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After buying a screen which has only a USB-C DP-Alt-Mode input, I was recently in the market for a matching cable. My only requirements were “it should be as lo

After buying a screen which has only a USB-C DP-Alt-Mode input, I was recently in the market for a matching cable. My only requirements were “it should be as long as possible, at least 2 meters” and “it needs to support DP-Alt-Mode”. Now I thought this would be easy, just ask Google what kind of cable I need, right...? Well... no. Not at all. I wasn’t able to find any information whatsoever what kind of USB-C cable is needed for supporting Alt-DP-Mode. I guessed (really guessed, couldn’t find information) a USB 2.0 USB-C cable wouldn’t be good enough. But is a 5Gbps cable enough? Or is a 10Gbps cable needed? Or maybe neither and I need to buy one of those really expensive USB-C Thunderbolt 3 cables...? In the end I just bought a 2 meter USB-C 3.2 5 Gbps and just hoped for the best. And indeed it works. Yay! The thing is... I’m a technical person, and even I can’t figure this out. How is a non-technical person supposed to navigate this? And by the way: one piece of information I did find about USB-C and Alt-DP-Mode is that the current spec for Alt-DP-Mode doesn’t allow use of active cables, so length is limited to 2 meters. That’s another pitfall restriction.

mrb 7y ago
«But is a 5Gbps cable enough? Or is a 10Gbps cable needed?» Here is the answer: if you need DisplayPort 1.0-1.2, a 5 Gbps cable is enough. If you need DP 1.3-1.4 (where they upped the transfer rate for higher resolution and fps,) you need a 10 Gbps cable. If you need DP 2.0 (I don't think products are out yet, the standard was finalized last month,) you will need a USB4 20 Gbps cable.
- djsumdog 7y ago
  DP1.2a should be enough for 60Hz at UHD/2160p. 1.4 is needed for HDR support, 5K, higher refresh rates, etc.
  - kllrnohj 7y ago
    DP 1.2a goes up to 21.60 Gbit/s, and 4k 60hz (which does work fine over 1.2a) needs 12.54 Gbit/s. I'm not sure how the 5Gbit/s and 10Gbit/s USB-C cables fit into this. It's obviously not just based on the cable's "rated" bandwidth, as if it was neither the 5Gbit/s nor 10Gbit/s connection would work at all for display. But it does, so it must not be, so what is it? Is it 5Gbit/s per twisted pair? That would make sense as displayport uses 4 pairs so 4 * 5 comfortably gets you the 12.54 with plenty left over for regular data. But then it would matter for the 10gbit/s cables if it's talking about superspeed 1x2 (2x5gbit/s) or 2x1 (1x10gbit/s).
    - mrb 7y ago
      «I'm not sure how the 5Gbit/s and 10Gbit/s USB-C cables fit into this.» A USB3 cable has 4 differential pairs. When in alt mode, all 4 pairs transmit in the same direction, so a 5 Gbit/s cable can transmit 20 Gbit/s.
derefr 7y ago
The answer is supposed to be easy; it's "you need to buy one of those really expensive USB-C Thunderbolt 3 cables, because those cables—the ones that do everything—are supposed to be the only type of USB-C cables." USB-C cables are supposed to be universal, i.e. have all the features, all the time; and thus, USB-C cables should (in 2019) be very expensive. Any USB-C cable that isn't very expensive (in 2019) isn't following the standard.
- Dylan16807 7y ago
  There are plenty of cables that are cheap and support everything that's actually in a USB standard. They only go up to 1 meter, though. Even thunderbolt 3 isn't too expensive over short cables. They don't need to be expensive. At the other end of the spectrum, there don't seem to be any cables that support both thunderbolt 3 and USB 3 at 2 meters, no matter how much you're willing to spend.
- sambroner 7y ago
  Can you link to some cables that are certified to implement the entire standard? Even that has been difficult for me to find.
  - breatheoften 7y ago
    I actually don’t think any of the above commentary is true. More expensive doesn’t necessarily mean more support ... thunderbolt is not usb-c even tho they have the same connector on the end ... If you are in the market for an expensive and long thunderbolt cable — caldigit makes one. I just bought it and felt annoyed at paying 50 dollars for a cable — but I’m also glad for the technology needed to make this cable possible to exist so ... maybe I can swallow this as funding the future? https://www.amazon.com/CalDigit-Intel-Certified-Thunderbolt-Cable/dp/B01N4MFG7J/ref=sr_1_3?crid=32KJAAZAWWY9A&keywords=caldigit+thunderbolt+3+cable&qid=1562854004&s=gateway&sprefix=caldigit+thun%2Caps%2C159&sr=8-3 https://www.amazon.com/CalDigit-Intel-Certified-Thunderbolt-...
- ben-schaaf 7y ago
  > USB-C cables are supposed to be universal I may be wrong here, but from what I understand this doesn't seem to be the case (DP, Thunderbolt, etc. are all "optional"). It would also mean that all cables would be limited to 50cm.
AceJohnny2 7y ago
> It needs to support DP-Alt-Mode For future reference, a Thunderbolt 3 cable (which is USB-C connector) will work.
- llampx 7y ago
  Also the most expensive option and limited in terms of maximum length.
  - djsumdog 7y ago
    How are the Thunderbolt cables wired? Do they have more than the 10 USB3 wires or is it just a higher standard of cable? Isn't USB4 = the next Thunderbolt standard?
- Dylan16807 7y ago
  Not true! Active thunderbolt 3 cables often only support thunderbolt 3.
  - AceJohnny2 7y ago
    Per the Thunderbolt FAQ [1] > What is Thunderbolt 3? > Computer ports with Thunderbolt 3 provide 40Gbps Thunderbolt – double the speed of the previous generation, USB 3.1 10Gbps, and DisplayPort 1.2. I'm curious: which active cable did you use that didn't support DP? [1] https://thunderbolttechnology.net/tech/faq https://thunderbolttechnology.net/tech/faq
    - Dylan16807 7y ago
      Note: This cable does not support native DisplayPort 1.2 or Thunderbolt 3 connections to a DisplayPort monitor. https://amazon.com/StarTech-com-Thunderbolt-Cable-40Gbps-Charger/dp/B01N9J47EG/ https://amazon.com/StarTech-com-Thunderbolt-Cable-40Gbps-Cha... Regular USB-C monitor is not support, USB 3.1/3.0/2.0 and USB-C is not support https://amazon.com/Thunderbolt-Certified-Nekteck-Compatible-Alienware/dp/B074JZVD2M/ https://amazon.com/Thunderbolt-Certified-Nekteck-Compatible-... USB 2.0 ️[check], USB 3.0 [ ], DisplayPort [ ] https://amazon.com/Belkin-Thunderbolt-Cable-Feet-Meters/dp/B072KPBKS3/ https://amazon.com/Belkin-Thunderbolt-Cable-Feet-Meters/dp/B... Can you point me to any 2-meter thunderbolt@40GHz cable that does support USB 3 and/or DisplayPort? None of the ones in this chart can do it: https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9dMDWqENiY2kgBJUu29f_TX8/pubhtml# https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9... Only the 1-meter active cable can.
bArray 7y ago
The mystery might not even be completely solved then, have you confirmed that it's not performing some unwanted compression to get your data over a lower-bandwidth cable? Maybe a good indication would be to check your CPU usage before and after using 5Gb/s and 10Gb/s cables. Even then it's not a great indication, many modern processors have dedicated modules on the CPU for video compression/decompression (given how large the use case is, it makes sense). And then you have other factors that may prevent you getting full speed: * Connection between the cable and the device on both sides (oxidization, scratches, etc) * Manufacturing flaws or damage during delivery/use in the cable (un-shielded areas, breakages in the cable, imperfections in metals, etc) * Temperature - if you're pulling 20W through this cable it's not entirely impossible you might start noticing some heat, especially if it wasn't designed to take the power draw (increased heat due to power pull = greater resistance = worse signal) My pointy is, as we turn up the requirements of these cables, just making sure they deliver on their promises will become more difficult. Most people won't have an oscilloscope that can even measure these cables anymore and just the act of putting the oscilloscope on the lines increases capacitance and changes how the signal looks. A while back I had issues with two Ethernet cables (CAT 7 I think), both straight out of the packet, one performed at half speed and the other at full. I was tearing my hair out for a while before I realized why the network was bottle necked.
jrochkind1 7y ago
Why don't they give NAMES to these different types of cables? They seem to have either no names or too many names where it's unclear what is intended for the consumer. Just giving the cable a clear name (in words, not icons), so you could know what you were buying, and a device could say "you need this kind of cable", and a person could write a blog saying "to support DP-Alt-Mode you need X kind of cable" and all use the terminology... would seem to go a long way. It seems odd that the USB people have not figured this out. We can't even figure out what the CALL em all consistently.
- ajross 7y ago
  > Why don't they give NAMES to these different types of cables? Exactly! We can call the one for small peripherals "USB", the one for monitors "VGA", the one for networking "ethernet", the one for power "AC"... I suspect most users can figure out how to manage that. Snark aside, I actually agree with you. The market powers that be completely messed this up. Basically, phones have limited port space. And for their benefit, and only their benefit, we've tried to cram together the entirety of device I/O into one multi-pronged standard that was clearly never going to work. And those phones? Their fancy USB-C ports are almost exclusively idle. A median high end phone never does anything with that port it couldn't have gotten with a single barrel connector with ~10V DC.
  - Godel_unicode 7y ago
    Camera connectors and card readers work on most Android phones, and it's awesome to be able to swap them back and forth with my laptop. If you work at it a little so do USB drives and yubikeys. I can also charge my laptop, phone, camera, headphones, and tablet from one charger. I'll take 10 minutes extra effort every few years to order the correct cable in exchange for that...
  - Dylan16807 7y ago
    > Exactly! We can call the one for small peripherals "USB", the one for monitors "VGA", the one for networking "ethernet", the one for power "AC"... I suspect most users can figure out how to manage that. Wrong kind of names. For these cables, all you should need to know is a speed rating. And they almost work that way, but the ball got dropped in a few places and the cables are badly labeled, so it turns into a nightmare. > And for their benefit, and only their benefit, we've tried to cram together the entirety of device I/O into one multi-pronged standard that was clearly never going to work. I can't agree at all with that. The needs of phones were already satisfied by USB micro, long before any of this cramming started. USB-C's complication is not because of phones. And even though the data connection is rarely used, it sucks to not have it available for file transfers and backups and tethering. And barrel plugs are terrible for charging on the go. You have far fewer outlets than USB, and there are too many different sizes.
virtualwhys 7y ago
> After buying a screen which has only a USB-C DP-Alt-Mode input OT, but what screen did you buy? I'm in the market as well for a USB-C powered travel monitor and was about to head down the what-cable-works rabbit hole.
PhasmaFelis 7y ago
I didn't even know they made 2.0/C cables.
- kalleboo 7y ago
  The USB-C Charge Cable that Apple includes with their laptops is a 2.0 cable... (that supports 87W PD)
rcthompson 7y ago
Wait a minute, USB-C Thunderbolt 3 cables are also USB-C to USB-C cables, aren't they? Why aren't they included in this article? I guess there's 6 kinds of USB-C to USB-C cables, except for all the other kinds of USB-C to USB-C cables. How many are there really?
- fyfy18 7y ago
  TB3 is not part of the USB-C spec, they just happen to use the same connector. The cables are usually backwards compatible.
  - rcthompson 7y ago
    I know TB3 is not USB-C, but as long as a TB3 cable is USB-C compatible (can you really call it "backward" compatible if TB3 is not USB?), that cable is a USB-C cable. You can use it to connect 2 USB-C devices. That means there is more than 6 kinds of cables you can use to connect USB-C devices to each other, contrary to what the article says.
windexh8er 7y ago
I generalize them for friends who ask and break them down into these variants: * USB 3.1 (Type-C to Type-C) Charge Only * USB 3.1 (Type-C to Type-C) Charge and Data @5Gb * USB 3.1 (Type-C to Type-C) Charge and Data @10Gb * Thunderbolt 3 (Type-C to Type-C) Charge and Data @20Gb * Thunderbolt 3 (Type-C to Type-C) Charge and Data @40Gb I believe 5/20Gb cables are generally rated at 65W and 10/40Gb cables at 100W. But like you've noted there's no standard labeling. So it's hard to find what you're looking for half the time. It's just easiest to find Thunderbolt 3 cables since those are backwards compatible and if you buy the 40Gb ones you're going to be safer with regard to plugging both your laptop into a charger and your phone.
- cududa 7y ago
  I appreciate your response, but holy hell how is anyone supposed to memorize all that to buy a damn laptop or phone charger

mrb 7y ago

«But is a 5Gbps cable enough? Or is a 10Gbps cable needed?» Here is the answer: if you need DisplayPort 1.0-1.2, a 5 Gbps cable is enough. If you need DP 1.3-1.4 (where they upped the transfer rate for higher resolution and fps,) you need a 10 Gbps cable. If you need DP 2.0 (I don't think products are out yet, the standard was finalized last month,) you will need a USB4 20 Gbps cable.

djsumdog 7y ago
DP1.2a should be enough for 60Hz at UHD/2160p. 1.4 is needed for HDR support, 5K, higher refresh rates, etc.
- kllrnohj 7y ago
  DP 1.2a goes up to 21.60 Gbit/s, and 4k 60hz (which does work fine over 1.2a) needs 12.54 Gbit/s. I'm not sure how the 5Gbit/s and 10Gbit/s USB-C cables fit into this. It's obviously not just based on the cable's "rated" bandwidth, as if it was neither the 5Gbit/s nor 10Gbit/s connection would work at all for display. But it does, so it must not be, so what is it? Is it 5Gbit/s per twisted pair? That would make sense as displayport uses 4 pairs so 4 * 5 comfortably gets you the 12.54 with plenty left over for regular data. But then it would matter for the 10gbit/s cables if it's talking about superspeed 1x2 (2x5gbit/s) or 2x1 (1x10gbit/s).
  - mrb 7y ago
    «I'm not sure how the 5Gbit/s and 10Gbit/s USB-C cables fit into this.» A USB3 cable has 4 differential pairs. When in alt mode, all 4 pairs transmit in the same direction, so a 5 Gbit/s cable can transmit 20 Gbit/s.

derefr 7y ago

The answer is supposed to be easy; it's "you need to buy one of those really expensive USB-C Thunderbolt 3 cables, because those cables—the ones that do everything—are supposed to be the only type of USB-C cables." USB-C cables are supposed to be universal, i.e. have all the features, all the time; and thus, USB-C cables should (in 2019) be very expensive. Any USB-C cable that isn't very expensive (in 2019) isn't following the standard.

Dylan16807 7y ago
There are plenty of cables that are cheap and support everything that's actually in a USB standard. They only go up to 1 meter, though. Even thunderbolt 3 isn't too expensive over short cables. They don't need to be expensive. At the other end of the spectrum, there don't seem to be any cables that support both thunderbolt 3 and USB 3 at 2 meters, no matter how much you're willing to spend.
sambroner 7y ago
Can you link to some cables that are certified to implement the entire standard? Even that has been difficult for me to find.
- breatheoften 7y ago
  I actually don’t think any of the above commentary is true. More expensive doesn’t necessarily mean more support ... thunderbolt is not usb-c even tho they have the same connector on the end ... If you are in the market for an expensive and long thunderbolt cable — caldigit makes one. I just bought it and felt annoyed at paying 50 dollars for a cable — but I’m also glad for the technology needed to make this cable possible to exist so ... maybe I can swallow this as funding the future? https://www.amazon.com/CalDigit-Intel-Certified-Thunderbolt-Cable/dp/B01N4MFG7J/ref=sr_1_3?crid=32KJAAZAWWY9A&keywords=caldigit+thunderbolt+3+cable&qid=1562854004&s=gateway&sprefix=caldigit+thun%2Caps%2C159&sr=8-3 https://www.amazon.com/CalDigit-Intel-Certified-Thunderbolt-...
ben-schaaf 7y ago
> USB-C cables are supposed to be universal I may be wrong here, but from what I understand this doesn't seem to be the case (DP, Thunderbolt, etc. are all "optional"). It would also mean that all cables would be limited to 50cm.

AceJohnny2 7y ago

> It needs to support DP-Alt-Mode For future reference, a Thunderbolt 3 cable (which is USB-C connector) will work.

llampx 7y ago
Also the most expensive option and limited in terms of maximum length.
- djsumdog 7y ago
  How are the Thunderbolt cables wired? Do they have more than the 10 USB3 wires or is it just a higher standard of cable? Isn't USB4 = the next Thunderbolt standard?
Dylan16807 7y ago
Not true! Active thunderbolt 3 cables often only support thunderbolt 3.
- AceJohnny2 7y ago
  Per the Thunderbolt FAQ [1] > What is Thunderbolt 3? > Computer ports with Thunderbolt 3 provide 40Gbps Thunderbolt – double the speed of the previous generation, USB 3.1 10Gbps, and DisplayPort 1.2. I'm curious: which active cable did you use that didn't support DP? [1] https://thunderbolttechnology.net/tech/faq https://thunderbolttechnology.net/tech/faq
  - Dylan16807 7y ago
    Note: This cable does not support native DisplayPort 1.2 or Thunderbolt 3 connections to a DisplayPort monitor. https://amazon.com/StarTech-com-Thunderbolt-Cable-40Gbps-Charger/dp/B01N9J47EG/ https://amazon.com/StarTech-com-Thunderbolt-Cable-40Gbps-Cha... Regular USB-C monitor is not support, USB 3.1/3.0/2.0 and USB-C is not support https://amazon.com/Thunderbolt-Certified-Nekteck-Compatible-Alienware/dp/B074JZVD2M/ https://amazon.com/Thunderbolt-Certified-Nekteck-Compatible-... USB 2.0 ️[check], USB 3.0 [ ], DisplayPort [ ] https://amazon.com/Belkin-Thunderbolt-Cable-Feet-Meters/dp/B072KPBKS3/ https://amazon.com/Belkin-Thunderbolt-Cable-Feet-Meters/dp/B... Can you point me to any 2-meter thunderbolt@40GHz cable that does support USB 3 and/or DisplayPort? None of the ones in this chart can do it: https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9dMDWqENiY2kgBJUu29f_TX8/pubhtml# https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9... Only the 1-meter active cable can.

bArray 7y ago

The mystery might not even be completely solved then, have you confirmed that it's not performing some unwanted compression to get your data over a lower-bandwidth cable? Maybe a good indication would be to check your CPU usage before and after using 5Gb/s and 10Gb/s cables. Even then it's not a great indication, many modern processors have dedicated modules on the CPU for video compression/decompression (given how large the use case is, it makes sense). And then you have other factors that may prevent you getting full speed: * Connection between the cable and the device on both sides (oxidization, scratches, etc) * Manufacturing flaws or damage during delivery/use in the cable (un-shielded areas, breakages in the cable, imperfections in metals, etc) * Temperature - if you're pulling 20W through this cable it's not entirely impossible you might start noticing some heat, especially if it wasn't designed to take the power draw (increased heat due to power pull = greater resistance = worse signal) My pointy is, as we turn up the requirements of these cables, just making sure they deliver on their promises will become more difficult. Most people won't have an oscilloscope that can even measure these cables anymore and just the act of putting the oscilloscope on the lines increases capacitance and changes how the signal looks. A while back I had issues with two Ethernet cables (CAT 7 I think), both straight out of the packet, one performed at half speed and the other at full. I was tearing my hair out for a while before I realized why the network was bottle necked.

jrochkind1 7y ago

Why don't they give NAMES to these different types of cables? They seem to have either no names or too many names where it's unclear what is intended for the consumer. Just giving the cable a clear name (in words, not icons), so you could know what you were buying, and a device could say "you need this kind of cable", and a person could write a blog saying "to support DP-Alt-Mode you need X kind of cable" and all use the terminology... would seem to go a long way. It seems odd that the USB people have not figured this out. We can't even figure out what the CALL em all consistently.

ajross 7y ago
> Why don't they give NAMES to these different types of cables? Exactly! We can call the one for small peripherals "USB", the one for monitors "VGA", the one for networking "ethernet", the one for power "AC"... I suspect most users can figure out how to manage that. Snark aside, I actually agree with you. The market powers that be completely messed this up. Basically, phones have limited port space. And for their benefit, and only their benefit, we've tried to cram together the entirety of device I/O into one multi-pronged standard that was clearly never going to work. And those phones? Their fancy USB-C ports are almost exclusively idle. A median high end phone never does anything with that port it couldn't have gotten with a single barrel connector with ~10V DC.
- Godel_unicode 7y ago
  Camera connectors and card readers work on most Android phones, and it's awesome to be able to swap them back and forth with my laptop. If you work at it a little so do USB drives and yubikeys. I can also charge my laptop, phone, camera, headphones, and tablet from one charger. I'll take 10 minutes extra effort every few years to order the correct cable in exchange for that...
- Dylan16807 7y ago
  > Exactly! We can call the one for small peripherals "USB", the one for monitors "VGA", the one for networking "ethernet", the one for power "AC"... I suspect most users can figure out how to manage that. Wrong kind of names. For these cables, all you should need to know is a speed rating. And they almost work that way, but the ball got dropped in a few places and the cables are badly labeled, so it turns into a nightmare. > And for their benefit, and only their benefit, we've tried to cram together the entirety of device I/O into one multi-pronged standard that was clearly never going to work. I can't agree at all with that. The needs of phones were already satisfied by USB micro, long before any of this cramming started. USB-C's complication is not because of phones. And even though the data connection is rarely used, it sucks to not have it available for file transfers and backups and tethering. And barrel plugs are terrible for charging on the go. You have far fewer outlets than USB, and there are too many different sizes.

virtualwhys 7y ago

> After buying a screen which has only a USB-C DP-Alt-Mode input OT, but what screen did you buy? I'm in the market as well for a USB-C powered travel monitor and was about to head down the what-cable-works rabbit hole.

PhasmaFelis 7y ago

I didn't even know they made 2.0/C cables.

kalleboo 7y ago
The USB-C Charge Cable that Apple includes with their laptops is a 2.0 cable... (that supports 87W PD)

rcthompson 7y ago

Wait a minute, USB-C Thunderbolt 3 cables are also USB-C to USB-C cables, aren't they? Why aren't they included in this article? I guess there's 6 kinds of USB-C to USB-C cables, except for all the other kinds of USB-C to USB-C cables. How many are there really?

fyfy18 7y ago
TB3 is not part of the USB-C spec, they just happen to use the same connector. The cables are usually backwards compatible.
- rcthompson 7y ago
  I know TB3 is not USB-C, but as long as a TB3 cable is USB-C compatible (can you really call it "backward" compatible if TB3 is not USB?), that cable is a USB-C cable. You can use it to connect 2 USB-C devices. That means there is more than 6 kinds of cables you can use to connect USB-C devices to each other, contrary to what the article says.

windexh8er 7y ago

I generalize them for friends who ask and break them down into these variants: * USB 3.1 (Type-C to Type-C) Charge Only * USB 3.1 (Type-C to Type-C) Charge and Data @5Gb * USB 3.1 (Type-C to Type-C) Charge and Data @10Gb * Thunderbolt 3 (Type-C to Type-C) Charge and Data @20Gb * Thunderbolt 3 (Type-C to Type-C) Charge and Data @40Gb I believe 5/20Gb cables are generally rated at 65W and 10/40Gb cables at 100W. But like you've noted there's no standard labeling. So it's hard to find what you're looking for half the time. It's just easiest to find Thunderbolt 3 cables since those are backwards compatible and if you buy the 40Gb ones you're going to be safer with regard to plugging both your laptop into a charger and your phone.

cududa 7y ago
I appreciate your response, but holy hell how is anyone supposed to memorize all that to buy a damn laptop or phone charger