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node knows the exact position of the nodes in its transmission range and neighbors'
transmission ranges.
It is clear that it is so complex to implement SGF since it uses many securing
techniques whether with the location service or the forwarding strategy. SGF
assumes the existence of pair-wise shared secret keys between the nodes which is
difficult to implement in large area networks; so it has medium scalability. Moreover,
it has a high packet overhead due to the periodically sent reputation information
report and list of neighbors HELLO messages, in addition to the large-size packets
due to the security techniques used. These security techniques lead also to high
processing overhead. SGF loop freedom depends on the used optimization criteria
(directional or other). Finally, SGF is preferred to be implemented in moderate
density networks; since greedy forwarding may have problems in sparse networks.
On the other hand, implementing it in a dense network will increase the size of the
periodic list of neighbors and reputation information HELLO messages, which may
consume the network bandwidth and nodes' memory.
4.5
Directions of Future Research
In this chapter we have shown that there are many approaches to perform
position-based packet forwarding. However, there still exist a number of issues and
problems that need to be addressed in future research.
Position-based protocols make it possible to have larger networks without
scalability problems. However, geographical routing also offers attackers new oppor-
tunities, especially since most protocols broadcast position information in the clear
allowing anyone within range to receive. Hence, node position can be altered, making
other nodes believe that it is in a different position. This may make nodes believe
that the attacker is the closest node to the destination and choose it as the next hop.
Consequently, this attacker will be able to alter or drop packets. Thus, it is of worth
that more intensive work be done to enable secure-position-based routing protocols
to defend against several attacks not only from malicious nodes, but also from the
compromised ones. Additionally, location privacy is one of the most major issues
that need to be addressed, since location privacy is hard to achieve when a node
identifier can be immediately associated with its position. Finally, alternative secu-
rity schemes that are not based on infrastructure for key distribution should be
considered, especially since they suffer from high processing requirement (due to
signing and signature verification of every packet) and may be a perfect target for
Denial of Service (DoS) where attackers try to exhaust a nodes processing time and
battery, by forcing them to spend time doing cryptographic calculations that are not
required. Moreover, approaches that suggest the usage of symmetric cryptography
suffer from a scalability problem since every pair of nodes would require a unique
shared key.
Geographical routing protocols depend strongly on the existence of distributed
scalable location services, which are able to provide the location of any host at any
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