Figure 1.6. Three links have a capacity of 12 and one link has a capacity of 8. The Structure and Functions of Networks Capacity = 5 Capacity = 5 Capacity = 5 Capacity = 5 Figure 1.7. Capacity at the nodes of the network. of the arrangements of nodes and links within a network. Often, upgrades in a network's transmission capacity require corresponding adjustments both of the capacity of equipment at the nodes and of the capacity of links. For example, with links in fiber optic data networks having terabit capacity, the switching and routing centers developed into bottlenecks and had to be replaced by larger-capacity optical switches and routers (McDermott 2002). In addition to capacity, network links can also be described by geographic distance. Some networks, such as computer intranets, can be confined to a building or a campus. Telecommunications networks can be local, regional, national, or international. Undersea telecommunications cables are links that connect nodes across oceans. Satellites extend communications links into outer space. A basic telecommunications system for a regional telephone company might involve links of many different lengths that range from the basic local loop from the curb to the home to regional fiber backbones. Figure 1.8 illustrates a single network with links of varying lengths. 4 miles 5 miles 3 miles 4 miles Figure 1.8. A network with links of varying lengths. Networks in Telecommunications Figure 1.9. A complete graph representing a point-to-point network. The graph has n = 6 nodes and =n(n-1)=15 links. 2. The Shapes of Networks Networks come in many different configurations. The many shapes of networks reflect design efficiencies to take advantage of the performance of network compo- nents and the costs of various combinations of components. Network designs also reflect regulatory requirements, the costs of land, and technological alternatives. Network designs can depart from efficient configurations because networks evolve over time through additions and abandonments reflect