Which layer of the OSI model is responsible for reliable data transfer?

The Transport layer of the OSI model is responsible for reliable data transfer between systems. This layer ensures that data is delivered error-free and in sequence, managing the flow of data and providing error recovery mechanisms. It segments the data into smaller packets and takes care of the reassembly at the receiving end. Protocols like TCP (Transmission Control Protocol) operate at this layer, which includes features such as acknowledgment of packet receipt, retransmissions of lost packets, and maintaining the order of packets. These functionalities are crucial for applications that require a reliable communication channel, such as file transfers, video streaming, and other transactional data exchanges.

In contrast, the other layers serve different functions: the Network layer focuses on routing packets across the network, the Link layer deals with physical addressing and access to the physical medium, and the Application layer interfaces with end-user applications but does not handle the complexity of reliable transport. Each layer has its distinct responsibilities, with the Transport layer specifically designed to guarantee the integrity and reliability of the data being transmitted.