At which OSI layer is a source port number added to a PDU during the encapsulation process?
- transport layer
- application layer
- network layer
- presentation layer
Answers Explanation & Hints: The source 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 source and destination port numbers to the PDU header, which is used by the receiving host to deliver the data to the correct process. The Application layer is the top layer of the OSI model and it provides interfaces for application-level protocols. The Network layer is responsible for routing and forwarding data between different networks. The Presentation layer is responsible for data formatting and conversion.