What is OSI Layer Model?
The Open Systems Interconnection (OSI) model is one of the computer network models that is responsible for establishing a connection between the sender and the receiver and sending data in a seamless way. OSI model has seven layers and each layers defines a set of typical networking functions. OSI was introduced in 1983 by representatives of the major computer and telecom companies and was adopted by ISO as an international standard in 1984. Even though the modern Internet is not based on the OSI model, but it is still widely used since it impossible to understand the modern networking terminology without knowing the concept of OSI model. This is because OSI model helps to visualize how networks work and helps isolate and at the same time troubleshoot networking problems.
Encapsulation And De-Encapsulation
 |
| Process of moving the data between layers of the OSI Model |
Data Pathway from Lecturer's Computer to
Cobham College IT Center's Online Learning System Server
Layer 7 (Application)
This layer is known as the human-computer interaction layer. This is because the applications can directly access the network services. This layer provides services to the programs that the users can see. From the project scenario, for example, several functions will be performed at the application layer including detecting whether the Learning System server is available, coordinating the sending and receiving of applications, agreeing on error recovery and data integrity, and evaluating whether adequate resources are available for the communication between the lecturer's computer and Cobham College's online learning system server to take place.
Layer 6 (Presentation)
This layer controls how an application formats data for transmission over the network. The presentation layer enables an application to read (or comprehend) a message.
• Message encryption and decryption for security
• Message compression and expansion for efficient transmission
• Translation of content
Layer 5 (Session)
The Session Layer is the OSI model layer that handles computer conversations (connections). It connects the local and distant applications, manages them, and terminates them. It establishes check-pointing, adjournment, termination, and restart protocols, and it allows for :
- full-duplex
- half-duplex
- or simplex operation.
Server performs a function called Authentication.
Authentication is the process of verifying whether the user are lecturer or not. Server use username or password, if the data matched. A session or connection is established between lecturer's computer and Cobham College IT Center's Online Learning System server.Once the authenticating the lecturer successfull, authorization is checked.
Authorization is a process for the server to determine if the lecturer have the permission to access the file.
Layer 4 (Transport)
The Transport Layer facilitates the transparent movement of data between end-users while also offering dependable data transfer services to the upper levels. Flow control, segmentation, and desegmentation, and error control are all used by the transport layer to ensure the reliability of a specific link. Some protocols are based on state and connections. This implies the transport layer can keep track of segments and retransmit any that fail. If no problems occur, the transport layer additionally offers acknowledgment of successful data transmission and sends the following data.
Layer 3 (Network)
The Network Layer provides the functional and procedural methods of moving variable length data sequences from a source host on one network to a destination host on another network while maintaining the transport layer's quality of service requirements (in contrast to the data link layer which connects hosts within the same network). The network layer is responsible for network routing, fragmentation and reassembly, and reporting delivery failures. Routers work at this layer, transmitting data across the network and allowing the Internet to exist. The network engineer selects the settings for this logical non-hierarchical addressing system. The network layer contains a number of layer-management protocols, such as routing protocols, multicast group management, network-layer information and error, and network-layer address.
Layer 2 (Data Link)
Data link layer defines the format
of data on the network. This layer will receive data packets from the network
layer. Data packets received from the network layer contain IP addresses of the
student and Cobham College network facilities. Two types of addressing are
Logical Addressing and Physical Addressing. Logical Addressing is executed at
the network layer where students' and Cobham College network facilities's IP
addresses are assigned to each segment to form data packets. Physical
Addressing is executed at the data link layer where MAC addresses of students
and Cobham College network facilities are assigned to each data packet which
will be forming a frame. This layer allows the opening layer OSI Model to
access media, and controls how data is placed and received from the media.
Layer 1 (Physical)
Physical layer transmits raw bit stream over the physical medium. This layer will converts binary bits into signals and transmit over local media. It can be an electrical signal, light signal and air signal. For example, LAN cable for electrical signal, optical fiber for light signal and radio signal for air signal. Different types of media used to connect between student's device and Cobham College network facilities devices will generate different types of signal in the physical layer. At the student's device, physical layer will receives signal and converts to bits and eventually pass it to the data link layer as a frame.Data will moves through higher layers. When the data reaches the application layer, Application Layer Protocol makes the message from Cobham College visible in the application in the student's computer screen.
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