What is the OSI model?

We explain what is the OSI Model used in computer networks, and how it works. Also, what is it for and what are its layers.

1. What is the OSI model?

The OSI Model ( Open Systems Interconnection , that is, “Open Systems Interconnection”), is a reference model for the communication protocols of computer networks or computer networks . It was created in the 1980s by the International Organization for Standardization (ISO).

The OSI Model was initially published by the International Telecommunications Union (ITU) until 1983, and since 1984 it is also offered by the ISO itself, with standard. Its function was to standardize or serialize communications on the Internet , since at the beginning it was extremely chaotic.

Being a normative model, the OSI Model is really a theoretical construct , with no direct correlation in the world of the tangible. It is only an attempt to regulate the diverse and varied technological voices of the world, given that there are numerous manufacturers, companies and technologies in the world of telecommunications.

This model has been refined over time and today offers seven different layers with which to define the different phases that the information goes through in its journey from one electronic device to another connected in the network. No matter the geographical location of the user or the type of technology used, all means of global interconnection, such as the Internet , use this type of unified protocols.

2. OSI model background

The development of computer networks and their expansion in the early 1980s showed the need to interconnect systems from different sources , or the networks that they formed and maintained. As with people who speak different languages, telecommunications were unable to continue their expansive route.

Even the programs designed for interconnection had problems with each other , since copyright rules on computerized design were an additional barrier.

The idea of ​​creating the OSI Model as a solution to this problem arose after the ISO carried out an investigation in the matter. Thus, ISO set out to determine the general set of rules applicable to all networks .

3. How does the OSI model work?

The operation of the OSI Model depends directly on its seven layers, in which it decomposes the complicated process of digital communication . By compartmentalizing it, it assigns to each layer very specific functions, within a fixed hierarchical structure.

Thus, each communication protocol uses these layers in their entirety or only some of them, but by obeying this set of rules, it ensures that communication between networks is effective and, above all, in the same terms.

4. What is the OSI model for?

The OSI Model is fundamentally a conceptual tool for organizing telecommunications. It universalizes the way in which information is shared between computer networks or computerized systems, regardless of their geographical, business or other conditions that could make data communication difficult.

The OSI Model is not a network topology, nor a network model in itself, nor a protocol specification; It is simply a tool that defines the functionality of the protocols , to achieve a communication standard, that is, to ensure that all systems speak the same language. Without it, a network as vast and diverse as the Internet would be practically impossible.

5. Layers of the OSI model

The seven layers or levels of the OSI model are as follows:

• Physical Layer . The lower layer of the model is responsible for the network topology and the global connections between the computer and the network, referring to both the physical environment and the way in which the information is transmitted. It fulfills the functions of specifying information about the physical environment (types of cable, microwave, etc.), defining information about the transmission’s electrical voltage , the functional characteristics of the network interface and ensuring the existence of a connection ( although not the reliability of it).
• Data link layer . It deals with physical redirection, error detection, access to the medium and flow control during communication, being part of the creation of basic protocols to regulate the connection between computer systems.
• Network layer . It is the layer that is responsible for identifying the routing between the networks involved, so the data units are called “packets” and can be classified according to the routing protocol or routing 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 or routers.
• Transport Layer . This is where the transport of the data found within each package is carried out, from the source computer to the destination computer, regardless of the physical medium used for it. His work is done through logical ports and shapes the so-called IP Sockets: Port .
• Session layer . It is responsible for controlling and maintaining the link between the computers that exchange data, ensuring that, once communication between the two systems is established, the data transmission channel can be resumed if it is interrupted. These services may become partially or totally expendable, depending on the case.
• Presentation layer . This layer deals with the representation of the information, that is, its translation, ensuring that the data received at any end of the network is fully recognizable, regardless of the type of system used. It is the first layer that deals with the content of the transmission, instead of the way in which it is established and sustained. In addition, it allows the encryption and coding of the data, as well as its compression, its adaptation to the machine that receives them (a computer, a tablet, a cell phone, etc.).
• Application Layer . Since new communication protocols are continually being developed, as new applications emerge, this last layer defines the protocols that applications use for data exchange and allows them to access the services of any of the other layers. Generally, this whole process is invisible to the user, who rarely interacts with the application level, but with programs that interact with the application level, making it less complex than it really is.

The OSI Model layers can be remembered through the FERTSPA mnemonic rule : Physics, Data Link, Network, Transport, Session, Presentation and Application.