At which OSI layer is a destination port number added to a PDU during the encapsulation process?
- transport layer
- data link layer
- network layer
- application layer
Answers Explanation & Hints: The destination port number is added to a Protocol Data Unit (PDU) at the Transport layer during the encapsulation process. The Transport layer is the fourth layer of the OSI (Open Systems Interconnection) model, and it is responsible for end-to-end communication between processes running on different hosts. The Transport layer adds the source and destination port numbers to the PDU header, which is used by the receiving host to deliver the data to the correct process or application. The Data Link layer is responsible for data framing and error detection, while the Network layer is responsible for routing and forwarding data between different networks. The Application layer provides interfaces for application-level protocols.