Dell D6000 USB-C Extension Wire

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@Omzy  The cable claims to support all of the correct specs. However, there is a decent chance that adding an extension cable might result in a non-functional solution, even if the original cable and extension cable work separately.  The reason is that even if the individual cables in use all support the necessary characteristics, it doesn't always mean that the total assembly (dock cable plus extension) will still be able to do so.  There are limits to the length of cable that a particular type of signal will travel -- which is why for example USB-C cables that support USB 3.1 Gen 2 right now are only about 3 feet long.  In addition, using extension cables actually reduces the maximum possible length because the transition across the extension cable connectors is actually a significant source of signal loss, so using a longer single cable might work while using two shorter cables connected to each other might not.

But if you want to try it anyway despite that caveat, you would need a USB-C extension cable that supported up to USB Power Delivery up to 60W and USB 3.1 Gen 1 data.  (The D6000 carries even its video data as regular USB data since it uses DisplayLink technology, rather than using DisplayPort Alt Mode, fyi.)  And the cable you linked does claim to support both of those.

@jphughan thanks for your reply - it was very helpful.

Just one other thing I wanted to check with you before I make a purchase. The cable that I linked comes in to two lengths - 1.8m and 1m. If you look at the specs it says the 1.8m supports 5Gbps and the 1m supports 10Gbps.

The cable that I need is ideally the 1.8m one but I was wondering whether the reduced bandwidth would have an impact on the maximum video resolutions it would support?

Even if I went for the 1m one, the total length of the cable including the dock cable would be around 2m - so will this also reduce the bandwidth down to 5Gbps?

@Omzy  The questions you're asking indicate that you understand the exact problem I'm trying to explain, but unfortunately I can't predict what the results will be with those lengths.  It might even depend on how well manufactured the cables are.  For example, cable that barely performs to its specification might downgrade the entire link when used in an extension scenario, whereas a cable manufactured well enough to exceed the bare minimum quality required to meet its spec might not induce a downgrade -- and though both cables would be rated for the same feature support.

All that said, I don't think the D6000 supports USB 3.1 Gen 2 (10 Gbps) in the first place.  But using 3.1 Gen 1 definitely wouldn't affect the display setups you can run.  Technically the D6000 can run even on USB 2.0, although that isn't recommended because it will exacerbate the drawbacks already inherent in the DisplayLink "indirect display" technology that the D6000 uses.  (I wrote about those in detail in the post marked as the answer in this thread if you're curious.)  And I don't think its USB ports support 3.1 Gen 2 either, in which case using an extension cable capable of 10 Gbps wouldn't improve anything even if the extension didn't induce a downgrade -- and even if the cable incorporated into the D6000 itself supported 3.1 Gen 2, which it might not.

So if you'd like to have the total cable run length that you'd get by buying the 1.8m version, then I would start with that and see what happens.  If it works, then you got exactly what you wanted.  Just be aware that it might not.  For reference, the longest USB-C I've seen that supports USB 3.1 Gen 1 is 2m, and the longest cable I've seen that supports 3.1 Gen 2 is 1m.  But since I think you'd only need 3.1 Gen 1, maybe that will be achievable even over a cable run of 1.8m plus the length of the cable built into the D6000 and the transition loss that occurs at the coupling.  I just don't know since I haven't tried that.  Good luck!

@Omzy  Ok, well then you made your dock choice taking all of the right information into account, and based on your system and desired display setup, I would agree that you made the right choice.

Just fyi though, it's likely that the USB-C port on that system does in fact have 4 DisplayPort lanes available, but when you're using a docking station, then only 2 lanes will be available because the dock would have used the other 2 lanes within the USB-C connector to support carrying USB 3.x traffic.  If you were using something like a basic USB-C to DisplayPort cable, then you'd be able to use all four lanes for video, doubling your video bandwidth, but then you obviously lose the convenience of a dock -- and even then I think you'd only have enough bandwidth for dual 1440p.  Getting dual 1440p plus 1080p out of a single port I believe would require a system that had a Thunderbolt 3 port with two full DisplayPort interfaces wired from the GPU (i.e. 8 total lanes -- some Thunderbolt systems only wire a single interface for 4 lanes) and then a dock that supported Thunderbolt 3.  But it doesn't look like the Thinkpad 13s supports Thunderbolt 3.

Please do report back as to whether this setup works!

@Omzy  I just saw your note that you're running a triple display setup on the D6000.  That shouldn't change anything I've said above about cables, but just to amend a statement I made earlier, when the D6000 is used for only two displays, regardless of which outputs the displays are using, they both use DisplayLink "indirect display" technology.  But when it's running 3 displays, whichever display is connected to the HDMI output is run using DisplayPort Alt Mode, i.e. a native GPU DisplayPort output, not DisplayLink's "indirect display" technology that uses USB data.  As a result, using a third display is only possible when the D6000 is connected via USB-C to a system with a USB-C port that actually has a GPU output output wired to it.

The reason I say this shouldn't change anything I've said about cables is that on every USB-C cable I've seen, if it supports at least USB 3.1 Gen 1, it will also support DisplayPort Alt Mode -- because USB 3.1 Gen 1 and DisplayPort Alt Mode travel over the same types of pins within a USB-C cable.  The only reason I say "shouldn't" there is because I don't know if the cable tolerances for both of those signal types are the same.  So for example I suppose it's possible you might find that when you use an extension cable, only the two displays NOT connected to HDMI work, which could mean that your extension setup is able to carry USB data for DisplayLink, but not native DisplayPort traffic.  (And hopefully it would still be carrying data as USB 3.1 Gen 1 rather than USB 2.0, the latter of which in a USB-C cable travels over a completely different set of pins dedicated to USB 2.0.)  Again, I just don't mess with extension cables very often precisely because of these types of potential issues.

@jphughan thanks again. Yes I read your post on that thread earlier on, again very informative! To be honest I wanted to stay away from a DisplayLink dock, but it's the only one that outputs the optimum resolutions for my monitors. I have 2x 1440p and 1x 1080p.

The issue is the USB-C connection on my laptop only appears to support DP 1.2 with 2 lanes (the laptop I have is the Lenovo Thinkbook 13s-IML in case you're curios). The first dock I used was the HP G5 and this only output 1440p on one monitor and the other two were at lower resolutions. Even when I only connected the 2 1440p monitors to it, it would not output them both at 1440p.

So I figured it would be best - whilst still not ideal - to go for a DisplayLink dock that isn't restricted by the laptop itself.

@jphughan thanks - will do!

That's a bit confusing though to be honest. The HP G5 dock claims to support 2x 2.5k and 1x FHD displays, see below graphic:

You'll notice it can only do this when used in "High res DP Alt Mode (DP x4)". So this suggests it can use all 4 lanes for video where possible. Now as far as I'm aware my laptop supports DP Alt Mode but I'm not sure whether it's the "High res" variant and whether it has 4 DP lanes. The fact that it didn't output the maximum resolutions suggests probably not.

@Omzy  I can't yet see the image you uploaded since images are initially only visible to the person who uploaded them and Dell moderators until they get approved for public viewing, but I did find this QuickSpecs PDF outlining the capabilities of various docks, including the G5.  Page 5 does indeed indicate that dual QHD + FHD should be possible in High-Res Mode even from DP 1.2 systems, but only available in Multi-Function mode from a DisplayPort 1.4 system that supports DSC (DisplayPort Stream Compression).

But as far as I can tell, the choice between High Res Mode and Multi-Function is a configuration option specified on the dock somehow -- possibly through some sort of utility -- and NOT something related to the design or capabilities of the system you're using.  The documentation notes that Multi-Function is the default mode, and that when using High Res Mode, USB speeds will be limited to USB 2.0.  That all tracks with what I said above, namely that if a USB-C peripheral configures the USB-C link to dedicate all four high speed lanes within the USB-C cable to video, then it can support twice as much display bandwidth, but can only carry USB 2.0, since USB-C connectors have pins dedicated solely to USB 2.0 data.  If on the other hand it configures the USB-C link to carry USB 3.x, it has to allocate two high speed lanes to do that, which cuts display bandwidth in half.  Most docks only operate in what HP calls Multi-Function mode and don't allow this "High Res" mode, but this one seems to.  So if you'd be ok accepting only USB 2.0 speeds, then yes it would appear that you could use the G5 to drive your display setup.  I knew dual QHD was possible when using all high speed lanes for video, but I didn't realize there was enough bandwidth left over for an FHD display in addition.

@jphughan 

But as far as I can tell, the choice between High Res Mode and Multi-Function is a configuration option specified on the dock somehow -- possibly through some sort of utility -- and NOT something related to the design or capabilities of the system you're using.

I've tried looking into this, there doesn't appear to be any "utility" that could configure that feature on the dock itself. I think it is something that is determined by the host system - more specifically whether the system supports DisplayPort Alt Mode. This would allow it to utilise all 4 lanes. It appears that my laptop doesn't support Alt Mode as I can't find any mention of it in the manual/spec sheet or a setting for it in the BIOS.

@Omzy   I was just about to follow up to the post I just wrote to say that I suppose it's possible that HP systems have a BIOS setting that will force their USB-C output to work in one way or the other.  That would be strange, and unnecessarily limiting, but strange and unnecessary certain doesn't mean it couldn't exist.  But if it were implemented that way, the default mode would be what I described above which is that the system would allow 0, 2, or 4 lanes to be used for DisplayPort, but a dock that wanted to support USB 3.x would always choose 2 lanes for DisplayPort and 2 for USB 3.x.  But I suppose it would be possible for the system itself to offer a setting to prevent that entirely, in which case the USB-C port would only ever support 4 lanes for video and regular USB 2.0 data.  The downside to that design is that it would seem to prevent USB 3.x from being used at all.  Maybe there's a way to keep USB 3.x available for peripherals that only request data and request no video, while making it unavailable for any device that requests DisplayPort Alt Mode, thereby forcing it to operate with 4 lanes of video and only USB 2.0?  I'm not sure.  But looking at that PDF I linked earlier a bit more closely, the High Res/Multi-Function options do have a "Host" heading over them, rather than a "Dock Mode" heading or something.

I still think this type of choice would make more sense to implement on the peripheral side though, as Dell has done on their displays.  That allows hosts to offer maximum flexibility while the specific peripherals that can benefit from one mode or the other can be configured to operate in the optimal mode for the particular system.  But separate from all of that, it's true that if your USB-C port doesn't support DisplayPort Alt Mode at all, then you wouldn't be able to use any of the typical USB-C docks that rely on that capability for video.  It's not a question of how much bandwidth you can get and therefore what display setups you can run, but rather the fact that you can't run any displays at all via native GPU outputs -- which means DisplayLink would be your only option.

Anyhow, interesting discussion, and it appears I learned something new about how HP systems work today.

@Omzy  if it was something inherent to the design of the system, it wouldn't make sense for it to be noted that "Multi-Function Mode" is the default.  Saying that something is the default implies that it can be changed.  But again, this is also rooted in how USB-C works, which I've already explained.  DisplayPort Alt Mode is just the ability to send a DisplayPort signal over USB-C.  If your system didn't support DisplayPort Alt Mode, you wouldn't be able to use any non-DisplayLink docks for video output at all, or any typical adapters such as USB-C to DisplayPort cables/dongles.  That's certainly possible since there are systems with USB-C ports that don't support DisplayPort Alt Mode at all, but in that case the difference between High Res and Multi-Function would be completely irrelevant since the dock wouldn't be able to get video out of the system in the first place.

But for systems that DO support DisplayPort Alt Mode, the number of lanes in the USB-C link allocated to DisplayPort Alt Mode depends on how the attached peripheral wants to set up the link, and it can choose either 0, 2, or 4.  Some recent Dell displays actually have a "USB-C Prioritization" setting that does exactly the same thing as this High Res/Multi-Function choice that the dock offers, and for the same reason.  It is definitely a peripheral-driven choice, not a host-driven choice.  A 4-lane link is a full DisplayPort interface from the GPU.  I have not seen a single system that is limited to 2 lanes in all cases, because I'm not aware of a way to have only half of a DisplayPort interface wired from a GPU.

@jphughan Ah OK makes sense. In that case I am led to believe this is something that can only be enabled when it's connected to a compatible HP laptop. Have a look at this thread where this guy is using the G5 dock with a HP laptop and has enabled Alt Mode in the BIOS, presumably on the laphttps://www.reddit.com/r/Hewlett_Packard/comments/e1hk56/how_do_you_get_the_hp_usbc_g5_dock_to_output_dual/" target="_blank" rel="nofollow noopener noreferrer nofollow ugc noopener noreferrer">https://www.reddit.com/r/Hewlett_Packard/comments/e1hk56/how_do_you_get_the_hp_usbc_g5_dock_to_output_dual/

@jphughan it's pretty mad isn't it 

You'd think it would just be a lot more simpler - it's far from it!

Anyway I'm going to try and order that extension cable and give it a try.. fingers crossed it works. I'll let you know how I get on.

Thanks again for all your help - I've certainly learnt a lot from your posts

@Omzy  it is indeed a bit head-spinning.  USB-C was promised as the one universal connector to rule them all, but it's mired in confusion because so many capabilities of a USB-C port are optional and not always implemented, which has in turn caused even USB-C cables to become a minefield.  Realizing that it seemed a bit unreasonable to expect the average user to be aware of all this, I was inspired to write two "explainer" threads in this forum.  The first explains the various operating modes of USB-C and Thunderbolt 3, with particular focus on the implications to display setups that can be run (here), and the second explains the various ways in which USB-C and Thunderbolt 3 cables are differentiated (here).  We've covered a good chunk of that information over this discussion, but the fact that these discussions even have to occur is why I felt writing those posts was useful.  Hopefully Google has surfaced them for people!