An Overview of OSI Model
Introduction
OSI Stands for OPEN SYSTEM INTERCONNECTION MODEL. It is a reference model that explains how data from one computer's software application travels through a physical medium to another computer's software application. It is made up of seven layers, each of which performs a specific network function. The International Organization for Standardization (ISO) developed the OSI model in 1983, and it is now regarded as an architectural model for inter-computer communications. The OSI model divides the entire task into seven smaller and more manageable tasks. Each layer has a specific task assigned to it. Each layer is self-contained, so tasks assigned to each layer can be completed independently.
?This seven-layer model describes the process of data communication between two or more computers. The seven layers has its own unique function, starting with a physical layer, which defines the hardware such as cables, ports, and network interfaces. The data link layer is responsible for node-to-node delivery on a single network segment. Network layer, is responsible for addressing and routing between networks. The transport layer is responsible for end-to-end delivery of data. Session layer is responsible for managing dialogues between processes. Data representation, compression, and encryption are all handled by the presentation layer. Application layer, is responsible for user interface and data exchange. Knowing how each layer works and how they interact is key to understanding how data can be transferred between two computers, and the OSI Model makes this process much easier.
Characteristics of OSI Model
?In the OSI model, the upper layer deals with application-related issues, which are implemented only in software. The application layer is closest to the end user. Both the end user and the application layer interact with software applications. The lowest layer of the OSI model is responsible for data transport. In hardware and software, there are physical and data link layers. In the OSI model, the physical layer is the lowest and is closest to the physical medium. Putting information on the physical medium is primarily the responsibility of the physical layer.
Brief Description of OSI Model Layers
1. ? ? ? APPLICATION LAYER
In the application layer, the actual applications are interfaced with each other. A number of protocols are supported, such as HTTP, HTTPS, DNS, TFTP, and SSH. The user's data is the only source of data that this layer directly interacts with. Web browsers and email clients, for example, rely on the application layer to initiate communications. However, it should be noted that client software applications are not part of the application layer; rather, the application layer is in charge of the protocols and data manipulation on which the software relies to present meaningful data to the user. HTTP and SMTP are application layer protocols (Email communication is made possible by a number of protocols, one of which is Simple Mail Transfer Protocol).
2. ? ? ? PRESENTATION LAYER
In this layer, human-readable formats are converted to machine-readable formats. In addition to encrypting and decrypting data, this software also compresses and decompresses it.?
Two gadgets that communicate with one another because several encoding methods may be used when communicating. Layer 6 is responsible for transforming incoming data into a syntax that the receiving device's application layer can understand.
Layer 6 is in charge of applying encryption on the sender's end and decoding encryption on the receiver's end if the devices are interacting over an encrypted connection so that it may provide the application layer with unencrypted, readable data.
Finally, the presentation layer is in charge of compressing data from the application layer before passing it on to layer 5. This improves transmission speed and efficiency by reducing the quantity of data sent.
3. ? ? ? NETWORK LAYER
Rsponsible for logical addressing. It adds source ip address and destination ip address to the data. Data is divided into packet format. Data transfer between two distinct networks is made possible by the network layer. If the two communicating devices are on the same network, the network layer is not required. On the sender's device, the network layer divides segments from the transport layer into smaller units called packets, which are then reassembled on the receiving device. Routing is the process by which the network layer determines the best physical path for data to take to reach its destination.
4. ? ? ? TRANSPORT LAYER
This layer ensures that the data is delivered from source to destination end-to-end. There are two protocols used: TCP and UDP.
UD?
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5. SESSION LAYER
Sessions are maintained and terminated by this layer. Dialogue control will be determined by it (simple, half-duplex, or full-duplex). The communication between the two devices is opened and closed by this layer. The communication session is defined as the interval between the communication's opening and closing. To avoid wasting resources, the session layer ensures that the session remains open long enough to transfer all of the data being exchanged, and then promptly closes the session.
6. DATA-LINK LAYER
Responsible for physical addressing. It adds source mac address and destination mac address to the data. Data is divided into frames format. Similar to the network layer, the data link layer enables data transfer between two devices connected to the same network. The data link layer divides packets from the network layer into smaller units known as frames. In addition to the network layer, the data link layer is in charge of intra-network communication flow control and error control (For inter-network communications, the transport layer only handles flow control and error handling).
?7. PHYSICAL LAYER
It is the bottom most layer of the OSI Model, which is the physical and electrical representation of the system. It moves Bits (0 and 1) between devices. It consists of various network components such as power plugs, connectors, cable, etc. This layer encompasses the physical data transfer equipment, such as cables and switches. Data is transformed into a bit stream, which is a string of 1s and 0s, at this layer. In order to distinguish the 1s from the 0s on both devices, the physical layer of both devices must also agree on a signal convention.
?Transmission of Data in OSI Model
?This is how information moves through the OSI model. Assume you sent an email to a friend. The presentation layer receives your email after passing through the application layer. Your data will be compressed by this layer.
The session layer then starts communication. It will then be divided into segments in the transportation layer, packets in the network layer, and frames in the data link layer. It is then sent to the physical layer, where it is converted to 0s and 1s and transmitted via a physical medium such as cables.
The same layers, but in reverse order, are traversed when your friend receives the email via a physical medium. The 0s and 1s will be converted by the physical layer into frames that will be passed to the data link layer. In order to create packets for the following layer, this will reassemble the frames.
Data will be put together from the segments by the network layer. The data is then sent to the presentation layer, which terminates the communication session. When the application layer is ready, the presentation layer will transfer the data to it. Using the application layer, your friend will be able to read your email because it provides human-readable data to the email software.
Benefits of OSI Model
Other Topics to be Learn
The OSI model is the stepping stair. There are many more points in Networking which an aspiring network engineer should know. Here are the following:
In order to gain a thorough understanding of these concepts, enroll in Ns3Edu and become an exceptional Network Engineer.
Conclusion
The OSI layered paradigm supports abstraction (as explained). It is not necessary for the higher levels to comprehend how the lower layers perform their duties.
Furthermore, the lower levels are not needed to comprehend what the upper layers are doing with the lower layers' rewards of effort. Because of this abstraction, you may use the same web browser and HTTP protocol to interact on the Internet regardless of whether the lower-layer connection is a dial-up modem, a high-speed Internet connection, or something in between.
There will probably be variations in performance or speed, but not in functioning. As a result, OSI is still important in today's world since it defines the fundamental ideas of networking.