GeoMote: Geographic Network Architecture for Sensor Networks Joe Polastre Rachel Rubin

Motivation Sensor Network Data is typically interpreted based on a sensor’s location Current multihop beacon-based routing –Requires too much overhead –Only allows multihop to one node Routing by shortest number of hops results in large distance between hops Sensors often overloaded with participating in the network; not enough time to sense!

Goals Separate client sensing functions from network functions Enable clients with geographic information Provide a generalized architecture suitable for all client communications Maintain the same or less overhead in the geographic network architecture as in traditional multihop architectures

Applications of Geographic Services Geographic Multicast (GeoCast) Nearest Neighbor Service Discovery Geographic Network Reprogramming and Reconfiguration Low Power Pursuer/Evader Games

Low-Power Pursuer Evader Evader

Components Allow Geographic Architecture to be plugable service for client applications GENERIC_COMM Localization Location Services / Routing Client Application

Why Use Location? Permits messages to be sent between any two nodes in the network Gives routing algorithms an additional parameter to analyze Provides additional information to client applications

GeoCast Architecture Three Layer Architecture: GeoHosts GeoGateways GeoRouters Designed for powerful Internet workstations (Julio Navas, Tomasz Imielinski, 1997)

GeoHosts Endpoints of the network Run client processes Initiate message transfer Determines if a packet is destined for its current geographic region

GeoGateways Entry and exit points of the network Communicate with GeoRouters and GeoHosts through broadcast messages Cover a given region specified by a radius

GeoRouters Perform intelligent routing and message delivery tasks Know the location of nearby GeoRouters and GeoGateways Route packets to GeoRouters and GeoGateways to deliver the packet to the destination geographic region

Geographic Routing Architecture Client Process Client Process Direct Message Router Host Gateway Event

Geographic vs. Internet Architecture Geographic (sensor) –Routers may never talk to Hosts and vice versa –Gateways are entry/exit points but have no routing info –Broadcast medium dependant on distance from source Internet –Functions of the gateway and router are typically merged –Gateways perform routing functions and are entry/exit points –Broadcast medium dependant on physical network

Network Hierarchy 2 layers –Simple Implementation Layer 1: Hosts Layer 2: Routers –Reduced Overhead –Less hops per packet from source to destination n layers –More Complex –Can dedicate nodes to specific network functions –Allows optimization of resource usage Its not obvious what the optimum number of network layers is.

Geographic Routing Naïve Method: Route to “closest” router Probabilistic Algorithms –Local Search Directed Diffusion (Estrin et al) Beam Forming (Algorithms, Antennae)

Experimental Results Figure 2 Packet Throughput

Experimental Results Number of Hops

Future Work / Ideas Utilize the wireless broadcast medium to allow intermediate nodes to cache and aggregate data passively Evaluate and design new routing algorithms that leverage location information Collect and analyze results for controlled large-scale experiments