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Chapter 1 5

Chapter 1 5. Networks. Chapter Goals. Describe the core issues related to computer networks List various types of networks and their characteristics Explain various topologies of local-area networks Explain why network technologies are best implemented as open systems

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Chapter 1 5

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  1. Chapter 15 Networks

  2. Chapter Goals • Describe the core issues related to computer networks • List various types of networks and their characteristics • Explain various topologies of local-area networks • Explain why network technologies are best implemented as open systems • Compare and contrast various technologies for home Internet connections

  3. Chapter Goals • Explain packet switching • Describe the basic roles of various network protocols • Explain the role of a firewall • Compare and contrast network hostnames and IP addresses • Explain the domain name system

  4. 15.1 Networking • Computer network : A collection of computing devices that are connected in various ways in order to communicate and share resources • Usually, the connections between computers in a network are made using physical wires or cables. However, some connections are wireless, using radio waves or infrared signals. • The generic term node or host refers to any device on a network. • Data transfer rate : The speed with which data is moved from one place on a network to another. Sometimes the data transfer rate is referred to as the bandwidth of a network.

  5. 15.1 Networking • Another key issue in computer networks is the protocols that are used. Protocol : A set of rules that defines how data is formatted and processed on a network. • Computer networks have opened up an entire frontier in the world of computing called the client/server model Fig. 15.1 Client/Server interaction

  6. 15.1 Networking • Client/server model: A distributed approach in which a client makes requests of a server and the server responds. • File server : A computer that stores and manages files for multiple users on a network. • Web server : A computer dedicated to responding to requests (from the browser client) for web pages • Using networks and the client/server model, parallel processing can be accomplished by the client requesting that multiple machines perform a specific part of a problem. The client gather the responses from each to form a complete solution to the problem.

  7. 15.1 Networking Types of Networks • Computer networks can be classified in various ways. Local-area network (LAN) : A network that connects a relatively small number of machines in a relatively close geographical area. • Various configurations, called topologies, have been used to administer LANs. • Ring topology • Star topology See Fig. 15.2 • Bus topology • A bus technology called Ethernethas become the industry standard for local-area networks

  8. 15.1 Networking Types of Networks Fig. 15.2 Various network topologies

  9. 15.1 Networking Types of Networks • Wide-area network (WAN) : A network that connects two or more local-area networks over a potentially large geographic distance. • Often one particular node on a LAN is set up to serve as a gatewayto handle all communication going between that LAN and other networks. • Communication between networks is called internetworking : The Internet is essentially the ultimate wide-area network, spanning the entire globe. • Metropolitan-area network(MAN): The communication infrastructures that have been developed in and around large cities

  10. 15.1 Networking Types of Networks Fig. 15.1 Local-area networks connected across a distance to create a wide-area network

  11. 15.1 Networking Internet Connections • These smaller networks are often owned and managed by a person or organization. The Internet is really defined by how connections can be made between these networks. • Internet backbone : A set of high-speed networks that carry Internet traffic; These networks are provided by companies such as AT&T, GTE, and IBM • Internet service provider (ISP) : A company that provides other companies or individuals with access to the Internet. ISPs connect directly to the Internet backbone or they connect to a larger ISP with a connection to the backbone; America OnLine (AOL) and Prodigy.

  12. 15.1 Networking Internet Connections • There are various technologies available that you can use to connect a home computer to the Internet. • A phone modem converts computer data into an analog audio signal for transfer over a telephone line, and then a modem at the destination converts it back again into data • A digital subscriber line (DSL) uses regular copper phone lines to transfer digital data to and from the phone company’s central office • A cable modemusesthe same line that your cable TV signals come in on to transfer the data back and forth

  13. 15.1 Networking Internet Connections • Broadband :A connection in which transfer speeds are faster than 128K bits per second • DSL connections and cable modems are broadband connections • The speed for downloads (getting data from the Internet to your home computer) may not be the same as uploads (sending data from your home computer to the Internet) : DSL and cable modem suppliers use technology that devotes more speed to download

  14. 15.1 Networking Packet Switching • To improve the efficiency of transferring information over a shared communication line, messages are divided into fixed-sized, numbered packets • Network devices called routers are used to direct packets between networks Fig. 15.4Messages sent by packet switching

  15. 15.2 Open Systems & Protocols Open Systems • Proprietary system : A system that uses technologies kept private by a particular commercial vendor One system couldn’t communicate with another, leading to the need for • Interoperability : The ability of software and hardware on multiple machines and from multiple commercial vendors to communicate Leading to • Open systems : Systems based on a common model of network architecture and a suite of protocols used in its implementation

  16. 15.2 Open Systems & Protocols Open Systems • TheInternational Organization for Standardization (ISO) established the Open Systems Interconnection (OSI) Reference Model • Each layer deals with a particular aspect of network communication Fig. 15.5 The layers of the OSI Reference Model

  17. 15.2 Open Systems & Protocols Network Protocols • Network protocols are layered such that each one relies on the protocols that underlie it. • Sometimes referred to as a protocol stack : layers of protocols that build and rely on each other Fig. 15.6 Layering of key network protocols

  18. 15.2 Open Systems & Protocols TCP/IP • TCP stands for Transmission Control Protocol • TCP software breaks messages into packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination • IP stands for Internet Protocol • IP software deals with the routing of packets through the maze of interconnected networks to their final destination. • TCP/IP : A suite of protocols and programs that support low-level network communication.

  19. 15.2 Open Systems & Protocols TCP/IP • UDP stands for User Datagram Protocol • It is an alternative to TCP • The main difference is that TCP is highly reliable, at the cost of decreased performance, while UDP is less reliable, but generally faster. • An IP program called ping (Packet InterNet Groper) can be used to test the reachability of network destinations. • TCP/IP program called traceroute shows the route that a packet takes to arrive at a particular destination.

  20. 15.2 Open Systems & Protocols High-Level Protocols • Other protocols build on the foundation established by the TCP/IP protocol suite • Simple Mail Transfer Protocol (SMTP): e-mail • File Transfer Protocol (FTP) : file transfer • Telnet : remote login • Hyper Text Transfer Protocol (http) : WWW service • Several high-level protocols have been assigned a particular port number. Port : A numeric designation corresponding to a particular high-level protocol. Server and routers use the port number to help control and process network traffic.

  21. 15.2 Open Systems & Protocols High-Level Protocols Fig. 15.7Some protocols and the ports they use

  22. 15.2 Open Systems & Protocols MIME Types • MIME stands for Multipurpose Internet Mail Extension • MIME Type: A standard for defining the format of files that are included as email attachments or an websites • Based on a document’s MIME type, an application program can decide how to deal with the data it is given

  23. 15.2 Open Systems & Protocols Firewalls • Firewall : A machine and its software that serve as a special gateway to a network, protecting it from inappropriate access • Filters the network traffic that comes in, checking the validity of the messages as much as possible and perhaps denying some messages altogether • Enforces an organization’s access control policy • Thesystem administrators of an organization set up a firewall for their LAN that permits “acceptable” types of communication and denies other types. For example, denying a telnet connection to any computer inside the LAN by denying all traffic that comes in on port 23.

  24. 15.2 Open Systems & Protocols Firewalls Fig. 15.8 A firewall protecting a LAN

  25. 15.3 Network Addresses • Hostname : A unique identification that specifies a particular computer on the Internet. For example matisse.csc.villanova.edu condor.develocorp.com • Network software translates a hostname into its corresponding IP address (4 bytes) For example 205.39.145.18 Fig. 15.9An IP address is stored in four bytes

  26. Network address Host number 01011011 11100110 01011010 00001101 IP address (binary) ( Dotted decimal ) 155.230.90.13 condor.knu.ac.kr Hostname Computer name Domain name 15.3 Network Addresses • Relation betweenHostname IP address ICANN (Internet Corporation for Assigned Names and Numbers) local system administrator

  27. 15.3 Network Addresses Domain Name System • A hostname consists of the computer name followed by the domain name (ex. csc.villanova.edu). • A domain name is separated into two or more sections that specify the organization, and possibly a subset of an organization, of which the computer is a part • Two organizations can have a computer named the same thing because the domain name makes it clear which one is being referred to • The very last section of the domain is called its top- level domain (TLD) name.

  28. 15.3 Network Addresses Domain Name System Fig. 15.10 Top-level domains, including some relatively new ones

  29. 15.3 Network Addresses Domain Name System • Organizations based in countries other than the United States use a top-level domain that corresponds to their two-letter country codes Fig. 15.11Some of the top-level domain names based on country codes

  30. 15.3 Network Addresses Domain Name System • The domain name system (DNS) is chiefly used to translate hostnames into numeric IP addresses • DNS is an example of a distributed database • If that server can resolve the hostname, it does so • If not, that server asks another domain name server • Domain name server: A computer that attempts to translate a hostname into an IP address.

  31. Chapter 16 The World Wide Web

  32. Chapter Goals • Compare and contrast the Internet and the World Wide Web • Describe general Web processing • Write basic HTML documents • Describe several specific HTML tags and their purposes • Describe the processing of Java applets and Java server pages • Compare and contrast HTML and XML • Define basic XML documents and their corresponding DTDs • Explain how XML documents are viewed

  33. 16.1 Spinning the Web • Many people use the words Internet and Web interchangeably,but they are fundamentally different. • The Web : An infrastructure of distributed information combined with software that uses networks as a vehicle to exchange that information • Web page : A document that contains or references various kinds of data, such as text, images, graphics, and programs • Links : A connection between one web page and another that can be used “move around” as desired • Website : A collection of related web pages

  34. 16.1 Spinning the Web • The Internet makes the communication possible, but the Web makes that communication easy, more productive, and more enjoyable • Browser: A software tool that issues the request for the web page we want and displays it when it arrives. Netscape Navigator or Microsoft’s Internet Explorer Fig. 16.2 A browser retrieving a Web page

  35. 16.1 Spinning the Web • Web server:The computer that is set up to respond to web requests. • Web address : The core part of a Uniform Resource Locator, or URL, which uniquely identifies the page you want out of all of the pages stored anywhere in the world; http://www.villanova.edu/academics.html protocol hostname file name

  36. 16.1 Spinning the Web Search Engines • Search Engine : A website that helps you find other websites For example, Yahoo and Google are search engines You enter keywords and the search engine produces a list if links to potentially useful sites • There are two types of searches • Keyword searches • Concept-based searches attempt to figure out the context of your search.

  37. 16.1 Spinning the Web Instant Messaging • Instant messaging (IM) : An application that allows people to send and receive messages in real time. • Both sender and receiver must have an IM running. • Most IM applications use a proprietary protocol that dictates the precise format and structure of the messages that are sent across the network to the receiver. • Instant messages are not secure.

  38. 16.1 Spinning the Web Cookies • Cookie:A small text file that a web server stores on your local computer’s hard disk. • A cookie contains information about your visit to the site. • Cookies can be used • to determine number of unique visitors to the site • to customize the site for your future visits • to implement shopping carts that can be maintained from visit to visit • Cookies are not dangerous; Web-based technology .

  39. 16.2 HTML • Web pages are created (or built) using a language called the HyperText Markup Language, or HTML. Hypertext (jump from one place to another)  Hypermedia • The term markup language comes from the fact that the primary elements of the language take the form of tags that we insert into a document to annotate the information stored there. Tags are enclosed in angle brackets (<. . . >) Words such as HEAD, TITLE, and BODY are called elements and specify the type of the tag.

  40. 16.2 HTML Fig. 16.2A marked-up document

  41. 16.2 HTML Fig. 16.3The Student Dynamics Web page as displayed in Netscape Navigator

  42. 16.2 HTML Fig. 16.4The HTML document defining the Student Dynamics Web page

  43. 16.2 HTML Images and Links • An image can be incorporated into a web page using the IMG element, which takes an attribute that identifies the image file to display For Example : <IMG SRC = "myPicture.gif" > • A link is specified using the element A, which stands for anchor. The tag includes an attribute called HREF that specifies the URL of the destination document. For Example : <A HREF = "http://duke.csc.villanova.edu/docs/"> Documentation Central!</A> attribute name

  44. 16.3 Interactive Web Pages • When HTML was first developed, there was no way to interact with the information and pictures presented in a web page. HTML is static. • As users have clamored for a more dynamic web, new technologies were developed to accommodate these requests: Java Applets (Sun Microsystems), Active X (Microsoft) Java Server Pages (JSP) Java Applets • Java applet : A java program designed to be embedded into on HTML document, transferred over the Web, and executed in a browser.

  45. 16.3 Interactive Web Pages Java Applets • An applet is embedded into an HTML document using the APPLET tag <APPLETcode="MyApplet.class" width=250 height=150 > </APPLET> • Java programs are compiled into Bytecode, a low-level representation of a program that is not the machine code for any particular type of CPU • Java applets are restricted as to what they can do • The Java language has a carefully constructed security model • An applet, for instance, cannot access any local files or change any system settings

  46. 16.3 Interactive Web Pages Java Server Pages • A Java Server Page, or JSP, is a web page that has JSP scriptlets embedded in an HTML document. • Scriptlet : A portion of code embedded in an HTML document designed to dynamically contribute to the content of the Web page. • A JSP scriptlet is encased in special tags beginning with <% and ending with %> <H3> <% out.printIn(“hello there”); %> </H3>

  47. 16.3 Interactive Web Pages Java Server Pages • Note that JSPs are executed on the server side where the web page resides. • By the time it arrives at your computer, all active processing has taken place, producing a static (though dynamically created) web page. • JSPs are particularly good for coordinating the interaction between a web page and an underlying database.

  48. 16.4 XML • HTML has a predefined set of tags and each tag has its own meaning. HTML specifies how the information in a web page should be formatted, but doesn’t really indicate what the information represents. There is nothing about HTML tags that describes the true content of a document. • The Extensible Markup Language, or XML, allows the creator of a document to describe its contents by defining his or her own set of tags. • Metalanguage: A language for talking about, or defining, other languages XML is a metalanguage.

  49. 16.4 XML Fig. 16.5 An XLML document containing data about books

  50. 16.4 XML • Document Type Definition (DTD) : A specification of the organization of the document • The structure of a particular XML document is described by its corresponding DTD document Fig. 16.6 The DTD document corresponding to the XML books document

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