The Open Systems Interconnection model (OSI model) is a conceptual model that describes the universal standard and the communication functions of a telecommunication system or computing system, without concerns of the system's underlying internal technology and fixed protocol suites.

The OSI model was first introduced in 1983 by major computer and telecommunication companies and was later recognized and adopted in 1984 by the ISO as an international standard of network communication; Fundamentally, making it the first standardized international communication model to be accepted by all nations.

Note: The modern Internet is largely no longer based on OSI, but rather on the simpler TCP/IP model. Nonetheless, the 7 Layer IOS model is still commonly used, as it helps to visualize and communicate how computer networks operate and helps when isolating issues and troubleshooting networking problems.

The Application Layer is the Human-Computer Interaction, which contains the communications protocols and interface methods used in processing communications across an Internet Protocol (IP) computer network. The application layer only standardizes communication and depends upon the underlying transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a client–server or peer-to-peer networking model. Though the TCP/IP application layer does not describe specific rules or data formats, those applications must consider when communicating.

This layer is used by end-user software, such as web browsers, mobile apps and email clients. It provides protocols that allows software to send and receive meaningful data and present useful information to the end users. A Domain Name System (DNS), the File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), Post Office Protocol (POP), and Simple Mail Transfer Protocol (SMTP) are examples of the application layer protocols.

The Presentation Layer is the Data Formatting and Encryption layer and serves as the data translator for the network, it’s also known as the syntax layer, it responds to service requests from the application layer and issues service requests to the session layer through a specific presentation service access point (PSAP).

The presentation layer guarantees that the information that the application layer, of one system, sends out is readable by the application layer of another system. The sending system is responsible for the conversion to the standard, transmittable formats. On the receiving system side, it is responsible for the translation, formatting, and delivery of information for processing or display.

In many widely used applications and protocols, no distinction is actually made between the presentation and application layers.

The Session Layer has three primary functions - 1) It is responsible for opening specified ports, accessing and creating the connection channel to communication between devices, (called, The Session) and ensuring those ports remains open and functional during data transfer, 2) Creates checkpoints during data transfers, so there's a connection interruption, those devices can automatically reconnect with each other, resuming data transfer from its last data-packet point, and 3) Closing those data ports after transfer has ended.

The Transport Layer has three key tasks - 1) It takes the data being transferred in the session layer and breaks it into “datagrams” from the transmitting side, and reassembling those datagrams on the receiving side, then turning them back into usable data for the session layer, 2) The transport layer regulates data transfer flow, sending data at the rate that matches the connection speed of the receiving device, and 3) Does error control reviews, to ensure the data was received correctly, and if not, requesting the data again.

The Network Layer provides the means of transmitting variable-lengths of network packets from the source to the destination host via one or more local area networks. And in doing so, its two main functions are - 1) Breaking up datagrams into network packets and reassembling those packets on the receiving side. And 2) Is to discover the best path when routing those packets across a physical network, using network Internet Protocol addresses (IP address) to route those packets to its destination node.

The Data link Layer makes media access and physical addressing feasible, by establishes and terminates the connection between two physically connected communication endpoint (node) on a network.

Layer 2 breaks up packets into frames and sends them from the sending source to the destination. The data link layer has two features – 1) Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and 2) Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions when transmitting and receiving data. 

The Physical Layer makes raw bit stream transmission possible, by providing an electrical, mechanical, and procedural interface to the transmission medium. The shapes and properties of the electrical connectors, the frequencies to broadcast on, the line code used and similar low-level parameters, are specified by the physical layer.

In order for digital information to be readable by humans, it needs to be transferred from one network device to another, and the data travels through the seven layers of the OSI Model from the sending point to the seven layers on the receiving point.

The OSI model breaks down network communication into seven layers. These layers are beneficial to network technicians and engineers when troubleshooting and identifying network issues.