Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 74

of having long routes will increase, and since each node spends time in signing
and encrypting the messages, the probability of node movements and route breakage
will increase. For these three reasons SPAAR is considered to have a medium
scalability. Moreover, SPAAR has a high packet overhead because of the large-
size packets due to the security techniques used and increased number of packets
compared to greedy forwarding. These security techniques lead also to high
processing overhead.
Finally, SPAAR can be implemented in both, sparse and dense networks. It is
suitable for sparse networks since it uses the restricted directional flooding, not
greedy. At the same time, it is suitable for dense networks since increasing the number
of neighbors will case larger neighbor table but the computational overhead for the
encryption of messages remains constant [ 5 ].
In AODPR each PS keeps the position information of the nodes that hashed into
its VHR; hence, the used location service type is some-for-some. Accordingly, a
given node will be inaccessible upon the failure of the PSs of its VHR, i.e., its loca-
tion service has a medium robustness. AODPR uses the restricted directional flooding,
so its probability of using the optimal path is high. Moreover it is loop-free since it
depends on forwarding the packets to the nodes toward the destination and uses sequ
ence number.
AODPR tolerates position inaccuracy by using the expected region. Its robust-
ness is low since the failure of an individual node might result in packet loss and
the setting up of a new route. AODPR's implementation complexity is considered
to be medium since messages are signed only with the private key of each node. So
its complexity is less than SPAAR and SGF, since it does not use neighbor public
key or reputation system.
AODPR has a medium scalability, since increasing the number of nodes in the
network with the usage of the restricted directional flooding will increase the packet
overhead. However, it still has a higher scalability than SPAAR due to the reasons
mentioned in the discussion of SRAAR scalability. AODPR also has a less packet
overhead compared to SRAAR. Even though the number of sent packets in AODPR
is large, its packet size is smaller than that in SPAAR due to the later security tech-
niques; AODPR is considered to have a medium packet overhead and processing
overhead.
Finally, AODPR is applicable to any node density in a network [ 20 ]. It is suitable
for sparse networks since it uses the restricted directional flooding, not greedy. At
the same time, it is suitable for dense networks, since increasing the number of
nodes will cause larger position information tables in the PSs without affecting the
computational overhead for the encryption of messages.
In SGF each node should maintain a table of its immediate neighbors as well as
each neighbor's neighbors [ 21 ]. So the used location service type is all-for-some.
Accordingly, a given node will be inaccessible upon the failure of a subset of the
nodes; the robustness of its location service is medium. SGF uses the greedy
forwarding, so it exhibits some greedy properties such as uncertainty to use the
optimal path and the medium robustness. SGF tolerates position inaccuracy by the
list of neighbors HELLO messages that each node periodically broadcasts; each