Which OSI layer handles the end-to-end delivery and reliability between hosts?

• A. Data Link
• B. Network
• C. Session
• D. Transport

Answer: (D)

End-to-end delivery and reliability between hosts are handled by the transport layer. This layer provides process-to-process communication across a network, coordinating data transfer from one host’s application to another’s. It offers reliability features such as sequencing, acknowledgments, retransmission of lost segments, and flow control to prevent overwhelming the receiver. It also multiplexes multiple parallel conversations using ports. The network layer moves data between hosts and handles routing and addressing, but it does not guarantee delivery or maintain state across multiple hops. The data link layer takes care of framing, error detection, and access control on a single link, not across an end-to-end path. The session layer manages the establishment and maintenance of a session between applications, but does not by itself ensure reliable end-to-end transport. Therefore, the described role aligns with the transport layer.