Introduction
The initial growth of the Internet was defined by a certain amount of trouble. Each network organization created its own protocol and developed hardware and software to match. As a result, the hardware produced by one organization was incompatible with that of another. Building a new network without using hardware from the same company became impossible. To address this issue, the International Organization for Standardization (ISO) developed the Open System Interconnection (OSI) model, which included seven universally accepted layers.
The seven layer of the OSI Model is following:-
 |
Layer 1: Physical Layer
Layer 2: Data Link Layer
Layer 3: Network Layer
Layer 4: Transport Layer
Layer 5: Session Layer
Layer 6: Presentation Layer
Layer 7: Application Layer
Physical Layer:- The initial layer of the OSI model is where physical systems are made. This layer includes network cards, repeaters, hubs, and any other component that converts data (in the form of zeros and ones) into an electrical, optical, or radio signal, and vice versa.
Data Link Layer:- The second layer of the OSI model is the data link, which ensures that data is successfully transmitted from one device to another on the same network. It does this by controlling flow and identifying data errors. This layer is divided into two sub-layers:
MAC, or Media Access Control Layer, determines the physical address.
LLC, or Logical Link Control Layer, is responsible for frame synchronization, flow control, and error detection, which includes the use of Common Redundancy Check (CRC).
This layer uses a network device's MAC address to receive and forward data from the source address to the destination. Layer-2 switches are commonly referred to as such, because most network switches use MAC addresses to forward data to its correct destination.
Network Layer:- The network layer, also referred to as the third layer, is responsible for the handling of the routing process. Routing takes place when data is transmitted to a device over a network that differs from the one used by the sending device. The transmission of data between different networks is facilitated by network routers, which are commonly known as layer 3 devices. It is important to note that routing is not required when data is sent and received within the same network(subnet).
Transport Layer:- The Transport Layer, which is the fourth layer, is responsible for managing the flow of data and handling errors and retransmissions to guarantee the reliability of segment delivery. Essentially, the Transport Layer ensures that data is transmitted without any errors, losses, duplicates, and in the correct order.
Also, TCP/IP port numbers are used in the Transport layer to ensure that data is routed to the correct application for processing. For example, FTP (File Transfer Protocol) uses port 21, while DNS (Domain Name System) uses port 53.
Session Layer:- The Session layer, layer five of the OSI model, is responsible for the establishment, management, and termination of connections between applications. Sessions ensure that data for one application is separate from data for another.
Presentation Layer:- The Presentation Layer, positioned as the sixth layer, is responsible for encoding data in a manner that is understandable by the receiving party. It transforms data from one format to another, facilitating communication between two devices. This process can be likened to translating an English book into Russian: the core information remains consistent, but it is presented in a way that a Russian reader can comprehend. In the context of computing, this conversion takes place between ASCII and EBCDIC, and vice versa.
Application Layer:- The Application layer, located at the highest level of the OSI model, serves as the gateway to the user's application. In opposition to its name, this layer is not related to 'Microsoft Word' or any other user software. Instead, it focuses on a device's application services, which include file transfers, email, network printing, telnet, network file browsing, and other network-related capabilities.