计算机英语刘艺王春生第4版

Unit 8 Computer Network Section A Network Fundamentals The need to share information and resources among different computers has led to linked computer systems, called networks, in which computers are connected so that data can be transferred from machine to machine. In these networks, computer users can exchange messages and share resources such as printing capabilities, software packages, and data storage facilities-that are scattered throughout the system. The underlying software required to support such applications has grown from simple utility packages into an expanding system of network software that provides a sophisticated network wide infrastructure. In a sense, network software is evolving into a network wide operating system. Ⅰ. Network Classifications A computer network is often classified as being either a local area network (LAN) , a metropolitan area network (MAN), or a wide area network (WAN). A LAN normally consists of a collection of computers in a single building or building complex. For example, the computers on a university campus or those in a manufacturing plant might be connected by a LAN. Ⅰ. Network Classifications A MAN is a network of intermediate size, such as one spanning a local community. A WAN links machines over a greater distance — perhaps in neighboring cities or on opposite sides of the world. Ⅰ. Network Classifications Another means of classifying networks is based on whether the network's internal operation is based on designs that are in the public domain or on innovations owned and controlled by a particular entity such as an individual or a corporation. A network of the former type is called an open network; a network of the latter type is called a closed, or sometimes a proprietary network. Ⅰ. Network Classifications The Internet is an open system. In particular, communication throughout the Internet is governed by an open collection of standards known as the TCP/IP protocol