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Fig. 4.5 Angle-based forwarding to circumvent voids in ARP
voids. The intermediate node B has no neighbors closer to the destination D than
itself. In such a situation B selects a next hop that is making minimum angle toward
destination, i.e., node C. After selecting a next hop node, the intermediate node
appends its ID to the packet header. For each data packet, ARP header memorizes
a maximum of k last visited hops in order to avoid selecting a next-hop whose ID
presents in the ARP header. This memorization technique helps ARP in avoiding
local loops, but does not guarantee its loop freedom. It is clear that assigning k to
a small value will decrease the percentage of local loops avoided. On the other
hand, assigning it to a large value will enlarge the size of the packet which in turn
will increase the packet overhead.
The simulations in [ 1 ] showed that ARP is scalable, achieves high packet delivery
rate while incurring low overhead compared to GPSR. Emitting hello packets on
need-basis reduces the problems associated with beaconing. Also, using the angle-
based forwarding to circumvent voids increases the probability of finding a path
(not necessarily the optimal one) in sparse networks.
Most position-based routing protocols use forwarding strategies based on distance,
progress, or direction. Improved progress Position Based BeaconLess Routing
algorithm (I-PBBLR) [ 4 ] combines the traditional progress with the direction metric
to form the improved progress definition. There are many methods to combine the
progress with direction, such as weighted addition, simple multiplication. The
authors have chosen the cosine of the angle since its value is between 0 and 1, and
it is even. If the traditional progress is multiplied by the cosine of the angle, both
the minimum and maximum of the progress are not changed. Also, it fits for the
need that the node has smaller angle will forward packet earlier. Finally, they
guarantee loop freedom as the packets are always forwarded a step closer to the
I-PBBLR tries to eliminate the beaconing drawbacks by using a beaconless
protocol. In beaconless protocols the sender makes nondeterministic routing decisions,
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