OSI Layer Model

 

This figure shows the logical network flow from student’s home network to UTeM campus network. A student is trying to access the Ulearn system located in UTeM network facilities. In this article, we are going to see how data travels from student’s computer to reach the Ulearn system server using OSI Model.

 

What is OSI Model?

Open System Interconnection (OSI) Model is a conceptual framework that describe the working of networking system. It is a 7 layered architecture where each layer perform different functionality in the communication system. The seven layers are:

1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer

The travel of data from student’s computer to reach the Ulearn system server is as below:

 

Application Layer (Layer 7)

The application layer is responsible for providing services to user. It provides services for network applications with the help of protocols which allows the student to access to the network resource. From the student’s computer, a browser is used to send HTTPs protocol request to access the Ulearn system.

Network component: client’s PC, web browser (Google Chrome, Firefox, Safari), application layer protocols (HTTP, FTP, DHCP)

 

Presentation Layer (Layer 6)

The presentation layer is responsible for syntax and semantics of the information exchanged between two systems. The functions of the presentation layer are translation, encryption/decryption and compression/decompression. In presentation layer, the data from the application layer (sent by student’s computer) is translated, encrypted and compressed to required format to transmit over the network then decrypt and decompress when reach the Ulearn Server.

Network component: Gateways, Firewalls

 

Session Layer (Layer 5)

The session layer maintains, establishes and synchronizes the interaction between communicating systems. A session is established whenever two devices get connected and will be terminated once the connection is not required to avoid waste of resources. In session layer, student’s computer side is always synchronized with the Ulearn server by adding various checkpoints to the data. This allows data to be resumed from the last checkpoint if system crash occurs.

Network component: Gateways, Firewalls

 

Transport Layer (Layer 4)

The transport layer responsible for delivery of a message from process to process. It performs flow control and error control to ensure proper data transmission. At student’s side, data received from session layer is segmented, the source and destination port numbers are included in the header file. When the data reaches Ulearn server, reassembly and sequencing of data occur. It will read the port number of the data to direct the data towards the proper application.

Network component: Gateways, Firewalls

 

Network Layer (Layer 3)

The network layer responsible for the delivery of packets from the original source to the destination. It also performs logical addressing and routing. Routing is performed in this layer by using routers. In network layer, data segments from transport layer are break into packets and reassemble into segments when it reaches the Ulearn server.

Network component: Routers, Switches

 

Data Link Layer (Layer 2)

The data link layer transmits frames from one node to the next. It also performs the physical addressing of data. In data link layer, packets from network layer are break into data frames and convert into packets again when it reaches the Ulearn server.

Network component: Bridges, Modems, Switches

 

Physical Layer (Layer 1)

The physical layer transmits individual bits from one node to the next. It is responsible for the actual physical connection between the devices. The physical layer contains data in the form of bits or signals. The type of signal being generated depends upon the transmission medium. In this layer, data is got from data link layer and convert into bitstream and send it through physical channel such as cable. When it reaches the Ulearn server, the bitstreams is convert back to frames.

Network component: Hubs, Repeaters, Cables, Fibers, Wireless