Control of Communication Networks
Tarıq Samad · 2009
Two other chapters in this volume discuss new application areas for control: intelligent transportation systems (Chapter 14) and civil structures (Chapter 17). This chapter focuses on a third, and equally exciting, one: the control of communication networks. It is a sign of the enduring vitality of controls as a solution technology that industries of recent vintage are recognizing its relevance for solving a new generation of problems. In areas such as communication networks, many of these problems simply did not exist in anything like their present form when the foundations of modem control were being laid some decades ago.Communication networks pose a number of control problems, all of which can generally be related to ensuring reliable and rapid transmission of heterogeneous digital data over large-scale, geographically distributed channels and processing nodes. Four problems of particular importance are admission control when real-time service is desired, congestion control through regulation of transmission rates, packet routing, and scheduling of available node bandwidth among multiple sources. These problems have different manifestations, depending on the type of network and traffic and on quality of service (QoS) requirements. The chapter notes specific considerations for the Internet and asynchronous transfer mode (ATM) networks. Other types of communication networks, as used in distributed control systems in the building control and process control industries, are briefly discussed in Chapters 16 and 12, respectively.Communication network control problems are spawning new theoretical developments in control, for example, in discrete-event systems (Chapter 2). At the same time, established control techniques such as linear quadratic gaussian (LQG) and calculus of variations remain directly applicable. This chapter also identifies a number of central implementation issues for the control of communication networks. These include the measurement interval used for calculating queue lengths, the feedback mechanisms employed for network control and "fairness" issues in allocating bandwidth.