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2. Less packet collisions.Packet collisions occur more frequently when the network is veryloaded. Less transferred packets is translated into less packetcollisions.3. Less redundant readings.In the case of Direct Delivery, where all the individual readings aredelivered separately to the host node, it is a common phenomenonthat a node sends its values to multiple parents. This results inreception of the same packet multiple times by the sink. In dataaggregation, the filters drop the redundant packets (caching is used).4. Increase in accuracy of results.If a sensor node is temporarily down, its parent can estimate avirtual value based on node’s previous readings. Thus the totalaggregate value is not significantly affected. Of course, this benefitholds in slow-changing environments.3.2 Query ProcessingA user can send queries to the sensor network, in order to retrieve information aboutits state. The query is usually injected into the network from specific nodes (e.g. sink or agateway). There are several proposed approaches for syntax of a query, its lifetime, itsscope, its propagation and finally its parametrization.In Directed diffusion [3] the queries are formed as “interests” which are expressionswith multiple attribute-value pairs (Figure 10). Predefined attribute categories andsubcategories and application specific data representation characterize interests. Usuallydata are also named in a similar way and so, the application filters are able to performdata aggregation.Interest message Exampletype = wheeled vehicleinterval = 20 ms // send events every 20 msduration = 10 s // for the next 10 srect = [-100; 100; 200; 400] // from sensors within rectangle.Figure 10