Gugrajah_Yuvaan_ Ramesh_2003.pdf

Routing Protocols for Ad Hoc Networks Chapter 2
communicate between zones. ZRP uses knowledge of routing zone connectivity to
guide its global route discovery. Rather than blindly broadcasting route queries from
a node to all its neighbours, ZRP employs a service called bordercasting, which
directs the route request from a node to its peripheral nodes. Peripheral nodes that
have been covered'by the route query and that belong to the routing zone of a node
that has already bordercast the query ignore the bordercast thus preventing further
unnecessary bordercasts. This encourages the query to propagate outward, away
from its source.
Multiple hop paths within the routing zone can bypass link failures. Similarly, sub
optimal route segments can be identified and traffic can be re-routed along shorter
paths. The difficulty in implementing ZRP is determining the optimum zone radius.
The zone radius affects the overhead traffic since if IARP is used more frequently
then the negative effects of proactive protocols are experienced, while if IERP is
used more frequently then the negative effects of reactive protocols need to be
endured. The general rule of thumb [Haas99] is that a sparse network favours a large
routing zone while a dense network favours a small routing zone. Figure 2-8
illustrates the ZRP zone routing radius optimisation.
o
o
c=::> Zone A
@
o A
• o
o
@ Peripheral node of zone A
o o
o
o 00 0
o 0
00
o
Figure 2-7, Concept of a zone in ZRP. (zone radius = 2 hops)
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