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

The Transport layer is responsible for end-to-end communication in the OSI model. Its primary role is to ensure that data is transferred reliably and without errors between host systems. This layer is tasked with establishing, maintaining, and terminating connections between communicating devices. It manages the transmission of data segments, facilitates flow control, and provides error recovery mechanisms.

By providing these services, the Transport layer allows for the proper sequencing and integrity of data packets, ensuring that they arrive in the correct order and are complete. Protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) operate at this layer, where TCP is particularly noted for its reliability features which are essential for applications that require guaranteed delivery.

In contrast, other layers such as the Physical layer focus on the physical transmission of data over a medium, the Network layer is concerned with the routing of packets across different networks, and the Application layer provides interfaces and protocols for applications to communicate. Each layer has its distinct responsibilities, but it's the Transport layer that directly handles the end-to-end communication aspect, making it vital for applications that depend on reliable data transmission.