Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 69

MFR 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. Such an approach is very easy to
implement and scalable since it does not need routing discovery and maintenance [ 22 ].
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. MFR is
probed to be a loop-free algorithm [ 23 ] since it always forces message to make a
step closer to the destination. Generally, greedy routing may not always find the
optimum route, even it may fail to find a path between source and destination when
one exists [ 6, 21 ]; their probability of finding optimal path is considered as medium.
Finally, all basic distance, progress, and direction-based methods such as MFR and
DIR have high delivery rates for dense graphs, and low delivery rates for sparse
graph [ 24 ].
As a greedy forwarding protocol, DIR has the same criteria as MFR, except that
DIR and any other method that includes forwarding message to neighbor with closest
direction, such as DREAM, are not loop-free as shown in [ 23 ].
GPSR also exhibits all the properties of greedy forwarding except that its imple-
mentation effort is considered to be of medium complexity due to planarizing under-
lying network and using perimeter routing. On the other hand, using the right hand
thumb rule and perimeter mode routing made it applicable in sparse networks as
well as dense ones.
ARP exhibits all the properties of greedy forwarding except that memorizing the
last visited hops in the packet header avoids local loops, but does not guarantee its
loop freedom. Moreover, using angle-based forwarding scheme to circumvent voids
makes it applicable in sparse networks as well as dense ones.
I-PBBLR inherited all the properties of greedy forwarding; however, the used
location service was not discussed at all. Moreover, using a beaconless protocol
slightly increases the robustness and scalability, reduces the packet overhead,
improves the performance in sparse networks, and increases tolerability to position
inaccuracy compared to traditional greedy protocols. Finally, using the improved
progress, guarantees loop freedom as the packets are always forwarded a step
toward the destination.
Restricted directional flooding protocols, such as DREAM and LAR, are robust
against position inaccuracy since they use the expected region concept. They have
higher communication complexity than greedy ones and, therefore, have less scal-
ability to large networks; their scalability and packet overhead are considered to be
medium. However, their processing overhead is low due to nonsecure routing. Moreover,
both of them include forwarding packets to neighbors with closest direction, so
both are not loop-free [ 23 ]. On the other hand, they are very simple to implement
and have high probability of finding the optimal path. Finally, they may be imple-
mented in both dense and sparse networks; they are better for sparse networks than
greedy forwarding, and even if they are used in dense ones they will have good
performance due to low processing and medium packet overheads.
DREAM's location service is fundamentally different from other location ser-
vices in that it requires that all nodes maintain position information about every