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implicitly allowing opportune receiving nodes to determine a packet's next hop
through contention at transmission time. In I-PBBLR, if a source node has a data
packet to send, it first determines the position of the destination, stores these geo-
graphical coordinates along with its own current position in the header of the
packet, and broadcast the packet to all neighboring nodes (since it does not possess
knowledge of neighboring nodes positions).
Nodes located within the forwarding area of the relaying node, apply Dynamic
Forwarding Delay (DFD) prior to relaying the packet, whereas nodes outside this area
drop the received packet. The value of the DFD depends on the relative position
coordinates of current, previous, and destination node. Eventually, the node that com-
putes the shortest DFD forwards the packet first by broadcasting it to all neighboring
nodes after replacing the previous node's position by its current position in the
header). Every node in the forwarding area detects the further relaying of the packet
and cancels its scheduled transmission of the same packet. This mechanism allows
selecting one neighbor as next hop in a completely distributed manner without having
knowledge of the neighboring nodes, which is achieved by applying the concept of
DFD. The simulation results showed that position-based beaconless routing using the
improved progress reduced the overhead and increased delivery rate by 3-5% com-
pared with using the traditional progress.
4.3.5
DREAM
Distance Routing Effect Algorithm for Mobility (DREAM) [ 11 ] is an example of
restricted directional flooding routing protocols, that within them, the sender will
broadcast the packet toward nodes in a limited sector of the network; to all single hop
neighbors toward the destination [ 11, 12 ]. DREAM algorithm is a proactive protocol
that uses a limited flooding of location update messages [ 24 ]. In DREAM, each node
maintains a position database that stores position information about all other nodes in
the network. Its location service can therefore be classified as an all-for-all approach.
Thus, each node regularly floods packets to update the position information main-
tained by the other nodes. The higher the speed of a node the more the frequency with
which it sends position updates. Also, the distance that a position update may travel
before it is discarded provides accurate position information in the direct neighbor-
hood of a node and less accurate information at nodes farther away, but this does not
cause a problem since intermediate hops are able to update the position information
contained in the data packet [ 6, 10 ]. In DREAM the message is forwarded to all
neighbors whose direction belongs to the region that is likely to contain the destina-
tion D, called the expected region. Expected region is determined by the tangents
from the source S to the circle centered at D and with radius equal to a maximal
possible movement of D since the last location update [ 6, 23 ]. The neighboring hops
repeat this procedure using their information on D's position.
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