Which OSI layer is identified as Layer 4 in the model?

• A. Session Layer
• B. Application Layer
• C. Transport Layer
• D. Network Layer

Answer: (C)

Layer 4 is the Transport Layer. It provides end-to-end delivery of data between hosts by taking data from the upper layers, segmenting it, and ensuring those segments arrive correctly. It handles reliability and sequencing for reliable connections, flow control to prevent overwhelming a receiver, and multiplexing multiple conversations through port numbers. This layer sits above the Network Layer, which does routing and addressing, and below the Session Layer, which manages the setup and maintenance of communication sessions. The other layers handle session management or routing, but the defining role of this layer is end-to-end transport with reliability and multiplexing.