The Network in 1990s

In this chapter, you will have a brief impression of computer network. We will introduce some basic knowledge and the use of the network to you. Just sit on your chair, we will lead you exploring in the magic world.

1. Uses of Computer Networks

1) Networks for Companies

2) Networks for People

3) Social Issues

2. Brief Introduction of Network

1) Local Area Networks

2) Metropolitan Area Networks

3) Wide Area Networks

4) Internetworks

Summary

Computer networks can be used for numerous services, both for companies and for individuals. For companies, networks of personal computers using shared servers often provide flexibility and a good price/performance ratio. For individuals, networks offer access to a variety of information and entertainment resources.

Roughly speaking, networks can be divided up to LANs, MANs. WANs and internetworks, each with their own characteristics, technologies, speeds and niches. LANs cover a building, MANs cover a city, and WANs cove a country or continent. LANs and MANs are unswitched (i.e. do not have routers); WANs are switched.

Networks software consists of protocols, or rules by which process can communicate. Protocols can be either connectionless or connection-oriented. Most networks support protocol hierarchies, with each layer providing services to the layers above it and insulating them from the details of the Protocols used in lower layers. Protocol stacks are typically based either on the OSI model or the TCP/IP model. Both of these have network, transport, and application layers, but they differ on the other layers.

Well-known networks have included Novell's NetWare, the APARNET (now defunct), NSFNET, the Internet, and various gigabit testbeds. Networks services have included DQDB, SMDS, X.25, frame relay, and broadband ISDN. All of these are available commercially, from a variety of suppliers. The marketplace will determine which ones will survive and which ones will not.

1. Uses of Computer Networks

Before we start to examine the technical issues in detail, it is worth devoting some time to pointing out why people are interested in computer networks and what they can be used for.

1)Network for Companies

Many organizations have a substantial number of computers in operation, often located for apart. Then at some point, management may have decided to connect than to be able to extract and correlate information about the entire company.

The issue here is resource sharing, and goal is to make all programs, equipment and especially data available to anyone on the network without regard to the physical location of the resource and the user.

The first goal maybe summarized by saying that it is an attempt to end the "tyranny of geography."

The second goal is to provide high reliability by having alternative sources of supply.

Another goal is saving money. Then there comes the client-server model.

Another networking goal is scalability; the ability to increase system performance gradually as the workload grows just by adding more process.

Yet another goal of setting up a computer network has little to do with technology at all. A computer network can provide a powerful communication medium among widely separate employees. Using a network, it is easy for two or more people who live far apart to write a report together. When one worker makes a change to an on-line document, the others can see the change immediately, instead of waiting several days for a letter. Such a speedup makes cooperation among far-flung groups of people easy where it previously had been impossible. In the lory run, the use of networks to enhance human-to-human communication will probably prove more important them technical goals such as improved reliability.

2)Network for People

The motivations for building computer networks are an essentially economic and technological in nature. If sufficiently large and powerful mainframes were available at acceptable prices, most companies would simply choose to keep all their data on them and give employees terminals connected to them. In the 1970s and early 1980s,most companies operated this way. Computer networks only became popular when networks of personal computers offered a huge price/performance advantage over mainframes.

Staring in the 1990s, computer networks began to start delivering services to private individuals at home. These services and the motivations for using them are quite different than the "corporate efficiency" model described in the previous section. Below we will sketch three of the more exciting ones that ate starting to happen:

1. Access to remote information

2. Person-to-person communication

3. Interactive entertainment

Access to remote information will come in many forms. One area in which it is already happening is access to financial institutions. Many people pay their bills, manage their bank accounts, and handle their investments electronically. Home shopping is also becoming popular. Newspapers will go on-line and be personalized. The next step beyond newspaper (plus magazines and scientific journals) is the on-line digital library. Another application that falls in this category is access to information systems like the current World Wide Web, which contains information about the arts, business, cooking, government, health, history, hobbies, recreation, science, sports, travel, and too many other topics to even mention. All of the above applications involve interactions between a person and a remote database. The second broad category of network use will be person-to-person interactions. Electronic mail or Email is already widely used by millions of people and will soon routinely contain audio and video as well as text. Smell in messages will take a bit longer to perfect.

Real-time email will allow remote users to communicate with no delay, possibly seeing and hearing each other as well. This technology makes it possible to have virtual meetings, called videoconference, among far-flung people.

One-third category is entertainment, which is huge and growing industry. The killer application here is video