Cognitive Networks: Towards Self-Aware Networks

3.1. Introduction

As illustrated in Figure 3.1, modern networks are complex systems composed of many heterogeneous nodes, links and users. Modern networks are often operating in environments where network resources (e.g., node energy and link quality), application data (e.g., the location of data) and user behaviors (e.g., user mobility and user request pattern) experience changes over time. Those changes can degrade network performance and cause service interruption. For example, when the quality of a link being used for data transmission degrades, data being transmitted on the link may be lost. Also, when a user moves to a different location, data that needs to be delivered to the user may be mistakenly sent to the previous location, causing service interruption for the user. In order to maintain performance and service continuity under dynamic environments, networks must provide mechanisms to adapt to changes. Such adaptive mechanisms are implemented within four basic network functions: constructing hop-by-hop connectivity; routing data; scheduling data transmission; and controlling transmission rate. A network adapts to changes by adjusting the behaviors of one or more of those network functions.

This chapter closely examines networks that adapt. It first examines three dynamic factors that trigger network adaptation, namely the dynamic factors of network resources, application data and user behaviors. This chapter then introduces four basic network functions and illustrates ...