OSI Model

 OSI Layer Model

In this section, we will be explaining on how the data travels from the student’s computer to reach the OnlineLearning System server which is in the OUM IT Center. The explanation should be related the OSI Layer Model. The possible network components involves throughout the communications will be explained. 

WHAT IS THE OSI MODEL?

The OSI Model (Open Systems Interconnection Model) is a conceptual framework used to describe the functions of a networking system. The OSI model characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software. 

The International Organization for Standardization (ISO) first adopted the Open Systems Interconnection (OSI) model in the late 1970s. It is a standard that encompasses all aspects of network communications. The OSI model's goal is to demonstrate how to make communication between various systems easier without requiring changes to the underlying hardware and software logic.

In the OSI reference model, the communications between a computing system are split into seven different abstraction layers: 

1. Physical
2. Data Link
3. Network
4. Transport
5. Session
6. Presentation
7. Application

To be more understanding about how data flows based on the OSI model, we’ll describe the OSI layers “top-down” from the application layer that directly serves the end-user, down to the physical layer based on the Project Scenario

7. APPLICATION LAYER

This is the OSI model's topmost and seventh layer. This layer communicates with end-users and serves as an interface between them and the underlying network connections.

From the scenario, The student will access the OnlineLearning system using web browser or other tools and initiates an HTTP request to the specified port on the server. The request is made and it will establish a TCP connection to the server's designated port. The HTTP server listens to that port for requests sent by the student. Upon receipt of the request, the server sends a status line (to the student) and (response) a message body that may be a requested file, an error message, or some other information. The information obtained by the application layer will be shown to the student and data exchange services will be provided. Then, it will pass the data to the presentation layer . 

6. PRESENTATION LAYER

The presentation layer prepares the data for consumption by applications. Data translation, encryption, and compression are all handled by the presentation layer. Since the sender and receiver may use different encoding methods for communication, this layer is responsible for translating them so that the two systems can communicate on the same platform and understand each other.

Based on the scenario, when the student enters the account login information to the server via the Internet, it used a secure connection provided by the presentation layer. The presentation layer encrypted the information prior to transmission. Then, it will decrypt the information making it available for processing in the OnlineLearning system server. The data is encrypted and decrypted for protection purposes. Then, the layer will compress multimedia data before transmitting it because the length of multimedia data is very large, and transmitting it over media would take a lot of bandwidths. This data is compressed into small packets and decompressed at the receiver's end to restore the original data length in its original format. Compression can aid in the speed and reliability of data uploading. After that, it will pass to the session layer.

5. SESSION LAYER

A session is a structured dialog between two application.  The Session layer work as a 'dialog controller'. It allows the system to communicate in half-duplex or full-duplex mode of communication. 

Session layer is responsible for establishing, managing, synchronizing, and terminating the session (connection) between end-user application processes - in this scenario, the sender is the student, and the receiver is the OUM IT center. 

Session layer helps the sender to sign-in into the Online Learning system and the server will verify students' username and password before establish the connection. When the authentication is successful - the connection is establish, the sender (student) now have the permission to access the OnlineLearning system. 

Sender can send data such as text and images to the server and the data will stored in the server in separated file.  Sender also can browse the data and download the data in data packets form. 

The session layer synchronized the task by placing the checkpoint in the data flow.  This is to ensure that the data streams up are received successfully and acknowledged. 

The layer implements dialog control between the communication process. Session layer help manage the data flow and passes the data to the next layer, transport layer until the session is terminated.

4. TRANSPORT LAYER

The transport layer is responsible for delivering the entire message from the application program on the source device to a similar application program on the destination device. It provides flow control, error handling, and segmentation. A common example of transport layer protocol is Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). 

Segmentation is the process of the data receives from the session layer is divided into smaller units which are segment and numbers them in sequence along with the port address. It to ensure that the segments arrive correctly at the receiver in correct order and then reassembles them. 

The transport layer provides an error-free point-to-point cannel for both connections - student and the OnlineLearning system. The transport layer also identifies errors such as damaged packets, lost packet, duplication of packets and provide adequate error-correction techniques.

Transport layer control the amount of data transmitted. It will use automatic repeat request scheme to retransmit the loss or corrupted data if the data did not arrived at the destination. TCP ensure the quality than speed which provide feedback while UDP provide the speed than quality so it is faster. 

This layer is responsible for ensuring that the data is transferred from sender to receiver without any error, then passes the data to the network layer.​

3. NETWORK LAYER

The network layer is responsible for the delivery of packets from the original source to the final destination where its duties include logical address and routing. This layer is where datas such as images or texts will be moving from the source to destination in the form of packet.

Based on the scenario given, what would happen in the network layer is that the data in the form of packets from the student will be send through her modem which is connected to the public network. Then, the data will be connected to the OUM facilities before being forwarded to IT Center where the OnlineLearning System server is located.

2. DATA LINK LAYER

The data link layer is responsible for transmitting frames from one node to the next. Framing, physical addressing, flow control, error control, and access control would also be excuted in this layer.

By changing every packets into frames of units of information while also checking for errors, frames of information will be sent from student's to the OUM facilities. In each frame, it will consist the source address, the student's IP address, and destination address, the OnlineLearning System server's IP address other than trailer and the data to be send.

1. PHYSICAL LAYER

The physical layer is responsible for transmitting individual bits from one node to the next. In this layer, physical characteristic of interface and media, representation of bits, data rate, and synchronization of bits will be executed.

Frames from data link layer will be turned in the form of bits in physical layer before going through transmission medium and went through physical layer on the receiver's side. All information will be represent by bits in the physical layer.

Hence, based on the scenario, data sent by student using the home network will eventually be turned into bits before going through transmission medium and received by OUM campus network.

All of this is known as data encapsulation, and it occurs when data flows from the Application Layer (Layer 7) to the Physical Layer (Layer 1).

To summarise the explanations above,