Which OSI layer is responsible for preparing data for transport by segmentation and port assignment?

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

Answer: (C)

Segmentation and port assignment happen at the transport layer. This layer takes data from the upper layers, breaks it into segments sized for reliable or best-effort delivery, and adds port numbers so the receiving host can deliver each segment to the correct application process. This is how end-to-end communication is multiplexed and demultiplexed across different applications on each end. The network layer handles routing and logical addressing, the data link layer deals with frames and hardware addressing on a single link, and the application layer provides the software interfaces and protocols used by programs. So, the transport layer is responsible for preparing data for transport through segmentation and port assignment.