PSA: For Thunderbolt 3 over distance; use *OPTICAL Thunderbolt 1/2 cables!*

[Hessel89]

No, this in entirely incorrect and/or unrelated.

Dude calm down lol. How’s it unrelated? The Mac Pro’s in the Apple store are utilizing the exact same solution. My point is that you can’t prove it’s 5K by simply consulting system ID. Yes, the 5K is rendered internally, but then downscaled to fit through a TB2 cable. But hey if believing it is 5K makes you happier, go ahead. Most people can’t really discern the difference anyway.

 

[jimthing]

@Hessel89 and @Detnator – OK, so I'm going to retest this in a couple of days, as it's been bugging me, again!

Is there anyway you may suggest I can prove (or disprove) to you that the display is working at full 5K when doing this; because AFAICT the evidence I gave from the System Info before accurately describes this (as otherwise it'd say the lower resolution, given that's what Sys Info is designed to do)?

I have available:
- both 10m (30ft) and 30m (100ft) optical Thunderbolt 1/2 cables.
- two different 2m non-optical copper Thunderbolt 3 cables (one the original LG-supplied, the other CalDigit: both are active full-40Gb/s 100W cables).
- two different 2m non-optical copper Thunderbolt 1/2 cables (1x WD and 1x StarTech).
- 3x Apple TB 1/2<>3 adapters.

Please do let me know, as I genuinely want to give accurate results to other MR users.
And as you've kept insisting Sys Info is giving (apparently) wrong results, I'd be interested to find out. Thanks.

 

[Detnator]

@Hessel89 and @Detnator – OK, so I'm going to retest this in a couple of days, as it's been bugging me, again!

Is there anyway you may suggest I can prove (or disprove) to you that the display is working at full 5K when doing this; because AFAICT the evidence I gave from the System Info before accurately describes this (as otherwise it'd say the lower resolution, given that's what Sys Info is designed to do)?

I have available:
- both 10m (30ft) and 30m (100ft) optical Thunderbolt 1/2 cables.
- two different 2m non-optical copper Thunderbolt 3 cables (one the original LG-supplied, the other CalDigit: both are active full-40Gb/s 100W cables).
- two different 2m non-optical copper Thunderbolt 1/2 cables (1x WD and 1x StarTech).
- 3x Apple TB 1/2<>3 adapters.

Please do let me know, as I genuinely want to give accurate results to other MR users.
And as you've kept insisting Sys Info is giving (apparently) wrong results, I'd be interested to find out. Thanks.

Unfortunately, I don't really have any answers to this. What I do know is that what System Info is presenting appears to be unreliable, based on what I know about other Macs, particularly the cylinder Mac Pro. And so: "as otherwise it'd say the lower resolution, given that's what Sys Info is designed to do" isn't reliable in this scenario.

So, I'm sorry to say I don't know what to advise or suggest here, other than perhaps to say that what we know about the specs is what we do have, and maybe we just go with that. Sorry I can't be much more help on that.

 

[theluggage]

This '5K' comment of theirs being entirely unprovable, as not a single non-TB3 vanilla USB-C 5K3K exists on the market, circa four months since they announced/released the 2018 iPad Pros.

Here's one: https://iiyama.com/gb_en/products/prolite-xb2779qqs-s1/ - not sure if its in the shops yet, but its a 'vanilla' DisplayPort 1.4 so the iPad should be able to drive it with a USB-C to DP adapter that meets USB-C standards (which always included DP1.4 - although Thunderbolt 3 didn't support that to start with). If you buy one of those and the iPad won't drive it, call a lawyer. In other news, there probably weren't any 40Gbps peripherals on the market when TB3 first launched.

But the Apple TB3 to TB2 adapter is not capable of anything more than TB2 bandwidth

That's a plausible claim, but its not definite without more details of exactly what the TB2-3 adapter does. Your claim assumes that the adapter is effectively a box with a TB2 controller, an internal PCIe/DisplayPort bus and a TB3 controller. It wouldn't apply to a purely passive, physical plug adapter. AFAIK the TB2-TB3 adapter is neither of those things.

Don't get me wrong - If I had to bet $5 I'd put it on you, but as it stands its not evidence enough to conclusively debunk an claim of "but it actually works".

Is there anyway you may suggest I can prove (or disprove) to you that the display is working at full 5K when doing this;

Create a bitmap with alternating fine black and white stripes, resize it until you can only just distinguish the stripes when squinting close-up on your definitely-5k screen, measure its real-world-size with a ruler, then display it on the maybe-5k screen and check with the ruler that its the same physical size. Then, photos or it didn't happen - screenshots are no good because they're always at 2x the 'looks like' resolution, not what actually gets sent to the screen.

...but first, make sure that your 5k screen really is running in 5k mode even with the TB3 cable. The difference between "looks like 2560x1440" on a 5k display (actually 5120x2880 with HiDPI) and "looks like 2560x1440" (the same image, downsampled to 4k) is there, but its not night-and-day. Also, the 'default/best for display' screen modes chosen by MacOS may change when you change the connection.

The information from System Info is tricky because it sometimes shows the "looks like" resolution (e.g. for external/3rd party displays) and sometimes the actual physical resolution (e.g. for internal displays).

 

[Alan Wynn]

Spoke to the Corning rep at NAB. He was showing their Thunderbolt 3 optical cable and said it should be out within a month or two (likely by WWDC, but that was just a target). Same prices and lengths as the Thunderbolt 2 versions. Looking forward to this.

 

[jimthing]

Spoke to the Corning rep at NAB. He was showing their Thunderbolt 3 optical cable and said it should be out within a month or two (likely by WWDC, but that was just a target). Same prices and lengths as the Thunderbolt 2 versions. Looking forward to this.

Sure, but at this stage I'll believe it when I see it.
Other sources in the past have said it's not possible to do optical TB3 because of all the various different protocols it's supposed to do.

Colour me skeptical for the moment.

 

[theluggage]

Other sources in the past have said it's not possible to do optical TB3 because of all the various different protocols it's supposed to do.

That's just the good old TB3 vs. USB-C vs. USB 3.1 / USB-C DisplayPort alt mode vs. DisplayPort over Thunderbolt confusion (and the general "USB-C means whatever I choose it to mean" problem).

A TB3 optical cable would be just the TB-3 protocol, and wouldn't offer all the other USB-C features - power, USB 3.1, DisplayPort alt mode etc. The same is true of the existing optical TB2 cables - they don't offer the power or legacy DisplayPort features of the regular copper TB2 cables. Same applies to some "active" copper TB3 cables (certainly the earlier ones) that didn't do USB 3.1.

There's no real problem with that - just hang the appropriate Thunderbolt-to-whatever adapter on the far end of the cable. In fact, if the peripheral you're using has a thunderbolt 3 "through" port, that can still act as a full-featured USB-C port - because the TB3 protocol itself carries 2 DisplayPort streams and the USB 3.1is provided by the peripheral's TB3 controller chip.

The only practical upshot is that you'd need at least one "proper" TB3 device on the end of the cable - you'd lose the 'economy' option of hanging a cheap USB/DisplayPort device directly off the cable - and it would need to be powered - which is going to apply to any sort of optical connection... but if you're going optical then you wouldn't expect the "economy option".

 

[Kier-XF]

They are apparently coming... 'soon'.

https://twitter.com/macvfx/status/1115746090177818624

 

[Luba]

That's just the good old TB3 vs. USB-C vs. USB 3.1 / USB-C DisplayPort alt mode vs. DisplayPort over Thunderbolt confusion (and the general "USB-C means whatever I choose it to mean" problem).

A TB3 optical cable would be just the TB-3 protocol, and wouldn't offer all the other USB-C features - power, USB 3.1, DisplayPort alt mode etc. The same is true of the existing optical TB2 cables - they don't offer the power or legacy DisplayPort features of the regular copper TB2 cables. Same applies to some "active" copper TB3 cables (certainly the earlier ones) that didn't do USB 3.1.

There's no real problem with that - just hang the appropriate Thunderbolt-to-whatever adapter on the far end of the cable. In fact, if the peripheral you're using has a thunderbolt 3 "through" port, that can still act as a full-featured USB-C port - because the TB3 protocol itself carries 2 DisplayPort streams and the USB 3.1is provided by the peripheral's TB3 controller chip.

The only practical upshot is that you'd need at least one "proper" TB3 device on the end of the cable - you'd lose the 'economy' option of hanging a cheap USB/DisplayPort device directly off the cable - and it would need to be powered - which is going to apply to any sort of optical connection... but if you're going optical then you wouldn't expect the "economy option".

Is there a standard way that manufacturers label their cables so we know what it's capable of?

 

[theluggage]

Is there a standard way that manufacturers label their cables so we know what it's capable of?

There are some standard logos - whether or not particular manufacturers use them consistently is another matter:

https://en.wikipedia.org/wiki/USB-C#/media/File:USB-C_Protocol_Chart.png

...and I'm not sure if they cover all the bases (like will "active" 40Gbps TB3 cables > 0.5m carry USB 3.1 and DisplayPort, or charge up to 100W? Early ones could not, although that might have changed today).

 

[jimthing]

And prices? I bet they won't have come down, will they.

The most popular 10m length TB1/2 ones were ~$250. I bet this isn't gonna be any less, unfortunately. Especially given copper active TB3 cables max-out at just 2m, compared with 3m for TB1/2.

More need for being forced to use an optical cable with TB3's even more limited copper max length. :-/

What's more annoying is I have a spare brand new/unused/boxed full-length 60m Corning optical TB1/2 cable (originally costing £1000) that I don't need. Bugger.

 

[joevt]

Thunderbolt has four lines, two for receive and two for transmit.

A Thunderbolt 3 port transmits bits at 20 Gb/s over two lanes (displayed as "Current Link Width: 0x2" in System Information.app). The two lanes are aggregated together (displayed as "Speed: Up to 40 Gb/s x1" in System Information.app).

A Thunderbolt 2 port transmits bits at 10 Gb/s and also has two lanes (20 Gb/s total).

A Thunderbolt 3 port transmits at Thunderbolt 2 speeds if you use a Thunderbolt 3 cable that does not support 40 Gb/s or if you use an Apple Thunderbolt 3 to Thunderbolt 2 adapter. This appears as Speed: 20 Gb/s x1 (Current Link Width: 0x2). I have also seen a case that has "Speed: Up to 20Gb/s x2 Current Link Width: 0x1" which might mean that one of the lines is not being used because of a link negotiation problem (bad cable?).

20 Gb/s is not enough for 5K. This is true for both copper and optical Thunderbolt 2 cables.

To prove a display is running at 4K 60Hz instead of 5K 60 Hz, use SwitchResX to view the timing information of the current resolution. The pixel clock will be > 900 MHz for 5K and < 600 MHz for 4K.

 

[jimthing]

Well these optical TB3's still aren't available yet, seemingly.

But in the meantime, several sites have noticed the ncgMP (new cheese grater Mac Pro) has special 'Pro' versions of the copper TB3 cables, with one coming in at 3m length (over the previous max 2m seen up to now).

https://www.apple.com/mac-pro/specs

Interesting. No doubt they'll be $1000 too, lol!

 

[jimthing]

New info has also come to light, perhaps pertaining to the delays in long optical TB3 cables arriving over the last nearly 3-years.

See here:
https://macperformanceguide.com/blo...ating-killing-Thunderbolt-optical-cables.html

tl;dr:
Apparently Corning didn't realise the TB1/2 spec didn't mandate thermal dumping on the TB port was not allowed. Meaning at least on some TB2 hosts (possibly TB1 hosts too, though that's not clear from the article), heat was dumped through the TB port, shortening the cables lifespan.

Optical TB3 cables shouldn't have the problem, as the spec disallows such behaviour.

Interesting. But where the heck are these optical TB3 cables... Are we ever actually going to see their commercial availability at an affordable price, anytime soon, you have to wonder??

 

[shansoft]

I have personally tried this before, the actual resolution on the screen using ResX isn't real 5K when using optical TB2. T
hough it did show 2880x1440 in system info for some reason.

If you look at the actual pixel on display, it's much blurry than true 5K connection using TB3.

IIRC, 5K is using about 28Gbps bandwidth, no way TB2 can handle that unless you running at 30Hz or less color mapping.

 

[jimthing]

Another connected point...

One has to wonder if companies like Corning et al. are holding this back and waiting for (40 Gb/s) USB4 to be properly released, so they have a larger audience for the optical cable? (USB4 was announced back in Mar 2019.)

According to info online, USB4 is "compatible with Thunderbolt 3", making it more versatile a cable able to connect to both TB3 devices and seemingly all versions of USB (well 3.x and 2.x, at least; with those cheap $2 adapters on the cable):

https://en.wikipedia.org/wiki/USB#USB4

 

[jimthing]

They are apparently coming... 'soon'. [May 15, 2019]

https://twitter.com/x/status/1115746090177818624

Lol, 'soon' meaning... never? Nearly 6-mths later and... nothing. :-(

This is especially annoying given we can all see one in the above photo (though I suppose it could be a semi-functioning dummy for display only, perhaps)! Yet they cannot seemingly get it together and actually manufacturer them for retail.

One only wonders if the release of the Mac Pro soon might be a justifiable reason to suddenly announce them for the 'super pro' market who'll likely need them and might buy them in enough quantity. Who knows at this stage.

 

[joevt]

Lol, 'soon' meaning... never? Nearly 6-mths later and... nothing. :-(

 

[jimthing]

Great link, thanks!

Yeah on further investigation I found the press release from an apparent Sonnet/Archiware demo at IBC 2019 event:
https://www.sonnettech.com/news/pr2019/pr091119-sonnet-archiware.html

As ever, more of this endless "coming soon" business, but at least we know 50m is likely to be the longest length, presumably also with shorter lengths... if we ever actually see them for sale, that is. ;-)

Guessing monsieur Linus got one/some magically sent to him from Corning PR for a future just-before-release video, and given the video is dated 14 Oct 2019, hopefully that means sooner rather than later. Lucky git, lol.

 

[joevt]

Great link, thanks!

Yeah on further investigation I found the press release from an apparent Sonnet/Archiware demo at IBC 2019 event:
https://www.sonnettech.com/news/pr2019/pr091119-sonnet-archiware.html

As ever, more of this endless "coming soon" business, but at least we know 50m is likely to be the longest length, presumably also with shorter lengths... if we ever actually see them for sale, that is. ;-)

Guessing monsieur Linus got one/some magically sent to him from Corning PR for a future just-before-release video, and given the video is dated 14 Oct 2019, hopefully that means sooner rather than later. Lucky git, lol.

Hopefully the cable will work with different signals: USB2 (1.1 to 480 Mbps half-duplex), USB3 (5 Gbps) USB4 (10 and 20 Gbps x2 duplex), Thunderbolt (10.3125 and 20.625 Gbps x2 duplex), DisplayPort (2.7, 5.4, 8.1 Gbps x4 simplex). I don't think a real Thunderbolt 40 Gbps cable works with all those other signal types so there may be similar compromises with an optical Thunderbolt cable. They might have different optical cables for different USB-C alt modes. USB2 uses the same pins for send/receive - can you do that with a single optical cable? USB 3.x with DisplayPort alt mode has pins with different speeds. Would the cable consist of a single optical fibre with different wavelengths for each pin? Or a different optical fibre for each pin? A diagram of the Thunderbolt 2 cable indicates two transmitters and two receivers which rules out DisplayPort x4 in that case. They have a separate USB Type A cable but it maxes out at 5 Gb/s. Interestingly, a diagram shows only a single transmitter and receiver, so how can it do USB 2.0 and 3.0 at the same time?

 

[jimthing]

Hopefully the cable will work with different signals: USB2 (1.1 to 480 Mbps half-duplex), USB3 (5 Gbps) USB4 (10 and 20 Gbps x2 duplex), Thunderbolt (10.3125 and 20.625 Gbps x2 duplex), DisplayPort (2.7, 5.4, 8.1 Gbps x4 simplex). I don't think a real Thunderbolt 40 Gbps cable works with all those other signal types so there may be similar compromises with an optical Thunderbolt cable. They might have different optical cables for different USB-C alt modes. USB2 uses the same pins for send/receive - can you do that with a single optical cable? USB 3.x with DisplayPort alt mode has pins with different speeds. Would the cable consist of a single optical fibre with different wavelengths for each pin? Or a different optical fibre for each pin? A diagram of the Thunderbolt 2 cable indicates two transmitters and two receivers which rules out DisplayPort x4 in that case. They have a separate USB Type A cable but it maxes out at 5 Gb/s. Interestingly, a diagram shows only a single transmitter and receiver, so how can it do USB 2.0 and 3.0 at the same time?

If it's similar to my current Corning optical TB1/2 cables, it'll only do TB3 and no USB modes at all. Maybe also limited TB3 functionalities that perhaps might need a TB3 dock at the end where you might want to connect certain devices it might not natively support on its own.

Although given TB3 shares the USB-C connector type, it'll be interesting to see what these actually offer.

 

[jimthing]

Well these optical TB3's still aren't available yet, seemingly.

But in the meantime, several sites have noticed the ncgMP (new cheese grater Mac Pro) has special 'Pro' versions of the copper TB3 cables, with one coming in at 3m length (over the previous max 2m seen up to now).

https://www.apple.com/mac-pro/specs
View attachment 841707

Interesting. No doubt they'll be $1000 too, lol!

Well, Mac Pro day arrived, and now we do not have the 3 metre version of the cable. To be specific, it's not listed anywhere on Apple's site currently anymore.

FWIW, Apple are supplying a 2 metre "Apple Thunderbolt 3 Pro Cable" with the XDR Display (it is braided apparently), but that's not for sale separately as of now. Go figure. :-/

 

[jimthing]

BING BONG... your attention please...

Optical TB3 cables have FINALLY been announced! See main thread below:

Optical Thunderbolt 3 Cables Begin Rolling Out in Lengths Up to 50 Meters

The Thunderbolt 3 standard has been available for roughly four years now, but cable lengths have so far generally been limited to a couple of meters due to signal degradation over long distances of copper wiring. While the use of copper Thunderbolt 3 cables limits their length, it does allow for...

forums.macrumors.com

(strong suggestion to keep comments on the above thread, rather than this now obsolete one, please!)

 

[Detnator]

Yep. I saw that too. Exciting stuff and about time. lol. Thanks for sharing. I'll go play in that thread from here.