OSI MODEL

    In this section, we will explain about the OSI model and on how the data travels from the student's computer to reach the OnlineLearning System server which is in the OUM IT Center. 

    The OSI model is a conceptual model that describes how the communication functions, how the computers should behave so that the data we sent and receive are properly and correctly done. The OSI model have 7 layers where each layer will communicate to the corresponding layer between the sender and the receiver. The data will passed through the 7 layers from top to bottom for sending device and from bottom to top for receiving device.

REAL WORLD APPLICATION:

How  the student's computer to reach the Online Learning System server in the OUM IT Center. the data travels from the student's computer to reach the Online Learning System server in the OUM IT Center.

OSI LAYER

7th: Application Layer

    On this application layer, you can think of it as that application’s way of formatting the data according to the specified protocol. On this case, when the student uses a web browser to access the OUM Online Learning System, the application layer will be making the HTTP request. Among all the layers on OSI model, this application layer will be the layer that the student interacts directly with. The application used is the browser. The browser then will select which web server it is sending to. In this case, it will go to the OUM Online Learning browser, contacts the server and send the request. When the response is returned, the browser displays the desired content on the web page. Component involved: Laptop/ computer/ end devices.

6th: Presentation Layer

    Presentation layer is where the data will be encapsulation and encryption. It also provides a mapping of different syntaxes to a unified data representation. From the application layer, the presentation layer will translate between application and network format based on the requirement that the application will accepts. Most commonly, a web page will contain a different format of data such as HTML files, JavaScript files, image, files and many more. For our OUM student’s case, this presentation layer will transform the files by Abstract Syntax Notation One into XML format to be displayed on the browser. When presentation layer received data from application layer, it will convert the data in such a format that can be sent over the network. On the side of receiving, when the data received data from session layer, it reconverts the data in such a format that the application will accepts and student(user) can understand. 

5th: Session Layer

    Session layer will control the connection between two computers by establishing, managing, and terminating sessions. Whenever the student visits the website or browser, the student’s computer/ device will be creating a session with the web server. When the student requests a web page, the web browser opens a TCP/ UDP connection to the web server. Then the web server sends back the web page and closes the connection. Each TCP/UDP connection is a session. When an application makes a network request, session layer will check whether the requested resource is available in local system or in remote system. If requested resource is available in remote system, it tests whether a network connection to access that resource is available or not. If network connection is not available, it sends an error message back to the application informing that connection is not available. If network connection is available, it establishes a session with remote system. When data transmission is completed, it terminates the session.

4th: Transport Layer

    Transport layer is end-to-end communication and reliability. The transport layer provides host-to-host communication services for applications. Despite for its purpose, this layer is responsible to deliver data to the appropriate application process on the host computers. The transport layer also coordinates the data transfer process such as the quantity of the data to be send, its rate, behaviours and many more. Two important protocols for this layer are the TCP (Transmission Control Protocol) and the UDP (User Datagram Protocol). TCP is the original implementation which provides a delivery of data between hosts, or end systems, running via an IP network while UDP is a protocol that instructs how the data-transporting process in the Transport layer should go about. On the student’s computers, it breaks data stream into smaller pieces before transmission. Each piece is known as segment and the process of breaking data into smaller pieces is known as segmentation. On the other side, (OUM server), it joins all segments back in data stream so that the session layer receive data in the format in which it was sent. Through the use of port numbers, this transport layer provides connection multiplexing to allows multiple applications to send and receive data simultaneously.

3th: Network Layer

    Path determination and logical addressing will be done in the network layer of OSI model. The network layer will be transferring variable-length network packets from a source to a destination, possibly through several proxies (networks). The modem used by the student is to connects to the public network. An important protocol for this layer is Internet Protocol (IP). IP is a piece of software that operates at the Network Layer of the OSI model. It provides unique addresses (IP addresses), connectionless communication, routing, and unicast/broadcast/multicast. The IP address is for anything connected to an internet. These addresses can change, but they are guaranteed to be unique. The OUM web page will also have a valid IP address.

2th: Data Link Layer

    Physical addressing is done at this data link layer. Data link layer provides error-free transfer of data frames from one node to another over the Physical Layer. The data transferred are decoded into frames of bits. Besides, it will manage and handles all the errors occur in the physical layer. Data link layer will also flow control and frame synchronization. Component involved: Modem to connects to the public network before able to connect to the OUM facilities.

1th: Physical Layer

    The physical layer is the first layer of OSI model. This layer specifies the standards for devices, media and technologies which are used in moving the data across the network. Physical layer will also do the media, signal and binary transmission. The raw data are transported in the form of bits which is 0 and 1. The data can be in the form of electrical, mechanical or radio waves. On the student’s computer/ devices (sending device), the physical layer will convert digital signals received from the Data Link Layer into analog signals and loads them in physical media while on the OUM server (receiving computer), it picks analog signals from media and then converts them in digital signals to transfer to the Data Link Layer for further processing. Component involved: wireless to connect between the devices and the modem.