OSI LAYER MODEL (BASED ON SCENARIO)

OSI LAYER MODEL SENDER (STUDENT)

Data SENT through all the 7 layers from application layer to physical layer.

1. APPLICATION LAYER

        Application layer is where human-computer interaction happen, where all the applications can access the network service. In doing so, this layer is responsible for providing services to the user. Back on the project scenario, the data from student’s computer or any device (sender side) travels to reach the Online Learning System server in Cobham College IT Centre. Through the use of network applications like web browsers, it provides a data transmission and reception application layer protocol. Example of protocols in this layer are :-

        In this case, the student’s use Hypertext Transfer Protocol (HTTP). This protocol generate data that must be transferred via the network (search engine). For instance, https://www.online-learning-system-cobham-college.com.my. Thus, the data format will be specified by the application layer, and the data will be transmitted to the presentation layer which is layer 6.

2. PRESENTATION LAYER

        In this presentation layer, the data from the application layer is retrieved and processed here so that it may be transmitted across the network in the required format. Another process that will happen in this layer is :-

        Thus, the data from student’s computer will be done process translation, data encryption, and data compression. The presentation layer also performs data compression for multimedia data before transmitting because the length of the multimedia data is very big and much bandwidth will be required. So, the data get compressed into small packets before pass on to the next layer (layer 5).

3.SESSION LAYER

        A student send a message using a Messenger programme that is currently operating in their browser. In this case, the "Messenger" serves as the application layer and offers the user (students) an interface for entering data. In order to be communicated, this message, or so-called Data, is compressed, encrypted (if any secure data exists), and turned into bits (0s and 1s). This layer will handle the data flow and transfer the data to the transport layer.

4.TRANSPORT LAYER

         To ensure proper data transfer, the transport layer gets the prepared data from the upper layers, performs segmentation, and also includes Flow and Error control. In addition, it transmits the segmented data to the Network Layer while adding source and destination port numbers to its header.

5. NETWORK LAYER

        This layer is in charge of handling packet delivery from the sender to the receiver. The network layer will decide the IP address and split the transport layer segment into packets. The data link layer will receive the packets after that.

6. DATA LINK LAYER

        At the sender side (student) , the data link layer receives packets from the Network layer and divides them into small frames, then, sends each frame bit-by-bit to the physical layer. 

7. PHYSICAL LAYER

        The physical layer will get the data from the upper layer which is data link layer and convert it into bitstreams (0's and 1's) and send it through a physical channel. In this scenario the physical channel used are wireless and wired media.

 

 

OSI LAYER MODEL RECEIVER (SERVER -  IT CENTER)

Data RECEIVED through all the 7 layers from physical layer to application layer.

 

1. PHYSICAL LAYER

        Data is received through physical channel from server at the IT center to the student. In this physical layer, it will convert the bitstreams into frames to be passed to the data-link layer (layer 2)

 

2. DATA LINK LAYER

        The data link layer receives the information in the form of packets from the physical layer, The frames will be converted back into packets and transferred to the network layer.

3.  NETWORK LAYER

      The packet will be returned from the data link layer to the transport layer during this section. The data link layer packet will be converted back into segments and sent to the transport layer. Once the IP address has been confirmed, the transport layer will be reached.

4.TRANSPORT LAYER

Transport Layer transmits the data it has received to the appropriate application by reading the port number from its header. The segmented data are additionally sequenced and reassembled. Then, data will be transferred to session layer. 

The functions of the transport layer are as follows :  

- Segmentation and Reassembly : The communication is split into smaller components and received from the (session) layer by this layer. Each segments that is created has a heading that goes with it. The message is put back together by the transport layer at the final station. 

- Service Point Addressing : The transport layer header contains a form of address known as a service point address or port address in order to send the message to the appropriate process. The transport layer ensures that the message is delivered to the appropriate process by supplying this address.

The services provided by the transport layer :  

a) Connection-Oriented Service : 

– Connection Establishment 


– Data Transfer 


– Termination / disconnection 

After a packet or set of packets is received in this sort of communication, the receiving device sends an acknowledgement to the source. This form of transmission is trustworthy and safe.

b) Connectionless Service : It consists of Data Transfer and is a one-phase operation. The receiver in this transmission style does not confirm receipt of a packet. This method enables considerably quicker device connectivity. Connection-oriented service is more reliable than connectionless Service.

5.SESSION LAYER

The interaction between communication systems is maintained, established, and synchronised by the session layer. Determines which communication stream the data belongs to using the session information. Once a decision has been made, the data will be transmitted to Layer 6 or the Presentation Layer.

6. PRESENTATION LAYER

    At the presentation layer (receiver) side which is the Online Learning System server in the Cobham College IT Centre, it receives data from the session layer and performs the data translation, decryption, and decompression.

    Unlike data encryption, data decryption reverses the encryption process, restoring the communication to its original state.

7. APPLICATION LAYER

        At the application layer (receiver) side, Online Learning System server will determine whether the protocol provide from the sender is same as its protocol. Before this, the student use Hypertext Transfer Protocol (HTTP). If the protocol same as the sender use, the sender will have permission to access the Online Learning System

THE COMMUNICATION PROCESS IN THE OSI MODEL:

 

1.       In upper layers, each layer of the sender, as illustrated in the picture will moves the full package immediately to below the layer by adding its information to the message received from above that layer.

2.       Headers were inserted by each layer to add their information. At the message level, headers are appended (6, 5, 4, 3, and 2).

3.       At the physical layer, communication is direct, for example, the sender sends a stream of bits to the receiver. At the physical layer (layer 1) the entire package is converted into a form that can be transferred to the receiver. On the receiver side, each process is accompanied layer-by-layer to receive and delete message data.

4.       Always the upper OSI layers are implemented in the software (Transport layer, Session layer, Presentation layer, Application layer (4, 5,) and the lower layers are a combination of hardware and software (layer 2, 3), except for the physical layer which is mostly hardware. Layer 1, 2, and 3 (physical layer, data link layer, and network layer) are network support layers. They deal with physical aspects of moving data such as electrical specifications, physical connections, physical address, and transport time and reliability from one device to another. Layer 4, Transport layer end to end ensures reliable data transmission.

5.       Thus, each layer takes data from the adjacent layer, handles it according to these rules, and then sends the processed data to the next layer on the other side.