TAG: a Tiny AGgregation Service for Ad-Hoc Sensor Networks

This paper targets sensor networks which include devices that are in a low powered, distributed wireless environment. The sensor nodes communicate and gather data from the environment collectively and pass the data around through the wireless network. The paper proposes a language and communication mechanism for these network of motes to communicate and pass information. Because of its lower power nature, communication is best done by using multiple short hops instead of one long hop, which uses more power. Also, instead of a centralized server that all nodes send data to, several local interactions are used first to sum up the data gathered, then passed along. A tree routing topology is used so data is passed from the leafs up to the root, but each sub root sums up the data from its child nodes, so the amount of data that needs to be passed up is less, which saves power. The language proposed is a declarative language similar to SQL database query language which allow the users to query sensor data and filter, group the data gathered. Several aggregates can be specified by the language, which is all locally computed and then passed up the tree to the root.

I enjoyed reading this paper a lot, it was very clear in expressing its ideas, and the communication was definitely power efficient because you send out less messages due to the aggregation of data. Several optimizations have also been mentioned. These include mechanisms to maintain the topology and recover from errors and node losses. Also, adding a cache to cache data values also proves as a valuable optimization. Overall, for sensor networks which communicate a collective data set and require low power, the proposed methods seem promising.