The Nikon UT-1 Communication Unit and WT-5A Wireless Transmitter combination, when connected to the D810, D810A, D800, D800E, D750, D7200, D7100 or D7000 DSLRs, allows the camera to connect wirelessly to a computer or FTP server for downloading of images, in addition to controlling the camera remotely using Nikon's Camera Control Pro 2 software. The UT-1 is powered by an EN-EL15 Li-ion rechargeable battery; It can also be powered by the optional EP-5B power connector and EH-5b or EH-5/EH-5a AC Adapter.
The UT-1 (with the WT-5 attached to it) attaches to the DSLR via the accessory hot shoe, or the optional SK-7 bracket. To use the UT-1 with a D7100, use the UC-E6 USB cable, which is provided with the camera, to connect the UT-1 with the D7100. The unit works in two modes one is Transfer mode used to transmit images and movies to a host (computer or FTP server) from the camera. In transfer mode, you have the option of turning on Auto Send, which automatically downloads images to the computer/FTP server immediately after they're recorded to the camera's memory card. The default setting is OFF; when used, you select images for downloading while in playback mode. The other is PC mode to transfer images to a computer from the camera directly, instead of saving the images to the media card first, (however, movie files must be saved first to the media card, then downloaded to the computer), as well as control the camera from a computer using Nikon's Camera Control Pro 2 software.