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and delegating the searching responsibility to the gateway hosts. Its packet and pro-
cessing overheads are considered to be low due to reduced number of small nonse-
cure routing packets. Grid uses a specific field to detect duplicate request packets
from the same source, so endless flooding of the same request can be avoided, i.e.,
it is loop-free. On the other hand, GRID uses long paths since packets are forced to
be routed through grid leaders.
Finally, it is better to implement Grid in dense networks due to performing routing
in a grid-by-grid manner through grid leaders. So, the number of packets related to
route search is insensitive to the network density. On the contrary, the cost slightly
goes down as the host density increases, since routes become more stable with
denser hosts. On the other hand, if it is implemented in sparse networks, each node
will be the gateway of its grid, and GRID may become like native LAR; so it will
consume network resources in dividing the area into grids and electing gateways
without any benefit.
TERMINODES provide hierarchical approach to position-based Ad Hoc routing.
For long-distance routing it uses a greedy approach and, therefore, has characteristics
similar to those of greedy forwarding. However, due to the usage of a non-position-
based approach at the local level, it is more tolerant to position inaccuracy. As other
greedy forwarding protocols, in TERMINODES all nodes maintain a one-hop neigh-
bor table; it uses all-for-some location service. Hence, a given node will be inacces-
sible upon the failure of a subset of the nodes; its location service has a medium
robustness. Moreover, it may fail to find the optimum route and has higher delivery
rates for dense graphs.
TERMINODES robustness is medium since the failure of an individual node may
cause the loss of a packet in transit, but it does not require setting up a new route, as
would be the case in topology-based Ad Hoc routing. Due to using the two-level hier-
archy approach, TERMINODES is considered to have medium implementation com-
plexity. Such an approach is scalable since it does not need routing discovery and
maintenance in long-distance routing. Moreover, it has a low packet and processing
overhead because of its fewer number of small-size packets compared to other secure-
position-based protocols. TERMINODES is considered to be a loop-free algorithm
[ 24 ] since it always forces message a step closer to the destination.
LABAR is a hierarchal protocol since it uses zone-based routing. In LABAR the
virtual backbone structure is used to update location information between Gnodes in
a proactive manner; the used location service type is some-for-all. Generally, the
robustness of such approaches is medium, since the position of a node will become
unavailable if a subset of the nodes fails. LABAR exhibits some properties of greedy
forwarding such as high scalability, low packet overhead, and its suitability to be
implemented in dense networks. LABAR tolerates position inaccuracy due to relay-
ing the user packets toward the direction of the destination's zone and not toward the
exact position of it.
In the case of a failure in the directional route of LABAR, the virtual backbone
will be used to relay the packets, i.e., LABAR's robustness is high since a failure of
a single intermediate node does not prevent the packet from reaching its destination.
LABAR's implementation complexity is considered to be medium due to using
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