Geographic routing (position-based routing) is used in GPS. Graphic routing is a routing principle that relies on geographic position information. It is mainly proposed for wireless networks and based on the idea that the source sends a message to the geographic location of the destination instead of using the network address. The idea of using position information for routing was first proposed in the 1980s in the area of packet radio networks and interconnection networks.
Geographic routing requires that each node can determine its own location and that the source is aware of the location of the destination. With this information a message can be routed to the destination without knowledge of the network topology or a prior route discovery.
There are various approaches, such as single-path, multi-path and flooding-based strategies (see for a survey). Most single-path strategies rely on two techniques: greedy forwarding and face routing.
Greedy forwarding tries to bring the message closer to the destination in each step using only local information. Thus, each node forwards the message to the neighbour that is most suitable from a local point of view. The most suitable neighbour can be the one who minimizes the distance to the destination in each step.
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Face routing was the first geometric routing algorithm that guaranteed message delivery without flooding. Face routing is applied on a plane sub graph of the network graph.
A plane graph divides the plane into faces. The line segment between the source node and the destination node intersects some faces. In face routing, the packet is forwarded along the boundaries of these faces. A specific face routing protocol provides a set of rules for each node to decide where to send a packet using only the local information.
Position Based Routing
Since mobile ad-hoc networks change their topology frequently and without prior notice, routing in such networks is a challenging task.
Position-based routing algorithms eliminate some of the limitations of topology-based routing by using additional information. They require information about the physical position of the participating nodes in the network their availability.
Commonly, each node determines its own position through the use of GPS or some other type of positioning service. Position based routing is mainly focused on two issues:
A location service is used by the sender of a packet to determine the position of the destination and to include it in the packet's destination address.
A forwarding strategy used to forward the packets. A location service can be any one of the four
The routing decision at each node is then based on the destination's position contained in the packet and the position of the forwarding node's neighbours. Position-based routing does not require the establishment or maintenance of routes. The nodes neither have to store routing tables nor do they need to transmit messages to keep routing table’s up-to date.