[pgeorgi]

USB Type C provides a standardized protocol for protocol negotiation. I assume that Thunderbolt uses that.

It's already used in Type C to enable plugging in USB, chargers (PD spec), HDMI or DP adapters (https://www.chromium.org/chromium-os/dingdong) and I think even to route PCIe over Type C. Adding Thunderbolt to the mix shouldn't be too hard.

[jordanthoms]

I think the issue is, that if you have a thunderbolt over USB-C display, and plug it into a normal USB-C port on your laptop (say the latest macbook), it won't work, since the laptop doesn't support the thunderbolt signaling. So it's a new point of confusion - USB devices which are physically compatible but not electrically.

It's something that could possibly be solved through the markings on the devices etc and I still think doing thunderbolt over the USB-C port is great. Perhaps the display example could fall back to supporting a display-over-usb standard, it won't work as well but could help.

[cmsj]

I don't think we have enough detail about Thunderbolt 3 yet to know whether devices will be able to detect that they are connected to a USB port and not a Thunderbolt port. If they can detect that, they may well be able to choose to degrade.

It seems like an ideal way for Apple to be able to ship a display which can be connected to both thunderbolt and USB-C hosts, without the user having to care.

Obviously some Thunderbolt devices (e.g. PCI-E chassis) wouldn't reasonably be able to degrade to USB, but a good proportion of them, would.

I very much hope this is what is going to happen!

[pgeorgi]

The Type C spec also mentions a PCIe alternate mode. The main complication is to support both wrapper protocols given that thunderbolt pushes twice the bits per second over the same wire (if using active cabling)

[lsaferite]

Wrapper protocol?

The alt-mode stuff is a physical signal multiplexing, not a protocol encapsulation.

[jessaustin]

I don't think you're allowed to sell a device with a USB jack that won't work with USB, because the consortium has a trademark on it. Or perhaps you just can't advertise it as USB?

[pgeorgi]

I'd hope they gave up on their own DP signalling and just use the type C one.