Question

The difference between the wired and wireless versions of HART are at the: Network layer Physical layer Data link layer All of these

Answer 1

This is an interesting question.

The correct answer is All of these. The difference between wired and wireless HART is of a physical layer, data link layer, and network layer. Wired HART doesn't contain physical layer. It includes 5 layers, physical layer, data link layer, network layer, transport layer, and application layer. The wireless protocol makes it easier and cheaper to use HART technologies.
 
Hope this will prove helpful for you.

Answer 2

Answer is - All of these

The difference between the wired and wireless versions of HART are at the physical, data link and network layers. Basically wired HART does not have support for a network layer.

The differences between them are:

Output signal

Wired HART - 4-20 mA

Wireless HART - IEC 62591

Power supply

Wired HART - 24V DC loop powered

Wireless HART - Intrinsically safe battery

Update rate

Wired HART - 1 sec

Wireless HART - 1 sec to 60 min

Protection type / enclosure

Wired HART - Explosion proof

Wireless HART - Intrinsically safe