List the four end-to-end layers of the OSI model.June/July 2020

The OSI (Open Systems Interconnection) model is a conceptual framework that is used to understand how communication occurs between different devices on a network. It consists of seven layers, which are organized into two main categories: the end-to-end layers and the intermediate layers.

The end-to-end layers are:

1. Application layer: The application layer is the top layer of the OSI model and is responsible for providing services to the user. It includes protocols that are used to support applications such as email, file transfer, and web browsing.
2. Presentation layer: The presentation layer is responsible for formatting and encoding data for transmission. It includes protocols that are used to convert data into a form that can be understood by the application layer at the receiving end.
3. Session layer: The session layer is responsible for establishing, maintaining, and terminating communication sessions between devices. It includes protocols that are used to manage the flow of data between devices and to ensure that data is delivered reliably.

The intermediate layers are:

1. Transport layer: The transport layer is responsible for providing end-to-end communication services to the upper layers. It includes protocols that are used to segment and reassemble data, and to provide error correction and flow control.
2. Network layer: The network layer is responsible for routing data between devices on a network. It includes protocols that are used to determine the best path for data to take and to address and route data packets.
3. Data link layer: The data link layer is responsible for providing reliable transmission of data over a link between two devices. It includes protocols that are used to detect and correct errors, and to provide flow control.
4. Physical layer: The physical layer is the lowest layer of the OSI model and is responsible for transmitting bits over a communication channel. It includes protocols that are used to define the physical characteristics of the communication channel, such as the voltage levels, frequency, and modulation scheme.