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Unit 5 Network Systems

Unit 5 Network Systems. 5.1 Internet Basics 5.2 Local and Wide Area Networks 5.3 Client-Server Framework 5.4 Communications 5.5 Internet Architecture. Communications. What are computer communications 通信 ?.

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Unit 5 Network Systems

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  1. Unit 5 Network Systems • 5.1 Internet Basics • 5.2Local and Wide Area Networks • 5.3Client-Server Framework • 5.4Communications • 5.5Internet Architecture

  2. Communications • What are computercommunications 通信?

  3. Sending device— initiates instruction to transmit data, instructions, or information Communications device — connects the sending device to the communications channel Communications channel— media on which data, instructions, or information travel Communications device — connects the communications channel to the receiving device Receiving device— accepts transmission of data, instructions, or information Communications • What is needed for successful communications?

  4. Uses of Computer Communications • What are some uses of communications technology? Internet Web E-Mail InstantMessaging Chat Rooms Newsgroups Internet Telephony WebFolders Fax Machine or Computer Fax/Modem FTP VideoConferencing

  5. Text messagingallows users to send and receive short text messages on a smart phone or PDA Wireless instant messagingallows wireless mobile devices to exchange messages Picture messaging allows users to send graphics, pictures, video clips, sound files, and short text messages Uses of Computer Communications • What are wireless messaging services无线信息服务? Video messaging

  6. Uses of Computer Communications • What are wireless Internet access points and cybercafés? • Wireless Internet access point (无线Internet接入点)allows wireless connection to Internet in public location • 3G network • Cybercafé(网吧)is coffee house that provides computers with Internet access

  7. Uses of Computer Communications • What is a global positioning system (GPS,全球定位系统)? Step 1.GPS satellites orbit Earth. Every thousandth of a second, each satellite sends a signal that indicates its current position to the GPS receiver. Step 2.A GPS receiver (such as in a car, a watch, a smart phone, a handheld device, or a collar) determines its location on Earth by analyzing at least 3 separate satellite signals from the 24 satellites in orbit.

  8. Uses of Computer Communications • What are collaboration and groupware? • Collaboration 协作is working with other users connected to a server • A document management system provides for storage and management of a company’s documents • Groupware群体软件is softwarethat allows peopleto shareinformation p. 302 Fig. 8-6

  9. Uses of Computer Communications • What are voice mail and web services? • Voice mail (音频邮件)is voice message converted to digital form • Web services (Web服务)describe standardized software that enables programmers to create applications that communicate with other remote computers over the Internet or over an internal business network p. 302

  10. 5.1 Internet Basics • What’s Internet (国际互联网,英特网)? • Internet is a collection of local, regional, national and international computer networks that are linked together to exchange data and distribute processing tasks.

  11. Networks and the Internet • Why do users access the Internet? • Communications • Information • Shopping • Banking and Investing • Classes • Entertainment 7. Download Music 8. Share Information p. 9 Fig. 1-7

  12. Internet History (1) • The Internet began as a Cold War project to create a communications network that was immune to a nuclear attack. • In 1969, the U.S. government created ARPANET(阿帕网), connecting four western universities and allowing researchers to use the mainframes of any of the networked • ARPANET was a project of the Advanced Research Projects Agency of the federal government's Department of Defense (美国国防部高级研究计划局).

  13. ARPAnet (OUT) INTERNET (BEGINS) Internet History (2) • There were 23 Internet sites in 1971, 111 in 1977, and up to almost 4 million in 1994. • In 1984ARAPnet - divided into MILNET and ARPANET. MILNET the military and ARPANET the advanced research component • In 1986, another U.S. government agency, the National Science Foundation (NSF), set up a network of five supercomputer centers called NSFnet. • In 1990 ARPAnet ceases to exist. The network is now officially referred to as theINTERNET. • In1997, the Internet has 19.5 MILLION HOSTS; 1 Million WWW sites; 71,618 Newsgroups.

  14. Internet Growth • The size of the Internet based on • Number of people using it. • Number of computers connected • Quantity of data flowing. • Internet host 主机: A computer on the Internet that provides services • data routing • e-mail • Web pages • Today there are millions of host computers available. • There are around 200 million Internet users. • Internet traffic: Number of bytes transmitted from one host to another computer.

  15. Internet traffic

  16. What’s Available in the Internet? • E-mail 电子邮件服务 • World Wide Web (WWW) 万维网 • BBS 电子公告板系统 • Telnet 远程登录服务 • FTP 文件传送服务 • E-commerce 电子商务 • Internet Telephony 网络电话 • Blogs 博客?Web BLOG

  17. Internet Technology The Internet makes the Web possible It is the infrastructure behind the Web

  18. The Internet Backbone • Internet backbone 主干网 • Major internet communication links. • Network service provider (NSP网络服务提供商) • Construct and maintain the Internet backbone, such as AT&T • Network access point (NAP网络访问点) – point on the Internet where several connections converge

  19. The Internet Backbone

  20. Internet Structure • 大致上可将因特网分为以下五个接入级 • 网络接入点 NAP • 国家主干网(主干 ISP) • 地区 ISP • 本地 ISP • 校园网、企业网或 PC 机上网用户

  21. ISP • You connect to the Internet by connecting to an ISP which connects to the Internet backbone. • ISP (Internet Service Provider,Internet服务提供商)- company that maintains an Internet host computer • provides Internet access to businesses and individuals • charges monthly fee • offered over telephone lines, cable TV, or satellite dish • Dial-up connection 拨号连接: A connection that uses a phone line to establish a temporary Internet connection.

  22. Nation-wide Internet Service Providers in China • There are four Nation-wide Internet Service Providers in China • CERNET: China Education and Research Network • CSTNET: China Science and Technology Network • CHINANET: China Public Computer Internet • GBNNET: Golden Bridge Information Network • To be permitted to connect with Internet backbone directly

  23. Internet Servers • Many computers are on the Internet • Yours – called a client computer • Internet server computers – computers that provide information and services on the Internet

  24. Internet Servers

  25. Internet Servers Web server: provides information and services to Web surfers

  26. Internet Servers Mail server: provides e-mail services and accounts

  27. Internet Servers FTP (file transfer protocol) server: maintains downloadable files

  28. Internet Servers IRC (Internet Relay Chat ) server: supports discussion groups and chat rooms

  29. Data Transmission 数据传送 • Cables, wires and satellites carry internet data from an inter-linked communications network. • Data traveling from one internet host to another is transmitted from one link in the network to another, along the best possible route

  30. Communications Protocols • Information moves on the Internet according to communications protocols • Communications protocol (通信协议)– set of rules that every computer follows to transfer information • Most widely used • TCP/IP • HTTP • FTP

  31. Communications Protocols • TCP/IP (Transport Control Protocol/Internet Protocol传输控制协议/Internet协议)– primary protocol for transmitting information over the Internet • HTTP (Hypertext transfer protocol超文本传输协议 )– supports the movement of information over the Web • FTP (File transfer protocol,文件传输协议)– the communications protocol you use to transfer information from one computer to another

  32. Internet Address and Domains • IP Address (IP地址): An identifier for a computer or device on a TCP/IP network. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 204.194.30.130 • Router (路由器): Device which checks the IP address of the data at every intersection on the back bone, that carries the IP address of its destination . • Many host computers have an easy-to-remember name which is officially called a fully qualified domain name. • Most people call it a domain name

  33. Domain Names 域名 • Typed in lowercase • Ends with three letter extension which is its top-level domain • A name that identifies one or more IP addresses • A computer with a domain name is referred to as a site. • Web site - location in a computer somewhere on the Internet.

  34. Domain Name Space 域名空间 地理顶级域名 类别顶级域名

  35. Internet Top-level domains 顶级域名

  36. Finding IP Address with “nslookup”

  37. Internet Address and Domains

  38. Web Basics

  39. Web • What is the Web 万维网? • Billions of documents, called Web pages 网页, available to anyone connected to the Internet A Web site is a collection of related Web pages You can share information by creating Web pages or posting photos on a photo sharingcommunity A podcast is recorded audio stored on a Web sitethat can bedownloaded A Web page contains text, graphics, audio, video, and links to other Web pages A blog consists of time-stamped articles ina journal format

  40. Web • The World Wide Web, or “the Web” was created in 1990 at the European Laboratory for Particle Physics (欧洲原子核研究组织CERN) in Geneva, Switzerland • The Web • Internet service that stores and provides information • easy to use source of graphical information • consists of documents (Web pages) that contain information on a particular topic • Consists of one or more links that point to other web pages which makes it easy to follow a thread of related information.

  41. Difference between the Web and Internet • In the words of Tim Berners-Lee, • On the Net, you find computers; on the Web, you find the documents, sounds, videos, and information • On the Net, the connections are cables between computers; on the Web, connections are hypertext links • The internet is a communications systems; and the web is an interlinked collection of information that flows over the Net

  42. Websites 网站 • Websites are composed of a series of Web pages. • each page stored as a file • HTTP • stands for Hypertext Transfer Protocol超文本传送协议 • is the protocol that allows Web browsers to communicate with Web servers • HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands

  43. MicrosoftInternetExplorer Netscape Mozilla Firefox Opera Safari Web browser • What is a Web browser 浏览器? • Program that allows you to view Web pages

  44. Web Browser • Request a web page from a web server by typing URL • The server sends the data for the web page which contains the information to be viewed and a set of instructions that tells your browser how to display it. • Microsoft Internet Explorer • Netscape Navigator • Firefox

  45. The World Wide Web • What is a home page主页? • The first page that a Web site displays • Often provides connections to other Web pages • What is downloading下载? • The process of a computer receiving information • Depending upon connection speed, downloading can take from a few seconds to several minutes

  46. Step 2.Web browser looks up the home page setting Step 1.Click the Web browser program name Step 4.The home page displays in the Web browser The World Wide Web • How does a Web browser display a home page? Step 3.The Web browser communicates with the ISP’s server to retrieve the IP address. The IP address is sent to your computer.

  47. URL • The uniform resource locator (URL,统一资源定位符) is the unique identifier of a web page. • The location window displays the URL of the current page.

  48. name of the resource, specified by a path communication protocol identifier host name More Detail about URL • URL is the address of a Web resource • http://www.icarnegie.com/courses.html might be interpreted this way: Using hypertext transfer protocol(http), retrieve the file on www.icarnegie.com named /courses.html.

  49. URLs • The format is: protocol://host.domain[:port number]/path/filename • Protocol will be used to retrieve the information. Some of the options are • file: find a file on your computer • http: hypertext transfer protocol - find an html file on a WWW server • ftp: file transfer protocol - find a file on the Internet • telnet: connection to a telnet service (a terminal emulator) • mailto: send a mail message, use SMTP

  50. Absolute and relative URLs • Absolute URLs 绝对URL • Like a complete street address, e.g., “140-09, 155th street, New York, USA” • E.g., “http://www.scu.edu/department/” • Usually used to link pages between sites • Relative URLs 相对URL • Like directions, e.g., “down the street and turn left at the traffic lights” • E.g., “sc/resources.htm” • Usually used to link pages within a site

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