There are 7 layers total in OSI Layer Model. When the student uses the public network to connect to UTEM facilities. The data will have to go through these 7 layers. When a computer successfully communicates with a host, it will go through all of the 7 layers from the top to the bottom or from the bottom to the top. The communications are shown as below.
APPLICATION LAYER (LAYER 7)
Firstly, the student is using her modem to connect to a public network so that she can connect to the OUM network. This process will go through to Application Layer in the OSI model. What happens is the layer will provide the interface to the user with instructions on how to handle the data. In this scenario, since OUM network facilities probably uses SMTP protocol, the computer will then be given instructions on how to handle the data. At this layer, both the end user which is the student and the application layer which is the OUM's OnlineLearning interact directly with the software application. This layer sees network services provided to end-user applications such as a web browser. The application layer identifies communication partners, resource availability, and synchronizes communication between the student and the OnlineLearning system.
PRESENTATION LAYER (LAYER 6)
The presentation layer formats or translates data for the OnlineLearning website based on the syntax or semantics that the application accepts. Because of this, it at times also called the syntax layer. This layer can also handle the encryption and decryption required by the application layer. This layer makes the data presentable for student to view audios, images and audio. It is also responsible for translation, encryption, and compression of data. Presentation layer will translate incoming data from the OnlineLearning web into a syntax that the application layer of the receiving device can understand.
SESSION LAYER (LAYER 5)
When student and the OUM OnlineLearning server connect to each other, they need to “speak” with one another, hence a session needs to be created, and this is done at the Session Layer. Functions at this layer involve setup, coordination on how long should a system wait for a response and termination between the applications at each end of the session. For example, if the student wants to download a file from the OnlineLearning system and the time taken to download it is managed in this layer. It also then promptly closes the session in order to avoid wasting resources.
TRANSPORT LAYER (LAYER 4)
Layer 4 is responsible for end-to-end communication between the student computer and the OUM OnlineLearning server. This includes taking data from the session layer and breaking it up into chunks called segments before sending it to layer 3. The transport layer on the receiving device which is the student's computer is responsible for reassembling the segments into data the session layer can consume.
The transport layer is also responsible for flow control and error control. Flow control determines an optimal speed of transmission to ensure that the OUM OnlineLearning server with a fast connection doesn’t overwhelm the student from home with a slow connection. The transport layer performs error control on the receiving end which is the student's home network by ensuring that the data received is complete, and requesting a retransmission if it isn’t.
NETWORK LAYER (LAYER 3)
For network layer, it takes data segment from transport layer and then it will create a logical address which is known as IP address to the data segment. Once IP address and other related information are added in segment, it becomes packet.
At this layer, it will be decided whether the packet is intended for local system or remote system. This layer also specifies the standards and protocols which are used in to move the data packets across the network.
To move the data from the student’s home network to the OnlineLearning System server which is at OUM campus network, a device known as router is used. Router uses logical address (IP address) from the student’s network to take routing decision to go to its final destination which is OUM campus network. It is also responsible for sending packets of information from the student’s server out into the internet and the OUM network will be receiving them.
DATA LINK LAYER (LAYER 2)
Data link layer receives packet from network layer and they will define how networking components access the media and what transmission methods they will use. In this layer, switches will operate and this layer provides a reliable link between two directly connected nodes. It is also responsible for detecting and possibly fixing any packet errors that may form on the physical layer.
This layer performs physical addressing. It will add the sender’s (the student) and receiver’s (OnlineLearning System server) MAC address to the data packet to form a data unit called a frame. Data link layer enables frames to be transported via local media such as copper wire, optical fibre or air.
This layer has a sub layer which is the LLC (Logical Link Control). On the student’s computer, it encapsulates the information of the Network Layer protocol in LLC header from which the Data Link Layer receives the data packet. On the OnlineLearning System server’s computer, it checks LLC header to get the information about the network layer protocol. This way, a data packet is always delivered to the same network layer protocol from which it was sent.
PHYSICAL LAYER (LAYER 1)
Physical layer converts the binary from the upper layers into signals and transmits them over local media. It also specifies the standards for devices, media and technologies which are used in moving the data across the network such as type of cable used in connecting devices, type of interface card used in networking device, type of connector used to connect the cable with network interface and etc.
In this scenario, the student’s computer will transfer the data in bits form through local media in the form of electrical, light, or radio signals until it reaches the destination which is OUM campus network. When OUM campus network receives the data, the data are decapsulated meaning that it will be translated back into binary and the into application data so the OnlineLearning System server at OUM campus can see the message or data.
