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.