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.