Cross-layer design and optimization is a new technique which can be used to design and improve the performance in both wireless and wireline networks. The central idea of cross-layer design is to optimize the control and exchange of information over two or more layers to achieve significant performance improvements by exploiting the interactions between various protocol layers. In this paper, we propose a cross-layer design and optimization framework and the concept of using an optimization agent to provide the exchange and control of information between the various protocol layers to improve the performance in wireless sensor networks. The approach is to investigate the effects of the wireless channel and the physical layer performance of a small scale wireless sensor network (WSN) to develop insights that can be used in the design and development of the optimization agent in the proposed cross-layer framework. Performance measurements were conducted to study the effects of interference and transmission range for a group of networked wireless sensors.