OSI Layer Model

Project Scenario

The scenario of this project can be referred to Figure 1. Figure 1 shows the logical network flow from a home network to UTeM facilities. In this figure, a UTeM’s student is trying to access the Ulearn system located in the UTeM network facilities. The student is using her modem to connect to the public network before able to connect to the UTeM facilities. From the UTeM network, the data then was forwarded to IT Center where the Ulearn System server is located.

Students are required to suggest private addressing scheme used in UTeM network. Explain how you calculate the subnetting using FLSM based on the number of the faculties. The number of students of each faculty is within 500 – 1000 students. Each faculty is given their network address. Assign IT Center as another subnet with their own network address. From this network address, assigned as the 5th available address as the address of the Ulearn System Server. 

The OSI Model known as Open System Interconnection Model was established by International Organization for Standardization (ISO) in 1984. It requires a standard that allows different computer systems to communicate with one another.

OSI model contains 7 layers which begin with the physical layer, data link, network, transport, session, presentation and lastly is application layer as shown in figure 1. Each OSI layer performs a distinct function and communicates with the layers above and below it.

7) Application Layer

Layer 7 of the Open Systems Interconnection (OSI) communications model is where the application layer is located. It guarantees that applications can interact efficiently with other apps running on various computers and networks.

For example, in this project, a UTeM’s student who is trying to access the Ulearn system because they want to upload the assignment work sheet into the Ulearn system which located in the UTeM network facilities. Firstly, the process will occurred at the student’s personal computer (PC) and they will enter the website interface which provided by the Application layer. Next, when the student uploaded the work sheet into the system, the data will exchange and traversed by using protocols. The protocol used which is file transfer protocol (FTP) will pass the data to the presentation layer. Meanwhile, the protocol used to reach the Ulearn server which is at IT Centre is HTTP for data transfer. 

 

6) Presentation Layer 

The presentation layer, which is located at Layer 6 of the Open Systems Interconnection (OSI) communications architecture, guarantees that the communications that flow through it are in the correct format for the destination application. In other words, from the application layer's perspective, it displays the data in a readable format.

For this project, the data received from the student’s computer will be standardized and the encryption process which will be referred to the communication connection type will be completed if necessary. When the data arrives at the Ulearn server, it will be decrypted. This process of encryption and decryption data are for the security purposes. Next, the presentation layer will compress the data which can help improving the speed and the efficiency of the data uploaded and will pass it to the session layer.  

 

 

5) Session Layer

In the Open System Interconnection (OSI) paradigm, the Session Layer is the fifth layer. This layer enables users on various devices to communicate with one another in real time. It's in charge of establish, maintaining, synchronising, and terminating sessions between end-user programmes.

During this session layer, the communication session between transport layer and application layer will be initialised by sending request and responses. This session is created when both of the systems which are the student’s computer and also the Ulearn server want to enter into a dialogue. It determines whether the requested session is legitimate or not and if it yes, the data next will be pass to the next layer. However, this session layer will be terminate if the communication between the systems are not available. For example, if the connection is timeout or when the student already finish accessing the system. 

 

 

4) Transport Layer

In the open systems interconnection (OSI) network paradigm, the transport layer is the fourth layer. Error correction, as well as segmenting and desegmenting data before and after it is transferred through the network, are all activities performed by the transport layer. This layer is also in charge of flow control and ensuring that segmented data is delivered in the right order through the network. Layer 4 (the transport layer) performs its functions using the transmission control protocol (TCP) and the user data protocol (UDP).

In this stage, the transport layer will provides multiplexing through the implementation of TCP AND UDP protocols which will enables the host to receive and send corrected data error. The data will be segmented and broken up into packets at the network layer and the flow and error control will be performed in this layer.

 3) Network Layer

Network layer is responsible for delivering packets from the original source to the destination. It has two functions which is dividing segments into network packets and reassembling the packets into messages. Another one is it routes the packets by identifying the best path across the physical network. Thus, this layer uses network addresses to route packets to a target node.

            In this project, the student sends the data to the ULEARN web page from their laptop where the data is sent by packet to the ULEARN web page by the IT Centre. Thus, the packets are divided into the smallest pieces when the data arrives at the IT Centre. Therefore, the source address is the IP address which the student must address in her laptop. Meanwhile, the IT Centre will be the destination for target data.

 2) Data Link Layer

In this layer, node-to-node delivery will be used which will transmit frames from one node to another. In this process, all the errors that may have occurred in the past layer will be corrected. The data link layer contains physical addresses as header frames to identify the physical address. Thus, the data link layer also provides a protocol for detecting the devices that have control over the link at any time.

 1) Physical Layer

Physical layer is the lowest layer in the OSI Model. Physical layer is a physical device which can transmit the message to another. For example, network interface card (NIC), switch, router, wireless access point, modem, and fiber optic. Thus, it is responsible for transmitting individual bits across the network from one device to another.

Based on the project scenario, the devices included are such as Network Interface Card (NIC), switch, router, wireless access point, and modem. Network Interface Card (NIC) is a hardware component that can connect a computer to a network. In this case, NIC will connect the student's laptop and the wireless access point which means it enables connection between the student's laptop and WIFI by using a modem. Thus, it also will connect with the local network (LAN) which is a group of connected computers which share a centralized network.

Student’s laptop will send the request to NIC which it will convert into an electrical signal when the student trying to access the web page of ULEARN. Individual bits will be carried from one node to the next across the transmission media by this electrical signal. The bits will be delivered to the data link layers through this mechanism. Those data are delivered to the router via a coaxial cable network. Therefore, the router will send the data through the internet before being sent to UTeM campus network server, IT Centre and FTMK faculty. Thus, UTeM campus network server will obtain the data by router through the internet and will responds by transmit the data back to the IT Centre. ULEARN web page will be appeared as a response after IT Centre receive the data through router as synchronisation of bits that occur in electrical signal. NIC will obtain the signal and translates into the data which where the ULEARN web page will be appeared in student’s laptop.