1 Along & across algorithm for routing events and queries in wireless sensor networks Tat Wing Chim Department of Electrical and Electronic Engineering The University of Hong Kong, Pokfulam Road, Hong Kong International Symposium on Intelligent Signal Processing and Communication Systems (ISPACS' 05)

2 Outline Introduction Related work Along & across algorithm Simulation Conclusion

3 Introduction A Wireless sensor network –Sensor nodes of a large number –Nodes with sensing, limited computation and communication powers To elongate the lifetime of a WNS is a critical issue Propose an efficient strategies for routing event and queries

4 Major approaches for dissemination date The push approach –Broadcast throughout the network The pull approach –Interested clients to broadcast queries throughout the network –Sensor nodes transmit data according to the demands The third approach –Sensor nodes and interested clients propagate sensed data attributes and queries –To seek for a match

5 Event Rumor Routing Algorithm For Sensor Networks Source

6 Rumor Routing Algorithm For Sensor Networks

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8 Basic idea Event attributes distributed Using an Along strategy Along same hop level nodes Queries propagated Using an Across strategy Across hop levels Three major parts: –Build of hop tree –Distribution of event attributes –Propagation of queries

9 Building of Hop Tree A hop tree –Initiated by a random root node –Tree_Build packet Receive the packet Update the value of hop Replaces senderID by node’s ID Rebroadcasts the packet to all its neighbors

10 Distribution of Event Attributes An event source witnesses an event Includes the event into its Event Table Forms an Event_Dist packet Check neighbor list having the same hop level If yes, forward the packet If not, forward the packet to EventSrcLevel -1 EventSrcLevel Any node receive an Event_Dist packet Check the Event Table Whether receive before If yes, ignores the packet If not, records EventAttributes into Event Table

11 Basic Propagation of Queries When a node receives a query Checks its Event Table whether match If not, forms a Query_Prop packet Determine forward the packet upwards or downward A node receive a Query_Prop packet Update HopList Checks its Event Table whether match If yes, its neighbor leading to the event according to its Event Table If not, forwards the packet to a neighbor

12 Basic Propagation of Queries The node already has the lowest or highest level The query can’t be answered in the selected direction Forms a Query_Failed packet forward back to the query source The source receive the Query_Failed packet Forms a new Query_prop packet Forward it to a direction opposite

13 Basic Propagation of Queries If the query source the Query_Failed packet from both upper and lower directions it means the query can’t be answered Flooded across the whole sensor network to seek

14 Advanced Propagation of Queries A Query_Prop packet upwards –Intermediate node may not find an upper level neighbor A Query Routing Table (QRT) –Maintained by all node

15 Advanced Propagation of Queries A node without upper level neighbors Forms a QRT_Build packet Forward the packet to a lower level neighbor at random A node receive a QRT_Build packet Stores the value of HighestHop and corresponding incoming direction into its QRT Removes all entries with lower HighestHop value The root build up a QRT with information about how to reach the top of the tree

16 Advanced Propagation of Queries A node receives a query Checks its Event Table whether match If not, forms a Query_Prop packet Forward the packet downward The packet reach the root Forward the packet upward Random picking up a neighbor Can lead to the top of the hop tree Ensures a packet go through all hop level

17 Optimization of Return Path The event source receives a Query_Prop packet –Forward a Query_Answer packet –To query source using the reverse path –This reverse path may be longer Propose an optimization method to shorten the reverse path Query source Event source

18 Simulation Written in C++ language 500 nodes Distributed across area: 50m * 50m Transmission range: 5m Event: 15 Query: 150

19 Simulation M e :transmission overhead for event distribution M q :transmission overhead for query propagation without flooding A q :percentage of answered queries without flooding D :average hop delays experienced by queries T :total transmission overhead

20 Conclusion Proposed along & across algorithm –Efficient routing of events and queries Event attributes are routed along hop level Queries routed across hop levels to seek for match Less transmission overhead than Rumor Routing algorithm