Category Archives: OSI Model

OSI Layer Model

The International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) Reference Model to define functional communications standards. This reference model is widely used by equipment manufacturers to assure their products will interoperate with products from other vendors. The OSI model describes the functions that are performed in data communications. The model architecture is seven layers those are listed below with each layer defining specific functions.

Osi Layer Model OSI Layer Model

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Tags: osi layer, osi layer model, IOS model, Application Layers, osi architecture, communication layers, osi layers, osi model layers, layer model, ios layer

The Application Layer – Layer 7

The Application layer provides three basic services to applications:

  • It makes sure the resources needed to carry out a session are present.
  • It matches the application to the appropriate communication protocol or service.
  • It synchronizes the tgransmission of data between the application and its protocol.

The Application Layer Layer 7 246x300 The Application Layer   Layer 7The Application layer is used to support the following services:

  • File services – store, move control access to, and retrieve files
  • Print services – send data to local or network printers
  • Message services – transfer text, graphics, audio, and video over a network
  • Application services – process applications locally or through distributed processing
  • Database services – allow a local computer to access network services

In addition, the Application layer advertises any services that are being offered and determines whether requests made by the client should be processed locally or remotely (through another network resource).

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Tags: application layer, yhs-default

The Presentation Layer – Layer 6

The main function of the presentation layer is to define the data formats used to provide a number of services to the Application layer.

Included in these services the ones you need to know are:

The Presentation Layer Layer 6 246x300 The Presentation Layer   Layer 6

  • Data encryption – coding data so that it is protected from unauthorizaed access
  • Data compression – reducing the number of packets required for transport
  • Data formatting
  • Data conversion
  • Conversions standards defined on the Presentation Layer for data conversion and formatting:

    Category Standards
    Data Conversion ASCII, EBCDIC, encryption
    Audio/video conversion MIDI, MPEG, QuickTime, AVI
    Graphics conversion GIF, JPEG, PICT, TIFF
    Tags: Presentation layer, what is presentation layer

    The Session Layer – Layer 5

    Layer 5 of the OSI model is the Session Layer, which establishes, manages, and terminates sessions between applications.

    Following are some of the communication tasks performed at this layer:

    • Establishing connections
    • Maintaining connections
    • Synchronizing communications
    • Controlling dialogues
    • Terminating connections

    The Session Layer Layer 5 246x300 The Session Layer   Layer 5When you create a connection, you authenticate the user account at the sending and receiving computers. Connection creation also involves determining the type of communication that will take place and the protocols that will be used by the lower layers.

    Data transfer and dialogue control are used to determine which computer is making requests and which computer is making responses. This also determines whether acknowledgments are required for data transmission.

    A session is a series of related connection-oriented transmissions between network nodes. Another way to look at it is that a session is the interrelated communications between two or more presentation entities, which emphasizes that the Session layer provides services to the Presentation layer.

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    Tags: session layer

    The Transport Layer – Layer 4

    The four main functions of the Transport layer are:

  • Segment and assemble upper-layer applications
  • Transport segments from one host to another host
  • Establish and manage end-to-end operations
  • Error recovery
  • The Transport Layer Layer 4 246x300 The Transport Layer   Layer 4In carrying out its duties, the Transport layer performs a range of support activities, including:

  • Maintaining data integrity through flow control techniques
  • Multiplexing the data from upper layer applications
  • Setting up and tearing down any virtual circuits established to transport the data over the network
  • Hiding any network-dependent information from the upper layers (which will only confuse them)
  • Breaking down Session layer (layer 5) datagrams into segments
  • Monitoring the error-free delivery of the data to its destination
  • Providing for general connection management and data transfer services
  • Providing for the reliable (but, not guaranteed) delivery of data
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    Tags: frame packet segment datagram, transport layer, frame packet segment, packets frames and segments