On the design and management of heterogeneous networks: A predictability-based perspective

While great strides have been made in the design and deployment of commercial networks over the past two decades, relatively little progress has been made toward the realization of large-scale tactical military networks. The primary reasons for this disparity include the fact that commercial telecommunication networks are predominantly wired, relatively stable infrastructures, whereas tactical networks consist largely of wireless mobile nodes with unique operating characteristics in hostile environments. Wireless networks must cope with dynamic link conditions not present in wired infrastructures, which place a heavy burden on quality of service management solutions. Managing QoS in the face of constantly changing operating conditions demands dynamic management approaches that span multiple layers in the protocol stack. Such cross-layer design approaches have recently received attention in the context of cellular and mobile ad hoc networks. However, there are still a wide range of opinions and definitions about what exactly CLD entails, and there is no fundamental guidance concerning how to apply CLD techniques in various environments. In this article we introduce the notion of network predictability and describe its relationship to achievable QoS. This relationship is used to propose a framework for CLD that can be used to guide development efforts and direct investment decisions for future military networks. The framework also contains the notion of a cross-layer coherence length, which determines the protocol layers across which the highest degree of coupling, or correlation, should be present in order to realize the greatest possible gains in achievable QoS.