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There's also Thunderbolt over USB-C that does DisplayPort, but it doesn't support all the same versions as DisplayPort over USB-C. And there's also USB 4 but I

There's also Thunderbolt over USB-C that does DisplayPort, but it doesn't support all the same versions as DisplayPort over USB-C. And there's also USB 4 but I don't know/understand if it changes anything.

masklinn 3y ago
I think the most applicable bit is that USB4 adds tunneling modes, aside from alternate mode. I'm not entirely clear, but from my understanding alternate mode means the physical connection gets switched over, while tunneling means the tunneled data is sent over USB (so the communication on the wire is USB all along, you get nesting).
- jsmith45 3y ago
  This is essentially correct, although the encapsulation format is really the Thunderbolt encapsulation format, which is only USB in that it is now officially defined in the USB4 specification. USB4 hubs/docks for example, need to have the ability to translate from encapsulated DisplayPort to alternate mode for its downstream ports. USB4 hosts need to support both encapsulated and alternate modes in the downstream ports. The idea is that if a display device does not want to implement any other non USB 2.0 peripherals (2.0 has dedicated lines so it can support those), it can implement only alternate mode, (and not need to support the complexities of encapsulating USB4), plus all USB4 hosts needing to support DisplayPort means you know you can connect such a screen to any USB4 device and have it work (although supporting multiple screens like this is optional). One thing to not though is that DisplayPort alternate mode has the option of reversing the device->host wires of USB-C lanes and thus get 4 lanes of host->device data, for 80Gbps at Gen 3 speeds if using both lanes. USB4 V1.0 does not support lane reversal, and USB4 V2.0 can reverse only one bidirectional lane, since it still needs to support device->host data. I think this lane reversal is only possible when using the new new Gen 4 speeds, which provided 80Gbps symmetric, or 120/40 Gbps asymmetric.

masklinn 3y ago

I think the most applicable bit is that USB4 adds tunneling modes, aside from alternate mode. I'm not entirely clear, but from my understanding alternate mode means the physical connection gets switched over, while tunneling means the tunneled data is sent over USB (so the communication on the wire is USB all along, you get nesting).

jsmith45 3y ago
This is essentially correct, although the encapsulation format is really the Thunderbolt encapsulation format, which is only USB in that it is now officially defined in the USB4 specification. USB4 hubs/docks for example, need to have the ability to translate from encapsulated DisplayPort to alternate mode for its downstream ports. USB4 hosts need to support both encapsulated and alternate modes in the downstream ports. The idea is that if a display device does not want to implement any other non USB 2.0 peripherals (2.0 has dedicated lines so it can support those), it can implement only alternate mode, (and not need to support the complexities of encapsulating USB4), plus all USB4 hosts needing to support DisplayPort means you know you can connect such a screen to any USB4 device and have it work (although supporting multiple screens like this is optional). One thing to not though is that DisplayPort alternate mode has the option of reversing the device->host wires of USB-C lanes and thus get 4 lanes of host->device data, for 80Gbps at Gen 3 speeds if using both lanes. USB4 V1.0 does not support lane reversal, and USB4 V2.0 can reverse only one bidirectional lane, since it still needs to support device->host data. I think this lane reversal is only possible when using the new new Gen 4 speeds, which provided 80Gbps symmetric, or 120/40 Gbps asymmetric.