Open Systems Interconnect

OSI MODEL

The OSI (Open Systems Interconnection) model is a framework for understanding how different networking protocols and technologies interact with each other. It divides the processes involved in transmitting data over a network into seven different layers, each of which is responsible for specific functions:

Physical layer:

• The physical layer is responsible for the physical transmission of data over a network. It defines the electrical, mechanical, and procedural characteristics of the connection between devices.

Some examples of tasks performed at the physical layer include:

• Specifying the type of physical connection to be used (e.g. coaxial cable, fiber optic cable, twisted pair wire, etc.)
• Specifying the voltage levels and signaling methods used to transmit data over the physical connection
• Specifying the type of connectors and cables to be used
• Defining how data is encoded and transmitted over the physical connection (e.g. using NRZ, Manchester encoding, etc.)
• Defining how devices synchronize with each other to transmit and receive data
• The physical layer is the lowest layer of the OSI model and is responsible for the physical transmission of data over a network. It plays a critical role in ensuring that data is transmitted reliably between devices.

Data link layer:

• The data link layer is the second layer of the OSI model and is responsible for creating a link between two devices on the same network segment and ensuring that the data is transmitted error-free.

Some examples of tasks performed at the data link layer include:

• Framing: Dividing the data into smaller units called frames that can be transmitted over the network.
• Error detection and correction: Adding checksum values to each frame to detect and correct errors that may have occurred during transmission.
• Flow control: Managing the flow of data between devices to prevent one device from overwhelming the other.
• Access control: Managing which device has access to the network at a given time (e.g. using a protocol like CSMA/CD).

The data link layer is responsible for creating a reliable link between two devices on the same network segment and ensuring that the data is transmitted error-free. It plays a critical role in ensuring the reliability of data transmission over a network.

Network layer:

• The network layer is the third layer of the OSI model and is responsible for routing data between different devices on the network. It determines the best path for the data to take based on various factors such as network congestion and available bandwidth.

Some examples of tasks performed at the network layer include:

• Addressing: Assigning unique addresses to devices on the network to identify them and enable communication between them.

• Routing: Determining the best path for data to take based on factors such as network congestion, available bandwidth, and the location of the destination device.

• Flow control: Managing the flow of data between devices to prevent one device from overwhelming the other.

• Error handling: Detecting and handling errors that may occur during transmission.

The network layer is responsible for routing data between different devices on the network. It plays a critical role in ensuring that data can be transmitted efficiently between devices, regardless of their location on the network.

Transport layer:

• The transport layer is the fourth layer of the OSI model and is responsible for ensuring that data is delivered reliably and in the correct order to its destination. It also provides flow control and error recovery mechanisms.

Some examples of tasks performed at the transport layer include:

• Segmentation and reassembly: Dividing data into smaller units called segments for transmission and reassembling the segments back into their original form at the destination.

• Flow control: Managing the flow of data between devices to prevent one device from overwhelming the other.

• Error recovery: Detecting and correcting errors that may occur during transmission.

• Multiplexing: Allowing multiple application programs to share the same network connection.

The transport layer is responsible for ensuring that data is delivered reliably and in the correct order to its destination. It plays a critical role in ensuring the reliability and efficiency of data transmission over a network.

Session layer:

• The session layer is the fifth layer of the OSI model and is responsible for establishing, maintaining, and terminating connections between devices. It allows devices to communicate with each other in a structured way.

Some examples of tasks performed at the session layer include:

• Session establishment: Setting up a communication session between two devices.

• Session management: Maintaining the communication session between devices and handling events such as timeouts or disconnections.

• Session termination: Closing the communication session between devices.

• Synchronization: Coordinating the actions of the devices participating in the communication session.

The session layer is responsible for establishing, maintaining, and terminating connections between devices. It plays a critical role in allowing devices to communicate with each other in a structured and reliable way.

Presentation layer:

• The presentation layer is the sixth layer of the OSI model and is responsible for converting data into a format that can be understood by the application layer. It also performs any necessary encryption or compression.

Some examples of tasks performed at the presentation layer include:

• Data conversion: Converting data into a format that can be understood by the application layer

• Data compression: Reducing the size of data to be transmitted more efficiently

• Data encryption: Encrypting data to protect it from being read by unauthorized parties

• Data decryption: Decrypting encrypted data to make it readable.

The presentation layer is responsible for converting data into a format that can be understood by the application layer. It plays a critical role in enabling different devices and systems to communicate with each other, regardless of their underlying hardware and software implementations.

Application layer:

• The application layer is the highest layer of the OSI model and is responsible for providing the interface between the network and the application or service being used.

Some examples of tasks performed at the application layer include:

• Providing access to network resources: Enabling applications to access resources on the network, such as servers, databases, or other devices

• Managing communication between applications: Allowing applications to communicate with each other over the network

• Network services: Providing services such as email, file transfer, and web browsing to users

The application layer is the highest layer of the OSI model and is responsible for providing the interface between the network and the application or service being used. It plays a critical role in enabling users to access and use network resources and services.