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    Deepak RautDeepak RautRoll n0.108Roll n0.108

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    7 Application

    6 Presentation

    5 Session

    4 Transport

    1 Physical

    2 Data Link

    3 Network

    OSI REFERENCE MODEL

    1. Physical Layer

    a) Convert the logical 1s and 0s coming fromlayer 2 into electrical signals.

    b) Transmission of the electrical signals over a

    communication channel.

    Main topics:

    Transmission mediumsEncoding

    ModulationRS232 and RS422 standardsRepeatersHubs (multi-port repeater)

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    7 Application

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    1 Physical

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    OSI REFERENCE MODEL

    2. Data Link Layer

    a) Error control to compensate for theimperfections of the physical layer.

    b) Flow control to keep a fast sender from

    swamping a slow receiver.

    Main topics:

    Framing methodsError detection and correction methods

    Flow controlFrame formatIEEE LAN standardsBridgesSwitches (multi-port bridges)

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    7 Application

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    1 Physical

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    OSI REFERENCE MODEL

    4. Transport Layer

    a) Provides additional Quality of Service.

    b) Heart of the OSI model.

    Main topics:Connection-oriented and connectionless servicesTransmission Control Protocol (TCP)User Datagram Protocol (UDP)

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    OSI REFERENCE MODEL

    5. Session Layer

    a) Allows users on different machines to establishsessions between them.

    b) One of the services is managing dialogue

    control.c) Token management.

    d) Synchronization.

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    7 Application

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    5 Session

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    1 Physical

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    3 Network

    OSI REFERENCE MODEL

    6. Presentation Layer

    a) Concerned with the syntax and semantics of theinformation.

    b) Preserves the meaning of the information.

    c) Data compression.

    d) Data encryption.

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    OSI REFERENCE MODEL

    7. Application Layer

    a) Provides protocols that are commonly needed.

    Main topics:

    File Transfer Protocol (FTP)HyperText Transfer Protocol (HTTP)Simple Mail Transfer Protocol (SMTP)Simple Network Management Protocol (SNMP)Network File System (NFS)Telnet

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    SERVICES

    Each layer provides services to the layer above it.

    1. TerminologiesE ntities active elements in each layer (e.g.process, intelligent I/O chip).

    Peer E ntities entities in the same layer ondifferent machines.

    Service Provider Layer N.

    Service User Layer N + 1.

    Service Access Points places where layer N + 1can access services offered by layer N.

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    SERVICES

    2. Connection-Oriented and ConnectionlessC onnection-Oriented before data is sent, the

    service from the sending computer must establisha connection with the receiving computer.

    C onnectionless data can be sent at any time bythe service from the sending computer.

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    SERVICES

    3. Service PrimitivesR equest entity wants the service to do somework

    Indicate entity is to be informed about an eventR esponse entity responds to an eventC onfirm entity is to be informed about its request

    Sending Computer Receiving Computer

    3 Network

    1. request

    3 Network

    2. indicate 3. response4. confirm

    4 Transport 4 Transport

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    Thank you