Which statement describes a characteristic of the frame header fields of the data link layer?

The choice indicating that the frame header fields of the data link layer vary depending on protocols is correct. In the data link layer, which encompasses various protocols like Ethernet, Wi-Fi, and Point-to-Point Protocol (PPP), each protocol defines its own set of fields and formats within the frame header. This protocol-specific design allows different types of networks and communication technologies to effectively manage how data is structured and transmitted over physical mediums.

For instance, Ethernet frames will include fields such as source and destination MAC addresses, while PPP frames will contain fields specific to point-to-point data connections. This variability is crucial for supporting diverse networking environments and addressing the unique requirements of different data link protocols.