I own a 4k @ 60Hz monitor. If I were to buy a laptop, I'd like to connect it and a bunch of USB devices via a single USB C cable. Easy, right?
Except that the monitor only supports DisplayPort 1.2. 4k60 requires a bandwidth of 12.54 Gbit/s. DP 1.2 consists of four data lanes, each providing 4.32 GBit/s, so my monitor requires four full lanes. DP 1.3 and up provide at least 7.48 Gbit/s, so 4k60 would only require two lanes for that.
USB C consists of 4 data lanes. When using the DisplayPort alternate mode, it can assign either 1, 2, or 4 data lanes to DP. The other lanes can be used for USB. In addition to that, it also offers a single USB 2.0 lane.
If a dock - even an expensive one - supports a resolution of 4k60 via DP and provides USB 3 ports, will it actually work for me? It could use DP 1.2 by assigning four data links to DP , but that means USB gets downgraded to 2.0 and I don't think any hub actually supports this. It could use DP 1.3+ and assign two data links to DP and two to USB, but if it outputs that same DP signal, it won't provide the bandwidth my monitor needs so it must actively convert two-link DP 1.3 to four-link DP 1.2. Again, I don't think any hub actually supports this.
The hardware I need can definitely exist. It's a pretty normal thing to ask for. A lot of docks, even the expensive ones, will claim to support what I need, but as far as I can tell not a single dock actually can. Because USB C has so many protocol options, figuring out what is supported has become nearly impossible.
Yep, docks are known not to request 4 lanes for DP even when there's only a display plugged in. In fact even dongles that don't have anything other than a display output on them sometimes only ever request 2 lanes, sadly.
You can't really blame them, though. The vast, vast majority of users will be absolutely fine with 2 lanes, especially with DP 1.3+. USB C is mainly used on laptops, and your office projector just isn't going to support 8K120 with HDR. Why spent the extra money if virtually nobody needs it?
An external GPU box would work for you, since the offboard GPU would have a full-bandwidth link to the monitor. Depending on which GPU you put in it, though, it would probably be cheaper to buy a new monitor.
That would absolutely be a (albeit very expensive) solution, I didn't even think of that! But that would require Thunderbolt support, which is still a bit rare. And I don't think that would support USB at the same time, right?
They use a Thunderbolt hub (CalDigit TS3 Plus) to a Thunderbolt GPU box. (Razer core X) A single cable goes to the hub, GPU box and all your USB peripherals plug into the hub. The hub itself claims it can run a DP 1.2 monitor, so you could skip the GPU box, if you don't need graphics performance.
Except that the monitor only supports DisplayPort 1.2. 4k60 requires a bandwidth of 12.54 Gbit/s. DP 1.2 consists of four data lanes, each providing 4.32 GBit/s, so my monitor requires four full lanes. DP 1.3 and up provide at least 7.48 Gbit/s, so 4k60 would only require two lanes for that.
USB C consists of 4 data lanes. When using the DisplayPort alternate mode, it can assign either 1, 2, or 4 data lanes to DP. The other lanes can be used for USB. In addition to that, it also offers a single USB 2.0 lane.
If a dock - even an expensive one - supports a resolution of 4k60 via DP and provides USB 3 ports, will it actually work for me? It could use DP 1.2 by assigning four data links to DP , but that means USB gets downgraded to 2.0 and I don't think any hub actually supports this. It could use DP 1.3+ and assign two data links to DP and two to USB, but if it outputs that same DP signal, it won't provide the bandwidth my monitor needs so it must actively convert two-link DP 1.3 to four-link DP 1.2. Again, I don't think any hub actually supports this.
The hardware I need can definitely exist. It's a pretty normal thing to ask for. A lot of docks, even the expensive ones, will claim to support what I need, but as far as I can tell not a single dock actually can. Because USB C has so many protocol options, figuring out what is supported has become nearly impossible.