>OSI Model

The OSI Model (Open Systems Interconnection Model) is a conceptual framework used to describe the functions of a networking system. It characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software.

The 7 Layers of the OSI Model

Physical Layer

-Concerned with electrically or optically transmitting raw unstructured data bits across the network from the physical layer of the sending device to the physical layer of the receiving device.

-Can include specifications such as voltages, pin layout, cabling, and radio frequencies.

-At the physical layer, one might find “physical” resources such as network hubs, cabling, repeaters, network adapters or modems.

Data Link Layer

-Directly connected nodes are used to perform node-to-node data transfer where data is packaged into frames. The data link layer also corrects errors that may have occurred at the physical layer.

-Has two sub-layers of its own:

  • Media access control (MAC), provides flow control and multiplexing for device transmissions over a network. 
  • Logical link control (LLC), provides flow and error control over the physical medium as well as identifies line protocols.

Network Layer

-Responsible for receiving frames from the data link layer, and delivering them to their intended destinations among based on the addresses contained inside the frame.

-Finds the destination by using logical addresses, such as IP (internet protocol).

– Routers are a crucial component used to route information where it needs to go between networks.

Transport Layer

-Manages the delivery and error checking of data packets.

-Regulates the size, sequencing, and the transfer of data between systems and hosts.

-One of the most common examples is TCP (Transmission Control Protocol).

Session Layer

-Controls the conversations between different computers.

-A session or connection between machines is set up, managed, and terminated here.

-Also includes authentication and reconnections.

Presentation Layer

-Formats or translates data for the application layer based on the syntax or semantics that the application accepts.

-Sometimes called the ‘syntax layer.’

-Handles the encryption and decryption required by the application layer.

Application Layer

-Both the end user and the application layer interact directly with the software application here.

-Sees network services provided to end-user applications such as a web browser or Office 365. 

-Identifies communication partners, resource availability, and synchronizes communication.

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