A vendor normally provides an IP remote control or application for a device.
The vendor also provides a device, sometimes called a NUK, that the remote or application communicate with using IP protocol.
The nook connects to devices it controls using IP. In this case, one of those devices would be a set-top box (STB).
The user of the remote or app triggers commands. Those commands transmit as codes over the IP connection all the way to a receiving application on the STB.
The STB maps the code to RF4CE commands. Those commands route to the application as if they were normal RF remote control commands.