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Comment by starsinspace | Hacker News Reader

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.

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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.

> 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.

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...

> 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.

Also, barrel jacks don't have just one polarity. I learned that the hard way when I fried my guitar amp as a kid.

They usually have the polarity written down, in a tiny font on a label back down on the charger. That's why I always put labels on barrel connectors, since the manufacturers can't be bothered.

Didn't EU legislation have some impact on this?

Legislation set the USB-A connector on the transformer, but not the other end of the cable.

Before the legislation, most phone chargers had the wire fixed to the transformer, and were unique to each manufacturer. The law reduced the e-waste from obsolete chargers, but didn't care so much for the wire.

This doesn't match what German Wikipedia says:

Der Micro-USB-Standard bezeichnet eine Regelung auf Basis des USB-Standards, nach der ab 2011 die Steckverbinder für die Stromversorgung von Mobiltelefonen und anderen elektronischen Geräten in Europa vereinheitlicht wurden (Norm EN 62684:2011). [...] Das Kabel kann entweder fest oder durch einen Stecker mit dem Ladegerät verbunden sein. Bei einem steckbaren Kabel ist ein Standard-USB-Stecker (Typ A) zur Verbindung mit dem Ladegerät zu nutzen.

The Micro-USB standard is a regulation on the basis of the USB standard, according to which the plug for charging mobile phones and other electronic devices has been unified since 2011 (European Norm EN 62684:2011). [...] The cable can either be fixed to the charger or connected with a plug. In the latter case a USB-A plug is to be used.

"... An Adaptor can also be a detachable cable." and Apple's non-standard connector being compliant suggests this is either permitted, or a very wide loophole in the legislation.

https://en.wikipedia.org/wiki/Common_external_power_supply#R...

> Why don't they give NAMES to these different types of cables?

The whole catchy idea behind USB-C (unfortunately perpetuated here by people who should know better) is that there is ONE SOCKET, ONE PLUG and ONE CABLE. Oh, the dream of using a single connector.

Unfortunately, this is far from reality and the result is a complete mess, which is why I'm not a big fan of the whole USB-C thing. Especially given that I'm a hostage, because a certain computer company whose computers generally suck the least, decided to show courage by moving to USB-C even though the ecosystem is nowhere near mature — let's put pressure on the manufacturers by getting hostages (oops, "users") on board.

I wish USB-C mandated some sort of connector marking: color strips, or whatever, that would let me figure out what would work.

I wish USB-C mandated one cable. Just one. If you cut anything out of it, if you did anything out of spec, it's not a valid USB-C cable anymore. You either have all features, or no features.

There's nothing benefiting customers from this cable mess. It only enables dishonest businesses, as customers can't tell cables apart until they plug them in and try to use them.

You would get usb-C bootleg cables with missing features. Instead of having USB-C branding on them, they'll have generic 'works with any modern phone!' etc.

I mean cable with all the features is damn expensive if you compare it to the usual(shitty quality) USB2.0 cables. Most folks would buy cheaper one because difference in prices between USB2.0 and USB-C with all features would be too high. It would feel like a rip-off to them.

You'd still get the problem of devices either supporting various modes or features or not.

The whole idea of "one connector that does everything" is flawed, unless you standardize what "everything" means and give users visual clues. Such as, oh, a different type of connector, like we used to have.

I get precisely ZERO benefit from using a USB-C connector for my monitor, I only get a large amount of pain.

You're right.

The line I'm trying to stride here is, on the one hand, avoiding what USB-C ended up being, but on the other hand not returning back to the days of feature phones, where you had as many physically and electrically distinct charger and data ports as there were phone models. There must be a sane state somewhere in the middle.

There is. USB 3.0 micro.

That would certainly mean cutting features. Thunderbolt limits the length of the cable to ~50cm, but that's way too short for a power cord.

Thunderbolt 3 cables can definitely be different from fully featured USB-C cables though. They're also labelled differently, with the Thunderbolt lightning bolt mark.

I read somewhere that they are going to merge Thunderbolt in the USB 4 spec, so they won't be so different soon :)

> Unfortunately, this is far from reality and the result is a complete mess, which is why I'm not a big fan of the whole USB-C thing. Especially given that I'm a hostage, because a certain computer company whose computers generally suck the least, decided to show courage by moving to USB-C even though the ecosystem is nowhere near mature — let's put pressure on the manufacturers by getting hostages (oops, "users") on board.

I still remember when the iMac came out with two USB ports, a CD drive, and nothing else. It was a couple of years too early, or did it prove that you could make a successful computer without vital things like a parallel port and a floppy drive?

> Especially given that I'm a hostage, because a certain computer company whose computers generally suck the least, decided to show courage by moving to USB-C

Since when was USB-C such a major issue on Thinkpads?

They did, kind of. USB2, USB3.1 gen 1, and USB 3.1 gen 2 are 480mbps, 5gbps/DP-alt-mode and 10gbps/DP-alt-mode, respectively. The problem is really that people won't remember that distinction unless they need to know it regularly, and unless you know to Google "difference between USB 3.1 gen 1 gen 2" you won't be able to figure it out.

All they need to do now is to drop the name USB in favour of SPC/OSB - Single Purpose Cable w/ Optional Serial Bus.

The whole thing makes a mockery of the core reason for USB to exist, which was so we wouldn't need a unique cable for each device. And so here we are...

Thats absolutely right as the U stands for universal, and theres nothing universal in it anymore

Have you ever seen those names on a box or Amazon listing?

I have been told those names were not intended for the consumer. (And indeed "USB 3.1 gen 2" vs "USB3.1 gen 1", seriously?).

I think there is another set of names, also inconsistent and unparallel with each other or the first set of names, intended for the consumer, that nobody can seem to figure out.

More precisely: "Why don't they give them _reasonable_ usable names, and only one set so everyone uses the same one?"

This still seems to be an obvious part of the design of the product to me.

I think the GP also meant more memorable names.

Would be easier to rename "USB 3.1 gen 2" -> "USB 3.2".

And the latter two would be "USB 3.3", "USB 3.4", problem solved :)

They really only ever make it worse.

Initially, there was USB 3.0 at 5Gbps, USB 2.0 at 480Mbps, and USB 1.1 at 12 Mbps.

Then, when they added a 10Gbps mode, they called it USB 3.1 Gen 2, and renamed USB 3.0 to USB 3.1 Gen 1.

They already have plans for USB 3.2: 5Gbps will be USB 3.2 Gen 1, 10Gbps will be USB 3.2 Gen 2, and 20 Gbps will be USB 3.2 Gen 2x2. Yup, Gen 2x2 is next.

And there is no more USB 3.0 - presumably no vendor wants to have to sell an older number, so they rename them all so consumers are confused and think they are all the latest 3.x

ref: https://arstechnica.com/gadgets/2019/02/usb-3-2-is-going-to-...

At this point, I don't blame Apple for holding on to Lightning.

As soon as its phones go USB-C, they're going to have to deal with half a million people on the internet complaining that their junk shop cable doesn't work right or do what they thought it would.

> their junk shop cable doesn't work right

This already happens though. I have a dollar store "Lightning" cable that only has a third of the pins and only works one way.

So apparently, according to TFA, the DP capable cables are "SuperSpeed" and marked with an SS.

Learning just that one fact made it worth the click. I now know to just always look for SuperSpeed (or the SS marking) on any cable I buy.

If we could just all start calling them SuperSpeed cables, SuperSpeed10 for 10Gbps, and I assume we will eventually have SuperSpeed20, etc... that would be just fine by me! Honestly, better marketing IMO as well.

The time for the "USB" acronym has passed. Especially since the debacle of "USB3" and Gen1 Gen2 nonsense. "SuperSpeed", optionally followed by a number which indicates a data rate would be just lovely.

it's all usb cables. that what the usb people thought up and thats how u call em. on that note, a lot of usb cables seem broken :D

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.

Note that Thunderbolt 3 is not part of the USB 3.2 standard. It's the basis for USB 4, but right now to be fully standards compliant with everything USB-C itself can fully do you do not need to be Thunderbolt 3 compatible, because thunderbolt 3 is not part of the spec at all.

And even if you wanted to be Maximum Compatibility even with Thunderbolt 3 you may not have that option as TB3 tops out at a cable length of 2 meters, and at that length you're dealing with half-rate bandwidth (just 20Gbps instead of the full 40Gpbs - which you only get up to 0.5m)

> Note that Thunderbolt 3 is not part of the USB 3.2 standard.

It may be better to say that Thunderbolt 3 is a 'superset' of USB: TB is its own protocol, which allows for the carrying of USB over it (as well as PCIe and DisplayPort).

> isn't following the standard

This is just plain wrong.

The USB standard explicitly allows cables that have a USB-C connector and don't support any USB features above USB 2.0.

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.

> 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.

There was the design intent, and then there was the final standard.

The USB-IF is composed of manufacturers that wanted to be able to cheap out on cables; so of course they made all the expensive features optional, at the expense of anything USB-C was designed to accomplish.

In an alternate world where USB-IF was headed by a benevolent-dictator-for-life, USB-C wouldn't have any optional features. (It'd also be in nearly nothing, because no manufacturer would want to pay the BOM costs of supporting it.)

> (It'd also be in nearly nothing, because no manufacturer would want to pay the BOM costs of supporting it.)

It'd be everywhere if manufacturers had no other choice. Mass production would keep the price low.

In that reality, Apple would be actually courageous for switching to USB-C and forcing everyone's hand. The EU could jump in to, and tell phone manufacturers that if they want to switch away from plain old USB, they can switch over to USB-C, but no going back to proprietary connectors bullshit. This would be a much nicer world indeed.

>Apple would be actually courageous for switching to USB-C and forcing everyone's hand.

Last time Apple was courageous ─ the headphone jack got killed. The word 'courage' was used to onboard Airpods and move the general trend towards sealing off most ingress points on a device; contemporaneously selling an adapter for a pretty penny.

Whilst I agree that some manufacturers followed the above-mentioned trend. They were not pushed, but rather jumped willingly, as it made financial and commercial sense by applying the maxim - where Apple leads, others must usually follow. There were also unsubstantiated rumours of Apple abandoning their role in development of USB-C implementation, perhaps due to the lack of a moat[0]. Nevertheless, I don't expect them to be altruistic in their motives and fully expect them to monetise the USB-C standard via a plethora of cables and dongles, possibly under the umbrella of MFi program, especially targeting the lack of certification and/or the vacuum/ambiguity created by USB-IF, leaving the rest of the field to carry on dealing with the existing issues.

Also, I would much rather put up with the current botched up state of affairs, than have EU involved in meddling with it and make things even worse.

[0] https://9to5mac.com/2015/03/14/apple-invent-usb-type-c/

> Last time Apple was courageous ─ the headphone jack got killed.

Hence my use of the word "actually" - the headphone jack situation is IMO anticonsumer, not courageous.

As for EU involvement, it seems to have worked out for the best with forcing phone manufacturers to use USB for charging - I still remember the days of feature phones, where we were all drowning in phone chargers and (separate) data cables, as each brand and each model generation within the brand used different ports and voltages. It was ridiculous levels of plastic and electronics waste for the sake of business shenanigans.

>As for EU involvement, it seems to have worked out for the best with forcing phone manufacturers to use USB for charging - I still remember the days of feature phones, where we were all drowning in phone chargers and (separate) data cables, as each brand and each model generation within the brand used different ports and voltages. It was ridiculous levels of plastic and electronics waste for the sake of business shenanigans.

You are romanticising the notion of Apple and EU being the standard rod-bearers. Despite using electrical waste and dubious business practices as a reason for EU involvement, it would seem that you are unaware of the saga of the 'common charger' and the villainous role played by Apple.

A key take-away:

The EU's failure to regulate, in essence, provides Apple with an argument to keep their own solution.

For Apple, the common charger is a success story – of regulation avoided.

https://euobserver.com/news/144538

Can you link to some cables that are certified to implement the entire standard? Even that has been difficult for me to find.

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-...

I detected sarcasm. I'm not sure if that's just me or the other respondents so far have mislaid their detectors.

My Samsung phone came with a very thin USB-C cable that only supports USB 2.0 speeds. I think that's following the standard.

«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.

DP1.2a should be enough for 60Hz at UHD/2160p. 1.4 is needed for HDR support, 5K, higher refresh rates, etc.

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).

«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.

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.

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

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?

TB3 is not part of the USB-C spec, they just happen to use the same connector. The cables are usually backwards compatible.

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.

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.

> It needs to support DP-Alt-Mode

For future reference, a Thunderbolt 3 cable (which is USB-C connector) will work.

Not true! Active thunderbolt 3 cables often only support thunderbolt 3.

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

What you quote is not related at all to what Thunderbolt cables support beside Thunderbolt. It just states that you can use Thunderbolt to transmit DisplayPort signals. By that you're utilizing the Thunderbolt alternate mode to tunnel DisplayPort signals, instead of using the DisplayPort alternate mode [1]. Using Thunderbolt to transmit DisplayPort signals only works with devices which support Thunderbolt, not with screens supporting "just" DisplayPort. To make confusion even worse: All existing Thunderbolt controllers also support the DisplayPort alternate mode, so a lot of people who believe they're using Thunderbolt are probably just using the DisplayPort alternate mode instead. Afaik Thunderbolt cables usually support both, but I'm not sure if that's mandated somehow.

[1] https://en.wikipedia.org/wiki/USB-C#Alternate_Mode_partner_s...

Thanks for the clarification.

What a clusterfuck of a standard.

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-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-...

USB 2.0 ️[check], USB 3.0 [ ], DisplayPort [ ] 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/1vnpEXfo2HCGADdd9G2x9... Only the 1-meter active cable can.

Well shit, I stand corrected. Thanks for the links!

Also the most expensive option and limited in terms of maximum length.

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?

> 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.

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

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

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