OSI MODEL

 

In order for human-readable information to be transferred over a network from one device to another, the data must travel down the seven layers of the OSI Model on the sending device and then travel up the seven layers on the receiving end. 

OSI Model defines and is used to understand. How data is transferred from one computer to another in a computer network. In this section, we will explain how the data travels from the lecturer’s computer to reach the OnlineLearning System server which is in the Cobham College IT Center. 

🛰Layer 7: Application Layer 

Network applications use the application layer. A network application is a computer program that uses the internet, such as Google Chrome, Firefox, Microsoft Outlook, Skype, and so on. An open system provides services directly to the application process through this layer. HTTP and SMTP are application layer protocols (SMTP is a protocol that enables email communication). 

The lecturer is attempting to access an online learning system in this study. So the lecturer uses a web browser application on his computer to search for OnlineLearning and then presses 'enter.' His web browser will send his query to the application layer, which will select a protocol (HTTP). The browser chooses the web server to which it will transmit data, contacts the server, and sends the request. When the browser receives a response, it displays the requested content on the web page. 

🛰Layer 6: Presentation Layer

The presentation layer allows you to define the form in which the data is to exchange between the two communicating entities. It also helps you to handle data compression and data encryption. 

Once the lecturer's web browser application will pass his search to the application layer, which will pick a protocol (HTTP) and pass the data along to the presentation layer. The presentation layer will then compress the data and then it will hit the session layer, which will initialize the communication session. In the presentation layer, these files are transformed by Abstract Syntax Notation One into XML format to be displayed on the browser. The data inserted will be transferred from raw to computer format. 

🛰Layer 5: Session Layer 

                                                                                    

Session Layer controls the dialogues between computers. It helps you to establish starting and terminating the connections between the local and remote applications. 

To keep track of individual connections to remote servers, sessions are used. You can see how sessions work in your web browser. In this study, a web browser (google chrome, firefox, outlook, skype) opens a OnlineLearning page. It may contain text, graphics, and Macromedia Flash objects. On OnlineLearning, the graphics and Flash objects are stored in separate files. To access them, a separate download must be started. OnlineLearning opens a separate session in your web browser to download each file. The session layer keeps track of which packets and data belong to which file, and tracks where they go (in this case, to your web browser). 

🛰Layer 4: Transport Layer

The transport layer builds on the network layer to provide data transport from a process on a source machine to a process on a destination machine. It is hosted using single or multiple networks, and also maintains the quality of service functions. 

In this case, when the lecturer's computer is communicating with an OnlineLearning website, this layer will decide how much data can transfer and receive at a given point in time. Also, this layer provides a reliable process to process message delivery and error recovery.     

🛰Layer 3: Network Layer 

                                                                        

The network layer provides the functional and procedural means of transferring variable length data sequences from one node to another connected in “different networks”. Message delivery at the network layer does not give any guarantee to be reliable network layer protocol.  

Layer 3 transmits data segments between networks in the form of packets. When you access OnlineLearning, this layer assigns source and destination IP addresses to the data segments. Your IP address is the source, and the OnlineLearning web page is the destination. Layer 3 also determines the best paths for data delivery. 

🛰Layer 2: Data Link Layer 

Data link layer corrects errors that can occur at the physical layer. The layer allows you to define the protocol to establish and terminate a connection between two connected network devices. 

To send data out of the lecturer’s computer, it will go to the data link layer where the data will be framed. At the layer, the data is decoded into bit frames. It manages and handles errors in physical layers, flow control, and frame synchronization. This is the layer where the Switch operates. Since the router operates at the network level, then we can say that the MAC address is at the data link layer. All computers in a particular network are plugged into the switch so they can communicate with each other.  

🛰Layer 1: Physical Layer

The physical layer helps to define the electrical and physical specifications of the data connection. This level establishes the relationship between a device and a physical transmission medium. The physical layer is not concerned with protocols or other such higher-layer items. 

Once the lecturer’s computer receives the bit stream through a physical medium (such as wifi), the data will flow through the same series of layers on her device, but in the opposite order. The physical layer will convert the bitstream from 1s and 0s into frames that get passed to the data link layer.  

Then, the whole process will traverse from Physical Layer to Application Layer after the data has been sent through network media. 

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