Location based services are becoming increasingly popular - navigation systems, tracking and logistic systems, mobile billing (e.g. toll) or mobile advertising are just some of them. Search for objects/information located in some area are part of many search engines or navigation systems. Additionally, devices that determine the geographical position (e.g. a GPS receiver) are already integrated in many Pocket PCs and integration into standard laptops and other end-systems can be expected soon. This location information enables for more convenient, highly personalized services for users, like for example, finding the closest restaurant. In existing solutions for location-based search the search results are often incomplete or outdated. Information in a peer-to-peer-based solution could be kept updated much better than in centrally managed systems even with the fast growth of the system. The cases of passing by a gasoline station while our navigation system shows that the closest gasoline station is 5 km away, or navigating through a blocked road can be avoided. Further, the system could be operated with low costs, because of the natural scalability and administration-free character of peer-to-peer systems. In spite of the fact that the peer-to-peer research community is very active since the last seven years, current state-of-the-art overlays cannot fulfill the requirements for efficient and fully retrievable location-based search. Globase.KOM, a tree-based peer-to-peer overlay enables fully retrievable area search, lookup, and finding the geographically closest node.
Globase.KOM (Geographical LOcation BAsed SEarch) is a fully decentralized system for scalable, efficient, and fully retrievable location-based search. It is a superpeer-based overlay forming a tree enhanced with interconnections. The hybrid approach allows us to exploit and support the heterogeneity of participating nodes. We use the more powerful nodes with good network connectivity, which tend to stay online for a long time as supernodes in Globase.KOM. Supernodes are responsible for indexing all nodes/services in one clearly defined geographical area. The "normal" (non-super) nodes in the network simply offer and consume services without having additional responsibilities.
The world projection is divided into disjoint, non-overlapping zones. Each zone is assigned to a supernode located inside the zone which keeps overlay/underlay contact addresses for all nodes in that zone. Supernodes form a tree where node A is called the parent of node B when B's zone is inside A's zone.
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[KHLS08] Aleksandra Kovacevic, Oliver Heckmann, Nicolas Liebau, Ralf Steinmetz:
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