chapter 6 : Networks

6.1 What Is a Computer Network?

A computer network is a system  that connects computers via communications media so that data and information can be transmitted among them.

 The two major types of networks are 
local area networks [LANs] 
 wide area networks [WANs]

[LANs] encompass a limited geographic area and usually are composed of one communication medium.

[WANs] encompass a broad geographic area and usually are composed of multiple communication medium.

6.2 Network Fundamentals

Types of wireline communications medium :

• Twisted pair wire: the most prevalent form of communications wiring consist of strands of copper wire twisted in pairs

Advantages : inexpensive, available and easy to work with.

Disadvantages: slow in transforming data, subject to interface from other electrical source and it is easily tapped unintended receives.

• Coaxial cable: consists of insulated copper wire.

  Advantages : less susceptible to electronic interference than twisted pair wire and can carry more data.

Disadvantages: expensive, difficult to work with and it is inflexible.

•  Fiber optic cables : consist of thousands of very thin filaments of glass fibers that transmit information via light pulses generated by lasers.
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  Advantages : small and light, transmit far more data and they provide great security.

Transmission Technologies

• Digital Subscriber Line: a high-speed, digital data transmission technology using existing analog telephone lines.
• Asynchronous Transfer Mode: data transmission technology that uses packet switching and allows for almost unlimited bandwidth on demand.
• Synchronous Optical Network: an interface standard for transporting digital signals over fiber optic lines that allows users to integrate transmissions from multiple vendors.
• T-Carrier System: digital transmission system that defines circuits that operate at different rates, all of which are multiples of the basic 64 Kbps user to transport a single voice call.

Network Protocols

A protocol : is the set of rules and procedures governing transmission across a network.

Ethernet is a common LAN protocol.

Transmission Control Protocol/Internet Protocol (TCP/IP) : is a file transfer protocol that can send large files of information across sometimes unreliable networks with assurance that the data will arrive uncorrupted

6.3 The Internet and the World Wide Web

Internet: is a global network of computer networks, using a common communications protocol.

the World Wide Web : is a system that stores, retrieves, formats and displays information accessible through a browser 

6.4 Network Applications

• Discovery allows users to browse and search data sources, in all topic areas,

Search engines are computer programs that search for specific information

     by key words and report the results.

Metasearch engines search several engines at once and integrate the findings of  the various search engines to answer queries posted by users. 

• Communication
• Collaboration
• E-Learning and Distance Learning
• Virtual Universities
• Telecommuting