1. Sam_CN_UNIT- I 1 3/10/2016 Computer Networks Textbook: Computer Networks 4th ed., by A.S. Tanenbaum

2. Sam_CN_UNIT- I 2 3/10/2016 COMPUTER NETWORKS Ch. Samson M.E, (Ph.D) M.E, (Ph.D) Associate Professor & Associate Head, Dept of IT

3. Sam_CN_UNIT- I 3 3/10/2016 UNIT- I: INTRODUCTION What is a network? UNIT- I: INTRODUCTION What is a network? Set of devices communicating with each other Could be a CPU, monitor and other peripheral devices connected (and exchanging data) to each other Could be a group of people …. A network of friends Or, could be a set of computers communicating with each other

4. Sam_CN_UNIT- I 4 3/10/2016 Computer Network Technology and architecture of the communications networks used to interconnect devices Technology and architecture of the communications networks used to interconnect devices An interconnected collection of autonomous computers is called computer network An interconnected collection of autonomous computers is called computer network Examples: LAN,MAN,WAN, Internet etc. Examples: LAN,MAN,WAN, Internet etc.

5. Sam_CN_UNIT- I 5 3/10/2016 Why Networks? Point-to-point communication is not usually practical because Point-to-point communication is not usually practical because Devices are too far apart Devices are too far apart Requires large number of connections between all devices Requires large number of connections between all devices Too expensive Too expensive Solution is a communications network Solution is a communications network

6. Sam_CN_UNIT- I 6 3/10/2016 Uses of Computer Networks Availability of Resource / Resource sharing - Resources become available regardless of the user’s physical location Load Sharing - Jobs processed on the least crowded machine High Reliability - File and processor redundancy Human-to-Human Communication - Telephone - Long distance education and collaboration

7. Sam_CN_UNIT- I 7 3/10/2016 Applications of Computer Networks Business Applications Business Applications Home Applications Home Applications Mobile Users Mobile Users Social Issues Social Issues

8. Sam_CN_UNIT- I 8 3/10/2016 Business Applications of Networks The client-server model involves requests and replies Fig: A network with two clients and one server

9. Sam_CN_UNIT- I 9 3/10/2016 Home Network Applications Access to remote information Access to remote information - - World Wide Web Person-to-person communication Person-to-person communication - - Electronic mail, Videoconference Interactive entertainment Interactive entertainment - - Video-on-Demand, Games Electronic commerce Electronic commerce

10. Sam_CN_UNIT- I 10 3/10/2016 Home Network Applications Some forms of e-commerce.

11. Sam_CN_UNIT- I 11 3/10/2016 Mobile Network Users Combinations of wireless networks and mobile computing -Cellular Phones, Personal Digital Assistant (PDA) and Smart hones (PDA+ Handset+ GPS+…)

12. Sam_CN_UNIT- I 12 3/10/2016 Social issues Intrusions Privacy Copyright Pornography Anonymity Security Worms and Virus responsibility of the service providers

13. Sam_CN_UNIT- I 13 3/10/2016 Network Hardware Network design dimensions: Transmission technology( broadcast networks, Point- to-point networks) Transmission technology( broadcast networks, Point- to-point networks) Scale( LAN, WAN, Internet etc..) Scale( LAN, WAN, Internet etc..)

14. Sam_CN_UNIT- I 14 3/10/2016 Network Classifications Based on transmission technology networks are divided into Broadcast and Point to Point networks   Broadcast Networks use one communication channel that is shared by all the machines. Packets are sent to the shared channel and are “listened to” by all machines.(for smaller, geographically localized networks)

15. Sam_CN_UNIT- I 15 3/10/2016 Network Classifications (cont’d)   Point - to - Point network : A network in which a physical communication path exists between 2 end-systems with no other devices involved

16. Sam_CN_UNIT- I 16 3/10/2016 Network Classifications (cont’d) Classification based on scale Local Area Networks( LAN): Room, Building /Campus Metropolitan Area Networks ( MAN): City Wide Area Networks (WAN): Country, Continent Wireless Networks Home networks Internetworks: Global

17. Sam_CN_UNIT- I 17 3/10/2016 Local Area Network Network in small geographical Area (room,building or a campus) is called LAN A LAN is a data communication system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communication channel of moderate data rates.

18. Sam_CN_UNIT- I 18 3/10/2016 Local Area Network (Cont’d) Short geographical distance (a few kilometers) High speed (Larger than 1 Mbps up to 100 Mbps ) Multiple access (Many can use it at the same time) Sharing (hardware, software etc.) IEEE standard 802.3 IEEE standard 802.3 The most reliable network The most reliable network

19. Sam_CN_UNIT- I 19 3/10/2016 LAN Topologies

20. Sam_CN_UNIT- I 20 3/10/2016 Metropolitan Area Networks Network in a City is call MAN (Metropolitan Area Network) MAN is distinguished by its adopted standard DQDB (Distributed Queue Dual Bus (IEEE standard 802.6) and it contains two unidirectional buses which all the computers are connected A metropolitan area network based on cable TV

21. Sam_CN_UNIT- I 21 3/10/2016 Definitions Network: Interconnected collection of autonomous computers Host: machine running user application Subnet: Communication subnet carries messages between hosts Channel: Logical Line of communication (circuit) Router: Network router is a device or a piece of software in a computer that forwards and routes data packets along networks

22. Sam_CN_UNIT- I 22 3/10/2016 Wide Area Networks Network spread geographically (country or across Globe) is called WAN. WAN contains hosts that are connected by a communication subnet The job of the subnet is to carry messages from host to host like telephone system carries words from speaker to listener Store-and-forward network

23. Sam_CN_UNIT- I 23 3/10/2016 Wide Area Networks Wide Area Networks (Cont’d) Fig: Relation between hosts on LANs and the subnet

24. Sam_CN_UNIT- I 24 3/10/2016 Wide Area Networks Wide Area Networks (Cont’d) Figure: A stream of packets from sender to receiver

25. Sam_CN_UNIT- I 25 3/10/2016 Networking Devices HUB, Switches, Routers, Wireless Access Points, Modems etc.

26. Sam_CN_UNIT- I 26 3/10/2016 Wireless Networks Categories of wireless networks: (used for) System interconnection (used for) System interconnection Wireless LANs Wireless LANs Wireless WANs Wireless WANs

27. Sam_CN_UNIT- I 27 3/10/2016 Wireless Networks (Cont’d) (a) Bluetooth configuration (b) Wireless LAN

28. Sam_CN_UNIT- I 28 3/10/2016 Wireless Networks (Cont’d) ( ( a) Individual mobile computers (b) A flying LAN

29. Sam_CN_UNIT- I 29 3/10/2016 Internetworks internet: a collection of interconnected networks Internet: specific worldwide internet Subnets: (WAN) collection of routers and communication lines (without hosts). Ex: telephone subnet Networks: combination of subnet and its hosts. Ex: telephone network = telephone subnets+ telephones internetwork: formed when distinct networks are connected together. Ex: connecting LAN and WAN

30. Sam_CN_UNIT- I 30 3/10/2016 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 etc.) Telemetry (utility meter, burglar alarm etc.)

31. Sam_CN_UNIT- I 31 3/10/2016 Network Software Protocol Hierarchies Design Issues for the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to Protocols

32. Sam_CN_UNIT- I 32 3/10/2016 A protocol is an agreement that standardizes the way communication will be handled It is a set of rules and conventions that governs exchange of data between two systems A set of layers and protocols is called a network architecture A list of protocols used by a certain system, one protocol per layer, is called a protocol stack Protocol

33. Sam_CN_UNIT- I 33 3/10/2016 Protocol Hierarchies Networks are organized as a stack of levels or layers We build each layer on the one below it Layers differ in number and function from one network to another Each layer hides underlying details from the one above it – sort of like a virtual machine Each layer talks to the ones above & below it

34. Sam_CN_UNIT- I 34 3/10/2016 Network Software Protocol Hierarchies Fig: Layers, protocols, and interfaces

35. Sam_CN_UNIT- I 35 3/10/2016 Data Transfer No data is transferred directly from one machine to another on that layer – the layers can only talk to the ones above or below them on their host. A message from layer 5 will have to travel to layer 1, move across the physical medium, and then back up to layer 5 on the different machine. Layer 1 is the only layer able to move data from one machine to another, through the physical medium.

36. Sam_CN_UNIT- I 36 3/10/2016 Design Issues for the Layers A mechanism for identifying senders and receivers (naming and addressing) rules of transfer (simplex, half-duplex, full-duplex) error control (error correction and error detection) ordering and sequencing flow control, congestion control message or packet size (disassembling and reassembling) multiplexing and demultiplexing routing security

37. Sam_CN_UNIT- I 37 3/10/2016 Connection-Oriented and Connectionless Services Six different types of service

38. Sam_CN_UNIT- I 38 3/10/2016 Connection-Oriented and Connectionless Services Initial Destination Packet Error Flow Option setup address sequence control control negotiation Issue Connection Oriented Connection- less required not possible only needed during setup needed for every packet guaranteed not guaranteed by network layer by transport layer by transport layer by network layer Yes No

39. Sam_CN_UNIT- I 39 3/10/2016 Service Primitives Five service primitives for implementing a simple connection-oriented service

40. Sam_CN_UNIT- I 40 3/10/2016 The Relationship of Services to Protocols A service defines what operations the layer is prepared to perform on behalf of its users, but it says nothing at all about how these operations are implemented. A protocol, in contrast, is a set of rules governing the format and meaning of the frames, packets, or messages that are exchanged by the peer entities within a layer. Entities use protocols in order to implement their service definitions.

41. Sam_CN_UNIT- I 41 3/10/2016 Reference Models The OSI Reference Model In the late 1970s, to promote the compatibility of network designs, the International Organization for Standardization (ISO) proposed an architecture model called the open systems interconnection references model (OSI model) layer N layer N-1 layer N layer N-1 PDUs (protocol data unit) actual data flow on the lowest level services

42. Sam_CN_UNIT- I 42 3/10/2016 The OSI Reference Model

43. Sam_CN_UNIT- I 43 3/10/2016 The OSI Reference Model application presentation session transport network data link physical 7 6 5 4 3 2 1transmission of bits transmission of packets on one given link end-to-end transmission of packets end-to-end delivery of messages setup and management of end-to-end conversation formatting, encryption, and compression network services (email, file transfer)

44. Sam_CN_UNIT- I 44 3/10/2016 OSI Layers Application Presentation Session Transport Network Data link Physical Application Presentation Session Transport Network Data link Physical Application Presentation Session Transport Network Data link Physical App YApp X Data H H H H H H Outgoing Packets Incoming Packets Physical Path

45. Sam_CN_UNIT- I 45 3/10/2016 The Physical Layer Transmission of a raw bit stream Transmission of a raw bit stream - forms the physical interface between devices -Makes sure that when one side sends a 1 bit,the other side receives it as a 1. -Makes sure that when one side sends a 1 bit,the other side receives it as a 1. - Covers all aspects for communication - Covers all aspects for communication Mechanical interface defines the connectors used, number of pins, their placement, size, material used. Mechanical interface defines the connectors used, number of pins, their placement, size, material used. Electrical interface defines the voltage/current levels of signals. Electrical interface defines the voltage/current levels of signals.

46. Sam_CN_UNIT- I 46 3/10/2016 The Data Link Layer Data link layer attempts to make physical link reliable May divide upper layer packet into multiple frames Ensure that peer entity will recognize frame boundaries May introduce sequence numbers and acknowledgments Provides reliable transfer of information between two adjacent nodes Creates frames, or packets from bits and vice versa Provides frame-level error control Provides flow control

47. Sam_CN_UNIT- I 47 3/10/2016 The Network Layer Network layer is designed to facilitate communication between systems across a communication network Implements network routing and message delivery through networks to the correct destination Congestion control can also be done at network layer Internetworking Internet protocol or IP is one example Responsible for routing decisions

48. Sam_CN_UNIT- I 48 3/10/2016 The Transport Layer Provides reliable end-to-end communication May detect erroneous packets Reorders packets which arrive out-of-sequence. Ensures that there is no loss or duplication of packets May provide connection-less or connection-oriented type of service Provides for the connection management. Multiplexing and demultiplexing Packetization, flow control, etc. Examples: TCP and UDP Establishes and deletes connections across the network

49. Sam_CN_UNIT- I 49 3/10/2016 The Session Layer Allows users on different computers to establish a session This layer requests for a logical connection to be established based on an end-user's request This layer provides services like dialogue discipline which can be full duplex or half duplex Session layer can also provide check pointing (or synchronization) mechanism If a failure occurs between checkpoints, all data can be retransmitted from the last checkpoint May perform synchronization and token management between several communicating applications

50. Sam_CN_UNIT- I 50 3/10/2016 The Presentation Layer Performs specific functions that are requested regularly by applications Performs specific functions that are requested regularly by applications Presentation layer defines the data format to be exchanged between the programs. Presentation layer defines the data format to be exchanged between the programs. Manages abstract data structures, and converts them host-representation to network- representation and vice versa. Manages abstract data structures, and converts them host-representation to network- representation and vice versa. Encryption Encryption

51. Sam_CN_UNIT- I 51 3/10/2016 The Application Layer Application layer protocols are application dependent Application layer protocols are application dependent Implements communication between two applications of the same type Implements communication between two applications of the same type - FTP - FTP - SMTP (email) etc. - SMTP (email) etc.

52. Sam_CN_UNIT- I 52 3/10/2016 What is TCP/IP ? The name TCP/IP refers to a suite of data communication protocols Its name comes from two of the more important protocols in the suite: the Transmission Control Protocol (TCP) and the Internet Protocol (IP) The most common of all network protocol suites, is the ‘standard’ in modern networks, used for communication on the Internet Although designed for the Internet it is used to build LANs, WANs and MANs Most widely used protocol suite, used within Unix, Windows and Macintosh platforms

53. Sam_CN_UNIT- I 53 3/10/2016 The TCP/IP Reference model

54. Sam_CN_UNIT- I 54 3/10/2016 The TCP/IP Reference model Protocols and networks in the TCP/IP model initially

55. Sam_CN_UNIT- I 55 3/10/2016 Network Access (Host-to-network) Ethernet, Token Ring, FDDI Frame Relay, ATM, ISDN Access commn network LAN and WAN technologies Internet Transport Application Application Path determination – routing IP, ARP, ICMP, DHCP TCP, UDP DNS FTP HTTP Telnet SMTP SNMP TFTP HTTP POP3 Provides access to network services for the user and application programs Provides end-to-end transport The TCP/IP Protocol Suite Four-Layered ModelProtocols

56. Sam_CN_UNIT- I 56 3/10/2016 Host-to-Network Layer The TCP/IP model does not really say much about what happens here, except to point out that the host has to connect to the network so it can send IP packets to it Access the communication network

57. Sam_CN_UNIT- I 57 3/10/2016 Internet Layer Routes data between hosts Connectionless Every packet routed independently Does not guarantee reliable or in-sequence delivery

58. Sam_CN_UNIT- I 58 3/10/2016 Internet Layer (cont’d) The internet layer defines an official packet format for and protocol called Internet Protocol (IP) The internet layer defines an official packet format for and protocol called Internet Protocol (IP) It is the responsibility of the internet layer to get the IP packets to their destination It is the responsibility of the internet layer to get the IP packets to their destination The TCP/IP internet layer is similar in functionality to the OSI network layer The TCP/IP internet layer is similar in functionality to the OSI network layer

59. Sam_CN_UNIT- I 59 3/10/2016 Transport Layer The transport layer is intended to allow two machines to carry on a conversation, just like the OSI transport layer There are two protocols defined for this: TCP (Transmission Control Protocol) reliable, connection-oriented UDP (User Datagram Protocol) unreliable, connectionless

60. Sam_CN_UNIT- I 60 3/10/2016 Application Layer This layer contains all of the higher-level protocols telnet FTP SMTP DNS HTTP

61. Sam_CN_UNIT- I 61 3/10/2016 The differences between the TCP/IP and OSI models OSI model clearly defined the distinction between services, interfaces and protocols, where the TCP/IP model does not This fits in nicely with OO programming concepts as the layer hide information Protocols can easily be replaced in the OSI model, but not in the TCP/IP model

62. Sam_CN_UNIT- I 62 3/10/2016 The Differences (cont’d) The OSI model has no biases for protocols, but the OSI model was overly general and did not help with the creation of new protocols OSI supports connectionless and connection-oriented in the network layer, but only connection-oriented in the transport layer, providing no choice to the user TCP/IP supports only connectionless in the network layer, but both in the transport layer, giving user a choice

63. Sam_CN_UNIT- I 63 3/10/2016 A Critique of the OSI Model and Protocols Why OSI did not take over the world? Bad timing Bad technology Bad implementations Bad politics

64. Sam_CN_UNIT- I 64 3/10/2016 Bad Timing The apocalypse of the two elephants

65. Sam_CN_UNIT- I 65 3/10/2016 A Critique of the TCP/IP Reference Model Service, interface, and protocol not distinguished Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to replace

66. Sam_CN_UNIT- I 66 3/10/2016 Hybrid Model The hybrid reference model to be used in this book

67. Sam_CN_UNIT- I 67 3/10/2016 Example Networks The Internet(ARPA NET) Connection-Oriented Networks: X.25, Frame Relay, and ATM Ethernet Novell Netware Wireless LANs: 802:11

68. Sam_CN_UNIT- I 68 3/10/2016 The ARPANET The original ARPANET design

69. Sam_CN_UNIT- I 69 3/10/2016 Internet Usage Traditional applications (1970 – 1990) E-mail News Remote login File transfer