From the link:

Uh, yeah, ethernet is a two-way communication protocol, so what difference could "directional markings" make? (Although, to be fair, this Denon Link connection probably isn't quite ethernet and may, in fact, just transmit in one direction. On the other hand, let's not mention the obvious issues about digital error-checking and transmission -- but no need to bring reality into this.)

Man, this product makes me distrust EVERYTHING about Denon quality. This is a scam, pure and simple.