Answer

(iv) Channel coding

Explanation

The Data Link layer is responsible for functions such as framing, error control, and flow control. Channel coding, in the sense of encoding bits for reliable physical transmission over a medium, is primarily associated with the Physical layer.

• Framing: Data Link layer groups the bit stream into frames.
• Error control: Data Link layer can detect/correct errors or arrange retransmission.
• Flow control: Data Link protocols can prevent a fast sender from overwhelming a receiver on a link.
• Channel coding: Primarily a Physical-layer transmission function.

Final answer: (iv) Channel coding.