1. Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

2. 2 Network n A Network is an Any-to-Any Communication System – Can connect any station to any other

3. 3 “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

4. 4 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

5. 5 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

6. 6 Voice and Video Networks n Hierarchy of switches n Trunk lines connect switches Switch Trunk Line

7. 7 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

8. 8 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

9. 9 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

10. 10 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

11. 11 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

12. 12 Analog Transmission n In analog transmission, rising and falling smoothly in intensity among an infinite number of states – State may be voltage, frequency or other line signal characteristic 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. Time Strength Clock Cycle Time State 1 Stays Same Abrupt Change State 2

13. 13 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

14. 14 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

15. 15 Elements of a Simple LAN Hub or Switch Wiring Hub or Switch connects all stations housing NIC Wiring is standard business telephone wiring (4 pairs in a bundle)

16. 16 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 (file storage & retrieval) – Legacy systems--systems created by your predecessors – Would not use the same platform today if built new; however, too expensive to rewrite all legacy applications at once Terminals Host

17. 17 PC Networks n The Most Common Platform in Organizations – Allows PCs to share resources n File Servers – Store files (data files and programs) n Programs are downloaded to client PC for execution, not on file server – The most common type of server in PC networks – Almost all file servers are themselves PCs Network Client PC Client PC PC Server

18. 18 Client/Server Processing n Client and Server Machines – Neither has to be a PC (Although the client usually is) n Platform independence: not limited to PC server – Two programs: client and server programs n Example: browser and webserver application program n Servers usually Workstation Servers – Look like PCs but… n More powerful (and expensive) than PCs n Do not use standard Intel PC microprocessors n Usually run the UNIX operating system Client Machine Server Client Program Server Program Request Response

19. 19 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

20. 20 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

21. 21 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

22. 22 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

23. 23 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

24. 24 The Internet n The Internet is a Worldwide Group of Networks – Not a single network – Individual networks on the Internet are called subnets n Routers – Connect the Internet’s individual networks (subnets) – Cooperate to give an end-to-end route for each packet (message) Routers Route Host

25. 25 The Internet n Network deliver messages based on network addresses – The Internet has two addressing systems for hosts n IP addresses (computer friendly) n Host names (user-friendly) n Host IP addresses (required) – 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

26. 26 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 n But “octet” is used in networking

27. 27 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

28. 28 The Internet n Host Names (otional) – Two or more text “labels” separated by dots n www.microsoft.com n Mtsu.edu n No relationship between segments and labels n Usually, only servers have host names

29. 29 The Internet n Internet Service Providers (ISPs) – Connects you to the Internet, via Carrier Access Line n May provide other services (e-mail account, etc.) – Costs n ISP = Approx. $20 per month, sometimes more – % for ISP expenses – % for Internet backbone to carry your messages n Carrier Access Line fee separate from ISP ISP Carrier Access Line Internet Backbone ISP Carriers

30. 30 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

31. 31 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

32. 32 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 ? ?

33. 33 Internet Standards n Application Layer Standards – specify how two application programs communicate – Example: browser on user PC and webserver application program on webserver n Webservice = HyperText Transfer Protocol (HTTP) n Transport Layer Standards – specify how two host computers will work together,regardless of platform types (PCs, workstations, mainframes) – Gives platform independence n HTTP Requires the Use Transmission Control Protocol (TCP)

34. 34 Internet Standards n Internet Layer Standards – specify how hosts and routers will act to route packets from source host to destination host, across many single networks (subnets) connected by routers n Internet Protocol (IP) The IP in “TCP/IP” – All internet layer messages are called packets – Subnets n single networks (LANs, WANs, point-to-point link) on Internet n Packets pass through several subnets in route across Internet n Different Subnets Can Have Different Subnet Protocols Route Single Network (Subnet) Host

35. 35 Subnets Standards n Subnet Standards Divided into Two Layers – Physical layer standards govern the transmission of individual bits within a subnet n Interpretation of bits is left to data link layer Serial Port External Modem Telephone Wire Wall Jack

36. 36 Subnets Standards – Data Link layer standards govern the transmission of messages within a subnet n Organize individual bits into structured messages or frames n Controls timing of message transmission n Point-to-Point Protocol (PPP) when accessing Internet from home via telephone modem n Only used between home and ISP! n Other subnets connecting routers are likely to use different subnet protocols!

37. 37 Standards Organizations and Architectures n Architecture – a Design or framework for Standards Creation – Specifies what types of standards are needed (application, transport, etc.) – After architecture is designed, individual standards of each type are created n Analogy: architecture of house specifies what rooms will be needed and their relationships. n After architecture is settled, individual rooms are designed

38. 38 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 – IETF standards dominate in corporations at the application, transport, and internet layers n OSI Standards (Reference Model of Open Systems Interconnection) – 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 (subnet) n Other architectures specify the use of OSI standards at these layers

39. 39 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

40. 40 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

41. 41 Quality of Service (QoS) n Congestion & Speed – Latency: amount of time packets are delayed due to congestion. Measured in milliseconds (ms), n Desired Latency = 50 ms maximum – Throughput: transmission speed. Measured in bits per second (bps) n Desired Throughput = 1 Million bps

42. 42 Quality of Service (QoS) n Reliability – Availability: percentage of time network is available. n Desired Availability = 99.999% – Error Rate: percentage of bits or messages with errors n 1999 average = 3% - 6% of all packets Desire much lower average

43. 43 Security n Encryption for Confidentiality – Sender encrypts (scrambles) messages before transmission – Receiver decrypt messages to original form n Access Control – Prohibits or authorizes access to various resources (files, programs) – Access control lists specify what & how a person may use a resource n Authentication – Sender of a message must prove their identity