What Is the OSI Model
The Open Systems Interconnection model, or OSI model, describes the seven layers that computer systems use to communicate over a network. This model was the first standard for network communications back in the early 1980s. The OSI model is widely used because it helps visualize and communicate how networks operate, and helps isolate and troubleshoot networking problems.
The Seven Layers
The Seven layers of the OSI model are as follows:
Let’s breakdown each layer of the OSI model.
7) The Application Layer
The application layer of the OSI model interacts with the lower layer, the presentation layer, and it’s often referred to as the service or software being used. The application layer is used by end-user software such as web browsers and email clients. The application layer provides protocols to present data to users, protocols such as, Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), and Domain Name System (DNS).
6) The Presentation Layer
The Presentation Layer performs the task of syntax processing. It’s responsible for converting data from one format to another. For instance, considering you’re trying to log into your profile on Facebook. After entering your username you’re prompted to enter your password. Facebook automatically encrypts your password information so third-party services can’t gain access to your account. This information is handed from Facebook down to the Presentation layer which translates that encrypted data into network format. After this data has been translated it’s then sent to the Session or the Application layer depending on if that data was being transmitted or received.
5) The Session Layer
At the Session layer, the construction, direction, and conclusion of connections between devices occur. This session also handles authentication were a network interruption were to occur. The Session layer creates communication channels, called sessions, between devices. It opens these sessions ensuring they remain open and functional while data is being transferred ,and closing them when the communication has ended.
4) The Transport Layer
The Transport layer is responsible for the transportation of data from devices on network connection. It takes the data from the session layer and breaks it into segments on the transmitting end. This layer handles how much data to send, how fast to send it, and where it goes as well.
3) The Network Layer
The Network layer handles the routing of data. After the data arrives at this layer, each frame of the data is analyzed to see if the data has reached it’s destination.
2) The 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. This layer is composed of two parts—Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.
1) The Physical Layer
The Physical layer is just what it’s name induces. The Physical layer is responsible for the physical wiring, and cables, and the connection between network nodes and devices. It’s responsible for sending raw data, or 0’s and 1’s.
As software developers, the first three layers apply most to us. However, learning all the layers broadly can assist in our knowledge of creating front and back in applications. The modern internet, however, isn’t based on OSI, but on the simpler TCP/IP model. The main difference between the two is that the TCP/IP Model groups up the many layers into a broader Model as shown below.
