ is received again, the node discards it. An intermediate node can only
reply to the route request if the intermediate node's recorded sequence number for
the destination is greater than or equal to that contained in the RREQ. Figure 2-2
demonstrates the route discovery procedure consisting of the RREQ and route reply
(RREP) phases.
While the RREQ is being forwarded through the network, each IN records in its
routing table the address of the neighbour from which the RREQ was first received
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