Unit 5 Network Systems 5.1 Internet Basics 5.2 Local and Wide Area Networks 5.3 Communication Strategies 5.45.4 Data Transfer Technologies 5.4 5.55.5 Internet. - презентация

1 Unit 5 Network Systems 5.1 Internet Basics 5.2 Local and Wide Area Networks 5.3 Communication Strategies Data Transfer Technologies Internet Architecture 5.5Assessments: –Exercise 5

2 5.1 Internet Basics Internet Basics MIME Types Internet Languages

3 5.1.1 Internet Basics Internet is a collection of local, regional, national and international computer networks that are linked together to exchange data and distribute processing tasks. 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 –connecting four western universities and allowing researchers to use the mainframes of any of the networked

4 Internet Basics ARPANET was a project of the Advanced Research Projects Agency (ARPA ) of the federal government's Department of Defense. There were –23 Internet sites in 1971, –111 in 1977, and –up to almost 4 million in In 1986, another U.S. government agency, the National Science Foundation (NSF ), set up a network of five supercomputer centers called NSFnet. The Internet has millions of users worldwide. It is referred as the Web

5 Internet Growth The size of the Internet based on –Number of people using it. –Number of computers connected –Quantity of data flowing. Internet host ( ): A computer on the Internet that provides services –data routing / / 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.

6 Internet Technology Network Service Provider (NSP, ) –maintains a series of communication links( ) for internet data. –These links interconnect at several Network Access Points (NAP ) so that data can flow through NSP. 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, Data traveling from one internet host to another is transmitted from one link in the network to another, along the best possible route,

7 Internet Technology Internet Backbone( ): –Major internet communication links. TCP/IP (Transport control Protocol/Internet Protocol) / : –A standard set of communication rules used by every computer that connects to the internet. –A standard set of communication rules used by every computer that connects to the internet.

8 Backbon e NSP

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

10 Web site Request in a Nut Shell

11 Internet Address and Domains IP Address IP : –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, Router : –Device which checks the IP address of the data at every intersection on the back bone, that carries the IP address of its destination.

12 Domain Names 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 –Most people call it a domain name –Typed in lowercase –Typed in lowercase Ends with three letter extension which is its top-level domain 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 Web - location in a computer somewhere on the Internet.

13 Internet Top-level domains

14 The Web The web was born in 1990 at the European Laboratory for Particle Physics (CERN). The web was born in 1990 at the European Laboratory for Particle Physics (CERN). Web: Internet service that stores and provides information. consists of – Web pages (documents) that contains information about specific topic. –One or more links that point to other web pages which makes it easy to follow a thread of related information. Websites are composed of a series of Web pages. –each page stored as a file

15 Websites HTTP,Hypertext Transfer Protocol, HTTP,Hypertext Transfer Protocol, –is the protocol that allows Web browsers to communicate with Web servers. HTTP defines –how messages are formatted and transmitted –how messages are formatted and transmitted –what actions Web servers and browsers should take in response to various commands. –what actions Web servers and browsers should take in response to various commands.

16 Websites URL (Uniform Resource Locator, ) is a global Internet address of a document on a computer that begin with –The first part of the address indicates what protocol to use –The second part specifies the IP address or the domain name where the resource is located. For example, Protocol Domain Name

17 URLs Web server Web Web server Web –computer with special software for transmitting Web pages over the Internet –domain names prefixed with www Must –domain names prefixed with www Must Home page / Home page / –identifies the site and contains links to other pages at the site Web Browser –Request a web page from a web server by typing either URL or a web page –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.

18 Other Types of Internet Servers Internet hosts also provide services such as – –file transfers –file transfers –discussion groups –discussion groups –real time chat. –real time chat. Internet includes FTP servers, which maintain a collection of files that you can transfer to your own computer. Internet includes FTP servers, which maintain a collection of files that you can transfer to your own computer. Usenet servers and IRC servers (Internet Relay Chat servers) handle the exchange of comments among members of Internet discussion groups and chat groups. Usenet servers and IRC servers (Internet Relay Chat servers) handle the exchange of comments among members of Internet discussion groups and chat groups.

19 Web Portals Web Portal Web : web site that provides a group of popular services, search engine, access, chat rooms and links to shopping, weather, news and sports. –Lycos / Sohu / Sina –America Online –Yahoo/Goolge/Baidu –Microsoft Network Access to these portal sites is free to anyone who accesses the page.

20 The World Wide Web, or the Web was created in 1990 at the European Laboratory for Particle Physics. 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

21 Displaying Web Pages A Web page may contain links that point to other Web pages. –makes it easy to follow a thread of related information You request a Web page from a Web browser by typing in a URL or clicking a Web page link. The page that displays when your browser first starts is called the home page

22 Getting on the Web Most computers come with a browser, such as Microsoft Internet Explorer or Netscape Navigator, which is pre-configured to take you to a Web portal. A Web portal is a Web site that provides a group of popular Web services. –search engines – accounts –chat rooms –links to shopping, weather, news, and sports

23 Internet Multimedia Media element such as sound, animation, and video stored in a file which is sent to your computer in two ways when a link for media element is clicked. –Web server sends you the entire file before playing it. Large files requires five minutes or more before playing. –Streaming media - computer plays a media file while receiving it In-place multimedia technology plays the media element as a part of the web page. In-place multimedia technology plays the media element as a part of the web page.

24 Internet Multimedia (continued) Multimedia Overlay technology adds a separate window to play the media element. Multimedia Overlay technology adds a separate window to play the media element. Plug-in, Player, Viewer: Software module that provides system the capability to run a specific type of file. –Media player of windows have controls to play media file types such as.wav and.avi files Multimedia overlay technology

25 File Transfers Downloading Downloading –Process of transferring the file from remote computer to your computer. Uploading Uploading –Process of sending a copy of files from your computer to remote computer. –Most browsers allow downloading but not uploading files. –FTP client software is used in uploading –Valid user accounts are required by FTP servers to upload files.

26 Web Installs The Internet is a good source of free software. Most downloadable software is stored as a self-extracting file, a single file that holds all of the modules for the software. –download sites include instructions for downloading software

27 Internet Interactions In addition to , people can interact on the Internet by joining a discussion group. –takes place asynchronously, meaning discussion participants are not online at the same time A chat group is a discussion group which takes place synchronously participants are online at the same time). Newsgroups are another way for people to communicate on the Internet –The browser must have access to a news server –Over 30,000 Usenet newsgroups, covering every conceivable topic –Over 30,000 Usenet newsgroups, covering every conceivable topic

28 5.1.2 MIME Types It is possible to attach images and other types of documents to an message. how is the mail client (that is, an application that reads ) supposed to know what to do with these documents? –The solution is to give each attachment a label explaining what kind of document it is. –The labels are called MIME types. Multipurpose Internet Mail Extension. Multipurpose Internet Mail Extension.

29 MIME Types MIME Types define how an attachment is to be read MIME Types define how an attachment is to be read –type/subtype –text/plain, text/html, image/gif, image/jpeg, application/msword With Web browsers, MIME types tell it what plug-ins to use

30 MIME Types The MIME types file permits wildcard specifications, such as – image/*, which matches any type of image file, –or even */*, which a mail client can use to provide a default behavior for any file type. A common choice of default behavior for unfamiliar types is "save to disk." –This allows the user to deal with the attachment manually at a later time.

31 MIME Types MIME types are not just for anymore. Web browsers use them as well. Web sites that contain sound or video clips, –for example, may require the mail client to launch a player program in order to present those files to the user. –The MIME types file tells the Web browser what kind of player to use. You can display and edit MIME types' settings using your Web browser by editing your preferences.

32 Microsoft Windows operating system also now uses this information. If you double-click a file icon, the file extension is looked up in the MIME types file to determine which application should be used to open the file. If you are using Windows Explorer to view your disk files, on the View menu, click Folder Options and then click the File Types tab. how to set ? If you are using Windows Explorer to view your disk files, on the View menu, click Folder Options and then click the File Types tab. how to set ? This window shows a list of all file extensions registered under Windows and displays the appropriate MIME type associated with each extension.

33 MIME extensions also specify the character encoding in messages. Languages such as French or Spanish require accent characters that are not part of the ASCII messages in nonwestern languages, such as Chinese, require a different character set. The MIME extensions provide a way to specify which encoding a message is using. –the mail client to translate that encoding into something that can be meaningfully displayed to the user. –Demo in source of web page

34 5.1.3 Internet Languages There are many Internet languages that are used to exchange data on the World Wide Web. –HTML –XML –JavaScript –Java

35 HTML HTML, Hyper Text Markup Language. An HTML file –is a text file –containing a set of predefined tags that are used to specify how data should be displayed in a browser or another application program. For example, inserting the built-in tag " " and " " around a phrase would italicized the phrase displayed. HTML is composed of text, –can create an HTML file using a text editor. To enable the Web browser to interpret how you want the page to be displayed, –must save the file with an "htm" or "html" file extension. Note –" " are indicates the beginning and end of a tag, respectively.

36 sample.html Page title This is an example of a Web page. A tag is used to make this text appear bold. Page title This is an example of a Web page. A tag is used to make this text appear bold.

37 HTML tags HTML tags, which are used for marking up documents, are predefined. the author of HTML documents can only use tags that are defined in the HTML standard to customize the look and feel of a web page. There are numerous resources on the Internet that you can use to learn how to create web pages with HTML. –using an Internet search engine such as Google, and type in "HTML tutorial" in the search box. Google

38 HTML Authoring HTML Authoring HTML or Hypertext Markup Language is a scripting language used for writing Web pages. Tags are used Tags are used –Usually a pair of tags beginning and ending –Java applets are embedded in HTML files –Of course, many other like Flash also can be embedded

39 Other Internet Technologies XML or eXtensible Markup Language XML or eXtensible Markup Language –User defined tags using a stylesheet JavaScript uses the syntax of Java in a scripting language – – Java – OOP language –Code is interpreted instead of compiled in the JVM (Java Virtual Machine Java ) Flash – small, compact, vector based animation tool QuickTime – larger, better video quality, bitmap

40 XML sample F8915 ASP 580 F8916 ASP IIS 4/5 550 F8915 ASP 580 F8916 ASP IIS 4/5 550

41 HTML v.s. XML HTML tags are primarily concerned with how text should be displayed XML tags can be used to describe what a piece of text means. Another major difference between HTML and XML is that –there are no predefined tags in XML. –Users have the freedom to define their own tags.

42 JavaScript JavaScript is a "scripting language," –the instructions the programmer writes are not compiled in advance. –are interpreted by an application when the script is run by the computer. Macros and Batch Script Files contain examples of simple scripting languages. JavaScript is a more complex scripting language that uses much of the structure and syntax of Java.

43 JavaScript The scripts are included inside an HTML document, using the tag. JavaScript provides operations for manipulating the Web browser (creating new pop-up windows), controlling interactions with the user, and generating Web page text on- the-fly. JavaScript provides operations for manipulating the Web browser (creating new pop-up windows), controlling interactions with the user, and generating Web page text on- the-fly.

44 JavaScript Demonstration function display() { document.body.bgColor = "black"; var ln1 = "Hello World!"; var ln2 = "This is the " + document.title + " page."; var str = ln1.fontcolor("lime") + " " + ln2.fontcolor("red"); document.writeln(str); alert(str); JavaScript Demonstration function display() { document.body.bgColor = "black"; var ln1 = "Hello World!"; var ln2 = "This is the " + document.title + " page."; var str = ln1.fontcolor("lime") + " " + ln2.fontcolor("red"); document.writeln(str); alert(str); } display(); } display();

45 Funny JavaScript Code javascript:R=0; x1=.1; y1=.05; x2=.25; y2=.24; x3=1.6; y3=.24; x4=300; y4=200; x5=300; y5=200; DI=document.images; DIL=DI.length; function A(){for(i=0; i-DIL; i++){DIS=DI[ i ].style; DIS.position='absolute'; DIS.left=Math.sin(R*x1+i*x2+x3)*x4+x5; DIS.top=Math.cos(R*y1+i*y2+y3)*y4+y5}R++} setInterval('A()',5); void(0); Open the source code source codesource code

46 Java import java.applet.Applet; import java.awt.Color; import java.awt.Graphics; public class Demonstration extends Applet { public void paint(Graphics g) { for (int i=1;i<=25;i++) { g.setColor(new Color(255-i*10,i*10,i*10)); g.drawRoundRect(10, 10, 10*i,10*i, 10, 10); }g.setColor(Color.red); g.drawString("Hello World!", 23, 280); }} Demo1 me me Demo1 atable atable

47 5.2 Local and Wide Area Networks

48 Local and Wide Area Networks A computer network is a collection of computers and other devices that communicate to share data, hardware and software. Local Area Network (LAN): –A computer network that spans a relatively small area –provides communication among computers over a relatively short distance, such as one floor of a building Wide Area Network (WAN): –A system of LANs connected is called a wide-area network. –the computers are located further away within a building, or across town, across the country, or across the world

49 Network Resources A local area network makes a stand-alone computer( ) a workstation on a network. The workstation provides you with: –your computers local resources hard drive, software Printer –access to network resources software storage space other printers

50 Network Resources

51 You typically cannot use network resources until you log into the network. provide a User account You typically cannot use network resources until you log into the network. provide a User account User account include User ID Password User account include User ID Password –provides access to network –accumulates information about network use –keeps track of when user log in and out User ID - derived from your real name –no spaces –some networks use case-sensitive IDs Password - set of characters without spaces –unique –easy to remember Network administrator Network administrator –person responsible for setting up user accounts and maintaining network

52 Drive Mapping Drive Mapping Workstation gains access to the server when the server hard drive is mapped to a drive letter. Drive mapping - network term for assigning a drive letter to a network server disk drive. –use the letter F: Windows Neighborhood Network is a utility that helps you see your workstations network drive mapping.

53 Using Programs on a Network When you start a program that is stored on a LAN, the program is copied to your workstations RAM, then runs normally. With proper licensing, many users on the same network can use the same program simultaneously, also known as sharing. With proper licensing, many users on the same network can use the same program simultaneously, also known as sharing. Sharing is effective because: –less disk storage space required –easier to update software –easier to update software –less expensive

54 Using Data Files on a Network Advantages to storing data files on a server: –can access from any computer on network –other network users can access files option of restricting access option of restricting access File locking File locking –precaution that locks an open file so other users cannot open it at the same time

55 Using a Network Printer To access other printers on a network, you first have to install its driver software. 1.Open the Printers window 2. Start the Add Printer Wizard

56 Using a Network Printer 3.Select Network printer and follow instructions

57 Using a Network Printer (continued) Default printer - printer you most frequently use One way to select a different printer is to select a printer using the Printers dialog box.

58 Local and Wide Area Networks (continued) Network Server Network Server –device on a network that manages network resources –Sharing of Programs / Sharing of Data A network interface card (NIC ) is the key hardware component for connecting a computer to a local area network. –small circuit board that sends data to and from workstations to the network –Provides the physical connection between the network and the computer workstation Different networks use different NICs. Popular network types include –Ethernet and Token Ring. –Ethernet and Token Ring.

59 Cable Media Twisted Pair Twisted Pair –A type of cable that consists of two independently insulated wires twisted around one another. One wire carries the signal while the other wire is grounded and absorbs signal interference –A type of cable that consists of two independently insulated wires twisted around one another. One wire carries the signal while the other wire is grounded and absorbs signal interference –UTP (unshielded twisted pair, ) –STP (shielded twisted pair ) –Looks similar to telephone cable –Uses square plastic RJ-45 connector Coaxial cable Coaxial cable –A type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference. –Resembles cable-TV cable –Uses round, silver BNC connector

60 Wireless Networks Wireless networks use radio or infrared signals to transmit data from one network device to another. –handy in environments where wiring is difficult to install historical buildings –provide mobility –provide mobility –good for temporary installations –good for temporary installations

61 Network Hub Cable from a workstation NIC connects to a network hub, a device that joins communication lines together. Hubs are commonly used to connect segments of a LAN. –A hub contains multiple ports. When a packet arrives at one port, –it is copied to the other ports so that all segments of the LAN can see all packets.

62 Network Hub A hub serves as a central connection point for workstation and server cables.

63 Network Servers Network Servers When connected to a network, the device that processes your data depends on the types of servers. A file server is a computer and storage device dedicated to storing files. Any user on the network can store files on the server. –Dedicated file server : delivers programs and data files to workstations. does not process data or run programs for workstations. –Non-dedicated file server : computer on a network that performs a dual role as both file server and workstation also called peer-to-peer capability

64 Dedicated File Server When connected to a network, the device that processes your data depends on the types of servers. –Dedicated file server delivers programs and data files to workstations. does not process data or run programs for workstations. A dedicated file server delivers programs and data to workstations, but does not process data for the workstations.

65 Non-Dedicated File Server A non-dedicated file server functions like any other workstation.

66 Application Server Application server Application server –computer that runs a specific application software package GIS Server web server DB server –also referred to as client/server architecture An application server splits processing between the workstation (client) and the network (server). An application server splits processing between the workstation (client) and the network (server).

67 Application Server An application server typically runs database software and performs database functions as requested by the workstations.

68 Print Server Print server : receives files from workstations and forwards them to a specific network printer –manages a print queue, a holding area for files waiting to be printed –A print job is a file that has been sent to a print queue.

69 Other Network Servers Some networks include a host computer, a minicomputer or a mainframe with attached terminals. / Some networks include a host computer, a minicomputer or a mainframe with attached terminals. / –Host: all processing takes place on it –Terminals: only display results of processing –also known as a time-sharing system –also known as a time-sharing system Terminal emulation software Terminal emulation software –connects a microcomputer to a host –Demo, telnet

70 Network Operating System Todays computers include software necessary to communicate with a network. –handles the communication between your workstation and the network server. Network operating system (NOS) software –manages network resources –controls flow of data –maintains security –tracks user accounts

71 Network Operating System (continued) Network operating systems have two components Network operating systems have two components Network server software (installed on file server) –controls file access from the servers hard disk –manages print queue –tracks user data IDs and passwords Network client software (installed on workstation) –gathers login information (from user) –handles drive mapping –directs printouts to network printer The server and client software components do not have to match. Many desktop operating systems have some server capabilities windows

72 Stand-Alone Operations on a Network Most software designed for stand-alone computers( ) can be installed on a network server. Some software has built-in networking features that only appear when software is installed on network. –ability to send a file to another network user –

73 Software on a Network After a program is installed on a network server, a workstation installation is also necessary. After a program is installed on a network server, a workstation installation is also necessary. A workstation installation copies some but not all of the program files to your local disk. –updates Windows registry –updates Windows Start menu

74 5.3 Communication Strategies Client-Server Framework Peer-to-Peer Connectivity Assessments: –Multiple-Choice Quiz 19

75 5.3.1 Client-Server Framework Client/Server architecture –A network architecture in which each computer or process on the network is either a client or a server.

76 Client-Server Framework Client –Client interacts with both user and server –Clients are PCs or workstations on which users run applications. –Clients rely on servers for resources, such as files, devices, and even processing power. Server –Server accepts requests from clients and performs some service and returns results –Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers ).

77 Two terms used in client-server framework are thin client and thick client –Thin client does relatively little work (processing) typically providing little more than a user interface –Thin client does relatively little work (processing) typically providing little more than a user interface –Thick client carries out a substantial portion of the overall work of the system –Thick client carries out a substantial portion of the overall work of the system Thin and Thick Clients

78 Client Machines Accessing Web Servers Client Network or Web server

79 Instead of having a central server C/S that all clients communicate with, Instead of having a central server C/S that all clients communicate with, –every member of a peer-to-peer network can communicate with any other member –Since peer-to-peer distribute processing( ), there are less potential communication bottlenecks –Since peer-to-peer distribute processing( ), there are less potential communication bottlenecks – –Bt –Bt Peer-to-Peer Connectivity

80 5.4 Data Transfer Technologies Protocols( ) – rules for interpreting data streams Communication medium( ) – cables, optical fiber, wireless, radio signals Assessments: –Multiple-Choice Quiz 20

81 Communications Data communications( ) is the process of transmitting and receiving data in an orderly way. –local communications (short distance) –telecommunications (long distance) Communications system - combination of hardware, software, and connecting links that transport data –efficiency of system depends on coding process( ) and noise ( interference that destroys the integrity of signals on a line)

82 Electromagnetic Signals Todays communications systems transmit messages and data in the form of electromagnetic signals (waves). Todays communications systems transmit messages and data in the form of electromagnetic signals (waves). –characterized by size and spacing –amplitude = height of wave –amplitude = height of wave –wavelength = distance between waves –wavelength = distance between waves Wavelength Amplitude

83 Communication Signals Frequency is the number of times per second the wave cycle repeats or oscillates. Frequency is the number of times per second the wave cycle repeats or oscillates. –shorter wavelengths produce higher frequencies Waves can have different shapes called waveforms. Waves can have different shapes called waveforms. –analog signals –analog signals have an unlimited range of values and a smooth curved waveform a smooth curved waveform –digital signals –digital signals represent discrete values and have a square or stepped wave pattern have a square or stepped wave pattern

84 Communication Signals It is possible to convert analog signals into digital signals. Digital signals: –less susceptible to noise –less susceptible to noise –require simpler circuitry –easier to clean

85 Communications Communications channel Communications channel –a physical path or frequency for a signal transmission telephone cables Communications medium Communications medium –carries one or more communications channels and –provide a link between transmitting and receiving data. twisted-pair cable coaxial cable fiber-optic cable fiber-optic cable

86 Communication Channel Communication Signals are transmitted through Communication Channel –What is a communication Channel refers to a communications path between two computers or devices. It can refer to the physical medium or to a set of properties that distinguishes one channel from another. –Communication Channel carries one or more communication channels. Different mediums are twisted pair, coaxial & fiber optical cable

87 Bandwidth Bandwidth - transmission capacity of a communications channel. –The capacity of a communications system depends on the bandwidth of the channel.

88 Bandwidth Broadband transmission (high capacity) –A type of data transmission in which a single medium (wire) can carry several channels at once. –E.g. Cable television Baseband transmission (less capacity than broadband) –A type of digital data transmission in which each medium (wire) carries only one signal, or channel, at a time. –E.g. Telephone

89 Data Transfer Rate Data Transfer Rate is rate at which data is transmitted Data Transfer Rate is rate at which data is transmitted –The speed with which data can be transmitted from one device to another. –Also known as Throughput –Also known as Throughput –When a communications channel is busy, it takes longer to send and receive data.

90 Data Transfer Rate Data is either transferred in serial transmission or parallel transmission. Serial transmission ( ) - one piece of information follows another –modem and network communications Parallel transmission ( ) - all of the bits for an entire byte are sent at the same time –for sending data to a printer

91 Communication System Topologies Topology Topology –The pattern or path of the interconnections in a communication system –Networks can use a single topology or a mixture of topologies There are three principal topologies: –Bus topology –Ring topology –Star topology

92 Bus Topology Bus Topology Bus topology - provides a common or shared communications pathway –All devices are connected to a central cable, called the bus or backbone. –Bus networks are relatively inexpensive and easy to install for small networks. –Ethernet systems use a bus topology. –Used by cable TV companies –String cables from house to house –No one user gets to use full bandwidth

93 Ring Topology Ring Topology Ring topology - connects devices in a continuous loop –All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. –Ring topologies are relatively expensive and difficult to install, but they offer high bandwidth and can span large distances. –Used in local area networks

94 Star Topology Star Topology Star topology - communications lines fan out from a central location –All devices are connected to a central hub. –Star networks are relatively easy to install and manage, –but bottlenecks can occur because all data must pass through the hub. –every connection is dedicated to one user, so expensive

95 Communication Protocols A communications protocol( ) is –a set of rules that ensures the orderly and –accurate transmission and reception of data. Used to prevent noise interference communication protocols are used.

96 Communication Protocols Protocols are agreed-upon format for transmitting data between two devices. The protocol determines the following: –the type of error checking to be used –data compression method, if any –how the sending device will indicate that it has finished sending a message –how the receiving device will indicate that it has received a message

97 Error-Checking Protocols To ensure accurate delivery of data Error checking is used. Parity checking refers to the use of parity bits to check that data has been transmitted accurately. The parity bit is added to every data unit (typically 7 or 8 bits ) that are transmitted. The parity bit for each unit is set so that all bytes have either an odd number or an even number of set bits –parity bits - describe the numbers of 0s and 1s in a sequence of data –even parity - number of 1 bits must be even –odd parity - number of 1 bits must be odd

98 Error-Checking Protocols Parity helps a communications system determine whether data has been corrupted during transmission.

99 Serial Communication Serial communication uses –Asynchronous transmission –Asynchronous transmission –Synchronous transmission –Synchronous transmission

100 Serial Communication Asynchronous Transmission –Communications in which data can be transmitted intermittently rather than in a steady stream. –Accomplished through a special start bit and stop bit at the beginning and end of each piece of data. –Transmits data as one or more series of bytes called a block –Transmits data as one or more series of bytes called a block

101 Serial Communication Synchronous Transmission –The sender and receiver are synchronized by a clock –Occurring at regular intervals –Usually synchronous and is governed by the microprocessor clock –E.g: Bus signals can occur only at specific points in the clock cycle.

102 Signal Direction Simplex communication - communication in one direction where one party is the transmitter and the other is the receiver (e.g. radio transmitter). Half-duplex communication - communications where only one party can transmit at a time. E.g: CB radio Full-duplex communication( ) - transmission of data in two directions simultaneously. E.g:Telephone Echoplex communication - communication sent and echoed back to check accuracy

103 Twisted-Pair Cable Voice-grade cable (Category 1 cable) –recommended for transmitting voice but not data Data-grade cable –suitable for data transmissions Select a Category 5 unshielded or shielded cable with RJ-45 connectors to connect your network interface card to a network hub. Twisted-pair cable terminates with a plastic RJ-45 connector.

104 Twisted-Pair Cables Two types –Shielded twisted pair (STP) cable –Unshielded twisted pair (UTP) cable One wire carries the signal while the other wire absorbs signal interference Categories –Category 1 voice only (telephone wire) –Category 2 data to 4 mbps (Local Talk) –Category 3 data to 10 mbps (Ethernet) –Category 4 data to 20 mbps (token ring 16 mbps) –Category 5 date to 100 mbps (fast Ethernet)

105 Coaxial Cable Coaxial cable - high-capacity communications cable consisting of a copper wire conductor –carries television signals Coaxial cable contains shielding which increases bandwidth.

106 Coaxial Cable Coaxial cable: –has excellent bandwidth –more expensive –more difficult to work with than twisted-pair Fiber-optic cable is replacing coaxial and twisted-pair cable where high bandwidth is required.

107 Fiber-Optic Cable Fiber-optic cable is a bundle of extremely small tubes of glass called optical fibers( ) surrounded by layers of plastic, that transmits data using light rather than electricity –thinner than human hair

108 Fiber-Optic Cable (continued) Fiber-optic cable: –new development –does not conduct or transmit electrical signals –miniature lasers send pulses of light –miniature lasers send pulses of light –each fiber is a one-way communications channel –light signals encounter little resistance

109 Fiber-Optic Cable (continued) Single-mode cable –very narrow core –transmission speeds exceed 50 gigabytes per second Multi-mode cable –wide, micron core –easier to install –choice for computer networks

110 Radio and Infrared Links It is possible to communicate without using wires. It is possible to communicate without using wires. Radio waves - provide wireless communications –cellular phones –requires FCC license Radio communications link uses a transmitter to send the signal and a receiver to pick up the signal. –slower than cables –susceptible to interference –susceptible to interference Infrared transmissions use a frequency rate below the visible light of spectrum. –does not require FCC license –transmitter that sends signal must have an unobstructed path to receiver an example of line-of-sight communication wireless mouse an example of line-of-sight communication wireless mouse

111 Microwave Links( ) Microwave - an electromagnetic wave with a frequency of at least 1 gigahertz (GHz) Microwave transmission sends a high- frequency signal from a transmitting station to a receiving station. –stations must be within 30 miles due to the earths shape Many communications systems transmit microwave signals between a land-based ground station and a satellite.

112 Satellite Links Direct Satellite Services: digital satellite system, a network of satellites that broadcast digital data. A telecommunications satellite contains a transponder( ) (receives signal, amplifies signal, and retransmits signal). Transmissions from a satellite transponder are sent to satellite dishes. Satellite dishes( ) –catch transmissions on parabolic surface –reflects these signals to a feedhorn Feedhorn - small metal probe that is a microwave antenna Low-earth orbit communications system

113 Telephone System The telephone network uses circuit switching technology. –temporarily connects one telephone to another for the duration of the call –can be used for Internet access The telephone communications system uses a tiered network to transport calls. The telephone network offers a variety of services for voice and data communications.

114 Telephone System POTS (plain old telephone service) is an analog service. Voiceband modem( ) - converts digital pulses into analog tones to send digital computer data over a POTS line –Modulation - change characteristics of a signal – digital to analog –Demodulation - change signal back to original state – analog to digital

115 Telephone System (continued) Primary advantage of the telephone system for computer communications is inexpensive access. A DSU (data service unit) is required on your computer to send computer data over a digital line. ISDN Integrated Services Digital Network, service transports data digitally over dedicated lines – permanent connections between two locations. –basic (64 kbps) –enhanced (128 kbps)

116 Telephone System (continued) ADSL service - supports data rates up to 9 Mbps when receiving and up to 640 Kbps when sending –ISDN and ADSL affordable for individuals and businesses T1 service - provides 1.5 Mbps send and receive capacity over a dedicated line T3 service - uses fiber-optic cables to provide service with a capacity of 45 Mbps

117 The Cellular Phone System Cellular phone systems have been pressed into service for data communications as well as voice. –mobility is the advantage –disadvantages high cost reliability lack of security, interference You should encrypt confidential data before sending it over cellular phone system. You should encrypt confidential data before sending it over cellular phone system.

118 The Cellular Phone System (continued) You can send and receive data over the cellular phone system using a number of devices: –cellular phones –modems Cellular modems are similar to voiceband modems but function in cellular environments. –available as PCMCIA cards Transmitting data over the cellular phone system is slow and less reliable.

119 Cable Television System Cable TV companies have installed miles of high-bandwidth coaxial cables. –carrying capacity far exceeds POTS lines A cable modem is a device designed to demodulate a signal from the cable and translate it back to Internet data.

120 Cable Modem (continued) Cable Modem –A modem designed to operate over cable TV lines

121 Direct Satellite Service Direct satellite service (DSS) uses a geosynchronous or low-earth orbit satellite to send television, voice or computer data directly to a satellite dish. –DirecPC was one of the first –transmits in one direction – downstream –requires a standard modem and phone line for upstream transmission

122 The Internet and Intranets An intranet, a mini-Internet within an organization, uses TCP/IP protocols and Internet software to handle data communications. –Web pages –Internet mail

123 The Internet and Intranets The Internet employs packet switching technology: –divides message into smaller units called packets –divides message into smaller units called packets

124 The advantage to packet switching is the efficient use of available bandwidth. 1. A message is divided into packets. 2. Each packet is addressed to its destination. 3. A packet might travel the shortest path to its destination. 4. If a route is congested or inoperable, packets can be rerouted to other links. 5. When the packets arrive at their destination, they are reassembled. The Internet and Intranets (continued)

125 Circuit Switching –A type of communications in which a dedicated channel (or circuit) is established for the duration of a transmission. –Used by Telephone system Modem is used for convert digital pulses to analog signal –modulator-demodulator –used over analog line

126 Most LANs use packet switching technology. Network access method - a set of specifications that defines how data will be physically transmitted –determined by type of network interface card and cables –popular network access methods include Ethernet and Token Ring Ethernet and Token Ring LANs

127 Ethernet Ethernet –A local-area network (LAN) protocol developed by Xerox Corporation –Uses Bus or Star Topology –Supports data transfer rate of 10/100 Mbps – CSMA/CD access method to handle simultaneous demands. – CSMA/CD access method to handle simultaneous demands.

128 Token Ring Based on Ring Topology Makes use of Tokens Makes use of Tokens –A token is a special series of bits that travels around a token-ring network. –The token acts like a ticket, enabling its owner to send a message across the network

129 A single network can use more than one communications protocol. People sometimes refer to their network by the server type, rather than the network access method. A single network can have several types of servers. Ethernet and Token Ring LANs (continued)

130 LAN Protocols IPX –Internetwork Packet Exchange, a networking protocol used by the Novell NetWare operating systems. –Similar to IP SPX –Sequenced Packet Exchange, a transport layer protocol used in Novell Netware networks –Similar to TCP NetBIOS –Network Basic Input Output System, an application programming interface (API) that adds special functions for LAN NetBEUI –NetBios Enhanced User Interface

131 Building A Low-Cost LAN At least two computers One network interface card for each computer 10BaseT hub –with five ports 10BaseT cables (network patch cables) –long enough to reach hub Philips-head screwdriver Philips-head screwdriver Building a Low-Cost LAN

132 Put network card in each computer. –follow manufacturers instructions Ground yourself. –use grounding straps or touch metal before you reach inside computer Locate unused expansion slot and plug in network card. Install Network Cards

133 Cables connect each computer to the hub. Follow manufacturers instructions for plugging your hub into a wall outlet. Install Cables and Hub

134 Windows will detect the network cards and display a wizard – a series of dialog boxes to guide you through the rest of the installation. –select Client for Microsoft Networks protocol Activate Network Software

135 5.5 Internet Architecture Routers and TCP/IP Domain Name Service Connectivity Internet Service Providers Assessments: –Multiple-Choice Quiz 21

136 5.5.1 Routers and TCP/IP Internet Protocol Routers Transmission Control Protocol

137 Routers and TCP/IP Internet Protocol (IP) –specifies the format of packets, also called datagrams, and the addressing scheme. –The current version of IP is IPv4 A host is any computer on a network Each host on the Internet has a unique IP address –Written as four numbers between 0 and 255 –Separated by periods, –Four bytes long

138 Routers and TCP/IP (continued) Router –A device that connects any number of LANs. –PING or traceroute tracert utilities to trace the hops Keeps a list of IP addresses, corresponding LAN addresses for host on that network When a router receives a packet it either delivers it or passes it on to another router A hop is a packet going from router to router Packets can travel via network backbones, high capacity communication lines

139 Transmission Control Protocol Transmission Control Protocol, TCP, uses another layer of protocol to insure packets are not lost in transmission –TCP enables two hosts to establish a connection and exchange streams of data. –TCP guarantees delivery of data, confirms receipt of all packets –If some packets are lost retransmits lost packets

140 END of Unit 5