9 ms·

Demystifying USB-C and Thunderbolt Docks (2017)

66 points by rubatuga 5y ago

wslh 5y ago
Repeat it again: XPS 13 with the TB16 Thunderbolt dock gives me 3 external monitors. I tried the dock with the Mac M1 and obviously one monitor is supported because... Apple limitations. The problem with the XPS 13 is that it doesn't have the same battery duration of the M1 but beyond that in term of features is a top notebook.
- raihansaputra 5y ago
  Mac M1 (non Mini, non M1 Pro/Max) only supports 1 external display due to SoC limitations. M1 is basically a modified iPad SoC.
  - wslh 5y ago
    That's what I said. It is because Apple.
chx 5y ago
I took ximeng's interpretation of my comment yesterday and worked on it. Here's my newest attempt at the USB-C explanation. A. The USB C cable physically consists of: 1. 60/100W power wire pair 2. USB2 speed data wire pair supporting 0.48Mbit/s 3. 4 high speed data wire pairs (“high speed lanes”). These can be ommitted. Each high speed lane supports at least 5/10Gbit/s depending on cable length. 4. Separate wire for negotiating power roles (source/sink) and data roles (upstream/downstream or host/peripheral). 5. eMarker cables are required for rapidly changing wattage of power supply (Programmable Power Supplies, PPS) B. Protocols (all over high speed lanes apart from USB2): 1. USB. 480mbit/s over the dedicated pair is always possible. 5/10gbps USB using two high speed lanes is the default mode for the high speed lanes depending on cable length. (four high speed lanes at 20gbps theoretically possible but rarely supported by hosts) 2. DisplayPort 1.2 (8.64Gbit/s video data over 2 high speed lanes) / DisplayPort 1.3/1.4 (12.96Gbit/s over 2 high speed lanes, double over 4). MST technology allows splitting the aggregate video data bandwidth across monitors but Mac doesn't support this. DisplayPort 1.4 supports video compression, but this is rarely supported by monitors. If using only 2 high speed lanes the other 2 can be used for USB data. This mode doesn't require any protocol converter to connect a DisplayPort device, only a simple USB C controller to negotiate DisplayPort mode. The USB C pins become DisplayPort pins, essentially. 3. Thunderbolt 3/4 (needed for Mac dual monitors). Thunderbolt 4 is USB4 with optional features mandatory (however in practice these optional features are likely to always be included so they can be treated as the same). TB3 carries PCI Express + DisplayPort packets, TB4 also native USB packets. Thunderbolt controllers are required on both ends. In a TB3 dock, this controller provides the USB root hub, in TB4 the USB data comes from the host. Bus bandwidth is maximum 40gbps, depends on host and cable both (this is why TB peripherals ship with so short cables). The bus can have two independent DisplayPort connections (which PCs can again split to even more). Laptops with TB4 and/or two Thunderbolt ports always have two, most TB3 laptops with a single port will only provide one -- and that one will only be DP 1.2. Note two ordinary independent DP cables can carry 51.84Gbit/s worth of video data (if the host and monitor both supports at least 1.3) but the TB bus is limited to 40Gbit/s. Finally, power: 5/9/15/20V. Requirements signaled by resistors on the device side if only 5V. More than 5V negotiated between devices: 1. Agree source and sink, by default the data upstream/host is source but this can be negotiated, 2. Source indicates how much power it can provide, either 3A or with a 20V cable optionally 5A. This assumes fixed power, some devices now support PPS.
- nfriedly 5y ago
  > Requirements signaled by resistors on the device side if only 5V. You might get a kick out of this (or nightmares...): https://www.nfriedly.com/techblog/2021-10-10-v90-usb-c/ https://www.nfriedly.com/techblog/2021-10-10-v90-usb-c/
- vardump 5y ago
  2. USB2 speed data wire pair supporting 0.48Mbit/s Should be 0.48Gbit/s, or better, 480 Mbit/s.
  - chx 5y ago
    Ah yes. Sorry. I will write 480mbit/s (0.48Gbit/s) ongoing.
mjevans 5y ago
Now if only the Docks and Laptops / other devices being docked mentioned modes they were capable of working in.
- Felger 5y ago
  Plus Power Delivery capabilities... Had Asus Expertbook B1500CEAE (11th gen Core and tb3 controller) a few weeks ago that sadly don't support USB-C power delivery plugged on the USB-C port of a multiport AV replicator setup, but charge ok if directly connected to the TB3 USB-C port. This same configuration (USB-C power supply plugged on the multiport's USB-C) works on an Apple Macbook Air M1 2020.
smoldesu 5y ago
I really miss the Thinkpad docking stations that existed on the bottom of your laptop. Yes, they were proprietary as hell. But they were also some of the coolest, most convenient connectors that existed. I know USB-C docks are technically better for a plethora of reasons, but I still find myself missing the Nintendo-Switch-like convenience of dropping my laptop onto my desk and watching my monitor and peripherals spring to life. Every time I did I could almost hear Jeff Goldblum saying "there is no step three" in my head.
- Felger 5y ago
  Here, we still use 2015' Dell laptops with PR02X and PR03X old fashioned docks. And some HP zbook with Ultraslim docking station 2013 , with few displayport issues on the first firmware releases. Next laptop generation will sadly be the end of all those proprietary yet reliable docks and the beginning of USB-C/TB3 wd15/wd19/tb16 era and its army of bugs, failures (WD15 someone ?) and painful and hazardeous firmware upgrades.
  - smoldesu 5y ago
    Ouch, that's gotta hurt. One of the things I loved about those old-fashioned docks were how cheap they were, especially secondhand: I ended up buying 3 docks for my T460s, one for work and two for home (one in the office, one at the media center). Cost me less than $50 for the lot of them, and now I can plop down my laptop anywhere I please and it automagically assumes the form of my setup. Hopefully they make a comeback...
    - Felger 5y ago
      Yes I can also find tons of second hand PR02/03X 5 minutes from home here, dirty cheap. But the 19v 130w PSUs are usually more expensive and difficult to find. But the PR and ultraslim dock series are so far very reliable, even after years of use. I dread the future massive switch to USB-C and TB3 entry dock. I hope a chip maker will eventually release a all-in-one TB controller with USB3.x/Display outputs/GbE Ethernet/Sound embedded. Currently, everything is split into differents ICs, hence the high cost and complexity.
lapetitejort 5y ago
Back in the tail end of 2019 I tried to go full Thunderbolt 3 (T3 from now on). I wanted to swap between my desktop rig and MBP '19 with just a single wire. I bought a T3 dock and prepared. Problems: 1. Nvidia RTX 2070 does not support T3. I could not use a T3 dock at all. Regular USB C docks could connect to the card and run everything else though. 2. My MoBo did not support T3. Not only would I have to upgrade it, I would also have to buy a PCIe card and use short DisplayPort cables to connect the graphics card to it in order to have video out. So I downgraded to a USB C dock. More problems: 1. My MBP '19 only allowed one monitor to connect. But I had a few year old ThinkPad that could drive two monitors! 2. The keyboard connection started to become unreliable. So I hard-wired it to the desktop. 3. Eventually the MBP stopped outputting video to the monitor. Apple said I had to update the firmware in the monitor. I declined. Eventually I gave up on docks. The USB C dock now acts as the most overpriced dock imaginable for a ChromeCast '20. Maybe one day I'll try with Thunderbolt 4 with plenty of planning beforehand. Or maybe not.
- lathiat 5y ago
  The single monitor thing is because apple doesn’t support DisplayPort MultiStream. It has long been confusing why because pre apple silicon it worked fine on their GPUs in windows but macOS has no support. Given their thunderbolt drive it seems silly.
  - month13 5y ago
    This is a long standing flaw of macOS. The common workaround is a lot of these docks will offer a TB3 passthrough, where a standard USB-C to whatever-you-need, will work.
    - smoldesu 5y ago
      That, and the issue where your Nvidia graphics card simply won't work over Thunderbolt 3 (or at all, for that matter). It's a long-standing and frankly petty omission that really leaves me wondering how serious ML researchers get their work done on the platform...
- 5y ago
kingcharles 5y ago
Very thorough explanation. I'm always confused by the sheer number of options USB-C and Thunderbolt provide through the same connector. This seeks to clarify it a bit, although USB4 might make everything even more complicated than the mess it is now.
Ataraxic 5y ago
I appreciate this article but fundamentally this is just a fault of the USB-C standard. One of the hardest parts is not just that it's sometimes confusing what is supported, a lot of the complexity is also pushed onto what any given usb-c cable supports. Sometimes, especially with video, there is a distinct direction built into many of these cables. Now you need to find in your cable bin/storage the right kind of cable for each application potentially killing a lot of re-usability (if you have neatly organized usb-c cables labeled by their technical capabilities you're much better than me). Not to mention, there are issues with power. Lots of laptops have video wired to usb-c which you can connect to a monitor, but I bought a portable monitor that took usb-c as an input using the DP standard last year and it was a nightmare to get it work correctly. My understanding was that usb-c => DP, most of the time the cable itself is unpowered from the usb-c side since the monitor accepting displayport will power the connection on its side (since it's usually plugged in). Since mine was a portable monitor this wasn't the case and I basically needed to use a wacom link to combine a DP signal, separate usb power into a combined signal out. Totally lame...
- Felger 5y ago
  I will be given the same task of get a USB-C portable monitor to work on a Huawei Mate D14 (1 USB-C) next week. Already preparing for that massive headache.
- kunai 5y ago
  I remember back in 2015-2016 when everyone was heralding USB-C as the one port to rule them all. Turns out, it's more like 17 ports in a trench coat to rule them none. It's been five years since USB-C became standard on MacBooks and we've seen Apple reverse course on the idea it could replace everything, and with the exception of a handful of ultraportables, most PC laptops and motherboards still include 2+ USB-A ports as well as other IO. In other applications, like cars, aircraft, public charging stations, USB-A is here to stay, and the advantages of USB-C are dubious at best. A more fragile port, for... what, reversibility? Having a clear use case for a port is invaluable. When I plug in an HDMI cable, I know it's going to be used for display output. MagSafe? Power delivery. USB-A/Firewire? A client peripheral connected to a master computer bus, like a printer or MIDI keyboard. USB-C eschews that philosophy entirely. In a way, it's almost like a step backwards to the days of serial ports and DIN cables, with different standards competing for supremacy and no way of knowing if Thing A works with Thing B without trial and error.
LeanderK 5y ago
I think a huge problem with usb-c is that there's software lacking explaining the situation to the user. There exist a huge number of standards and options but for users it only works or it doesn't, but ideally it should be explained in an easy way. For example with power-delivery: I need X watt, you charger can provide it but the cable can only handle up to Y Watt. Identifying what's at fault, why and what to do. Can one just write an app like this? For an macbook, the information should be there....although it sounds very, very complicated and involved.
- ct0 5y ago
  One of my favorite subreddits answers many of these questions, or at least tries to. https://old.reddit.com/r/UsbCHardware/ https://old.reddit.com/r/UsbCHardware/
  - deleted 5y ago
    [deleted]
  - SAI_Peregrinus 5y ago
    I think they mean it should show up as part of the error message provided by the OS. "Error, the cable you used to connect <human-readable monitor identifier> doesn't support <thing needed>." "Error, the dock <human-readable dock identifier> doesn't support <thing needed>, which <human-readable peripheral identifier> requires." Identify the limiting component, explain the what the new cable/dock/hub/etc needs to support so the customer has an actual chance of getting things to work!
    - LeanderK 5y ago
      yeah, that's what I mean! The OS should explain the situation.
broknbottle 5y ago
Just wait until you start having to deal with TB4 docks.. I bought the Kensington one earlier this year and attempted to use it with a XPS 9310 running Ubuntu 20.40 and what a total PITA. No matter the configuration I could not get two monitors to work at the same time. I ended up returning and buying a Corsair TB3 dock and it's been smooth sailing ever since.
- technobabbler 5y ago
  Ah, the wonders of Thunderbolt over USB-C. One connector, two sides, three generations, ten protocols, a hundred dollars and still one just one monitor. If you're lucky.
ggm 5y ago
They got one thing right. No heisenberg insertion problem, and its reasonably robust. They got everything else wrong. Cable differences, drivers, how people think about the space overall. Even in USB-C hubs (not docks) people make truly strange choices like "I will give you one USB-C power input, and one output tail, but I won't make another USB-C port available even though I could"
kellengreen 5y ago
I've had this page bookmarked for years now, so major kudos to the author. 5 years on, it's still the best of explanation of all the different USB-C modes. I would love to see an updated version to include Thunderbolt 4 and USB4.

66 points by rubatuga 5y ago

wslh 5y ago

Repeat it again: XPS 13 with the TB16 Thunderbolt dock gives me 3 external monitors. I tried the dock with the Mac M1 and obviously one monitor is supported because... Apple limitations. The problem with the XPS 13 is that it doesn't have the same battery duration of the M1 but beyond that in term of features is a top notebook.

raihansaputra 5y ago
Mac M1 (non Mini, non M1 Pro/Max) only supports 1 external display due to SoC limitations. M1 is basically a modified iPad SoC.
- wslh 5y ago
  That's what I said. It is because Apple.

chx 5y ago

I took ximeng's interpretation of my comment yesterday and worked on it. Here's my newest attempt at the USB-C explanation. A. The USB C cable physically consists of: 1. 60/100W power wire pair 2. USB2 speed data wire pair supporting 0.48Mbit/s 3. 4 high speed data wire pairs (“high speed lanes”). These can be ommitted. Each high speed lane supports at least 5/10Gbit/s depending on cable length. 4. Separate wire for negotiating power roles (source/sink) and data roles (upstream/downstream or host/peripheral). 5. eMarker cables are required for rapidly changing wattage of power supply (Programmable Power Supplies, PPS) B. Protocols (all over high speed lanes apart from USB2): 1. USB. 480mbit/s over the dedicated pair is always possible. 5/10gbps USB using two high speed lanes is the default mode for the high speed lanes depending on cable length. (four high speed lanes at 20gbps theoretically possible but rarely supported by hosts) 2. DisplayPort 1.2 (8.64Gbit/s video data over 2 high speed lanes) / DisplayPort 1.3/1.4 (12.96Gbit/s over 2 high speed lanes, double over 4). MST technology allows splitting the aggregate video data bandwidth across monitors but Mac doesn't support this. DisplayPort 1.4 supports video compression, but this is rarely supported by monitors. If using only 2 high speed lanes the other 2 can be used for USB data. This mode doesn't require any protocol converter to connect a DisplayPort device, only a simple USB C controller to negotiate DisplayPort mode. The USB C pins become DisplayPort pins, essentially. 3. Thunderbolt 3/4 (needed for Mac dual monitors). Thunderbolt 4 is USB4 with optional features mandatory (however in practice these optional features are likely to always be included so they can be treated as the same). TB3 carries PCI Express + DisplayPort packets, TB4 also native USB packets. Thunderbolt controllers are required on both ends. In a TB3 dock, this controller provides the USB root hub, in TB4 the USB data comes from the host. Bus bandwidth is maximum 40gbps, depends on host and cable both (this is why TB peripherals ship with so short cables). The bus can have two independent DisplayPort connections (which PCs can again split to even more). Laptops with TB4 and/or two Thunderbolt ports always have two, most TB3 laptops with a single port will only provide one -- and that one will only be DP 1.2. Note two ordinary independent DP cables can carry 51.84Gbit/s worth of video data (if the host and monitor both supports at least 1.3) but the TB bus is limited to 40Gbit/s. Finally, power: 5/9/15/20V. Requirements signaled by resistors on the device side if only 5V. More than 5V negotiated between devices: 1. Agree source and sink, by default the data upstream/host is source but this can be negotiated, 2. Source indicates how much power it can provide, either 3A or with a 20V cable optionally 5A. This assumes fixed power, some devices now support PPS.

nfriedly 5y ago
> Requirements signaled by resistors on the device side if only 5V. You might get a kick out of this (or nightmares...): https://www.nfriedly.com/techblog/2021-10-10-v90-usb-c/ https://www.nfriedly.com/techblog/2021-10-10-v90-usb-c/
vardump 5y ago
2. USB2 speed data wire pair supporting 0.48Mbit/s Should be 0.48Gbit/s, or better, 480 Mbit/s.
- chx 5y ago
  Ah yes. Sorry. I will write 480mbit/s (0.48Gbit/s) ongoing.

mjevans 5y ago

Now if only the Docks and Laptops / other devices being docked mentioned modes they were capable of working in.

Felger 5y ago
Plus Power Delivery capabilities... Had Asus Expertbook B1500CEAE (11th gen Core and tb3 controller) a few weeks ago that sadly don't support USB-C power delivery plugged on the USB-C port of a multiport AV replicator setup, but charge ok if directly connected to the TB3 USB-C port. This same configuration (USB-C power supply plugged on the multiport's USB-C) works on an Apple Macbook Air M1 2020.

smoldesu 5y ago

I really miss the Thinkpad docking stations that existed on the bottom of your laptop. Yes, they were proprietary as hell. But they were also some of the coolest, most convenient connectors that existed. I know USB-C docks are technically better for a plethora of reasons, but I still find myself missing the Nintendo-Switch-like convenience of dropping my laptop onto my desk and watching my monitor and peripherals spring to life. Every time I did I could almost hear Jeff Goldblum saying "there is no step three" in my head.

Felger 5y ago
Here, we still use 2015' Dell laptops with PR02X and PR03X old fashioned docks. And some HP zbook with Ultraslim docking station 2013 , with few displayport issues on the first firmware releases. Next laptop generation will sadly be the end of all those proprietary yet reliable docks and the beginning of USB-C/TB3 wd15/wd19/tb16 era and its army of bugs, failures (WD15 someone ?) and painful and hazardeous firmware upgrades.
- smoldesu 5y ago
  Ouch, that's gotta hurt. One of the things I loved about those old-fashioned docks were how cheap they were, especially secondhand: I ended up buying 3 docks for my T460s, one for work and two for home (one in the office, one at the media center). Cost me less than $50 for the lot of them, and now I can plop down my laptop anywhere I please and it automagically assumes the form of my setup. Hopefully they make a comeback...
  - Felger 5y ago
    Yes I can also find tons of second hand PR02/03X 5 minutes from home here, dirty cheap. But the 19v 130w PSUs are usually more expensive and difficult to find. But the PR and ultraslim dock series are so far very reliable, even after years of use. I dread the future massive switch to USB-C and TB3 entry dock. I hope a chip maker will eventually release a all-in-one TB controller with USB3.x/Display outputs/GbE Ethernet/Sound embedded. Currently, everything is split into differents ICs, hence the high cost and complexity.

lapetitejort 5y ago

Back in the tail end of 2019 I tried to go full Thunderbolt 3 (T3 from now on). I wanted to swap between my desktop rig and MBP '19 with just a single wire. I bought a T3 dock and prepared. Problems: 1. Nvidia RTX 2070 does not support T3. I could not use a T3 dock at all. Regular USB C docks could connect to the card and run everything else though. 2. My MoBo did not support T3. Not only would I have to upgrade it, I would also have to buy a PCIe card and use short DisplayPort cables to connect the graphics card to it in order to have video out. So I downgraded to a USB C dock. More problems: 1. My MBP '19 only allowed one monitor to connect. But I had a few year old ThinkPad that could drive two monitors! 2. The keyboard connection started to become unreliable. So I hard-wired it to the desktop. 3. Eventually the MBP stopped outputting video to the monitor. Apple said I had to update the firmware in the monitor. I declined. Eventually I gave up on docks. The USB C dock now acts as the most overpriced dock imaginable for a ChromeCast '20. Maybe one day I'll try with Thunderbolt 4 with plenty of planning beforehand. Or maybe not.

lathiat 5y ago
The single monitor thing is because apple doesn’t support DisplayPort MultiStream. It has long been confusing why because pre apple silicon it worked fine on their GPUs in windows but macOS has no support. Given their thunderbolt drive it seems silly.
- month13 5y ago
  This is a long standing flaw of macOS. The common workaround is a lot of these docks will offer a TB3 passthrough, where a standard USB-C to whatever-you-need, will work.
  - smoldesu 5y ago
    That, and the issue where your Nvidia graphics card simply won't work over Thunderbolt 3 (or at all, for that matter). It's a long-standing and frankly petty omission that really leaves me wondering how serious ML researchers get their work done on the platform...
5y ago

kingcharles 5y ago

Very thorough explanation. I'm always confused by the sheer number of options USB-C and Thunderbolt provide through the same connector. This seeks to clarify it a bit, although USB4 might make everything even more complicated than the mess it is now.

Ataraxic 5y ago

I appreciate this article but fundamentally this is just a fault of the USB-C standard. One of the hardest parts is not just that it's sometimes confusing what is supported, a lot of the complexity is also pushed onto what any given usb-c cable supports. Sometimes, especially with video, there is a distinct direction built into many of these cables. Now you need to find in your cable bin/storage the right kind of cable for each application potentially killing a lot of re-usability (if you have neatly organized usb-c cables labeled by their technical capabilities you're much better than me). Not to mention, there are issues with power. Lots of laptops have video wired to usb-c which you can connect to a monitor, but I bought a portable monitor that took usb-c as an input using the DP standard last year and it was a nightmare to get it work correctly. My understanding was that usb-c => DP, most of the time the cable itself is unpowered from the usb-c side since the monitor accepting displayport will power the connection on its side (since it's usually plugged in). Since mine was a portable monitor this wasn't the case and I basically needed to use a wacom link to combine a DP signal, separate usb power into a combined signal out. Totally lame...

Felger 5y ago
I will be given the same task of get a USB-C portable monitor to work on a Huawei Mate D14 (1 USB-C) next week. Already preparing for that massive headache.
kunai 5y ago
I remember back in 2015-2016 when everyone was heralding USB-C as the one port to rule them all. Turns out, it's more like 17 ports in a trench coat to rule them none. It's been five years since USB-C became standard on MacBooks and we've seen Apple reverse course on the idea it could replace everything, and with the exception of a handful of ultraportables, most PC laptops and motherboards still include 2+ USB-A ports as well as other IO. In other applications, like cars, aircraft, public charging stations, USB-A is here to stay, and the advantages of USB-C are dubious at best. A more fragile port, for... what, reversibility? Having a clear use case for a port is invaluable. When I plug in an HDMI cable, I know it's going to be used for display output. MagSafe? Power delivery. USB-A/Firewire? A client peripheral connected to a master computer bus, like a printer or MIDI keyboard. USB-C eschews that philosophy entirely. In a way, it's almost like a step backwards to the days of serial ports and DIN cables, with different standards competing for supremacy and no way of knowing if Thing A works with Thing B without trial and error.

LeanderK 5y ago

I think a huge problem with usb-c is that there's software lacking explaining the situation to the user. There exist a huge number of standards and options but for users it only works or it doesn't, but ideally it should be explained in an easy way. For example with power-delivery: I need X watt, you charger can provide it but the cable can only handle up to Y Watt. Identifying what's at fault, why and what to do. Can one just write an app like this? For an macbook, the information should be there....although it sounds very, very complicated and involved.

ct0 5y ago
One of my favorite subreddits answers many of these questions, or at least tries to. https://old.reddit.com/r/UsbCHardware/ https://old.reddit.com/r/UsbCHardware/
- deleted 5y ago
  [deleted]
- SAI_Peregrinus 5y ago
  I think they mean it should show up as part of the error message provided by the OS. "Error, the cable you used to connect <human-readable monitor identifier> doesn't support <thing needed>." "Error, the dock <human-readable dock identifier> doesn't support <thing needed>, which <human-readable peripheral identifier> requires." Identify the limiting component, explain the what the new cable/dock/hub/etc needs to support so the customer has an actual chance of getting things to work!
  - LeanderK 5y ago
    yeah, that's what I mean! The OS should explain the situation.

broknbottle 5y ago

Just wait until you start having to deal with TB4 docks.. I bought the Kensington one earlier this year and attempted to use it with a XPS 9310 running Ubuntu 20.40 and what a total PITA. No matter the configuration I could not get two monitors to work at the same time. I ended up returning and buying a Corsair TB3 dock and it's been smooth sailing ever since.

technobabbler 5y ago
Ah, the wonders of Thunderbolt over USB-C. One connector, two sides, three generations, ten protocols, a hundred dollars and still one just one monitor. If you're lucky.

ggm 5y ago

They got one thing right. No heisenberg insertion problem, and its reasonably robust. They got everything else wrong. Cable differences, drivers, how people think about the space overall. Even in USB-C hubs (not docks) people make truly strange choices like "I will give you one USB-C power input, and one output tail, but I won't make another USB-C port available even though I could"

kellengreen 5y ago

I've had this page bookmarked for years now, so major kudos to the author. 5 years on, it's still the best of explanation of all the different USB-C modes. I would love to see an updated version to include Thunderbolt 4 and USB4.