Why doesn't a real software controlled transceiver exist? Or does it?

I've been thinking about this for a while. Why aren't there any really integrated, IP controlled ham radios?

I envision a radio that has ethernet, power and antenna connections. Everything else is done in software. The radio could even be mounted on the tower to reduce feedline loses.

The client software on the PC would allow full control of the radio as well as handling the audio to and from the radio. Perhaps this could be integrated with SDR on the receive side for more advanced tuning and processing on the receiver.

To me this seems like it would be awesome. I could "login" to my radio from anywhere and use it from my laptop, or maybe even my mobile device. The control and audio channels could be encrypted and secure to ensure that you're the only one controlling your radio.

Does something like this exist?