In the past, network protocols in layered architectures were obtained on an ad hoc basis, and many of the recent cross-layer designs are also conducted through piecemeal approaches. Only recently were network protocol stacks instead analyzed and designed as distributed solutions to some global optimization problems in the form of generalized Network Utility Maximization (NUM), providing an insight on what they optimize and on the structures of the network protocol stacks.
This chapter will present material required for an understanding of layering as an optimization decomposition where each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems.
Decomposition theory provides the analytical tool for the design of modularized and distributed control of networks. This chapter presents the results of horizontal decomposition into distributed computation and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and channel coding. Key results from many recent works are summarized and open issues are discussed. Through case studies, it is illustrated how Layering as Optimization Decomposition provides a common framework for modularization, a way to deal with complex, networked interactions. The material presents a top-down approach to design protocol stacks ...