1. CEN 4500 Data Communications Instructor: S. Masoud Sadjadi http://www.cs.fiu.edu/~sadjadi/Teaching/ sadjadi At cs Dot fiu Dot edu Chapter 1: Introduction

2. CEN 4500, S. Masoud Sadjadi2 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

3. CEN 4500, S. Masoud Sadjadi3 History 18 th Century –The Great Mechanical Systems –Industrial Revolution 19 th Century –The age of the Steam Engine 20 th Century –Information gathering, processing, and distribution –Telephone, Radio, TV, Computer, and Satellites

4. CEN 4500, S. Masoud Sadjadi4 History Computer industry –is still young –comparing to automobiles and air transportation has made much better progress –First two decades Highly centralized, usually within a single large room A medium-sized company or university might have 1 Larger institutions had at most a few dozen –Twenty years later Equally powerful computers smaller than postage stamps At the time, this would be science fiction!

5. CEN 4500, S. Masoud Sadjadi5 History Merging of Computers and Communications –“Computer Center” is now obsolete –Old Model A single computer serving everyone in an organization –New Model A large number of separated but interconnected computers do the job These systems are called Computer Networks We study the design and organization of these systems –Future Model ?

6. CEN 4500, S. Masoud Sadjadi6 Computer Network A collection of autonomous computers interconnected by a single technology Two computers are interconnected –If they are able to exchange information –The connection can be via Copper wire, Fiber optics, Microwaves, Infrared, or Communication satellites How about Internet and WWW? –Internet is a network of networks –WWW is a distributed system on top of Internet

7. CEN 4500, S. Masoud Sadjadi7 Distributed System Should not be confused or used interchangeably with Computer Network So, then what is a distributed system? –In a distributed system, a collection of independent computers appears to its users as a single coherent system –Usually, it is a single paradigm or model that it presents to the users (WWW & documents) –Often a layer of software on top of operating system (called middleware) is responsible for implementing this model

8. CEN 4500, S. Masoud Sadjadi8 Uses of Computer Networks Business Applications –Resource sharing: programs, equipment, data –Communication medium: e-mial, IM, SMS, etc. –Doing business with suppliers (B2B) –E-Commerce (doing business with customers, B2C) Home Applications Mobile Users Social Issues

9. CEN 4500, S. Masoud Sadjadi9 Business Applications of Networks Resource sharing using client-server model –Data are stored in a powerful machine –Employees have a simpler machine called clients A network with two clients and one server.

10. CEN 4500, S. Masoud Sadjadi10 Business Applications of Networks The client-server model –Two processes are involved: one on the client machine and one on the server machine –Communication takes place by the client process sending a request and the server process sending a reply to the request.

11. CEN 4500, S. Masoud Sadjadi11 Uses of Computer Networks Business Applications Home Applications –Access to remote information (Web surfing) –Person-to-person communication (IM, Chat room) –Interactive entertainment (VoD, Game, etc) –Electronic commerce (shopping, paying bills, etc) Mobile Users Social Issues

12. CEN 4500, S. Masoud Sadjadi12 Home Network Applications Person to person communication via P2P –In peer-to-peer system there are no fixed clients and servers.

13. CEN 4500, S. Masoud Sadjadi13 Home Network Applications Some forms of e-commerce.

14. CEN 4500, S. Masoud Sadjadi14 Mobile Network Users Combinations of wireless networks and mobile computing. m-commerce –PDA cell phones as an electronic wallet, replacing … –Location-dependent services using GPS on cell phones Personal area networks –Wearable computers –Pervasive computing

15. CEN 4500, S. Masoud Sadjadi15 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

16. CEN 4500, S. Masoud Sadjadi16 Taxonomy of Computer Networks There is no widely accepted taxonomy Two dimensions that stand out 1.Transmission Technology 2.Scale 1.Transmission Technologies –Broadcast links (usually smaller networks) Have single, shared communication channel Short messages (packets) sent are received by all –Point-to-point links (usually larger networks) Consists of many connections between individual pairs Packets may have to visit some intermediate machines

17. CEN 4500, S. Masoud Sadjadi17 Taxonomy of Computer Networks 2.Scale Classification of interconnected processors by scale.

18. CEN 4500, S. Masoud Sadjadi18 Network Hardware Local Area Networks Metropolitan Area Networks Wide Area Networks Wireless Networks Home Networks Internetworks

19. CEN 4500, S. Masoud Sadjadi19 Local Area Networks LANs –Are privately-owned networks within a single building or campus of up to few kilometers –Two broadcast networks (a) Bus (e.g., IEEE 802.3 or Ethernet, up to 10 Gbps) (b) Ring (e.g., IEEE 802.5 or IBM token ring, FDDI)

20. CEN 4500, S. Masoud Sadjadi20 Metropolitan Area Networks MAN covers a city –Cable TV grew from community antenna systems in the areas with poor over-the-air TV reception) –Broadband wireless A metropolitan area network based on cable TV.

21. CEN 4500, S. Masoud Sadjadi21 Wide Area Networks WAN spans a large geographical area –Contains a collection of hosts interconnected by a communication subnet –Subnets: transmission lines move bits and switching elements (routers) connect two or more tls. Relation between hosts on LANs and the subnet.

22. CEN 4500, S. Masoud Sadjadi22 Wide Area Networks Store-and-forward or packet-switched subnet –Each packet will be received in its entirety on each router and stored there until an output line is free, and then forwarded –Cells: if the packets are small and the same size A stream of packets from sender to receiver.

23. CEN 4500, S. Masoud Sadjadi23 Wide Area Networks Routing decisions are make locally How to make a routing decision is called routing algorithm. Not all WANs are packet-switched –Satellite systems Each router has an antenna to send and receive packets Satellite networks are inherently broadcast and are most useful when the broadcast property is important.

24. CEN 4500, S. Masoud Sadjadi24 Wireless Networks Not a new idea –Ship-to-shore wireless telegraph in 1901 Categories of wireless networks: –System interconnection Ease of operation –Wireless LANs IEEE 802.11 –Wireless WANs Cellular phones

25. CEN 4500, S. Masoud Sadjadi25 Wireless Networks (a) Bluetooth configuration (b) Wireless LAN

26. CEN 4500, S. Masoud Sadjadi26 Wireless Networks Almost all wireless network hook up to wired network at some point –(a) Individual mobile computers –(b) A flying LAN

27. CEN 4500, S. Masoud Sadjadi27 Future of wireless networks Wireless is the wave of the future “Mobile wireless computers are like mobile pipeless bathrooms—portapotties. They will be common on vehicles, and at constructions sites, and rock concerts. My advice is to wire up your home and stay there.” –(Metcalfe, 1995) “Four or five computers should be enough for the entire world until the year 2000.” –(IBM chairman T.J. Watson, 1945)

28. CEN 4500, S. Masoud Sadjadi28 Home Network Categories Computers –desktop PC, PDA, shared peripherals Entertainment –TV, DVD, VCR, camera, stereo, MP3 Telecomm –telephone, cell phone, intercom, fax Appliances –microwave, fridge, clock, furnace, AC Telemetry –utility meter, burglar alarm, babycam Wired or Wireless? –Cost favors wireless, but privacy favors wired!

29. CEN 4500, S. Masoud Sadjadi29 Internetworks A collection of interconnect networks is called an internetwork or internet. –“Internet” with capital “I” is one specific internet. Subnets do not include the hosts, but WANs do. The combination of a subnet and its hosts forms a WAN The combination of he cables and the hosts forms a LAN (no subnet in a LAN). Rule of thumb –If different organizations paid to construct different parts of the network and each maintains its part, we have an internet –If the underlying technology is different.

30. CEN 4500, S. Masoud Sadjadi30 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

31. CEN 4500, S. Masoud Sadjadi31 Network Software Why a layered organization? –To address complexity most network are organized as a stack of layers or levels, each one is built upon the one below it. –The number, name, content, and function of layers are different from one network to the other –The purpose of each layer is to offer certain services to the higher layers, shielding those layers from the implementation details

32. CEN 4500, S. Masoud Sadjadi32 Network Software Protocol Hierarchies Design Issues for the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to Protocols

33. CEN 4500, S. Masoud Sadjadi33 Protocol Hierarchies Layer n Protocol –The rules and conventions used in for two layer n of a network on two machines to communicate. –An agreement between the communication parties on how communication is to proceed Peers –The entities comprising the corresponding layers on each different machines. –It is the peers that communicate by using the protocols. Interface –Defines which primitive operations and services the lower layer makes available to the upper layer. Layers, protocols, and interfaces.

34. CEN 4500, S. Masoud Sadjadi34 Network Architecture A set of layers and protocols are called a network architecture. –The specification of a network architecture must have enough information to allow an implementer to write a program or develop the hardware for each layer so that it will correctly obey the appropriate protocols. –Neither the details of implementation nor the specification of interfaces is part of the architecture because these are hidden inside a machine and not visible from the outside. Protocol Stack –A list of protocols used by a certain system, one protocol per layer, is called a protocol stack.

35. CEN 4500, S. Masoud Sadjadi35 Protocol Hierarchies The philosopher-translator-secretary architecture.

36. CEN 4500, S. Masoud Sadjadi36 Protocol Hierarchies Example information flow supporting virtual communication in layer 5.

37. CEN 4500, S. Masoud Sadjadi37 Design Issues for the Layers Addressing –Every layer needs a mechanism for identifying senders and receivers Error Control –Physical communication circuits are not perfect Flow Control –How to keep a fast sender from swamping a slow receiver with data Multiplexing –Not every arbitrarily long messages can be sent without disassembling, transmitting, and reassembling Routing –When there are multiple path between the senders and receivers

38. CEN 4500, S. Masoud Sadjadi38 Services Connection-Oriented Services –Modeled after telephone systems –Pick up the phone, dial a number, talk, hang up. –Acts like a tube –In most cases, the order is preserved, so that the bits will arrive in the same order they were sent. Connectionless Services –Modeled after postal system. –Each letter carries the full destination address –Each is routed throughout the system independently.

39. CEN 4500, S. Masoud Sadjadi39 Services Six different types of service.

40. CEN 4500, S. Masoud Sadjadi40 Service Primitives Five service primitives for implementing a simple connection-oriented service.

41. CEN 4500, S. Masoud Sadjadi41 Service Primitives (2) Packets sent in a simple client-server interaction on a connection-oriented network.

42. CEN 4500, S. Masoud Sadjadi42 Services to Protocols Relationship Service –A set of primitives (operations) that a layer provides to the layer above it, which relates to the interface between the layers Protocol –A set of rules governing the format and meaning of the packets, or messages that are exchanged by the peer entities within a layer The relationship between a service and a protocol.

43. CEN 4500, S. Masoud Sadjadi43 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

44. CEN 4500, S. Masoud Sadjadi44 Reference Models The ISO OSI Reference Model –Open systems: systems that are open for communication with other systems. –Not a network architecture, because it does not specify the exact services and protocols to be used in each layer. The TCP/IP Reference Model A Comparison of OSI and TCP/IP A Critique of the OSI Model and Protocols A Critique of the TCP/IP Reference Model

45. CEN 4500, S. Masoud Sadjadi45 Reference Models The OSI reference model.

46. CEN 4500, S. Masoud Sadjadi46 The ISO OSI Reference Model Physical layer –Is concerned with the transmission of raw bits over a communication channel. Data link layer –Is to transform a raw transmission facility into a line that appears free of undetected transmission errors. Network layer –Controls the operation of the subnet. Transport layer –End-to-end. Accepts data from above, split it up into smaller units if need be, pass these to the network layer, and ensures that the pieces all arrive correctly at the other end. Session layer –Allows users on different machines to establish a session. Presentation layer –Concerned with the syntax and semantics of the information transmitted. Application layer –Contains a variety of protocols that are commonly uses –HTTP, FTP, SMTP, NTTP, etc.

47. CEN 4500, S. Masoud Sadjadi47 Reference Models The TCP/IP reference model.

48. CEN 4500, S. Masoud Sadjadi48 Reference Models Protocols and networks in the TCP/IP model initially.

49. CEN 4500, S. Masoud Sadjadi49 Comparing OSI and TCP/IP Concepts central to the OSI model –Services (layer semantics) –Interfaces (layer syntax) –Protocols (layer’s own business) TCP/IP –Did not originally clearly distinguish between service, interface, and protocol –People have tried to retrofit it after the fact to make it more OSI-like

50. CEN 4500, S. Masoud Sadjadi50 A Critique of the OSI Model & Protocols Why OSI did not take over the world –Bad timing The competing TCP/IP protocols were already in widespread use by research universities by the time OSI protocols appeared. –Bad technology Both the model and protocols are flawed (the choice of layers were mostly political than technical) –Bad implementations Initial implementation were huge, unwieldy, and slow –Bad politics Push by the European and then US government.

51. CEN 4500, S. Masoud Sadjadi51 Bad Timing If the interval between the two elephants is very short (because everyone is in hurry to get started), the people developing the standards may get crushed! The apocalypse of the two elephants.

52. CEN 4500, S. Masoud Sadjadi52 A Critique of the TCP/IP Problems: –Service, interface, and protocol not distinguished –Not a general model –Host-to-network “layer” not really a layer, it is just an interface between the network and data link layers –No mention of physical and data link layers –Minor protocols deeply entrenched (ad hoc), hard to replace Telnet was designed for a ten char per second mechanical Teletype terminal

53. CEN 4500, S. Masoud Sadjadi53 Hybrid Model The hybrid reference model to be used in this book.

54. CEN 4500, S. Masoud Sadjadi54 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

55. CEN 4500, S. Masoud Sadjadi55 Example Networks The Internet Connection-Oriented Networks: X.25, Frame Relay, and ATM Ethernet Wireless LANs: 802:11

56. CEN 4500, S. Masoud Sadjadi56 The Internet Is not a network at all, but a vast collection of different networks that use certain common protocols and provide certain common services. It is an unusual system that –is NOT planned by anyone –And is NOT controlled by anyone It all started in the late 1950’s (cold war) –The DoD wanted a command-and-control network that could survive the nuclear war.

57. CEN 4500, S. Masoud Sadjadi57 The ARPANET (a) Structure of the telephone system. Vulnerable! (b) Baran’s proposed distributed switching system.

58. CEN 4500, S. Masoud Sadjadi58 The ARPANET (2) The original ARPANET design. –IMP: Interface Message Processors –Software: Subnet and Host –BBN and UC Berkeley: Berkeley UNIX Sockets

59. CEN 4500, S. Masoud Sadjadi59 The ARPANET (3) Growth of the ARPANET (a) December 1969. (b) July 1970. (c) March 1971. (d) April 1972. (e) September 1972.

60. CEN 4500, S. Masoud Sadjadi60 NSFNET In late 1970s, to get to the ARPANET, a university had to have a research contract with the DoD, which many did not have NSF response was to design a successor to ARPANET The NSFNET backbone in 1988.

61. CEN 4500, S. Masoud Sadjadi61 Internet Usage Traditional applications (1970 – 1990) –E-mail –News –Remote login –File transfer

62. CEN 4500, S. Masoud Sadjadi62 Architecture of the Internet Overview of the Internet.

63. CEN 4500, S. Masoud Sadjadi63 ATM Virtual Circuits A virtual circuit. –Connections are often called virtual circuits in analogy with physical circuits used within the telephone systems –A permanent virtual circuit is also supported in ATM –Cells are 53 (48+5) bytes long

64. CEN 4500, S. Masoud Sadjadi64 ATM Virtual Circuits (2) An ATM cell. –Cell is a small and fixed sized packet. ATM networks –Are organized like traditional WANs, with lines and switches (routers). –155 Mbps and 622 Mbps (or higher). For compatibility with AT&T’s SONET transmission system

65. CEN 4500, S. Masoud Sadjadi65 The ATM Reference Model The ATM reference model.

66. CEN 4500, S. Masoud Sadjadi66 The ATM Reference Model (2) The ATM layers and sublayers and their functions.

67. CEN 4500, S. Masoud Sadjadi67 Ethernet Architecture of the original Ethernet.

68. CEN 4500, S. Masoud Sadjadi68 Wireless LANs (a) Wireless networking with a base station. (b) Ad hoc networking.

69. CEN 4500, S. Masoud Sadjadi69 Wireless LANs (2) The range of a single radio may not cover the entire system.

70. CEN 4500, S. Masoud Sadjadi70 Wireless LANs (3) A multicell 802.11 network.

71. CEN 4500, S. Masoud Sadjadi71 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

72. CEN 4500, S. Masoud Sadjadi72 Network Standardization Who’s Who in the Telecommunications World Who’s Who in the International Standards World Who’s Who in the Internet Standards World

73. CEN 4500, S. Masoud Sadjadi73 ITU Main sectors –Radiocommunications –Telecommunications Standardization –Development Classes of Members –National governments –Sector members –Associate members –Regulatory agencies

74. CEN 4500, S. Masoud Sadjadi74 IEEE 802 Standards The 802 working groups. The important ones are marked with *. The ones marked with  are hibernating. The one marked with † gave up.

75. CEN 4500, S. Masoud Sadjadi75 Metric Units The principal metric prefixes.

76. CEN 4500, S. Masoud Sadjadi76 Agenda Introduction Network Hardware Network Software Reference Models Example Networks Network Standardization Summary

77. CEN 4500, S. Masoud Sadjadi77 Summary Computer networks can be used for numerous services for companies and individuals. –Client-Server and Peer-2-Peer models. Networks can be divided into LANs, MANs, WANs, and internetworks. –LANs and MANs are unswitched (no routers). Network software consists of protocols, which are rules by which processes communicate. –Connectionless or Connection-oriented –Protocol hierarchy and protocol stack; OSI and TCP/IP models –Design issues: multiplexing, flow control, error control, etc. Examples: Internet, ATM, Ethernet, IEEE 802.11.