In Network Processing and Data Aggregation in

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A routing algorithm is necessary to perform well no matter the network size ordensity. It is widely known that localized (need only local information) and distributedalgorithms scale very well.• Energy efficiencySince sensor nodes are battery powered it is of major concern the routing protocol tobe as energy efficient as possible. The network may have to operate for months withoutthe replacement or recharging of the power supplies. MANETS in contrary, usually havethis option and thereby many end-to-end routing protocols proposed for Ad-Hocnetworks are not applicable for WSNs. In addition, redundant data have to be eliminatedinside the network and load balancing between the nodes is essential since some nodes(especially the ones that are placed close to the sink) tend to consume more energy (theyperform too many transmissions - receptions).To minimize energy consumption, several routing techniques have been proposed andthey employ some well-known routing tactics as well as tactics special to WSNs, e.g.,data aggregation and in-network processing, clustering, different node role assignment,and data-centric methods were employed. Almost all of the routing protocols can beclassified according to the network structure as flat, hierarchical, or location-based.A taxonomy of the current routing schemes follows:Data CentricAll nodes have the same role and data is named in an attribute-value fashion. Therouting is performed regarding the data contents and no by using predefinedshortest paths (Directed Diffusion, SPIN-1 and SPIN-2).Clustering / HierarchicalClustering is performed to the nodes so that cluster heads can dosome aggregation and reduction of data in order to save energy(LEACH, TTDD, TEEN).Geographic / Location basedThey utilize the position information to relay the data to the desiredregions rather
than the whole network (GAF, GEAR).Presenting all the routing protocols is beyond the scope of this paper as it is focusedto the networking issues of the wireless sensor networks that are related (directly or not)with the in-network processing and especially with the data aggregation. For a nicesurvey of the current routing schemes the user is referred to [18].2.3.2 Data-centric RoutingMany end-to-end routing schemes have been proposed in the literature for mobile adhocnetworks but they are not appropriate under the requirements that we discussed in theprevious section (2.3.1). It is not possible to build a global addressing scheme for thedeployment of a huge number of sensor nodes. Therefore, classical IP-based protocolscannot be applied to sensor networks because of the great overhead that a binding serviceinduces. Most of the existing network protocols for MANETS (like DSR, AODV etc)assume a global identification of nodes, so they are not applicable to WSNs. Sometimesgetting the data is more important than knowing the IDs of which nodes sent the data.Data is usually transmitted from every sensor node within the deployment region withsignificant redundancy. Since this is very inefficient in terms of energy consumption,routing protocols that will be able to select a set of sensor nodes and utilize dataaggregation during the relaying of data have been considered. This consideration has ledto data-centric routing, which is different from traditional address-based routing whereroutes are created between addressable nodes managed in the network layer of thecommunication stack. In data-centric routing, the sink sends queries to certain regionsand waits for data from the sensors located in the selected regions. Since data is beingrequested through queries, attribute based naming is necessary to specify the properties ofdata. For example, if the query is something like [temperature > 60F], then sensor nodesthat sense temperature > 60F only need to respond and report their readings. Using datacentricrouting it is possible:(a) to combine the data on their way back to the sink,(b) to eliminate duplicates,
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Page 53 and 54: REFERENCES[1] W. Ye, J. Heidemann,

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