1. Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

2. 2 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

3. 3 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

4. 4 Network n A Network is an Any-to-Any Communication System – Can connect any station to any other

5. 5 “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

6. 6 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

7. 7 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

8. 8 Voice and Video Networks n Hierarchy of switches n Trunk lines connect switches Switch Trunk Line

9. 9 Voice and Video Networks n Circuit – End-to-End Connection between Phones – May pass through multiple switches – And trunk lines – Reserved (guaranteed) capacity during call Circuit

10. 10 Voice and Video Networks n Reserved Circuit Capacity is Expensive – 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 average of 60 seconds between brief downloads – Capacity is wasted between bursts; still must pay of capacity

11. 11 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

12. 12 Packet-Switched Data Networks n Packet 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 packet switch B? D? C? Switch A B C D Packet

13. 13 Packet Switched Data Networks n Multiplexing – Packets from many conversations are mixed (multiplexed) over each trunk line – Only pay for the trunk line capacity used – Dramatic trunk line cost savings – The reason for packet switching Multiplexing on Trunk Line

14. 14 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

15. 15 Digital Transmission n In digital transmission, time is divided into periods of fixed length called clock cycles n Line is in one state (voltage level, etc.) during each clock cycle; at end of cycle, stays same or changes abruptly. Clock Cycle Time State 1 Stays Same Abrupt Change State 2

16. 16 Digital Transmission n Only a few possible states – 2, 4, 8, 16, 32, rarely more – 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

17. 17 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 – Binary is a type of digital transmission DigitalBinary Two States Few States (4) 0 1

18. 18 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

19. 19 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

20. 20 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)

21. 21 Elements of a Simple LAN Client PC Client PCs are used by ordinary managers and professionals; receive service Have network interface cards (NICs) Servers provide services to client PCs Also have NICs There usually are multiple servers Have special server operating system Have service software (e-mail, etc.) Server NIC

22. 22 Terminal-Host Systems n Created in the 1960s – Central host computer does all the processing – Terminal is dumb--only a remote screen and keyboard – Largest hosts are mainframes n Dominate host business use today TerminalsHost

23. 23 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

24. 24 PC Networks n The Most Common Platform in Organizations – Allows PCs to share resources – Both Wintel (Windows/Intel) PCs and Macintoshes Network Client PC Client PC PC Server

25. 25 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

26. 26 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 – But downloaded (copied) to client PC for execution – Executed on client PC, not on file server File Server Client PC Stored on the File Server Download Executed on Client PC

27. 27 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

28. 28 Client/Server Processing n Client and Server Machines – Neither has to be a PC (Although the client usually is) n Platform independence – Two programs: client and server programs – Example: browser and webserver application program Client Machine Server Client Program Server Program

29. 29 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

30. 30 C/S Servers often are Workstation Servers n Workstations – Look like PCs but… – More powerful (and expensive) than PCs – Do not use standard Intel PC microprocessors – Usually run the UNIX operating system – Client and server workstations Special Microprocessor UNIX Operating System

31. 31 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

32. 32 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

33. 33 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

34. 34 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

35. 35 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

36. 36 Accessing the WWW from Home n A Common and Important Situation – Must be understood – Good way of introducing networking concepts

37. 37 The Internet n The Internet is a Worldwide Group of Networks – Not a single network – Individual networks on the Internet are called subnets

38. 38 The Internet n Routers – Connect the Internet’s individual networks (subnets) – Cooperate to give an end-to-end route for each packet (message) Routers Route

39. 39 The Internet n Hosts – Any computer attached to the Internet is a host – Webservers are host – Desktop and notebook PCs are hosts too Host

40. 40 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

41. 41 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

42. 42 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 n Note: Conversion is for human convenience; computers work with 32-bit sequences, not dotted decimal notation – Both octets and bytes are collections of eight bits n But “octet” is used in networking

43. 43 The Internet n Dotted Decimal Notation – Convert each binary (Base 2) octet into decimal (Base 10) n 10000000 binary is 128 decimal n 10101011 binary is 171 decimal n 00010001 binary is 17 decimal n 00001101 binary is 13 decimal

44. 44 Binary to Decimal Conversion 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

45. 45 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 – Not official names of hosts n Like nicknames – Usually, only servers have host names CNN.COM

46. 46 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

47. 47 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

48. 48 The Internet n Internet Backbone – Itself consists of many competing but interconnected backbone carriers – Sometimes, backbone carriers are also ISPs Internet Backbone Carriers ISP

49. 49 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

50. 50 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

51. 51 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 ? ?

52. 52 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 n Follow the HyperText Transfer Protocol (HTTP) standard if webservice application Browser Webserver Application program HTTP if webservice application

53. 53 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) – Gives platform independence PC PC or Other Computer

54. 54 Internet Standards n HTTP Requires the Use of the TCP Transport Standard at the transport layer – Transmission Control Protocol – TCP messages are called TCP segments TCP if webservice application (HTTP) TCP Segment

55. 55 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

56. 56 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

57. 57 Internet Standards n Subnets – A subnet is a 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 1 Subnet 2 Subnet 3

58. 58 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

59. 59 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

60. 60 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

61. 61 Internet Standards n Data Link Layer Standards – For accessing the Internet from home via telephone modem, use the Point-to-Point Protocol (PPP) – Only used between home and ISP! – Other subnets connecting routers are likely to use different subnet protocols! ISP PPP ?

62. 62 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

63. 63 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

64. 64 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

65. 65 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

66. 66 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

67. 67 Standards Organizations and Architectures n TCP/IP Architecture – Under the Internet Engineering Task Force (IETF) – TCP/IP is the architecture, while TCP and IP are individual standards n There are other TCP/IP standards – 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 to some degree

68. 68 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

69. 69 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

70. 70 Internet Standards n Recap: Accessing the WWW from Home with a Telephone Modem App Trans Int DL Phy User PC Int DL Phy Router App Trans Int DL Phy Webserver HTTP TCP IP PPP Modem IP ? ?

71. 71 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

72. 72 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

73. 73 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 data format for exchanging data Application Data Exchange in Common Format C (Transfer Syntax) Box Uses Data Format A Uses Data Format B

74. 74 OSI Divides the Application Layer n OSI Application Layer – Governs application-to-application communication freed from concerns about presentation format and transaction management Box

75. 75 Quality of Service (QoS) n Want network to have good quality of service (QoS)—work well! 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

76. 76 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

77. 77 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

78. 78 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