Despite being a core networking primitive, collection protocols today often suffer from poor reliability (e.g., 70%) in practice, and heavily used protocols have never been evaluated in terms of communication efficiency. Using detailed experimental studies, we describe three challenges that cause existing collection protocols to have poor reliability and waste energy: inaccuracies in link estimation, link dynamics, and transient loops. In this paper we present Magnet, a robust, efficient, and hardware-independent collection protocol. Magnet uses three novel techniques to address these challenges. Magnet’s link estimator addresses the inaccuracies in link estimation by using feedback from both the data and control planes, using information from multiple layers through narrow, platform-independent interfaces. Second, Magnet addresses link dynamics by using the Trickle algorithm for control traffic, sending few beacons in stable topologies yet quickly adapting to changes. Finally, Magnet addresses transient loops by using data traffic as active topology probes, quickly discovering and fixing routing failures. Magnet runs on six different mote platforms and we have tested it on four testbeds. In most experiments, Magnet achieves 99 % reliability, and in some cases 99.9%. In the most challenging testbed, the state-of-the-art collection protocol today (MultiHopLQI) achieves 70 % reliability: Magnet achieves 97%. Magnet achieves this ten-fold reduction in dropped packets with 25 % fewer transmissions. Magnet works seamlessly on top of existing low-power MAC layers. Together, these results suggest that Magnet can be the robust, efficient collection layer that so many sensor network applications and protocols need. 1

, interactions, food constituents, and responses to,diagnostic tests. The psychosocial and behavioraj. aspects, of smoking in women are discussed, along with the docffiented increases in- the risk of contracting lung cancer, heart,disease, or lung disease. The harmful effects of pregnant mothers smoking

I would like to thank Prof. Dr. Torsten Braun, head of the Computer Network and Distributed Systems group (RVS), for supervising this work and for his insightful advises. Prof. Dr. Torsten Braun encouraged and motivated me to publish my research results and he provided me the opportunity to present the work on various conferences, for which I thank him. I would also like to thank Prof. Dr. Roger Wattenhofer, responsible for the Koreferat of this work. Also, Prof. Dr. Oscar Nierstrasz who was willing to be the co-examinator of this work deserves many thanks. Many thanks go to my colleagues of the RVS group and of the IAM for our various interesting discussions about all kinds of topics and for making the institute a very pleasant and friendly place to work at. Special thanks go to David Steiner, Marc Steinemann, Matthias Scheidegger, Florian Baumgartner, Ruy De Oliveira, and Attila Weyland. There are many students who worked with me and helped a lot in developing and implementing. Among them I especially thankful to Thomas Bernoulli,

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I herewith certify that all material in this dissertation which is not my own work has been properly acknowledged.

, co-operating, creating guilt, "gifting" and sharing), irrespective of platform, technology or genre. This is why social games often go "viral". One core economic feature of F2P is the use of a social platform to attract new players. 27,28 Regarding microtransactions

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-powered incentives by the owners (Bradach 1997) to assuage agency concerns that managers might sacrifice long-term investments for short-term profits 2 With increased oversight by the corporate parent and less financial incentive to improve performance, managers of subsidiaries are less likely to engage in leniency