OSI Layer Model

1. OSI Layer Model

In the OSI Layer Model, there are 7 layers used as references to help and shows how networks operate. This OSI Layer Model was first introduced by The International Standard Organization (ISO) in the late 1970s.

According to the project scenario, the data travels from the student’s computer to the OnlineLearning System server which is in the OUM IT Center will pass through all the 7 layers for the data transmission.

Layer 7: Application Layer

As we know, Application Layer is the top layer of the OSI Model. According to the project scenario, the student’s computer are able to direct interact with the OnlineLearning System server which located in OUM IT Center by typing the link (https://www.oum.edu.my/) using any supported browsers such as Safari, Chrome or Mozilla Firefox. In this case, we can clearly say that the application layer are known as software provided for the end-user to interact with.

 

Layer 6: Presentation Layer

The presentation layer has three primary functions which is formats, or presents, data from the source device into a compatible form for receipt by the destination device. The next is compression of the data in a way that can be decompressed by the destination device. The third function is encryption of the data for transmission and the decryption of data upon receipt by the destination.

In this scenario, at the sender’s side which is the student’s computer, it receives the data from the application layer and performs data encryption and compression to it. At the receiver's side which is OnlineLearning System server, it receives the data from the transport layer and performs data translation, decryption, and uncompressed data.

 

Layer 5: Session Layer

The session layer is the fifth layer of OSI model. It is in charge of maintaining, synchronizing and starting the communication between two systems. Based on the scenario, the session layer from the student’s home network responsible for selecting appropriate protocols to support the services of application layer’s request. After that, it will check whether requested resource is available in OnlineLearning system. If the requested resource is available, it will try to establish a connection. If connection fails, it will send an error message back to application layer to notify the student about the failed connection. If succeed, this layer will start and maintain the session as long as needed.

From OUM campus network, when the student tries to access the OnlineLearning system, the OnlineLearning system server will try to authenticate who the user is and establish a session between them. In this layer, it will authorize and manage which files that the student wants to get access. Each requested files are in separate sessions. This will allow multiple application to send or receive data. Also, it has utility to provide checkpoints of the data to determine the continuation of the connection. After the student done accessing the OnlineLearning system, the session established will be terminated.

 

Layer 4: Transport Layer

The transport layer is responsible for establishing a temporary communication session between two applications and delivering data between them. This layer provides for the segmentation of data, and the controls necessary to reassemble these segments into the various communication streams. There are two common transport layer protocols, TCP (Transmission Control Protocol) and the UDP (User Datagram Protocol).

In this case, when the data is delivered, the protocols that were being used was TCP. When the computer wants to send data over TCP, first it needs to establish a connection with the OnlineLearning System server using a three-way handshake. Once done with the handshake, it will be ready to receive packets containing actual data. When a packet of data is sent over TCP, the server must always acknowledge what they received. The computer sends a packet with data and a sequence number. The server acknowledges it by setting the ACK bit and increasing the acknowledgement number by the length of the received data. Finally, the connection will be closed when they finished sending and receiving data. TCP connections can also detect lost packets.

 

Layer 3: Network Layer

This layer provides route and handles data transmission between two different networks. In this scenario, data received from transport layer, is encapsulated with the source and destination IP addresses. Then, the entire packet is sent to the receiver. Routers involved in this layer is home router and OUM IT Center.

 

Layer 2: Data Link Layer

In Data Link Layer, it will receive data packets from network layer which contain IP address of sender and receiver. The MAC address will be added in packets to form frame. In this layer, it transfers frames between two connected nodes on a network. The data frame is then converted into bits to reach to Physical Layer.

 

Layer 1: Physical Layer

Physical layer is the lowest layer in OSI Model which is concerned with electrically or optically transmitting raw unstructured data bit across the network from the sending device to the receiving device.

From the project scenario, there are 4 devices that are used for this project. First, we need one (1) PC which is student’s computer, one (1) router, one (1) switch and lastly, one (1) server which is OnlineLearning System Server. Therefore, the physical layer that used is copper straight through cable from student’s PC to switch and from switch to router. For router to server, copper cross over cable was used. The physical components transmit and carry the signals to represent the bits to layer 2, Data Link Layer.