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Computer Networks

Computer Networks. Why Computer Networks. Consider computers in ancient times, say the 1970s To communicate, two computers separated by a distance had to be connected by a rented phone line to communicate

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Computer Networks

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  1. Computer Networks

  2. Why Computer Networks • Consider computers in ancient times, say the 1970s • To communicate, two computers separated by a distance had to be connected by a rented phone line to communicate • If you wanted your computer to talk to two other computers, you needed two phone lines . . . and so on.

  3. Why Computer Networks • If you needed to communicate with 100 computers you needed 100 phone lines. • This approach did not, scale up.

  4. Arpanet • DARPA Defense Advance Research Projects Administration. (The bad guys in the X files • Responsible for coordinating much Defense Department Research • They and the Universities they dealt with owned the lions share of the worlds computers . . . and they needed to communicate.

  5. Arpanet • Dedicated p • Phone lines were impossible • A better idea was needed • Researchers had been exploring the idea of “networking” for five or six years • The better idea looked something like this . . .

  6. The Better Idea • Given computers A, B and C • Where A is connected to B • Where B is connected to C • If C needs to talk to A • Instead of renting another line • Let C send the message for A to B • Let B FORWARD the message to A • In other words, use existing phone lines

  7. The Better Idea • This was one of those simple ideas that would change the world • Appropriately, the contract was bid in 1968 and let in 1969 • The net came up in late 1969 and included • UCLA • UC Santa Barbara • Stanford • University of Utah

  8. Arpanet • The net was called Arpanet and is, in fact the internet we use today • The protocol used was TCP/IP which we will study • Originally, the computers that did the message forwarding were called IMPs (Interface Message Processors) We now call machines that forward, routers.

  9. Arpanet • Arpanet in 1977 • http://en.wikipedia.org/wiki/Image:Arpnet-map-march-1977.png

  10. Arpanet • Arpanet grew rapidly, by the mid eighties most colleges and Universities and private sector research facilities were on the net. • By the time of the Morris worm in the late eighties there were 10s of thousands of machines connect to what was by then know as the internet.

  11. Internet • In the early 90s, AOL became the first online service to provide its customers access to the internet. • The intenet community swelled from tens of thousands of users to millions of users quite literally overnight.

  12. World Wide Web • In 1990 CERN, a European physics center, began research on a hyperlinked document distribution system. • On August 6, 1991, a prototype of the system was launched. The collection of servers was called the World Wide Web • The first browser, Mosaic, was launched at this time.

  13. World Wide Web • Originally, the web included mostly researchers and research centers. • Then, on day, when AOL made web browsing available to their clients, the world arrived. • You know the rest of the story

  14. Computer Networks • In effect, the Internet makes it appear to your computer is directly connected to several million other computers. • Your computer has, as far as its concerned, a dedicated connection to that computer in an internet cafe in Kenya where that gentleman is having trouble gain access to 10 million dollars.

  15. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Look at the weather forecast

  16. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Buy a textbook

  17. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Check for a movie at a local theater

  18. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Print out an airline boarding pass

  19. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Check on your class assignments

  20. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Do a literature search for your assignment

  21. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Submit your assignment to your professor

  22. Computer Network BasicsComputer Networks • Networks make computers much more useful by connecting them to other systems worldwide. • By connecting them to a network, we can • Contact your friends to go out to celebrate finishing your assignment.

  23. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable.

  24. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can

  25. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can • Get attacked by a worm exploiting a buffer overflow weakness in your operating system.

  26. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can • Receive an Trojan horse in an email and inadvertently open it, turning your computer into a zombie.

  27. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can • Open a web page that infects your computer with spyware.

  28. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can • Get an email with a phishing attack that fools you into giving your credit card information to an online crook.

  29. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can • Give computer access to a friend, who sets up file sharing, getting you sued by the RIAA.

  30. Computer Network BasicsComputer Networks • Just as networks make computers much more useful by connecting them to other systems worldwide, they also make them more vulnerable. • By connecting them to a network, we can • You get your password for amazon.com stolen by an eavesdropper, who then buys himself a new gaming system at your expense.

  31. Computer Network BasicsComputer Networks • Network-based vulnerabilities and attacks are one of the most important security concerns.

  32. Computer Network BasicsIntroduction • Traditionally, the motivation in designing computer networks was to move information quickly and reliably between computers.

  33. Computer Network BasicsIntroduction • So the goal for modern computer networks was to be able to efficiently move information worldwide. • Security was initially not an issue. Speed and reliability were.

  34. Computer Network BasicsIntroduction • Networks must work for many different kinds of computers. • Computers with different • Processors, • Operating systems, and • Running different network access programs.

  35. Computer Network BasicsIntroduction • For that reason, networks are designed using agreed upon, standard rules, called protocols. • Any computer, operating system, and program that uses these protocols can interact with other computers over networks using the same protocols. • The protocol called TCP/IP, the Arpanet protocol, has become the defacto standard.

  36. Computer Network Basics The Client/Server Model • Computing in computer networks is organized into a client/servermodel.

  37. Computer Network Basics The Client/Server Model • As mentioned in Unit One, server computers provide services on the network. • For example, they host (provide) • Web sites, • Email services, • Calendars, • Databases, • Games.

  38. Computer Network Basics The Client/Server Model • Client computers and programs access servers to take advantage of their services.

  39. Computer Network Basics The Client/Server Model • Client computers and programs access servers to take advantage of their services. • For example, • Web browsers are clients that retrieve web pages from web servers, and then display them at the client computer.

  40. Computer Network Basics The Client/Server Model • Client computers and programs access servers to take advantage of their services. • For example, • Email clients like Outlook, Mail, and others embedded in web browsers read and send mail by communicating with mail server computers.

  41. TCP/IPTCP/IP Networks • TCP/IP is the networking protocol in the widest use. • It is the ONLY protocol used on the Internet • Networking protocols view networks as a series of layers. • Each layer is concerned with a different level of detail of transporting information across a network.

  42. TCP/IPLayers • The TCP/IP Internet model, has the following layers: • Application Layer • Transport Layer • Network Layer • Link Layer

  43. TCP/IPLayers • The different layers are how different parts of the computer view the task of transporting information across a network. • The layers hide detail that isn’t relevant to a particular part of the computer.

  44. TCP/IP Packets • As we mentioned in Section Two, information in computers is in digital format, usually organized as bytes.

  45. TCP/IP Packets • Multiple bytes of information to be sent across the network are organized into packets. • For example, a web server sending an image will send the information as one or more packets with the bytes making up the image.

  46. TCP/IP Application Layer • The application layer is concerned with one program sending packets of data to another program on another computer across a network. • They are not concerned with the details of how this happens. • That is the concern of “lower” layers.

  47. TCP/IP Application Layer • The application layer is controlled by programs that are part of the operating system. • When a program wants to send information, it calls the application layer program, and gives it the information to send.

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