Cognitive Networks: Towards Self-Aware Networks

6.1. Introduction

Communication networks have traditionally been engineered following the principle of protocol layering. This means designing specific network functionalities (such as flow control, routing, medium access) in isolation from each other, and putting together the complete system through limited interfaces between the layers performing these specific tasks. The layers, which are in fact distributed systems with collaborating entities distributed through the network [^[], p. 20], are arranged in a vertical hierarchy. Each layer makes use of the services provided by the layers below itself and, in turn, makes its services available to the layers above itself. Inter-layer communication happens only between adjacent layers and is limited to procedure calls and responses. Familiar examples of layered communication architectures are the seven-layer Open Systems Interconnect (OSI) model [^[], p. 20] and the four-layer TCP/IP model ^[].

Even though layered communication architectures have been instrumental in the development of many communication networks, most notably the Internet, in recent times, the suitability of protocol layering is being questioned in the research community. This is largely due to wireless networks becoming an integral part of the communications infrastructure, and hence occupying the center stage of research and development activity. Researchers argue that while designing protocols at the different layers in isolation and running them without much interaction ...