Which statement about the Transport layer is true?

Which statement about the Transport layer is true?

• A. Data Link layer
• B. Network layer
• C. Session layer
• D. Transport layer

Answer: (D)

The Transport layer acts as the end-to-end courier for communications between applications running on different hosts. It takes a stream from the sending process, segments it for efficient handling, and uses port numbers to keep multiple conversations separate on the same host. It can provide reliable delivery with error detection and retransmission (as TCP does) or offer best-effort delivery (as UDP does), giving control over how data is moved across the network. This end-to-end responsibility and support for multiplexing distinguish it from the layers below and above: the Data Link layer handles data transfer on a single link between devices, the Network layer manages routing and addressing across multiple hops, and the Session layer handles dialog control and session management. Identifying the layer by its transport duties—end-to-end delivery and port-based multiplexing—explains why this choice is true.

The Transport layer acts as the end-to-end courier for communications between applications running on different hosts. It takes a stream from the sending process, segments it for efficient handling, and uses port numbers to keep multiple conversations separate on the same host. It can provide reliable delivery with error detection and retransmission (as TCP does) or offer best-effort delivery (as UDP does), giving control over how data is moved across the network. This end-to-end responsibility and support for multiplexing distinguish it from the layers below and above: the Data Link layer handles data transfer on a single link between devices, the Network layer manages routing and addressing across multiple hops, and the Session layer handles dialog control and session management. Identifying the layer by its transport duties—end-to-end delivery and port-based multiplexing—explains why this choice is true.