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Unit 9 Section A

Unit 9 Section A. Network. What is a network?. A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. 网络由两个或多个连接在一起的计算机组成，以便共享资源、交换文件或进行电子通信。. How are networks classified?.

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Unit 9 Section A

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  1. Unit 9 Section A Network

  2. What is a network? • A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. • 网络由两个或多个连接在一起的计算机组成，以便共享资源、交换文件或进行电子通信。

  3. How are networks classified? • 1. according to geographical extent: LAN, MAN, WAN. • 2. according to the protocols used:BITNET, Ethernet, Internet, Novell, PSTN, network, ect.

  4. What is local Area Network (LAN)? • A LAN is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a lab, school, or building. Rarely are LAN computers more than a mile apart.

  5. What is Metropolitan Are Network (MAN) ? • MAN is a data network intended to serve an area the size of a large city. Such networks are being implemented by innovative techniques, such as running optical fibre through subway tunnels.

  6. What is Wide Area Network (WAN) ? • A WAN connects larger geographic areas such as Florida, the U.S.A, or the world. Delicated transoceanic cabling(专用的横越大洋的电缆）or satellite uplinks（卫星系统） may be used to connect this type of network.

  7. What is OSI-RM? OSI: open system interconnect 开放式系统互连 RM：reference model 参考模型 OSI-RM is a seven-layer model of network architecture and a suite of protocols to implement it, developed by ISO in 1978 as a framework for international standards in heterogeneous computer network architcture. 是一个七层网络结构模型和一组用以实现它的协议，它由国际标准化组织于1978年制订，作为不同种类型计算机网络国际标准的框架。

  8. What is protocol? • Protocol is a set of rules describing how to transmit data, especially across a network. 用来描述怎样传输数据尤其是跨网络传输数据的一组规则。 • Example: • CMIP common management information protocol 公共管理信息协议 • HTTP hypertext transfer protocol • 超文本链接传输协议 • FTP file transport protocol

  9. Internet • What is Internet? • The Internet is a computer network made up of thousands of networks worldwide. The Internet is the largest internet in the world.

  10. Internet • The Framework of Internet. • The Internet is a three level hierarchy composed of backbone networks, mid-level networks, and stub networks. • 因特网由三个层次组成：骨干网，中间层次网和子网络。

  11. Internet Untile the advent of the www in 1990, the Internet was almost entirely unknown outside universities and corporate research departments and was accessed mostly via command line interfaces such as telnet and FTP. 在1990年www出现以前，除了大学和一些研究机构以外， Internet几乎是完全不为人所知，数据通讯主要通过如telnet 和FTP命令行接口来实现。

  12. Internet Telnet: Telnet is a program that allows you to log into computers on the Internet and use online databases, library catalogs, chat servicers, and more.There are no graphics in telnet sessions, just text. To telnet a computer, you must know its address. With the popularity of the web, Telnet is less frequently used as a means of access to information on the Internet.

  13. Internet • File Transport Protocol (FTP): • FTP is both a program and the method used to transfer files between computers. Anonymous FTP is an option that allows users to transfer files from thousands of host computers on the Internet to their personal computer account. FTP sites contain books, articles, software, games, images, sounds, multimedia, course work, data sets, and more.

  14. World Wide Web (www) • Many people believe that the www is the same thing as the Internet, but they are different actually. The Internet works as the transport mechanism, but the www is an application that uses the transport mechanism. Other applications, such as the most widely used e-mail, are run on the Internet as well.

  15. World Wide Web (www) The www is a system of Internet servers that support hypertext to access several Internet protocols on a single interface. Almost every protocol type available on the Internet is accessible in the Web. This include e-mail, FTP, Telnet, and Usenet News. In addition to these, the www has its own protocol: HTTP.

  16. World Wide Web (www) • The operation of the Web relies primarily on hypertext as its means of information retrieval. Hypertext is a document containing words that connect to other documents. These words are called links and are selectable by the user. A single hypertext document can contain links to many documents. In the context of the Web, words or graphics may serve as links to other documents, images, video, and sound. Links may or may not follow a logical path, as each connection is programmed by the creator of the source document. Overall, the Web contains a complex virtual web of connections among a vast number of documents, graphics, videos, and sounds.

  17. Bodies associated with the running of the Internet: • The Internet Architecture Board • 因特网体系委员会 • The Internet Assigned Numbers Authority • 因特网地址分配机构 • The Internet Engineering and Planning Group • 因特网工程计划组 • Internet Engineering Steering Group • 因特网技术指导组 • The Internet Society 因特网协会

  18. Try to memorize the abbreviations • OSI ISO WWW LAN • MAN WAN ASN BER CMIP CMIS MHS WAIS FDDI SMDS RFC LEEE NIC HTML HTTP

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