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.
The Application layer provides three basic services to applications:
The Application layer is used to support the following 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).
Tags: application layer, 7 layers network, layer 7 application layerThe 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:
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 |
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:
When 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.
Tags: session layer, communication protocol layers, layers of communication protocol, communications protocols image, layer, Layer 5The four main functions of the Transport layer are:
In carrying out its duties, the Transport layer performs a range of support activities, including:
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