WHAT IS AN OSI LAYER?

OSI - The Open Systems Interconnection model (OSI model) is a reference model from the International Organization for Standardization that "provides a common basis for the coordination of standards development for the purpose of systems interconnection." In the OSI reference model, the communications between systems are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application

 Application Layer

The interaction with the user or the user application takes place at this stage. When identifying communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit.

Presentation Layer 

The data is converted into the syntax or semantics which an application understands. Before passing on the data any further, the data is formatted at this stage. Functions including compression, encryption, compatible character code set, etc. are also done at this layer of the model. It serves as a data translator for the network.

Session Layer

The session layer creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends.

Transport Layer

The transport layer takes data transferred in the session layer and breaks it into “segments” on the transmitting end. It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer.

Network Layer

The network layer has two main functions. One is breaking up segments into network packets and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network.

Data Link Layer

The data link layer establishes and terminates a connection between two physically connected nodes on a network. It breaks up packets into frames and sends them from source to destination. 

Physical Layer

The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.