Which layer is responsible for end-to-end communication and reliability in data transfer?

• A. Transport Layer
• B. Network Layer
• C. Data Link Layer
• D. Physical Layer

Answer: (A)

End-to-end communication and reliable data transfer are handled by the transport layer. This layer is responsible for establishing communication between end systems, breaking data into manageable segments, and ensuring those segments arrive correctly and in order. It provides reliability through mechanisms like acknowledgments, retransmission, and flow control (as seen with TCP). The network layer focuses on moving packets between networks (routing), the data link layer handles delivery between directly connected devices on the same network segment with local error checking, and the physical layer deals with the actual signaling over the medium. Because ensuring reliable, end-to-end delivery across possibly multiple networks is the Transport Layer’s job, it is the best fit.