the operating environment. Many EmNets will contain components that are constrained in terms of their physical size, amount of memory available, and/or availability of local energy sources. For these system components, both the need for efficiency and the constraints on how it is achieved will be more severe than is the case for more traditional distributed computing systems. Efficient system designs will exploit higher-capacity and resource-rich components where they exist in the overall system and will exploit the redundancy provided by deploying large numbers of inexpensive components. Many current efforts do not focus on systems that operate under these kinds of constraints. Work on the design of personal digital assistants (PDAs) and cell phones, for example, does not need to take into account very large numbers of interacting elements, distributed control, severe energy constraints, or the kinds of physical coupling that many EmNets must accommodate. Approaches taken in the design of smart spaces for homes or office environments are relevant, but such systems generally have more infrastructure to support them than many of the EmNets discussed here.

This chapter examines approaches to providing the mechanisms needed to support self-configuration and adaptive coordination of EmNets. The first section defines these key concepts. The second discusses the elements of self-configuration and adaptive coordination in existing distributed systems, serving as a primer on the state of the art. The final section of this chapter outlines the research needed to realize the vision for robust, scalable EmNets.

TERMINOLOGY

Self-configuration (sometimes referred to as reconfiguration) and adaptive coordination (sometimes referred to as adaptation) refer to the spectrum of changes that a system makes to itself in response to occurrences in its environment and internally. Neither of these terms is meant to convey infinite flexibility. The changes that self-configuration and adaptive coordination induce in a system should always be within the constraints of the system’s planned functionality (admittedly, one such change might be to modify the functionality of the system). For the purposes of this report, the terms self-configuration and adaptive coordination differ with respect to the frequency and degree of change they induce in or respond to from the EmNet. Making a sharp distinction between the two is not as important as recognizing that some techniques are more relevant to one than to the other. In the rest of this chapter the terms are distinguished in order to highlight the techniques that are more appropriate for each.

Self-configuration involves the addition, removal, or modification of elements contained in an EmNet, along with the resulting process of es-



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