In Network Processing and Data Aggregation in
In Network Processing and Data Aggregation in
In Network Processing and Data Aggregation in
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(c) to perform smart cach<strong>in</strong>g <strong>in</strong>side the network,(d) to compute several aggregate values <strong>in</strong>side the network <strong>and</strong> f<strong>in</strong>ally(e) to save energy by reduc<strong>in</strong>g the number of routed messages (less transmissionsmean less energy consumed by transceiver).Therefore, there are two rout<strong>in</strong>g models that a WSN can use:Address-centric Protocol (AC): Each source <strong>in</strong>dependently sends data along theshortest path to s<strong>in</strong>k, based on the route that the queries took (“end-to-end rout<strong>in</strong>g”).<strong>Data</strong>-centric Protocol (DC): The sources send data to the s<strong>in</strong>k, but rout<strong>in</strong>g nodeslook at the content of the data <strong>and</strong> perform some form of aggregation / consolidationfunction on the data orig<strong>in</strong>at<strong>in</strong>g at multiple sources.The ma<strong>in</strong> reason for the use of data-centric rout<strong>in</strong>g 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 terra<strong>in</strong>where small wireless sensor nodes are deployed. The nodes are able to perceive nonnormal sound levels <strong>in</strong> the environment. Let us suppose that the only nodes that areplaced near the pass<strong>in</strong>g-by track are Node A <strong>and</strong> Node B. Nodes C <strong>and</strong> D are with<strong>in</strong> thetransmission range of A <strong>and</strong> only node D is reachable by B. Both nodes C <strong>and</strong> D cantransmit directly to s<strong>in</strong>k.Case 1: Address-centric rout<strong>in</strong>gEach source (A,B) sends its own <strong>in</strong>formation separately to the s<strong>in</strong>k. The shortest pathsare used, so Node A routes packet_A to s<strong>in</strong>k through C <strong>and</strong> Node B routes packet_B tos<strong>in</strong>k through D. There is no way for the network to “know” that packet_A <strong>and</strong> packet_B<strong>in</strong>clude identical values for the measured noise. Therefore, all the <strong>in</strong>termediate nodes(C,D) forward bl<strong>in</strong>dly everyth<strong>in</strong>g they receive to the next hop. The data-contents ofpackets are not accessible to the network layer as the only <strong>in</strong>formation provided is theaddress of the sender <strong>and</strong> the address of the receiver. Th<strong>in</strong>k the same scenario for 100 or1000 small sensors near a volcano <strong>and</strong> 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: <strong>Data</strong>-centric rout<strong>in</strong>g
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