How to Understand (and Remember) the 7 Layers of the OSI Model
Understanding these Computer Networking Terms is necessary to learn networking, after getting a basic understanding of it, the next step comes to understand its OSI Model.
When you fully understand this OSI Model, it will prove to be a milestone in your networking career.
OSI Full Form
Full Form of OSI is – Open Systems Interconnection
OSI Full Form
OSI Ka Full Form is the full form of OSI – Open Systems Interconnection
What is OSI Model in English
The OSI model represents how data communications should take place. It divides the functions or processes into seven groups which are described as layers.
The Open Systems Interconnection (OSI) model defines a networking framework for implementing protocols at the layer, in which control is passed from one layer to the next. It divides the computer network architecture into 7 layers in a logical progression. The lower layer deals with electrical signals, segments of binary data, and routing of this data in the network. Higher layers cover network requests and responses, representation of data, and network protocols as seen from the user's point of view.
The Open Systems Interconnection (OSI) reference model has served as the most basic element of computer networking since its inception in 1984. The OSI Reference Model is based on a proposal developed by the International Standards Organization (ISO). The original purpose of the OSI model was to provide a set of design standards for equipment manufacturers to communicate with each other.
What does OSI mean?
Meaning of OSI in English
OSI Model in English – OSI stands for Open Systems Interconnection.
What is the history of OSI?
History of OSI Model in English
In the late 1970s, one project was administered by the International Organization for Standardization (ISO), while the other by the International Telegraph and Telegraph Consultancy Committee (CCITT). These two international standard bodies developed a network that defined the same networking model.
In 1983, these two documents were merged and named the Basic Reference Model of Open Systems Interconnection. This standard usually refers to the Open Systems Interconnection Reference Model, also known as the OSI Reference Model, or simply the OSI model.
It was published in 1984 as both the ISO standard ISO 7498 and the CCITT (now known as the Telecommunications Standardization Sector of the International Telecommunication Union or ITU-T) standard X.200.
OSI had two major components, an abstract model of networking, called the basic reference model or seven-layer model, and a set of specific protocols.
What is the purpose of the OSI Reference Model?
Purpose Of The OSI Reference Model
Everyone knows that breaking information into pieces makes it easier to understand and explain. The same applies for networking.
The OSI model represents a structured set of seven layers, which are connected with each other. Each layer in this model was developed to maintain the ability to connect devices, computers and network segments.
The OSI model was created for the following purposes:-
Creating a common platform for software developers and hardware to encourage the creation of networking products that can communicate with each other over a network.
These layers are created to assist network administrators by dividing the big data exchange process into smaller segments. Smaller segments are easier to understand, manage and troubleshoot. Dividing into layers will only troubleshoot the devices that are working in the faulty layer.
The OSI reference model is intended to guide vendors and developers in designing digital communication products and software programs, and to facilitate clear comparisons between communication tools. Most vendors involved in telecommunications try to describe their products and services in relation to the OSI model. Although the OSI model is useful for guiding discussion and evaluation, OSI is rarely implemented, as some network products or standard tools group all related functions together into all the defined layers associated with the model.
The model uses layers to give a visual description of what is going on with a particular networking system. This can help network managers and computer programmers narrow down the problem.
What are the characteristics of the OSI model?
Feature of OSI Model in English
The big picture of communication over the network can be understood through this OSI model.
We look at how hardware and software work together.
We can understand new technologies as they develop.
Troubleshooting is made easy by having different networks.
Can be used to compare basic functional relationships on different networks.
7 Layers of the OSI in English
OS Layer I is conceptually a collection of similar functions that provide service to the layer above it and receive service from the layer below.
The main concept of OSI is to divide the process of communication between two endpoints in a telecommunications network into seven different layers of related functions. Every communicating user or program is on a computer that can provide those seven layers of functions. So in a given message between users, the data flows down through the layers in the source computer and then up and down through the layers in the receiving computer.
Seven layers of functions are provided by a combination of applications, operating systems, network card device drivers, and networking hardware that are capable of sending signals over a network cable or over Wi-Fi or other wireless protocols.
In the OSI model, control passes from one level to another, starting at the application layer (layer 7) at one station, and moving down, moving to the next station on the channel and the hierarchy is backed up. The OSI model takes the task of inter-networking and divides it into what is referred to as a vertical stack which consists of the following 7 layers-
1) Physical Layer in English
The bottom layer of the OSI Reference Model is the Physical Layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for the actual physical connection between the devices. When receiving data, this layer receives signals. After this this layer converts it to 0's and 1's and sends them to the Data Link layer.
Examples of the physical layer include Ethernet cables and token ring networks. Additionally, hubs and other repeaters are standard network devices that operate at the physical layer, as are cable connectors.
At the physical layer, data is transmitted using a type of signal supported by the physical medium: electric voltage, radio frequency, or pulses of infrared or ordinary light.
Key Points of Physical Layer:
It activates, maintains and deactivates the physical connection.
It is responsible for the transmission and reception of unstructured raw data over the network.
The voltage and data rate required for transmission are defined in the physical layer.
It converts digital/analog bits into digital signal or optical signal.
Data encoding is also done in this layer.
2) Data Link Layer in English
When receiving data from the physical layer, the Data Link layer checks for physical transmission errors and packets the bits into data "frames". The Data Link layer also manages physical addressing schemes such as MAC addresses for Ethernet networks, controlling the access of any various network devices to the physical medium.
Since the Data Link layer is one of the most complex layers in the OSI model, it is often divided into two parts, the "Media Access Control" sublayer and the "Logical Link Control" sublayer.
Key Points of Link Layer:
The data link layer synchronizes the information that is transmitted at the physical layer.
The main function of this layer is to ensure that the data transfer from one node to another at the physical layer is error free.
Sequentially received transmission and data frames are managed by this layer.
3) Network Layer in English
The Network layer adds the concept of routing on top of the data link layer. When data arrives at the network layer, it checks the source and destination addresses inside each frame to ensure that the data has reached its final destination.
If the data has reached the final destination, it formats the data into packets that reach the Layer 3 transport layer. Otherwise, the network layer updates the destination address and pushes the frame back to the layer below.
To support routing, the network layer maintains logical addresses, such as IP addresses, for devices on the network. The network layer also manages the mapping between these logical addresses and physical addresses. In IP networking, this mapping is accomplished through the Address Resolution Protocol (ARP).
Key Points of Network Layer:
It routes the signal from one node to another through different channels.
It acts as a network controller. This subnet manages the traffic.
It decides which route the data should take.
It divides the outgoing messages into packets and assembles the incoming packets to the higher level.
4) Transport Layer in English
The transport layer sends the data across a network connection. TCP is the most common example of a Transport Layer 4 network protocol. Different transport protocols can support a range of optional capabilities, including error recovery, flow control, and support for re-transmission.
Key Points of Transport Layer:
Responsible for transparent transfer of data between end systems.
Responsible for end-to-end error recovery and flow control.
Responsible for the entire data transfer.
Here protocols like SPX, TCP, UDP work.
5) Session Layer in Hi ndi
When two devices, computers or servers need to communicate with each other, there is a need to create a session, and this is done at the Session Layer. Functions at this layer include setup, coordination (for example, how long the system will have to wait for a response), and termination between applications at each end of the session.
Key Points of Session Layer:
Responsible for the establishment, management and termination of connections between applications.
The Session layer sets up coordination, exchange and dialogue between applications on each end.
It works with session and connection coordination.
Protocols like NFS, NetBios names, RPC, SQL work on this layer.
6) Presentation Layer in English
The Presentation layer is also called the Translation layer. Here the data from the application layer is extracted and manipulated as per the format required to be transmitted over the network.
The functions of the Presentation layer are as follows:
Translation : For example, ASCII to EBCDIC
Encryption/ Decryption: Data encryption translates the data into some other form or code. Encrypted data is known as cipher text and decrypted data is known as plain text. A key value is used for encrypting and decrypting the data.
Compression: Reduces the number of bits that can be transmitted over the network.
Key Points of Presentation Layer:
The Presentation layer takes care that the data is sent in such a way that the receiver can understand the information and is able to use the data.
While receiving the data, the presentation layer is ready to transform the data for the application layer.
The language (syntax) may be different in the two communication systems. Under this situation the presentation layer plays the role of translator.
It performs data compression, data encryption, data conversion, etc.
7) Application Layer in English
On top of the OSI Reference Model is the Application layer, which is implemented by network applications. These applications produce data, which is transferred over the network.
This layer acts as a window to the application services for network access and displays the received information to the users.
Web browsers (Google Chrome, Firefox, Safari, etc.) or other apps – Skype, Outlook, Office are all examples of Layer 7 applications.
Key Points of Application Layer:
The application layer supports applications, apps, and end user processes.
Service quality.
This layer is responsible for application services for file transfer, e-mail, and other network software services.
Protocols like Telnet, FTP, HTTP work on this layer.
What are the advantages of the OSI model?
Advantages of OSI Model in English – Advantages of OSI Model in English
The OSI model has several advantages:
This is actually a generic model. And it is considered a standard model in computer networking.
In the OSI model architecture, the layers are separated according to services, interfaces, and protocols.
Since the protocols are hidden, any protocol can be implemented in this model. That's why I call it a generic model. It has all the flexibility to adapt to multiple protocols.
It supports connection-oriented as well as connectionless services. So we can use connection-oriented model when we need reliability and connection-less services when we need fast data transmission over internet.
It follows the divide and conquer technique. All the services are deployed in different layers. So the architecture and maintenance is straightforward and easy for these OSI model architectures.
It follows the layered architecture abstraction principle. Changes in one layer do not have much effect on other layers.
It is more secure and adaptable than bundling all the services in a single layer.
What are the disadvantages of the OSI model?
Disadvantages of OSI Model in English – Disadvantages of OSI Model in English
It does not define any particular protocol.
It can sometimes be difficult to fit new protocols into this model. This is because this model was created before the invention of any of these protocols.
The session layer is used for session management. Presentation layer deals with user interaction. Although they are useful, not as much as the other layers in the OSI model.
There is some duplication of services at different layers. As such, both the transport and data link layers have error control mechanisms.
There is also interdependence between the layers. These layers cannot work in parallel. They have to wait to get data from their predecessor.
FAQ on OSI Model
FAQ on OSI Model in English
Is the OSI model used today?
Today, it is the main protocol used in all Internet operations. TCP/IP is also a layered protocol but not all uses the OSI layer, although the layers are equivalent in operation and function. The Network Access Layer is equivalent to OSI Layers 1 and 2.
Why is the OSI model important?
The Open Systems Interconnection (OSI) model has led to networking discussions and documents. The general terminology used in the session is defined. It allows you to isolate a very complex communication process and evaluate its components.
Who changed the OSI model?
These rules are known as protocols, of which Transmission Control Protocol (TCP)/Internet Protocol (IP) is one of the most widely used. The TCP/IP model is popularly used in network description and is older than the OSI model.
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