I Introduction To Data Communications
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This document introduces data communications and computer networks. It defines data communication as relaying binary messages between two points, and computer networks as interconnected autonomous computers. The goals of networks are resource sharing, high reliability through replication, cost savings, and powerful communication. Networks can enable access to remote information, email, banking, libraries, bulletin boards, and online shopping. Networks are classified by the distance between communicating processors, from circuit boards to planets. Connectivity alternatives include stand-alone computers, time-sharing, and local area networks that share resources and applications.
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I Introduction To Data Communications
- 1. INTRODUCTION TO DATA COMMUNICATIONS DEFINITION OF TERMS F Data Communication is the act of relaying a message or information in binary form between two points (the transmitter and the receiver). F Computer Network is an interconnected collection of autonomous computers. Autonomous means that there should no clear master/slave relationship between the computers. NETWORK GOALS F Resource Sharing. One goal of establishing computer networks is to facilitate sharing of programs, equipment, and data without any regard to the physical location of resource and the user. F High Reliability. Computer networks provide high reliability by having alternative sources of supply. For example, all files could be replicated on two or three machines, so if one of them is unavailable (due to hardware failure), the other copies could be used. Introduction to Data Communications 1
- 2. F Cost Savings. Small personal computers connected in a network have a much better price/performance ratio than large ones such as mainframes. F Communication Medium. A computer network can provide a powerful communication medium among widely separated employees. Networks can enhance human-to-human communication. USES OF DATA COMMUNICATION AND NETWORKS F Access to Remote Information F Electronic Mail F Electronic Banking F Electronic Newspaper and Libraries F Electronic Bulletin Boards F Value-Added Services F On-line Department Stores/Groceries F Interactive Entertainment Introduction to Data Communications 2
- 3. NETWORK CLASSIFICATION F Networks are often classified by the distance of the communicating processors from each other. Interprocessor Processors located Example Distance in the same 0.1 m Circuit Board Data Flow Machine 1m System Multicomputer 10 m Room Local Area Network 100 m Building Local Area Network 1 km Campus Local Area Network 10 km City Metropolitan Area Network 100 km Country Wide Area Network 1,000 km Continent Wide Area Network 10,000 km Planet The Internet Data flow machines are highly parallel computers with many functional units all working on the same program. Multicomputers are systems that communicate by sending messages over very short, very fast buses. A Metropolitan Area Network (MAN) is basically a bigger version of a LAN and normally uses similar technology. Introduction to Data Communications 3
- 4. CONNECTIVITY ALTERNATIVES F Stand Alone Sharing of diskettes Modem and the public telephone system Temporary physical connection Local area network (but the network software is enabled only when needed) Applications and Data Personal Computer Introduction to Data Communications 4
- 5. F Shared Logic Sharing the capability of a single processor with more than one user time sharing In multiprocessor systems, shared logic means sharing the main processors or support processors with more than one user. user enters commands here applications execute here Shared Dumb Terminal Applications Storage and Shared Data Host Computer applications share (shared processor) data here Dumb Terminal Introduction to Data Communications 5
- 6. F Shared Resources Multi-user sharing of devices and/or peripherals applications execute here Shared Personal Computer Local Area Applications Network Storage and Shared Data Network File Server applications share data here Personal Computer applications execute here Issues: 1. Equitable sharing of devices 2. Integrity of data Introduction to Data Communications 6
- 7. F Shared Logic and Resources applications execute here user enters commands here Personal Computer Local Area Network Shared Shared Applications Applications Storage and Storage and Shared Data Shared Data Network File Server Host Computer (shared processor) applications share applications share data here data here applications execute here Introduction to Data Communications 7