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Write down the "OSI Model of communication" in de…

Write down the "OSI Model of communication" in detail.

Write down the "OSI Model of communication" in detail.

Chiranjibi Mar. 07, 2018

The International Standards Organization (ISO) developed a seven-layer Open Systems Interconnection (OSI) model to serve as a standard model for network architectures. Seven layers of OSI include the following:

Layer 7 or Application Layer

The Application layer supplies network services to end-user applications. Network services are typically protocols that work with user's data. For example, in a Web browser application, the Application layer protocol HTTP packages the data needed to send and receive Web page content. This Layer 7 provides data to (and obtains data from) the Presentation layer.

Layer 6 or Presentation Layer

Also referred as Syntax Layer, this layer is usually a part of an operating system that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). It further controls onscreen display of data, transforms data to a standard application interface, encryption and data compression. 

Layer 5 or Session Layer

This layer sets up, coordinates, and terminates conversations; exchanges and dialogs between the applications at each end. It deals with session and connection coordination and provides for full-duplex, half-duplex, or simplex operation, and establishes check pointing, adjournment, termination, and restart procedures.

Layer 4 or Transport Layer

This layer ensures reliable and transparent transfer of data between user processes; assembles and disassembles message packets and provides error recovery and flow control. Multiplexing and encryption are undertaken at this layer level.

Layer 3 or Network Layer

The Network layer adds the concept of routing above the Data Link layer. When data arrives at the Network layer, the source and destination addresses contained inside each frame are examined to determine if the data has reached its final destination. If the data has reached the final destination, this Layer 3 formats the data into packets delivered up to the Transport layer. Otherwise, the Network layer updates the destination address and pushes the frame back down to the lower layers.

To support routing, the Network layer maintains logical addresses such as IP addresses for devices on the network. The Network layer also manages the mapping between these logical addresses and physical addresses. In IP networking, this mapping is accomplished through the Address Resolution Protocol (ARP).

Layer 2 or Data Link Layer

The Data Link Layer responds to service requests from the Network Layer and issues service requests to the Physical Layer. This layer transfers data between adjacent network nodes in a WAN or between nodes on the same LAN segment. This layer also specifies channel access control method and ensures reliable transfer of data through the transmission medium. It provides the functional and procedural means to transfer data between network entities and detects and possibly corrects errors that may occur in the Physical Layer.

Layer 1 or Physical Layer

At Layer 1, the Physical layer of the OSI model is responsible for ultimate transmission of digital data bits from the Physical layer of the sending (source) device over network communications media to the Physical layer of the receiving (destination) device. Examples of Layer 1 technologies include Ethernet cables and Token Ring networks. Additionally, hubs and other repeaters are standard network devices that function at the Physical layer, as are cable connectors.

At the Physical layer, data are transmitted using the type of signaling supported by the physical medium: electric voltages, radio frequencies, or pulses of infrared or ordinary light.