At which layer of the OSI model does TCP operate?

Layer 1 is the Physical layer, responsible for transmitting raw bits over a physical medium such as cables or radio waves - it has no protocol-level awareness.

Layer 2 is the Data Link layer, which handles MAC addressing, frame creation, and reliable delivery within a local network segment.

Layer 3 is the Network layer where IP operates, providing logical addressing and routing between different networks - not transport-level reliability.

TCP (Transmission Control Protocol) is a Transport layer (Layer 4) protocol defined in RFC 793. It provides reliable, ordered, and error-checked delivery between application processes through mechanisms including the three-way handshake for connection establishment, sequence numbers for ordering, and acknowledgments for guaranteed delivery. The Transport layer is specifically responsible for end-to-end communication and data integrity between hosts.

Layer 5 is the Session layer, responsible for establishing, managing, and terminating logical communication sessions between applications.