In Network Processing and Data Aggregation in

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(c) to perform smart caching inside the network,(d) to compute several aggregate values inside the network and finally(e) to save energy by reducing the number of routed messages (less transmissionsmean less energy consumed by transceiver).Therefore, there are two routing models that a WSN can use:Address-centric Protocol (AC): Each source independently sends data along theshortest path to sink, based on the route that the queries took (“end-to-end routing”).Data-centric Protocol (DC): The sources send data to the sink, but routing nodeslook at the content of the data and perform some form of aggregation / consolidationfunction on the data originating at multiple sources.The main reason for the use of data-centric routing schemes is the reduction of theconsumed energy as we already have stated above. To get an idea of how this goal can beachieved we consider a simple scenario (Figure 8). A heavy track passes near by a terrainwhere small wireless sensor nodes are deployed. The nodes are able to perceive nonnormal sound levels in the environment. Let us suppose that the only nodes that areplaced near the passing-by track are Node A and Node B. Nodes C and D are within thetransmission range of A and only node D is reachable by B. Both nodes C and D cantransmit directly to sink.Case 1: Address-centric routingEach source (A,B) sends its own information separately to the sink. The shortest pathsare used, so Node A routes packet_A to sink through C and Node B routes packet_B tosink through D. There is no way for the network to “know” that packet_A and packet_Binclude identical values for the measured noise. Therefore, all the intermediate nodes(C,D) forward blindly everything they receive to the next hop. The data-contents ofpackets are not accessible to the network layer as the only information provided is theaddress of the sender and the address of the receiver. Think the same scenario for 100 or1000 small sensors near a volcano and try to realize how many transmissions of identical(duplicate) packets will be performed. As a result, a big amount of energy will bedissipated.Case 2: Data-centric routing
In the data-centric approach we assume that routing is not optimal. Node A routespacket_A to sink through a longer path (than that used in Address centric routing) withNode D being the last hop before sink. The data is named (attribute-value form) and thenetwork layer protocol can access this information. It is possible now to perform severalactions depending on the content the data packets. The most reasonable action that arouting protocol can perform is duplicate suppression. Thus, Node D checks its cache andrealizes that the packet_A (reached later than packet_B) is identical to packet_B and itnever transmits it to sink.Node ANode BNode ANode BNode CNode DNode CNode DSinkSinkDuplicateSuppressionAddress CentricData CentricFigure 8. Address-Centric Vs Data-Centric Routing2.3.3 Directed Diffusion [3]In-network processing must be supported by the network layer mechanism that isused. The implementation of data-centric routing protocols is ideal for such a purpose. Inthis section we present one of the most common routing protocols of this category, theDirected Diffusion.Directed diffusion is a data-centric (DC) and application-aware paradigm in the sensethat all data generated by sensor nodes is named by attribute-value pairs. The main ideaof the DC paradigm is to combine the data coming from different sources (in-networkaggregation) by eliminating redundancy and minimizing the number of transmissions;thus saving network energy and prolonging its lifetime. Unlike traditional end-to-end
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Page 7 and 8: Thus, in-network processing is one
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Page 29: than the whole network (GAF, GEAR).
Page 33 and 34: 3 Data Aggregation in WSNs3.1 Gener
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Page 53 and 54: REFERENCES[1] W. Ye, J. Heidemann,

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