Which layer of the OSI model is responsible for reliable network communications?

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

Answer: (C)

End-to-end reliability is provided by the transport layer, which delivers data across the network with guarantees like proper sequencing, acknowledgments, and retransmission when needed. Protocols in this layer, such as TCP, establish a connection-oriented service, break data into manageable segments, assign sequence numbers, confirm receipt, and retransmit lost or corrupted segments while also applying flow control to prevent overwhelming the receiver. This end-to-end reliability across multiple networks is what the transport layer is responsible for. In contrast, the Data Link layer handles error detection on a single link, the Network layer deals with routing and addressing, and the Application layer offers user-facing services—reliability cannot be guaranteed end-to-end from those layers alone.