Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 70

other node. This leads to large overhead due to position update and large position
information maintained by each node. Hence, DREAM's location service is the
least scalable position service and, thus, not appropriate for large-scale and
general-purpose Ad Hoc networks. On the other hand, a position query requires
only a local lookup and the position of a given node will be inaccessible only upon
the failure of all nodes, which makes it very robust. LAR however, does not use
such location service; it just uses the available position information from a route
that was established earlier.
DREAM is very robust against the failure of individual nodes since the data packet
goes through multiple paths, so the failure of a single intermediate node does not
prevent the packet from reaching its destination. This qualifies it for applications
that require a high reliability and fast message delivery for very infrequent data
transmissions [ 6 ]. LAR is robust during the route discovery since the RDP packet
goes through multiple paths; however, after route setup it is like any other protocol
that depends on route setup before sending the data packets, i.e., the failure of a
single node might result in packet loss and the setting up of a new route. Hence, its
robustness is considered to be low. On the other hand establishing a route before begin-
ning data sending makes it more suitable than DREAM in the cases that require
high volume of data transmissions.
LARWB exhibits all the properties of LAR except that its robustness is considered
to be medium since the failure of a single node might result in packet loss but does
not result in setting up of a new route due to the usage of the route backup. This
route backup also reduces the number of routing packets; however, we still cannot
consider LARWB's packet overhead as low as that in greedy.
MLAR has similar criteria as that of LAR except that its robustness is medium
since the failure of a single node might result in packet loss but does not result in
setting up of a new route due to the usage of the alternate paths. These alternate
paths also reduce the packet overhead; however, it is still higher than that of greedy.
Since MLAR caches the most recently received routes, the probability of using the
optimal path is very low. Lastly, since the packet header contains the entire source
route, all paths are checked easily as being loop-free at each node that stores routes;
loop freedom is guaranteed in MLAR.
Grid is a hierarchical routing that applies the concept of dominating sets. It is
like LAR, uses the available position information of the destination from a route
that was established earlier to implement a restricted directional flooding among
grids. So it is robust against position inaccuracy since it uses Grid-by-Grid routing
and expected region concept. Although Grid has strong route maintenance capabil-
ity and it is very robust toward node mobility, it is like any other protocol that
depends on route setup before sending the data packets in the sense that the failure
of a single node might result in packet loss and the setting up of a new route.
Moreover, the authors in [ 15 ] did not elaborate on route maintenance required when
a grid remains empty after its leader and only node leaves it [ 24 ]. Thus, its robust-
ness is considered to be medium.
Grid's implementation complexity is considered to be medium due to dealing
with the area as grids. Its scalability is high due to using restricted directional flooding