Which OSI model layer is responsible for end-to-end communication?

The Transport layer is responsible for end-to-end communication in the OSI model. This layer ensures that data is transferred reliably and in the correct sequence between applications on different devices. It provides functionality such as error recovery, flow control, and segmentation of data into manageable packets, which are then transmitted over a network.

By effectively managing sessions, the Transport layer allows multiple applications to communicate simultaneously over a single connection without interference. It utilizes protocols like TCP (Transmission Control Protocol) for reliable communication and UDP (User Datagram Protocol) for faster, less reliable transmissions. This means if there's any loss of data during transmission, the Transport layer can detect and handle the issue, ensuring that the data integrity is maintained between the source and destination applications.

In contrast, other layers have different responsibilities; for example, the Network layer is focused on routing the packets between devices, the Session layer is involved in establishing, managing, and terminating sessions between applications, and the Application layer deals with high-level protocols for end-user applications. They each play a crucial role within the OSI model, but it is the Transport layer that specifically handles the end-to-end communication aspect.