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Unformatted text preview: Foundation I must Create a System, or be enslavd by another Mans; I will not Reason and Compare: my business is to Create. William Blake uppose you want to build a computer network, one that has the potential to S grow to global proportions and to support applications as diverse as telecon- ferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design to integrate these P R O B L E M Building a Network building blocks into an effective com- munication service? Answering this question is the overriding goal of this bookto describe the available building materials and then to show how they can be used to construct a network from the ground up. Before we can understand how to design a computer network, we should first agree on exactly what a computer network is. At one time, the term network meant the set of serial lines used to attach dumb terminals to mainframe com- puters. To some, the term implies the voice telephone network. To others, the only interesting network is the cable network used to disseminate video signals. The main thing these networks have in common is that they are specialized to handle one particular kind of data (keystrokes, voice, or video) and they typically connect to special-purpose devices (terminals, hand receivers, and television sets). What distinguishes a computer network from these other types of networks? Prob- ably the most important characteristic of a computer network is its generality. Com- puter networks are built primarily from general-purpose programmable hardware, and they are not optimized for a particular application like making phone calls or deliv- ering television signals. Instead, they are able to carry many different types of data, and they support a wide, and ever-growing, range of applications. This chapter looks 2 1 at some typical applications of computer networks and discusses the requirements that a network designer who wishes to support such applications must be aware of. Once we understand the requirements, how do we pro- ceed? Fortunately, we will not be building the first network. Others, most notably the community of researchers responsible for the Internet, have gone before us. We will use the wealth of experience generated from the Internet to guide our design. This experience is embodied in a network architecture that iden- tifies the available hardware and software components and shows how they can be arranged to form a complete network system. To start us on the road toward understanding how to build a network, this chapter does four things. First, it explores the re- quirements that different applications and different communities of people (such as network users and network operators) place on the network. Second, it introduces the idea of a network ar- chitecture, which lays the foundation for the rest of the book.chitecture, which lays the foundation for the rest of the book....
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