OSI LAYER MODEL

    The OSI Model is a logical and conceptual model that describes network connectivity for networks that are open to interconnection and communication. The Open System Interconnection (OSI Model) also defines a logical network and uses different layers of protocols to efficiently explain computer packet transfer.

 Figure 1

PHYSICAL LAYER

    In this level, the raw data will be transmitted by any hardware devices. The data that student wants to transfer to OUM/IT facility will be transmitted by wireless device such as Radio signals. The data also can be transmitted by using another hardware device such as Fibre Optic Cable and Ethernet Cable.

Example : Fibre Optic Cable, Ethernet Cable and Radio Signals

DATA LINK LAYER

    Data link layer is the protocol layer in a program that manages data movement into and out of a network’s physical link. So, it will manage the data from the student’s computer to reach the Online Learning System server which is in the OUM IT Center. In the OSI architecture model for a set of telecommunication protocols, data link is layer 2. Before they are transported as frames between two adjacent nodes on the same LAN or WAN, data bits are encoded, decoded and organized in the data link layer. It also determines how devices recover from collisions that may occur when nodes attempt to send frames at the same time. Data link layer has three main functions. First, it handles problems that occur as a result of bit transmission errors. Second, it ensures that data is sent and received at a rate that is not overwhelming to the sending and receiving devices. Last but not least, it allows data transmission to layer 3 which is Network layer, where it is addressed and routed.

NETWORK LAYER

    Network layer is a layer 3 that is responsible for receiving frames from the data link layer and deliver the intended destinations among based on the addresses contained inside the frame. A network layer adds the source and destination address to the header of the frame. By using logical addresses such as IP (internet protocol), network layer finds the destination. Layer-management protocols that belong to the network layer are routing protocols, multicast group management, and network-layer address assignment. It determines the best path to move data from student’s computer to the OUM IT center based on the network conditions, the priority of services and other factors.

TRANSPORT LAYER

    On the receiving at the end, the transport layer takes the data transferred in the session layer and divides it into segments. It’s in charge of reassembling the segments on the receiving end and converting them back into data that the session layer can be use.

    It is also handling the flow control and error control. Data flow sends data at a rate that suits the receiving device's communication speed which is not too slow and not too fast. It is controlling number of bits per second. So, the message is transmitted to the correct process on the destination machine.

    Error control be used when some of data has been missing and not arrived at the destination. So, in this step, the Automatic Repeat Request is used to transmit the data back. If there are no errors occur, the transport layer acknowledges the efficient of data transmission and sends to the session layer.

    In this layer, connection-oriented transmission service is done by Transmission Control Protocol (TCP) and Connectionless transmission is done by User Datagram Protocol (UDP). UDP is fastest than TCP because it does not provide anu feedback while TCP is slow because it provides feedback. Therefore, loss data can be transmitted in TCP.

SESSION LAYER

    The session layer establishes communication channels between devices, known as sessions. It's in charge of starting sessions, making sure that they are stay open and usable while data is transferred, and closing them back when the communication is over.

    When the students open the OnlineLearning website of student.OUM.edu.my in chrome browser, then it creates a session between chrome browser and student’s email server so that data can be sent and received. It is also work synchronization of data between two systems then data is sent to the next layer.

    The session layer can also set the checkpoints during a data transfer and allowing the devices to restart a data transfer from the last checkpoint if the session is interrupted.

PRESENTATION LAYER

    Basically this layer is for delivery and formatting of information to application layer before it goes for further processing or display. In this layer also it will ensure that the information that application layer of another system sends can be understandable or readable by the system that receive it. In the scenario given, it can be either one between Online Learning System in OUM network facilities or the students’ computer system that is going be the receiver or the sender. If it is needed, this layer can translate between different data format using a common format.

APPLICATION LAYER

    Application layer is the last layer in OSI model after presentation layer. What is application layer? Application layer is a layer where it is responsible in display the information received to the user through user interface. So, when data received from OnlineLearning system in OUM network facilities it will be display at the students’ computer.