OSI Model | NBL 2078 IT Officer Paper

 Q. What are the different layers in Open System Interconnection(OSI) Model Reference Model? Provide a brief description of each layer.  (3+7)marks

answer:

The Open Systems Interconnection Model (OSI) is a conceptual framework used to describe the functionality of a networked system. The OSI model describes computing capabilities in a universal set of rules and requirements to support interoperability between different products and software. So basically the OSI model is a logical model/representation of how networked systems should transmit (or communicate) data to each other.

The purpose of the OSI reference model is to guide vendors and developers so that the digital communication products and software they create can work together and facilitate clear comparisons between communication tools. 

With a 7-tier architecture, each tier has a specific function to perform. All these seven layers work together to transfer data from one person to another around the world.

Image source: Wikipedia

Physical Layer

The physical layer transmits data through electrical, mechanical, or procedural interfaces. This layer is responsible for sending computer bits from one device to another over the network. The physical layer contains information in the form of bits. It is responsible for sending individual bits from one node to another. When it receives data, this layer takes the received signal and sends it to the data link layer, which converts them to 0s and 1s and reconstructs the frame.

Functions:

• Bit synchronization
• Bit rate control
• Physical topologies
• Transmission mode

Data link Layer

This layer is responsible for organizing bits into frames and for hop-to-hop transmission. This is the layer on which the switch operates. Since routers operate at the network layer, we can say that the MAC address is at the data link layer. All computers on a given network are connected to a switch so that they can communicate with each other

Functions:

• Framing
• Physical addressing
• Error control
• Flow Control
• Access control

Network Layer

The network layer is responsible for receiving frames from the data link layer and forwarding them to a destination based on the frame address. The network layer uses logical addresses such as Internet Protocol (IP) to find destinations. At this level, a router is literally an essential component used to direct information to where it should travel between networks.

Functions:

• Routing
• Logical Addressing

Transport Layer

This layer has a very important job. It decides how much information to send at one time. So when you communicate with a website, this layer decides how much data you can transmit and receive at any given time. Additionally, this layer provides a reliable process for handling message delivery and error recovery.

Functions:

• Segmentation and Reassembly
• Service Point Addressing

Session Layer

The session level controls conversations between different computers. A session or connection between machines is established, managed and determined at level 5. Session level services also include authentication and reconnections.

Functions:

• Dialog control
• Synchronization

Presentation Layer

The presentation layer is also known as the translation layer. Application layer data is extracted here and manipulated into the format required for transmission over the network. 

Functions:

• Translation
• Encryption/ Decryption
• Compression

Application Layer

Users and application processes can access network service through an application layer. It addresses issues such as network transparency, resource allocation, etc. The application layer performs the functions of an application. The network services are provided to the end-users. The network resources can be accessed through this layer.

 

These are all the 7 layers of OSI Reference Model.  

Pros and cons of the OSI model

Pros:

1. It is a truly generic model.
2. It works as a standard model in data communication.
3. It has the flexibility to adapt to many protocols.
4. OSI is more adaptable and secure than having all services bundled in one layer.
5. This model divides the all process of data communication into simpler and smaller

Cons:

1. The initial implementation of this model is slow.
2.  Implementation is costly.
3. It restricts its practical implementation.
4. It is a very complex model.
5. Layers can't work in parallel; each layer must wait to receive data from the previous layer.

Hope this is a useful content. Stay Safe .

Thank You!

@missionofficer