Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 72

zones and its processing overhead is low due to nonsecure routing. LABAR is not
considered a loop-free protocol since it uses directional flooding and does not use
any technique to indicate that a specific packet has been received by a specific node
before this time. However, the expired hop counters can be used to stop the loops
after a while.
One may think that LABAR's probability of finding optimal path is medium
since it uses greedy routing; however, their simulations showed that LABAR usually
uses a long path which sometimes reaches more than double the length of the optimal
path. This may be due to using directional route toward the direction of the destina-
tion's zone and not toward the exact position of it. So, LABAR's probability of
findinf optimal path is considered to be low.
In POSANT, the used location service was not discussed. However, the used
forwarding strategy is multiple greedy forwarding with the pheromone trail value
used as the optimization criteria; a source launches many forward ants from different
zones at regular time intervals and the pheromone trails values are used for making
a stochastic decision to select the next hop.
POSANT tolerates position inaccuracy by forwarding ants to different zones
(not to specific node position) and depending on the pheromone trail value as the
optimization criteria (which does not depend on the exact position of nodes).
POSANT's robustness is considered to be medium, since the failure of a single
node might result in packet loss but does not result in a new route establishment,
except if the only outgoing link of the source node that has a pheromone trail for D
breaks or a message from this link is received stating that there is no route to D.
Using periodic multiple greedy forwarding made POSANT's implementation
complexity, scalability, and packet overhead considered as medium. However, its
processing overhead is low due to nonsecure routing. POSANT is guaranteed to be
loop-free since repeated forward ants are destroyed. Moreover, it has a high prob-
ability of finding the optimal path since it is based on ACO which guarantees message
delivery and converges to a route which is very close to the optimum route even if
the network contains nodes with different transmission ranges.
Finally, POSANT may be implemented in both dense and sparse networks.
POSANT is better for sparse networks than traditional greedy forwarding; since if
no pheromone trail exists, the route discovery packet will not be dropped; however,
pheromone trail initialization is done. Moreover, if it is used in dense networks it
will have good performance due to low processing and medium packet overheads.
In the PAGs, all nodes use the low transmission range to discover their neighbors
periodically; the used location service is all-for-some. Thus, a given node will be
inaccessible upon the failure of a subset of the nodes; its location service has a
medium robustness. However, the technique that is used to enable the source to
know the position of the destination is not discussed.
The used forwarding strategy is a combination of power-adjusted greedy and
CFace algorithms. As with other greedy forwarding protocols, the position of the
destination needs to be known with an accuracy of a one-hop transmission range,
otherwise the packets cannot be delivered [ 6 ]. Moreover, PAGs have high scalability,
low packet overhead, and low probability of finding the shortest path. The robustness