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Thread: The 7 Layers of the OSI Model

  1. #1
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    Default The 7 Layers of the OSI Model

    The 7 Layers of the OSI Model

    The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.


    Application (Layer 7)
    This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.


    Presentation (Layer 6)
    This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.


    Session (Layer 5)
    This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.


    Transport (Layer 4)
    This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

    Network (Layer 3)
    This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

    Data Link (Layer 2)
    At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

    Physical (Layer 1)
    This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

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  2. #2

    Default

    when i had to memoryize this for networking class i used the phrase

    Please Do Not Throw Sausage Pizza Away
    for physical data network transport session presentation application

    helped me alot

  3. #3
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    What about TCP/IP layer , Could any body explain that also :d

  4. #4
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    As I was completing my Cisco certification I remeberd All people seem to need data processing: Application, Presentation, Session, Transport, Network, Data Link, Physical. as for your question about TCP/IP, that falls into the Network layer along with IPX.

  5. #5
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    Quote Originally Posted by alok.bizhat.com
    What about TCP/IP layer , Could any body explain that also :d
    TCP is layer 4, and IP is layer 3.

  6. #6
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    Default TCP/IP

    Quote Originally Posted by alok.bizhat.com
    What about TCP/IP layer , Could any body explain that also :d
    ok the tcp/ip model is not the 3rd and 4th layer of the OSI model,
    although whoever said that is right too, because IP protocol is used in the 3rd layer and TCP protocol is used in the 4th layer.....

    TCP/IP is another protocol suite, The U.S. Department of Defense created the TCP/IP reference model because it wanted a network that could survive any conditions.


    The Layers of TCP/IP are :


    1) Application - The application layer handles high-level protocols, representation, encoding, and dialog control

    2)Transport - The transport layer provides a logical connection between a source host and a destination host

    3)Internet - The purpose of the Internet layer is to select the best path through the network for packets to travel.

    4)Network Access - The network access layer allows an IP packet to make a physical link to the network media

  7. #7
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    Default

    thanks a lot for the networking tutorials.

  8. #8
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    Default

    alok u have to smaller the avatr.its against teh rules of the forum

  9. #9
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    Mera Bharat Mahan
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    I PMed him yesterday
    and waiting for the change

  10. #10
    Join Date
    Mar 2005
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    Default Re: TCP/IP

    Karma_police, you're compltetely wrong...
    Quote Originally Posted by Karma_police
    1) Application
    Wrong : IP and TCP don't care what is the purpose of the data they transport
    2)Transport
    This is only TCP
    3)Internet
    This is not a OSI layer...
    4)Network Access
    This is only IP

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