Publisher Summary This chapter explores three distinctly different network examples. The first example is a campus or enterprise network. Here, the same organization that uses the network owns it and pays to build and run it. The goal is to provide adequate network services to all users at the minimum overall cost. The second network is owned and operated by a network service provider. Here, the goal is to generate revenue by providing useful services to both content consumers and content providers. The network spans a large geographic area and offers a variety of attractive services to each of its customers. The third network is run by a content-distribution company; its primary goal is to generate revenue by providing premium content-distribution services to the content providers subscribed to its service. The network also has a large geographic span and includes features that ensure rapid content delivery to a large number of content consumers. This particular company does not own the wide area transmission facilities, such as the SONET links they use. Instead, they rent bandwidth from the companies that own and operate these transmission links. Network equipment is expensive to purchase, install, operate, and maintain. Network operators are in a very competitive business. Unless they provide good value compared to their competitors, they cannot expect to attract customers and generate revenue they need to sustain their businesses.