Unlike conventional computer networks such as office LANs or the Internet which can be used for a host of applications, wireless sensor networks are typically used for specific applications in mind. It is this fundamental difference combined with the fact that energy efficiency is of paramount importance in wireless sensor networks that a different approach needs to be taken when designing protocols. In this paper we first describe the main differences and benefits of the cross-layered

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... s used for sensor networks over the traditional OSI layered approach used for conventional networks. We then give two examples which illustrate how we extend usual sensor network cross-layered optimization by going beyond just MACrouting optimizations to optimizations between the application and the MAC layers. RELATED WORK Cross-layer optimization is a key term that is used frequently in sensor network research terminology. However, the term does not have a well-defined definition. Generally, as stated 1-4244-1502-0/07/$25.00