Since the late 1990s there has been significant interest and attention from the research community devoted to understanding the key drivers of how ISP networks are designed, built and operated. While recent work by empiricists and theoreticians has emphasized certain statistical and mathematical properties of network structures and their behaviors, this part of the book presents in great detail an optimization-based perspective that focuses on the objectives, constraints and other drivers of engineering design that will help the community gain a better insight into this fascinating world and enable the design of more “realistic” models.

In this chapter we introduce the area of IP network design and the factors commonly used to drive such a process. Our discussion revolves around IP-over-WDM networks, and we define the network design problem as the end-to-end process aimed at identifying the “right” IP topology, the associated routing strategy and its mapping over the physical infrastructure in order to guarantee the efficient utilization of network resources, a high degree of resilience to failures and the satisfaction of SLAs.

We start by providing a high-level overview of the IP-over-WDM technology. We highlight the properties of the physical and IP layers (the IP layer is also known as the logical layer), we discuss their relationship, and introduce the terminology that will be extensively used in the following chapters. Then, we introduce the processes encountered in IP network design and their driving factors.