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    Week-2 - Lesson-1 PDF

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    Mamun Ahmed joy
    The document discusses the OSI network model and its seven layers. It begins by explaining layered tasks and using the postal system as an example. It then discusses each layer of the OSI model in detail, including the physical, data link, network, transport, session, presentation, and application layers. For each layer, it outlines the key functions and responsibilities, such as framing data, addressing, error control, routing, and various protocols. It emphasizes that each higher layer builds upon the layers below it to complete end-to-end communication tasks from one application to another.

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    Week-2 - Lesson-1 PDF

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    Mamun Ahmed joy
    37 views26 pages
    The document discusses the OSI network model and its seven layers. It begins by explaining layered tasks and using the postal system as an example. It then discusses each layer of the OSI model in detail, including the physical, data link, network, transport, session, presentation, and application layers. For each layer, it outlines the key functions and responsibilities, such as framing data, addressing, error control, routing, and various protocols. It emphasizes that each higher layer builds upon the layers below it to complete end-to-end communication tasks from one application to another.

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    The document discusses the OSI network model and its seven layers. It begins by explaining layered tasks and using the postal system as an example. It then discusses each layer of the OSI model in detail, including the physical, data link, network, transport, session, presentation, and application layers. For each layer, it outlines the key functions and responsibilities, such as framing data, addressing, error control, routing, and various protocols. It emphasizes that each higher layer builds upon the layers below it to complete end-to-end communication tasks from one application to another.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    37 views26 pages

    Week-2 - Lesson-1 PDF

    Uploaded by

    Mamun Ahmed joy
    The document discusses the OSI network model and its seven layers. It begins by explaining layered tasks and using the postal system as an example. It then discusses each layer of the OSI model in detail, including the physical, data link, network, transport, session, presentation, and application layers. For each layer, it outlines the key functions and responsibilities, such as framing data, addressing, error control, routing, and various protocols. It emphasizes that each higher layer builds upon the layers below it to complete end-to-end communication tasks from one application to another.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    of 26

    DATA COMMUNICATION

    CSE 225/233

    WEEK-2, LESSON-1

    NETWORK MODEL
    Layered Task
    We use the concept of layers in our daily life. As an
    example, let us consider two friends who communicate
    through postal mail. The process of sending a letter to a
    friend would be complex if there were no services available
    from the post office. See the next slide.

    Data Communication Lecture Series, NRC, MAY2020 2.2


    Tasks involved in sending a letter

    Data Communication Lecture Series, NRC, MAY2020 2.3


    The OSI model
    Established in 1947, the International Standards
    Organization (ISO) is a multinational body dedicated to
    worldwide agreement on international standards. An ISO
    standard that covers all aspects of network
    communications is the Open Systems Interconnection (OSI)
    model. It was first introduced in the late 1970s.

    Data Communication Lecture Series, NRC, MAY2020 2.4


    Layers of the OSI model

    Data Communication Lecture Series, NRC, MAY2020 2.5


    The OSI model

    Data Communication Lecture Series, NRC, MAY2020 2.6


    Physical Layer

    Data Communication Lecture Series, NRC, MAY2020 2.7


    Functionalities of Physical Layer
    • Following are the various functions performed by the Physical layer of the OSI
    model.

    • Representation of Bits: Data in this layer consists of stream of bits. The bits must
    be encoded into signals for transmission. It defines the type of encoding i.e. how
    0's and 1's are changed to signal.
    • Data Rate: This layer defines the rate of transmission which is the number of bits
    per second.
    • Synchronization: It deals with the synchronization of the transmitter and receiver.
    The sender and receiver are synchronized at bit level.
    • Interface: The physical layer defines the transmission interface between devices
    and transmission medium.
    • Line Configuration: This layer connects devices with the medium: Point to Point
    configuration and Multipoint configuration.
    • Topologies: Devices must be connected using the following topologies: Mesh,
    Star, Ring and Bus.
    • Transmission Modes: Physical Layer defines the direction of transmission
    between two devices: Simplex, Half Duplex, Full Duplex.
    • Deals with baseband and broadband transmission.

    Data Communication Lecture Series, NRC, MAY2020 2.8


    Data Link Layer

    Data Communication Lecture Series, NRC, MAY2020 2.9


    Functionalities of Datalink Layer
    • Following are the various functions performed by the Datalink layer of the OSI
    model.

    • Framing: Frames are the streams of bits received from the network layer into
    manageable data units. This division of stream of bits is done by Data Link Layer.
    • Physical Addressing: The Data Link layer adds a header to the frame in order to
    define physical address of the sender or receiver of the frame, if the frames are to
    be distributed to different systems on the network.
    • Flow Control: A flow control mechanism to avoid a fast transmitter from running
    a slow receiver by buffering the extra bit is provided by flow control. This prevents
    traffic jam at the receiver side.
    • Error Control: Error control is achieved by adding a trailer at the end of the frame.
    Duplication of frames are also prevented by using this mechanism. Data Link
    Layers adds mechanism to prevent duplication of frames.
    • Access Control: Protocols of this layer determine which of the devices has control
    over the link at any given time, when two or more devices are connected to the
    same link.

    Data Communication Lecture Series, NRC, MAY2020 2.10


    Hop to Hop delivery

    Data Communication Lecture Series, NRC, MAY2020 2.11


    Network Layer

    Data Communication Lecture Series, NRC, MAY2020 2.12


    Functionalities of Network Layer
    • Following are the various functions performed by the network layer of the
    OSI model.

    • It translates logical network address into physical address. Concerned


    with circuit, message or packet switching.
    • Routers and gateways operate in the network layer. Mechanism is
    provided by Network Layer for routing the packets to final destination.
    • Connection services are provided including network layer flow control,
    network layer error control and packet sequence control.
    • Breaks larger packets into small packets.

    Data Communication Lecture Series, NRC, MAY2020 2.13


    Source to Destination delivery

    Data Communication Lecture Series, NRC, MAY2020 2.14


    Transport Layer

    Data Communication Lecture Series, NRC, MAY2020 2.15


    Functionalities of Transport Layer
    • Following are the various functions performed by the Transport layer of the OSI
    model.

    • Service Point Addressing: Transport Layer header includes service point address
    which is port address. This layer gets the message to the correct process on the
    computer unlike Network Layer, which gets each packet to the correct computer.
    • Segmentation and Reassembling: A message is divided into segments; each
    segment contains sequence number, which enables this layer in reassembling the
    message. Message is reassembled correctly upon arrival at the destination and
    replaces packets which were lost in transmission.
    • Connection Control: It includes 2 types:
    • Connectionless Transport Layer : Each segment is considered as an independent packet
    and delivered to the transport layer at the destination machine.
    • Connection Oriented Transport Layer : Before delivering packets, connection is made
    with transport layer at the destination machine.
    • Flow Control: In this layer, flow control is performed end to end.
    • Error Control: Error Control is performed end to end in this layer to ensure that
    the complete message arrives at the receiving transport layer without any error.
    Error Correction is done through retransmission.

    Data Communication Lecture Series, NRC, MAY2020 2.16


    Process to Process delivery of a message

    Data Communication Lecture Series, NRC, MAY2020 2.17


    Session Layer

    Data Communication Lecture Series, NRC, MAY2020 2.18


    Functionalities of Session Layer
    • Following are the various functions performed by the session layer of the
    OSI model.

    • Dialog Control : This layer allows two systems to start communication


    with each other in half-duplex or full-duplex.
    • Token Management: This layer prevents two parties from attempting the
    same critical operation at the same time.
    • Synchronization : This layer allows a process to add checkpoints which are
    considered as synchronization points into stream of data. Example: If a
    system is sending a file of 800 pages, adding checkpoints after every 50
    pages is recommended. This ensures that 50 page unit is successfully
    received and acknowledged. This is beneficial at the time of crash as if a
    crash happens at page number 110; there is no need to retransmit 1
    to100 pages.

    Data Communication Lecture Series, NRC, MAY2020 2.19


    Presentation Layer

    Data Communication Lecture Series, NRC, MAY2020 2.20


    Functionalities of Presentation Layer
    • Following are the various functions performed by the presentation layer
    of the OSI model.

    • Translation: Before being transmitted, information in the form of


    characters and numbers should be changed to bit streams. The
    presentation layer is responsible for interoperability between encoding
    methods as different computers use different encoding methods. It
    translates data between the formats the network requires and the format
    the computer.
    • Encryption: It carries out encryption at the transmitter and decryption at
    the receiver.
    • Compression: It carries out data compression to reduce the bandwidth of
    the data to be transmitted. The primary role of Data compression is to
    reduce the number of bits to be 0transmitted. It is important in
    transmitting multimedia such as audio, video, text etc.

    Data Communication Lecture Series, NRC, MAY2020 2.21


    Application Layer

    Data Communication Lecture Series, NRC, MAY2020 2.22


    Functionalities of Application Layer
    • Following are the various functions performed by the application layer of
    the OSI model.
    • Mail Services: This layer provides the basis for E-mail forwarding and
    storage.
    • Network Virtual Terminal: It allows a user to log on to a remote host. The
    application creates software emulation of a terminal at the remote host.
    User's computer talks to the software terminal which in turn talks to the
    host and vice versa. Then the remote host believes it is communicating
    with one of its own terminals and allows user to log on.
    • Directory Services: This layer provides access for global information about
    various services.
    • File Transfer, Access and Management (FTAM): It is a standard
    mechanism to access files and manages it. Users can access files in a
    remote computer and manage it. They can also retrieve files from a
    remote computer.

    Data Communication Lecture Series, NRC, MAY2020 2.23


    Summary of the layers

    Data Communication Lecture Series, NRC, MAY2020 2.24


    Exercises

    • Go through the exercises given at the end of the chapter. Note


    that, we are following the 4th Edition of Forouzan Book for this
    chapter.

    Data Communication Lecture Series, NRC, MAY2020 2.25


    Data Communication Lecture Series, NRC, MAY2020 2.26

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