What is it?
Open systems interconnection (OSI) is a reference model of the way applications interact through a network. It is intended to visualize the sequence of communication layers, from physical cabling to the app that communicates with other devices.
The goal of OSI is to help technology vendors and developers create interoperable products. Additionally, the open systems interconnection model provides a framework that illustrates the functionalities of networking and telecommunications systems.
How does it work?
OSI is employed to conceptualize how data is sent or received through the network. It distributes data transmission standards, processes, and protocols across seven layers. Each of them is designed to perform specific data-sending and data-receiving tasks.
According to the open systems interconnection model, communication between two endpoints in the network is broken down into the mentioned seven layers. Every single layer provides services to the layer above (except for the highest-level one) and receives services from the layer below.
This way, message exchange between users involves data flowing down through layers in the source computer, via the network, and finally up through layers in the receiving computer.
The seven layers in question are delivered by a set of apps, operating systems, network card device drivers, networking hardware, and protocols that empower signal transmission through the network over physical mediums.
7 OSI layers
The application layer makes it possible for the user to interact with the network or app anytime they choose to read messages, share files, or carry out other tasks concerning the network.
The presentation layer formats and translates data depending on the syntax or semantics accepted by the application. At the same time, it ensures encryption and decryption for the application layer.
The session layer sets, coordinates, and ends conversations between apps, performs authentication and reconnection after interruptions, and decides how long to wait for another app’s response.
The transport layer transports data through the network and provides means of error checking and controlling data flow. It defines how much data to transmit, where to send it, and at what rate.
The network layer moves data into and across other networks by packaging it with information on the network address, opting for network routes, and forwarding it to the transport layer.
The datalink (protocol) layer moves data into and out of a physical link in the network, deals with problems resulting from bit transmission errors, ensures the appropriate pace of data flow, etc.
The physical layer is responsible for transferring data with the help of electrical, mechanical, or procedural interfaces. It manages sending computer bits from device to device across the network.
Some of the advantages offered by the OSI model include the following:
- It is generally believed to be a standard computer networking model.
- OSI is compatible with connectionless and connection-oriented services.
- The model is flexible enough to adjust to multiple protocols.
- Security is achieved by not having all services accumulated in one layer.
Primary issues related to open systems interconnection are listed below:
- OSI does not fulfill the purpose of determining any specific protocol.
- The session layer and presentation layer are less useful than the others.
- Various layers, e.g., transport and datalink, happen to have the same services.
- Concurrent operation of layers is impossible: each must wait for the previous one.
OSI vs. TCP/IP
While OSI depicts the functionalities of telecommunication and networking systems, TCP/IP is actually a set of communication protocols that interlink network devices on the Internet.
Both models incorporate layers. For instance, TCP/IP entails four of them, just like OSI comprises seven. Another thing that TCP/IP shares in common with OSI is the application layer utilized as the upper one and given the same tasks. These tasks may differ depending on the information received.
OSI and TCP/IP transfer data packets, although they attain this aim by using different methods. They both determine networking standards, deliver frameworks for developing and adopting these standards as well as networking devices, allow manufacturers to produce items interoperable with products by other manufacturers, and deconstruct intricate functions into smaller parts.
Unlike OSI, which determines the functionality of top layers by leveraging the application, presentation, and session layers, TCP/IP is restricted to the application layer only.
On the other hand, the functionality of lower layers in OSI is defined by employing the physical and data-link layers, while TCP/IP includes a single link layer. Meanwhile, TCP/IP’s internet layer, which determines routing standards and protocols, is equivalent to the network layer in OSI.