1. Business Data Communications and Networking Raymond R. Panko Copyright 2001 Prentice Hall Revision 1: August 2000

2. Basic Concepts and Principles Chapter 1 Copyright 2000 Panko

3. 3 Stars n Mark material that is especially important, or n Mark material that is especially difficult or easy to confuse with similar material n In either case, the star indicates something to which you should pay special attention. n Multiple stars are for especially important or difficult material

4. 4 Ovals n Mark slide as not being from the chapter or module of the main PowerPoint presentation – New information added since the book went to press n Often available in the supplementary readings for the chapter or module – From Chapter 5 – From Module N – Corrects error in the original text – Material in box within chapter New Mod N Ch 5 Error Box

5. Part A: Business Data Communications and Networking What’s in a Title?

6. 6 Business n For IS (information systems) students in business schools – Computer science and electrical engineering students are trained to work in hardware, software, and networking vendor firms, such as Microsoft, IBM, Oracle, and Cisco Systems – IS graduates are trained to work in end user organizations, such as banks, government agencies, and manufacturing firms--organizations that use IT (information technology) to get their work done

7. 7 Business n The IS Job: Full life cycle support – To help firms understand how networking will help them work better – To do needs analysis – To plan and develop new networks – To manage new networks after they are developed

8. 8 Network n A Network is an Any-to-Any Communication System – Can connect any station to any other

9. 9 “Connect to GHI” Network n Each Station has a Unique Network Address – To connect, only need to know the receiver’s address – Like telephone number ABC DEF GHI JKL MNO

10. 10 Data Communications n Originally, There was a Sharp Distinction: – Voice and Video Communication versus – Data Communications, in which one or both parties is a computer n Database n Electronic mail n World Wide Web – Distinction is fading because voice and video communication are increasingly computer- based

11. 11 Voice and Video Networks n Telephone Network – Customer premises (home or office) – Local loop (access line) connects customer premises to first switching office Connection Switching Office Local Loop (Access Line) Customer Premises Customer Premises

12. 12 Voice and Video Networks n Hierarchy of switches n Trunk lines connect switches Switch Trunk Line

13. 13 Voice and Video Networks n Circuit – End-to-End Connection between Phones – May pass through multiple switches – And trunk lines Circuit

14. 14 Voice and Video Networks n Reserved Capacity – Circuit capacity is reserved during duration of each call – At each switch – On each trunk line Circuit Reserved Capacity Reserved Capacity

15. 15 Voice and Video Networks n Reserved Circuit Capacity Guarantees Throughput – Never get less than reserved capacity – Nothing like congestion on the Internet n Reserved Circuit Capacity is Expensive – Pay for it whether you use it or not – Good for voice, because conversations are fairly constant – Bad for data, because most data transmission is bursty; e.g., in World Wide Web, download, then stare at screen for a long time until next download

16. 16 Packet-Switched Data Networks n Packet Switching – Circuit switching is expensive due to reserved capacity – Packet switching breaks transmissions into messages – Messages are short (averaging a few hundred bytes) because switches handle short messages efficiently – Messages are called packets (sometimes, frames or other names) Message Packets

17. 17 Packet-Switched Data Networks n Switching Decision – When a packet arrives at a switch, the switch must decide which of several ports (connections) to use to send the packet back out – Complex – Made at each switch B? D? C? Switch A B C D Packet

18. 18 Packet Switched Data Networks n Multiplexing – Packets from many conversations are mixed (multiplexed) over each trunk line – Only pay for the capacity used – Dramatic trunk line cost savings – The reason for packet switching Multiplexing on Trunk Line

19. Part B: More Basic Concepts Analog and Digital Communication Modems LANs and WANs

20. 20 Analog Transmission n In analog transmission, the state of the line can vary continuously, rising and falling smoothly in intensity among an infinite number of states – State may be voltage, frequency or another line signal characteristic – The human voice is like this – When we speak into a telephone, we generate analogous (similar) electrical signals, hence the name Time Strength New

21. 21 Digital Transmission n In digital transmission, time is divided into periods of fixed length called clock cycles n The line is kept constant (in one state) during each clock cycle so that the receiver can sample it anywhere during the cycle and get the same result Clock Cycle Time Strength New

22. 22 Digital Transmission n The line is kept in one of only a few possible states (conditions) during each clock cycle – 2, 4, 8, 16, 32, rarely more – There are fairly large differences between states – If a signal is near one state but a bit off, the receiver will still read it correctly as being at that state Clock Cycle Time Strength New

23. 23 Digital Transmission n At the end of each clock cycle, the line may change abruptly to another of these few states – Can also stay the same Time Strength Abrupt Change Stays Same Clock Cycle

24. 24 Digital Versus Binary Transmission n Digital transmission: a few states (2, 4, 8, 16, etc.) n Binary transmission: exactly two states – One state represents 1, the other 0 DigitalBinary Two StatesFew States 0 1

25. 25 Digital Communication n Modems – Computers have digital output – Telephone network assumes analog input – Modem translates between digital device and analog line for data transmission over the phone system Digital Signal Modem Analog Signal

26. 26 LANs and WANs n Networks Have Different Geographical Scopes n Local Area Networks (LANs) – Small Office – Office Building – Industrial Park / University Campus n Wide Area Networks (WANs) – Connect corporate sites or – Connect corporate sites with sites of customers and suppliers

27. 27 Elements of a Simple LAN Hub or Switch Wiring Hub or Switch connects all stations Wiring is standard business telephone wiring (4 pairs in a bundle)

28. 28 Elements of a Simple LAN Server Client PC Server Client PCs are used by ordinary managers and professionals; receive service Servers provide services to client PCs Server

29. 29 Elements of a Simple LAN n Client PC – Begin with stand-alone PC – Add a network interface card (NIC) to deal with the network – Networks have many client PCs n Server – Most PC nets have multiple servers

30. Part C: Distributed Processing Terminal-Host Systems File Server Program Access Client Server Processing

31. 31 Terminal-Host Systems n Created in the 1960s – Central host computer does all the processing – Terminal is dumb--only a remote screen and keyboard – Created in the 1960s, when microprocessors for terminal intelligence did not exist TerminalsHost

32. 32 Terminal-Host Systems n Sizes – Mainframes are the largest business hosts n Optimized for business uses--file access speed is more crucial than mathematical processing

33. 33 Terminal-Host Systems n Many Mainframe Applications Were Created in the 1960s through 1980s – Legacy systems--systems created by your predecessors – Would not use the same platform today if built new – But too expensive to rewrite all legacy applications at once – Must live with many host legacy applications for now – Older networks can be legacy systems as well; “legacy system” is not just limited to mainframe applications

34. 34 PC Networks n The Most Common Platform in Organizations – Allows PCs to share resources – Both Wintel (Windows/Intel) PCs and Macintoshes Network

35. 35 PC Network Components n File Servers – Store files (data files and programs) – The most common type of server in PC networks – Almost all file servers are themselves PCs File Server

36. 36 File Server Program Access n File Server Program Access is the Most Common Way to Execute Programs in PC Networks – Program files are stored on the file server before execution File Server Client PC Stored on the File Server

37. 37 File Server Program Access n File Server Program Access – Program and data files are downloaded (copied) to the Client PC – Executed on the client PC, not on the file server – File server merely stores programs and data files File Server Client PC Downloaded to Client PC, Executed There

38. 38 File Server Program Access n PC Processing Power Limits FSPA Programs – Client PCs do not get very large – Only programs small enough to operate on limited client PCs can be used File Server Client PC Executed on the Client PC

39. 39 Client/Server Processing n Client and Server Machines – Neither has to be a PC – Platform independent Client MachineServer

40. 40 C/S Servers often are Workstation Servers n Workstations – Are computers more powerful (and expensive) than PCs – Do not use standard Intel PC microprocessors – Usually run the UNIX operating system – Client and server workstations – Confusingly, Windows NT client operating system is called Windows NT Workstation, where workstation is synonymous with “client”

41. 41 Client/Server Processing n Two Programs – Client program on client machine – Server program on server machine – Work together to do the required processing Client MachineServer Client Program Server Program

42. 42 Client/Server Processing n Division of Labor – Client program handles lighter work, such as user interface chores and light processing chores – Server program handles heavy work, such as database retrieval Client MachineServer Client Program Server Program

43. 43 Client/Server Processing n Cooperation Through Message Exchange – Client program sends Request message, such as a database retrieval request – Server program sends a Response message to deliver the requested information or an explanation for failure Client MachineServer Client Program Server Program Request Response

44. 44 Client/Server Processing n Widely Used on the Internet n For instance, webservice – Client program (browser) sends an HTTP request asking for a webserver file – Server program (webserver application program) sends an HTTP response message with the requested webpage HTTP Request Message HTTP Response Message

45. 45 Client/Server Processing n On the Internet, a Single Client Program--the Browser (also known as the client suite)--Works with Many Kinds of C/S server applications – WWW, some E-mail, etc. Browser Webserver E-mail Server

46. 46 Program Functionality (Size) n High program functionality requires large program size n File Server Program Access – Poor: client PCs are small, can only execute small programs n Client/Server Processing – Good: not limited to client PC processing power – Heavy work can be done on the server machine n Terminal-Host Systems – Good: Hosts can be very large

47. 47 Platform Independence n File Server Program Access – Poor: Only works with PC clients and PC file servers n Client/Server Processing – Excellent: use any server you want, also any client n Terminal-Host Systems – Poor: Hosts require terminals and only work with a few terminal types

48. 48 Scalability n Ability to grow as demand grows n File Server Program Access – Poor: client PCs do not get very large n Client/Server Processing – Very good: Platform independence allows servers to be larger than PCs – To grow, leave client machine the same, increase the size of the server machine n Terminal-Host Systems – Excellent: have an enormous range of processing power

49. 49 User Interface n File Server Program Access – Very good: uses local PC processing power n Client/Server Processing – Very good: uses local PC processing power for user interface n Terminal-Host System – Poor: Relies on distant hosts; user interface quality limited by high long-distance transmission costs – Monochrome, text-only screen; no animation

50. 50 Response Time (When User Hits a Key) n File Server Program Access – Very good: uses local PC processing power n Client/Server Processing – Very good: local PC processing power for user interface – But retrievals from the server can cause delays n Terminal-Host System – Poor: Relies on distant hosts; long delays if overloaded

51. Part D: Accessing the World Wide Web from Home Many students access the World Wide Web from home Here is how it works, in terms of standards

52. 52 Accessing the WWW from Home n A Common and Important Situation – Must be understood – Good way of introducing networking concepts

53. 53 The Internet n The Internet is a Worldwide Group of Networks – Not a single network – Individual networks on the Internet are called subnets

54. 54 The Internet n Messages are Broken into Small Packets for Transmission, as Noted Earlier – More efficient than sending long messages Message Packets

55. 55 The Internet n Routers – Connect the Internet’s individual networks (subnets) – Cooperate to give an end-to-end route for each packet Routers Route

56. 56 The Internet n Hosts – Any computer attached to the Internet is a host – Webservers are host – Desktop and notebook PCs are hosts too Host

57. 57 The Internet n Network deliver messages based on network addresses – The Internet has two addressing systems for hosts n IP addresses n Host names Host

58. 58 The Internet n Host IP addresses – Strings of 32 ones and zeros – Usually represented by four number segments separated by dots: dotted decimal notation – For example, 128.171.17.13 – Official addresses for hosts 127.18.47.145 127.47.17.47

59. 59 The Internet n Dotted Decimal Notation – IP addresses are really strings of 32 bits (1s and 0s) n 10000000101010100001000100001101 – To convert this to dotted decimal notation, first, divide them into four bytes (also called octets) n 10000000 10101010 00010001 00001101 – Both octets and bytes are collections of eight bits

60. 60 The Internet n Dotted Decimal Notation – Convert each binary (Base 2) octet into decimal (Base 10) n 10000000 is 128 n 10101011 is 171 n 00010001 is 17 n 00001101 is 13

61. 61 The Internet Value (2 N ) BitDecimal 1281 6400 321 1600 800 400 212 111 163 Position (N) 7 6 5 4 3 2 1 0 Binary 10100011 = Decimal 163 Note: Starts with 0 Position 7 Position 0

62. 62 The Internet n Why dotted decimal notation? – Strings of 32 bits are very difficult to memorize – Dotted decimal representations of IP addresses are (somewhat) easier to remember – So dotted decimal notation is merely a mnemonic device for representing IP addresses

63. 63 The Internet n Host Names – The other network addressing system on the Internet – Easy to remember n www.microsoft.com n voyager.cba.hawaii.edu n Two or more text “labels” separated by dots n No relationship between segments and labels CNN.COM

64. 64 The Internet n Host Names – Like nicknames n Not official addresses n Each host must have an IP address n But only some hosts have host names n If you give it a host name, your browser must look up IP address of host (Chapter 2 discusses how) CNN.COM

65. 65 The Internet n Internet Service Providers (ISPs) – You must have an account with an ISP – Connects you to the Internet – May provide other services (e-mail account, etc.) n Carrier Access Line – Usually provided by local telephone carrier – Connects you to the ISP – You pay for this separately from your ISP charges ISP Carrier Access Line

66. 66 The Internet n The Internet is Not Free – You pay your ISP around $20 per month, sometimes more – Part of this pays for ISP expenses – Part of this pays the Internet backbone to carry your messages n You Usually Also Pay the Telephone Carrier Separately for the Carrier Access Line ISP Carrier Access Line

67. 67 The Internet n Some ISPs are “free” – More correctly, they are advertiser supported – You must see advertisements every time you use a free ISP ISP Carrier Access Line New

68. 68 The Internet n Internet Backbone – Itself consists of many competing but interconnected backbone carriers – Sometimes, backbone carriers are also ISPs Internet Backbone Carriers ISP

69. 69 The Internet n ISPs – Began in the United States – Is being copied and adopted by other countries – However, not universal

70. Part E: Standards Layered Standards Architectures TCP, IP, and TCP/IP Other Architectures

71. 71 Standards n Standards are rules of operation that most or all vendors follow n Open standards are created and owned by public standards organizations – No single vendor controls these standards

72. 72 Standards Are Layered n For Internet Access to a Webserver, standards are set at five layers – Application – Transport – Internet – Data Link – Physical n Together, these standards provide all that is needed for application programs on different hosts on different networks to work together

73. 73 Internet Standards n Messages are Exchanged at Multiple Layers App Trans Int DL Phy User PC Int DL Phy Router App Trans Int DL Phy Webserver HTTP TCP IP PPP Modem IP ? ?

74. 74 Internet Standards n Application Layer Standards – Standards at the application layer specify how two application programs communicate – For example, browser on user PC and webserver application program on webserver Browser Webserver Application Program

75. 75 Internet Standards n HTTP (HyperText Transfer Protocol) – World Wide Web standard for browser-webserver application program exchanges – Other applications (E-mail, etc.) have different application standards Browser Webserver Application Program HTTP

76. 76 Internet Standards n Transport Layer Protocols – Standards at the transport layer specify how two host computers will work together, even if they are of different platform types (PCs, workstations, mainframes, and so forth) – For instance, PC and non-PC webserver PC PC or Other Computer

77. 77 Internet Standards n The Transport Layer Gives Platform Independence – Two computers do not have to be of the same platform type n A PC user does not even know what kind of computer the webserver is PC ?

78. 78 Internet Standards n HTTP Requires the Use of the TCP Transport Standard – Transmission Control Protocol – TCP messages are called TCP segments TCP

79. 79 Internet Standards n Internet Layer Protocols – Standards at the internet layer specify how hosts and routers will act to route packets end to end, from the source host to the destination host, across many single networks (subnets) connected by routers Route Single Network (Subnet) Host

80. 80 Internet Standards n The Internet Protocol (IP) is the Main Protocol for Routing Packets Across the Internet – The IP in “TCP/IP” – IP messages are called packets – All internet layer messages are called packets IP Packet

81. 81 Internet Standards n Subnets – Single networks (LANs, WANs, point-to-point link) on the Internet – A packet will pass through several subnets along its route across the Internet Subnet

82. 82 Internet Standards n Different Subnets Can Have Different Subnet Protocols – IP at the internet layer routes across different protocols at the subnet layer Point-to-Point Subnet Protocol 1 WAN Subnet Protocol 2 LAN Subnet Protocol 3

83. 83 Subnets Standards n Subnets are Single Networks on the Internet n Subnet Standards Divided into Two Layers – Physical layer standards govern the transmission of individual bits within a subnet – Data Link layer standards govern the transmission of messages within a subnet n Organize individual bits into structured messages

84. 84 Internet Standards n Data Link Layer Standards – Standards at the data link layer specify how to transmit messages within a single network – Messages at the data link layer are called frames 10010001001 Data Link Frame

85. 85 Internet Standards n Data Link Layer Standards – For accessing the Internet from home... – Point-to-Point Protocol (PPP) dominates – Only used between home and ISP! – Other subnets connecting routers are likely to use different subnet protocols! ISP PPP ?

86. 86 Internet Standards n Physical Layer Standards – While the data link layer is concerned with the organization and transmission of organized messages, standards at the physical layer specify how to transmit single bits one at a time – Work bit by bit; no frame organization

87. 87 Internet Standards n Physical Layer Standards in Internet Access from Home – Telephone jack (RJ11) – Telephone wire – Serial port connection to external modem – Modem Serial Port External Modem Telephone Wire Wall Jack

88. 88 Internet Standards n Subnet Versus Internet Layer Standards – Internet layer provides routing across multiple subnets – Subnet layer standards (data link and physical) provide for transmission within a single network Internet Layer Subnet Layer

89. 89 Internet Standards n Analogy for Subnet versus Internet – Take a vacation – Route from beginning to end (like internet layer) – For different parts, may travel by car, airplane, or boat (like subnet layer) Internet Layer Subnet Layer

90. 90 Standards Organizations and Architectures n Architecture is a Design for Standards Creation – Specifies what types of standards are needed (application, transport, etc.) – After architecture is designed, individual standards of each type are created – Analogy: architecture of house specifies what rooms will be needed and their relationships. – After architecture is settled, individual rooms are designed

91. 91 Standards Organizations and Architectures n TCP/IP Standards – Created by the Internet Engineering Task Force (IETF) – Named after its two most widely known standards, TCP and IP n TCP/IP is the architecture, while TCP and IP are individual standards n However, these are not its only standards, even at the transport and internet layers – IETF standards dominate in corporations at the application, transport, and internet layers n However, application, transport, and internet standards from other architectures are still used

92. 92 Standards Organizations and Architectures n OSI Standards – Reference Model of Open Systems Interconnection – Created by the International Telecommunications Union-Telecommunications Standards Sector (ITU-T) – And the International Organization for Standardization (ISO) – OSI standards dominate the data link and physical layers n Other architectures specify the use of OSI standards at these layers

93. 93 Internet Standards n 5-Layer Hybrid TCP/IP-OSI Architecture – Most widely used architecture in organizations today – Used on the Internet ApplicationTCP/IP TransportTCP/IP InternetTCP/IP Data LinkOSI PhysicalOSI

94. 94 Internet Standards n Recap: Accessing the WWW from Home App Trans Int DL Phy User PC Int DL Phy Router App Trans Int DL Phy Webserver HTTP TCP IP PPP Modem IP ? ?

95. 95 TCP/IP versus OSI n Lowest Four Layers are Comparable in Functionality TCP/IPOSI Application Presentation Session Transport InternetNetwork Data Link (use OSI)Data Link Physical (use OSI)Physical Box

96. 96 OSI Divides the Application Layer n OSI Session Layer – Sets up a connection between two application programs on different machines – Manage streams of transactions (session); if there is a break, can resume at the last roll-back point Transactions Box

97. 97 OSI Divides the Application Layer n OSI Presentation Layer – Handles presentation differences between the two machines (how data are stored and represented) – Two presentation layer processes select and use a common format for exchanging data Application Data Exchange in Common Format Box

98. 98 OSI Divides the Application Layer n OSI Application Layer – Governs application-to-application communication freed from concerns about presentation format and transaction management Box

99. F. Tomorrow Quality of Service (QoS) Security

100. 100 Quality of Service (QoS) n Throughput Problems and Guarantees n Congestion – When too many transmissions are on a network, traffic will slow down; this is congestion n Latency – Latency is the amount of time that packets or frames are delayed because of congestion. Measured in milliseconds (ms), – Want guarantees of worst-case latency n Throughput – Throughput is the guaranteed speed in bits per second

101. 101 Quality of Service (QoS) n Reliability Measures n Availability – Availability is the percentage of time the network is available to users. – Telephone system has 99.999% availability n Error Rate – Error rate is the percentage of bits or messages that contain errors – 3% - 6% of all packets are lost on the Internet

102. 102 Security n A Growing Problem n Encryption for Confidentiality – Sender encrypts messages before sending them so that anyone intercepting them en route cannot read them – Receiver can decrypt encrypted messages and read them – Have confidentiality (unreadability by interceptors) 47 Encryption 101101 Decryption 47 New

103. 103 Security n Authentication – Sender of a message must prove their identity – To thwart impostors who impersonate people n Access Control – Prohibits or authorizes access to various resources (files, programs, etc.) – Needs authentication but also more – Access control lists for resources specify what resources the authorized person may use and how they may use them