Greedy Perimeter Stateless Routing in Wireless network (English "„Greedy Perimeter choice of route in radio nets "“, abbreviation GPSR) is Routing minutes for mobile Ad-hoc-nets, thus a procedure, with which packets are to be guided in spontaneously developed computer networks to their regulation goal.

Minutes were developed by B. Karp and owe its names of its function mode, since it proceeds alternating purposefully like an Greedy algorithm and circles the goal on the Perimeter.

Coordinates instead of destination identifier

GPSR is a geo Routing procedure, i.e. packets are sent away not to special receivers, but at coordinates; the packages are to be set then for that network knot, which is geographically next these coordinates. A condition for the fact is natural that each network knot knows its own position in coordinates.

Neighbourhood

In the following the term "„of the neighbourhood is used "“. First are two knots neighbouring, if at least one of the two can directly reach the other one by means of the communication medium. In a Ad-hoc-network these neighbourhood relations is not obvious, because by the use of communication media with limited range - e.g. Radio - usually each knot cannot contact every different one directly. Later it can be necessary that some knots paint some their neighbours "„from the memory "“, see section planar one graph are a condition.

Minutes

Each knot of the network implements the following steps, if it receives a packet:

1. Final condition. If your name stands in the package header, then you are the knot, which is next the goal. Process the package and do not continue to send it not. Otherwise further with 2.
2. Greedy mode. Select that your neighbour, that is next the goal coordinates of the package. If this neighbour is closer at the goal than you, then send to him the package. Otherwise further with 3.
3. Perimeter mode. Write your names into the package header. Look toward goal and turn you so long against the clockwise direction, until you see first of your neighbours. Send to this the package.

The procedure is here very humanly avowed. The actual conversion of the last step determines the angle between the vector "„current knot - goal "“and all vectors "„current knot - neighbour knot "“and continues to send the package to that neighbours, to whom the smallest magnetic azimuth was computed. The direction of rotation against the clockwise direction is naturally arbitrarily selected, because it is the direction of rotation usual in mathematics; just as well it could in the clockwise direction be turned - only condition is that all knots use the same direction of rotation.

Planar graphs are a condition

A condition for the correct function mode of minutes is that the network is representable as planar graph: If one draws all knots in into a coordinate net and if all neighbouring knots connect, then these connecting lines may not cross anywhere. If they do it nevertheless, then the network must become smoothed "„"“, before GPSR minutes can function correctly - in addition some knots must some their neighbours "„forgotten "“. As such an algorithm looks to the Planarisierung, more in detail in the article planar one graph is treated.

If GPSR minutes in a non-planar network are used, then cycles can occur, i.e. a packet is sent again and again in the circle around, without ever achieving its goal. That is naturally unwanted, because packages in a cycle are lost and the network are stressed.

Literature

• B.Karp: Challenges in Geographic Routing: Sparse network, Obstacles, and Traffic Provisioning. In DIMACS Workshop on Pervasive Networking, Piscataway, NJ, May, 2001
• B.Karp: Geographic Routing for Wireless network. Ph.D. Thesis, Harvard University, Cambridge, mA, October, 2000
• B.Karp, H.T.Kung: Greedy Perimeter Stateless Routing for Wireless network. In Proceedings OF the Sixth Annual ACM/IEEE internationally Conference on mobile Computing and Networking (MobiCom 2000), Boston, mA, August, 2000, pp. 243-254

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