El OSI model It's very important in computer networks. Therefore, in this article, we'll explain what this network model is, how it works, what it's used for, the respective layers it comprises, and more.
What is the OSI model?
El OSI (Open Systems Interconnection) Model, or Open Systems Interconnection, is a reference model for computer network communication protocols. This model was created in the 80s by the ISO (International Standards Organization).
The OSI Model was initially published by the ITU (International Telecommunication Union). However, this would not be until 1983, since the following year it was offered by the ISO itself, as a standard. In fact, the objective of OSI is to standardize Internet communications to make it easier and seek interoperability of all network devices and software.
As the OSI Model is a normative type model, you could say it's a theoretical concept, although it serves to implement tangible things to enable various technologies and manufacturers in the telecommunications world to do their work correctly.
Over the years, the OSI model has been improved. Currently offers 7 layers to define the different phases that information goes through when connections are made between two nodes or devices on a network. Regardless of the type of information, the type of connected device, its technology, or its location, the same layers will always be involved.
A little history: Background
It must be said that the expansion of computer networks It began in the 80s, when the need to interconnect different devices spread across the globe to transfer information and stay connected became popular. Networks, on the other hand, were created long before that decade.
You sure remember the history of the origin of the Internet and its predecessors, such as the network known as ARPANET. Well, at that time, the OSI Model didn't exist, and the problem they encountered was that many network programs or devices had trouble communicating with each other. That's why ISO standardization was necessary to determine a set of rules applicable to all networks so that these interoperability problems wouldn't exist.
How does the OSI model work?
As I mentioned earlier, the OSI Model is made up of 7 different layers on which it depends. The operation is broken down into steps, since each layer fulfills a specific, hierarchical function in communications. Therefore, communication protocols will use all or some of these layers to ensure network communication.
What is the OSI model used for?
The OSI Model is fundamentally a conceptual tool for organizing telecommunications. What it does is standardize the way information is transferred on networks computer science
It must be said that the OSI Model is not a network topology, nor a network model in itself, nor specifications or protocols. It is a tool that defines the functionality so that manufacturers and developers can create products that can work with each other seamlessly as they did before.
OSI Model Layers or OSI Stack
The layers or levels that make up the OSI model, also known as the OSI Stack, are:
- Physical layer: It is the lowest-level layer of the OSI model. It handles everything related to network topology, physical connections, signaling, and binary transmission. In other words, it standardizes the physical level (cable types, waveforms for wireless connections, network interfaces, electrical voltage, etc.).
- Data link layer: deals with physical redirection, error detection, media access, and flow control during communication. For example, MAC and LLC addresses would be defined at this layer.
- Network layer: It is responsible for logical addressing and route determination. That is, for identifying the existing routing between the networks involved. The basic data units are called "packets" and can be classified according to the routing protocol or routable protocol they use. The former select the routes (RIP, IGRP, EIGRP, among others) and the latter travel with the packets (IP, IPX, AppleTalk, etc.). The objective of this layer is to ensure that the data reaches its destination, even if it involves using intermediate devices, such as routers.
- Transport layer: It is responsible for the end-to-end connection and the reliability of the transferred data. This is where the data contained within each packet is transported from one node to another, that is, from the source device to the destination device, regardless of the physical medium used. Its work is carried out through logical ports and shapes the so-called IP Sockets: Port.
- Session layer: It is the communication between devices on the network itself. It is responsible for controlling and maintaining the link between the connected devices that are exchanging data. It must also ensure that, once communication between both systems is established, the data transmission channel can be resumed if it is interrupted. These services may become partially or completely dispensable, depending on the case. That's why I mentioned earlier that not all 7 layers are always used...
- Presentation layer: As its name suggests, it is used to present transferred data. That is, these assembled packets are "translated" to make them recognizable or useful to the system. For example, a series of packets can result in a message, a file, etc. It also allows for data encryption and encoding, as well as compression and adaptation to the receiving machine.
- application layer: This is the top-level layer. Keep in mind that new communication protocols are continually being developed as new applications emerge. Therefore, this last layer defines the protocols used by apps to exchange data. This layer may result in the process the user ultimately sees, although this is not always the case. However, it should be noted that the user rarely interacts with the application layer; they interact with the apps that interact with the application layer. For example, it could be a chat app, a web browser, etc.
Finally, some people use a mnemonic rule to remember the 7 layers of the OSI Model, and that rule is FERTSPA (Physics, Data Link, Network, Transport, Session, Presentation and Application).