Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 58

to a G-node and G-nodes will know the IDs of their zone's S-nodes. The second step
is creating an easy-to-manage virtual backbone for relaying position information of
nodes. G-nodes in the virtual backbone are responsible for resolving the IP addresses
into geographical locations. To connect zones and get the virtual backbone to func-
tion, a G-node called the root sends connect messages to its adjacent zones. If the
particular adjacent zone is not connected yet to the backbone, then it will be added to
the backbone. Figure 4.8 shows an example of such a virtual backbone.
The last step is the directional routing. The source node queries the source G-node
node to map the destination IP address into the geographical location area of the
destination. Then the source G-node determines the vector pointing from its own
location to the destination's location. The resulting vector's direction is compared to
each of the adjacent zones' direction and distance to determine the neighboring zone
that will be used in relaying the data to the destination. Now, the source G-node will
instruct the source node on how to route the packet inside the zone to reach the next
zone with the least number of hops. The node that received the packet in the neighboring
zone will route the packet to the next zone by consulting its zone's G-node (which
will consume time). In the case of a failure in the directional route (determined, for
example, through expired hop counters), the source zone will be informed about the
failure and the virtual backbone will be used to relay the packets.
Thus, LABAR is a combination of proactive and reactive protocols, since a
virtual backbone structure is used to update location information between G-nodes
(in a proactive manner), while user packets are relayed using directional routing
toward the direction zone of the destination. One of the most important advantages
of LABAR is the reduction of cost and power consumption by the relaxation of the
GPS-equipment requirement in each node.

Root

G-node

S-node

Backbone

Tr ansmission radius

Zones

Fig. 4.8 Example of virtual backbone in LABAR