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GeoGrid: A scalable Location Service Network
Authors: J.Zhang, G.Zhang, L.Liu
Georgia Institute of Technology
presented by
Olga Weiss
Com S 587x, Fall 2007
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OverviewIntroduction
Problem addressedWhat is GeoGrid?Existing solutions review
Design of GeoGridBasic GeoGrid systemConstructionRoutingDual peer and Dynamic work load adaptation techniques
Experimental results and conclusion
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IntroductionProblem addressed
serving a large and growing number of mobile userscontinious delivery and dissemination of location-based information in real time
GeoGrid – a geographical location service overlay network system
DecentralizedGeographical location awareTechniques to improve fault-tolerance and workload balance
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Existing solutions reviewCurrent location-based services are
constrained to fixed set of moving objectsexpensive to maintain and expand
One approachCreate and maintain a centralized graphical location service. Drawbacks:
Response timeExpensive access to infrastructure communication serviceNot robustNo model for such large scale location-based service
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ChallengesCan we organize nodes into efficient service network that is geographical proximity aware?End-to-end communication b/w any two nodes is boundedHow to handle workload imbalance (hot spots)? How to minimize the possible service interruption?
Ex. Highway system can be heavily loaded during the rush hours
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GeoGrid DesignBasic GeoGrid systemGeoGrid constructionRoutingDual peer and Dynamic work load adaptation techniques
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Basic GeoGridA network of N nodes interconnected using GeoGrid topology and routing protocolA node is a point in 2dim geographical coordinate spaceSpace is dynamically partitioned into N disjoint rectangleEach node “owns” a rectangular region
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Basic GeoGridNodes self-organize into an overlay networkConnectivity is established through immediate neighbors of a nodeA mobile user connects his mobile device to one of the nodesEach node runs GeoGrid middleware and serves as a proxy for the mobile user
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Basic GeoGridAssumptions
Information services existence (provide geographical info)User can be either from outside of the network or from inside itNetwork nodes are not mobile
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GeoGrid ConstructionPlane is divided among N nodes into a set of rectangular regions r = <x,y,width,height>A node p is identified by a tuple <x,y,IP, port,properties>Each node maintains a list of its neighbors
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GeoGrid ConstructionGeoGrid is constructed incrementallyStart from one node owning the entire GeoGrid spaceSplit the space upon new nodes joining
decide which region the new node q belongs (say, of node p)split the region in halfhand one half to node qnotify neighbors (they must add q into their lists)create a list for q from the list of p
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GeoGrid ConstructionBasic bootstrapping process for a new node
Obtain geographical coordinate from a serviceObtain a list of existing nodes from a bootstrapping serverRandomly chose an entry node from the listInitiate a joining request contacting to the entry node
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Routing in GeoGridLocation queryRequest is tagged with (x,y)
p issues a query (x,y); q = pif q does not own (x, y) then forward the request to a neighbor closest to (x,y)
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Routing in GeoGridTwo critical issues:
Load balancingRouting efficiency
Solution:heuristic load balance scheme - workload dynamic adjusting
Dual peer techniqueLoad adaptation technique
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Dual peer technique
Improves the overall system reliabilityMaps region sizes to the capacities of region owner nodes
2 nodes share a region ownershipPrimary owner node is a node with the larger capacitySecondary owner node is a backup node
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Dual peer techniqueNode join:
First 3 steps are the same as in basic GeoGridChose a neighbor region that has one owner and the least capacityIf no such region exist, chose the region with the least primary node capacitySplit the region and becomes a primary owner node of the region
Node departureSecondary owner departure causes no changePrimary owner must inform neighbors
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Dual peer techniqueFailure recover
Status information is periodically synchronized b/w primary and secondary nodes
Failure of a node:If the primary node leaves, the secondary node becomes the primaryIf the secondary node leaves, the region becomes half-fullIf both nodes die, what happens?
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Dual peer techniqueAvantages
Improves the fault resilienceReduces the number of region split operationsImproves the system load balance
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Dynamic workload adaptation
Main idea: balance workload distribution by selectively assigning new nodes to the most heavily loaded regions in its neighborhoodThree basic rules:
Use local adaptation instead remote one (less operation overhead)Use secondary peer switching/moving (for primary peer the ops costs more)Region split/merge are expensive – should be used with less priority
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ConclusionExperimental results show that GeoGrid can reduce the workload load imbalance by an order of magnitudeUnique design:
Use of geographical mapping of nodes to regions; improved routingDual peer and Dynamic workload adaptation techniques reduce load imbalance and improve fault-tolerance