The basic component of a data communications system

Data Communications: How It All Began

Mail, telephone, radio, tv, books, newspapers, and periodicals-these are the principal ways we send and recieve information, and they have not changed appreciably in a generation. However, data communications system-computer system that transmit data over communications lines such as telephone lines or cables-have been gradually evolving since the mid-1960s. Let as take a look at how they came about.

In the early days of computing, centralized data processingplaced everything-all processing, hardware and software-in one central lokation. Computer manufacturers so that all departments within an organization could be serviced. Eventually, however total centralization proved inconvenient. All input data had to be physically transported to the computer, and all processed material had to be picked up and deliverd to thr users. Inisting on centralized data processing was like insisting that all conversations betweenpeople occur face-to-face in one designated room.

The next logical step was teleprocessing system-terminals connected to the central computer via communications lines. Teleprocessing systems permitted users to have remote acces to the central computer from their terminals in other buildings and over other cities. However even though acces to the computer system was decentralized, all processing was still centralized-that is, performed b a company's one central computer.

In the 1970s business began to use minicomputers, which were often at a distance from the central computer. These were clearly decentralized system because the smaller computer could do some processing on their own, yet some also had access to the central computer. This new setup was labeled distributed data processing. It is similar to teleprocessing, except that  it accommodates not only remote access but also remote processing.A typical application of a distributed data processing system is a business or organization with many locations-perhaps branch offices or retail outlets.

The whole picture of distributed data processing has changed dramatically with the advent of networks of personal computers. By network we mean a computer system that uses communications equipment to connect two or more computers and their resources. Distributed data processing systems are networks. But of particular interest in today's business world are local area networks (LANs), which are designed to share data and resources among several individual computer users in an office or building.

Putting Together a Network: A First Look

Even though the components needed to transmit data from one computer to another seem quite basic, the business of putting together a network can be extremely complex. We begin with the initial components and then move to the list of factors that a network designer would have to consider.

• Getting Started,

  The basic configuration-how the component are put together-is pretty staightforward, but there is a great variety of components to choose from, and the technology is ever changing. Assume that you have some data-a massage-to transmit from one place to another. The basic components of a data communications system used to transmit that massage are (1) a sending device, (2) a communications link, and (3) a recieving device. Suppose, for example, that you work at a sports store. You might want to send a message to the warehouse to inquire about a wilson tennis racquet, an item you need for a customer. In this case the sending device is your computer terminal at the store, the communications chanel is the phone line,and the recieving device computer at the warehouse. As you will see later, however, there are many other possibilities.
  
  
  There is another often-needed component thet must be mentioned in this basic configuration, as you can see the picture below
  
  
  Large computer system may have additional components. At the computer end, data may travel though a communication control unit called a front-end processor, which is actually a computer in itself. Its purpose is to relieve the central computer of some of the communications task and thus free it for processing applications programs. In addition, a front-end processor usually performs error detection and recovery function.

  

  communication system component

  
  

• Network Design Consideration

  The task of network design is a complex one, usually requiring the services of a professional spesifically trained inthat capacity. Although we cannot learn how to design a network in this brief chapter, we can ask some questions that help us appreciate what the designer must contemplate. 
  
  
  
  

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