6 ms·

As someone who knows next to nothing about how USB actually works and just uses it, what goes into making each USB generation faster? At the physical layer, is

As someone who knows next to nothing about how USB actually works and just uses it, what goes into making each USB generation faster? At the physical layer, is it the materials in the cables are getting better? Or new ways of using the same materials? At the protocol layer, is it newly developed computer science theory being applied or is it just old fashioned pragmatic engineering iteration, looking at usage and making the existing protocols more efficient with tricks and shortcuts etc?

randyrand 8y ago
Nope. Much simpler. Just enabling the use of the other data lanes that were already in the cable waiting to be used one day. USB-C has 4 differential twisted pair data lines.
- deleted 8y ago
  [deleted]
- artiscode 8y ago
  That sort of explains why USB cables have been getting more expensive. More copper.
  - chris_mc 8y ago
    Probably more like "better tolerances" or something like that. The labor/time put into a cable is the most pricey part, raw materials are probably only a few cents, even if you double the copper into it.
  - gumby 8y ago
    and more silicon. These cables are more than just wire.
  - metaphor 8y ago
    It's more the process of qualifying technology that's increasingly faster with every generation than the cost of raw materials.
- starpilot 8y ago
  Why not turn them on all at once?
  - NullPrefix 8y ago
    Crosstalk with other pairs.
- Dylan16807 8y ago
  Not 'just' at all. USB 2 has a single twisted wire pair, specced for moderate speed. USB 3 replaces that with two pairs with much tighter requirements, one for transmit and one for receive. This involves a tenfold speed boost (.5Gbps to 5Gbps), with much more modern transceivers using much higher frequencies on much better wires. But it also drops the length a single passive cable can be from about 5 to 2 meters. USB C doubled the number of pins while making the plug reversible, so they went ahead and made the special case of C-to-C cables connect to all the pins and have four pairs of wires. But that's only a doubling from 5Gbps to 10Gbps. How are we getting up to 20 or 40? It's mostly coming from restricting cable length even further, down to 1 meter or only half a meter. But on the bright side you can get an active cable, with chips inside, that can get you back up to 1 meter or 2 meters or 60 meters. As long as you're willing to pay enough.
  - kondro 8y ago
    Now, if only someone would actually ship a USB-C 3.2 (or Thunderbolt) active cable. :( I have a couple of situations I would like a 7m-ish Thunderbolt 3 cable but can’t seem to find one, even for the multiple-hundreds it would probably cost.
    - Dylan16807 8y ago
      Corning has several lengths of optical thunderbolt 2 cable, do you need it to be thunderbolt 3 specifically?
      - kondro 8y ago
        This is for 5K and docking station specifically.
        Dylan16807 8y ago
        Ah, so just barely more than thunderbolt 2 or USB 3.2 can handle at 60Hz. It's really disappointing that Display Stream Compression hasn't been built into everything for the last 5+ years, and is only now barely getting into equipment. 2:1 or 3:1 compressed display data looks fine, and being able to add more pixels or bit depth or refresh rate far more than makes up for the tiny losses. Without it, tons of screens are stuck at significantly reduced framerates or 4:2:0 subsampling.
- xxs 8y ago
  I still wonder why the 'S' in the name - USB has stopped being serial (or bus) for quite some time.
pkaye 8y ago
I'm no means an expert but up to USB 2.0 there were 4 pins (2 for power and 2 differential signals for bidirectional data) With USB 3.0 they added 4 more signals for separate transmit/receive. Initially they used 8b/10b encoding and then switched to 128b/132b encoding. They also increased the signaling rate with each generation. Also in the USB 2.0 and earlier the higher level protocols were kind of inefficient with lots of back and forth. So they improved upon that. And I'm sure they also tightened up on the cable and connection specs to increase the signaling rates. So a lot of little improvements added up.
- chrisseaton 8y ago
  > With USB 3.0 they added 4 more signals for separate transmit/receive So is it not actually serial any more?
  - _wmd 8y ago
    Transmit and receive previously shared pins, USB 3 split transmit and receive into separate pairs, which are still serial edit: yikes, looks like USB C doubled the number of those separate pairs, for a total of 6 data pins (2x RX, 2x TX, 2x USB 2.0 RX/TX)
    - projektfu 8y ago
      It’s better to say they were mirrored to make the connector work the same upside down, and then they expanded the spec to allow simultaneous use, effectively doubling the throughput.
  - TOGoS 8y ago
    Multiple serial connections in parallel.
  - matthewmacleod 8y ago
    It's more like… multiple serial connections over the same cable – kind of like PCI-E, SATA etc.
  - 8y ago
baybal2 8y ago
> At the physical layer, is it the materials in the cables are getting better? Yes, and more expensive on that. Laptop makers totally hate usb 3.0+ for that. The industry standard for internal digital connectivity was the FPC - flexible printed circuit board, a very economical and ergonomic solution, but then came USB 3.0. Regular polyimide FPC can't reliably handle the high frequency signalling. Still, many laptop makers still use it, to regrettable results. The few solutions left are the micro coax cable, running twisted pair inside the case, or passing it over a hard pcb bridge. All are very expensive, and hard on assembly lines. This is why in most budget laptops manufacturers do a following trick – they put all usb 3.0 ports on one side, and 2.0 on the opposite. This way they only have to run the low frequency, low lane count usb 2.0 to other side of the laptop. Only very recently, there came an FPC maker that makes custom cabling with some proprietary dielectric that can handle 3.0. And they charge more for it than for hard pcb bridge. Even if the cable material issue is solved, you still have to find way to connect it to PCB. High frequency connectors are not cheap either.
- metaphor 8y ago
  Thanks for sharing and interesting industry perspective. Color me unconvinced on one point though: > Only very recently, there came an FPC maker that makes custom cabling with some proprietary dielectric that can handle 3.0. A brief glance at IPC-4203A (which has been around since 2013) tells me this is a consequence of market cost sensitivity, not one driven by the inherent performance limitations of available material. The latest IPC-4203B was just published circa March 2018 last year. Is there something new worth looking into here, or is this "recent advancement" just a manufacturing process-driven one which has made high-performance FPC more viable in the throwaway consumer electronics market?
  - baybal2 8y ago
    It's more to finding FPC factories dealing with anything amounting to a "specialty product," and finding somebody who can engineer that FPC with all attention needed to signal integrity and fickleness of high frequency circuits.
  - baybal2 8y ago
deleted 8y ago
[deleted]
KSS42 8y ago
Others have mentioned tighter tolerance in the cable and PCB parameters. Each successive frequency increase has required more complex PHY design. On the digital side : more sophisticated bit encoding schemes On the analog side : tighter tolerances for clocking and signal jitter, more sophisticated transmitter and receiver technology (better emphasis/deemphasis, better equalization) Here's taste of the PHY changes : https://www.chipestimate.com/Type-C-USB31-PHY-Challenges-in-Analog-and-Digital-Design/SilabTech/Technical-Article/2016/02/23 https://www.chipestimate.com/Type-C-USB31-PHY-Challenges-in-...

randyrand 8y ago

Nope. Much simpler. Just enabling the use of the other data lanes that were already in the cable waiting to be used one day. USB-C has 4 differential twisted pair data lines.

deleted 8y ago
[deleted]
artiscode 8y ago
That sort of explains why USB cables have been getting more expensive. More copper.
- chris_mc 8y ago
  Probably more like "better tolerances" or something like that. The labor/time put into a cable is the most pricey part, raw materials are probably only a few cents, even if you double the copper into it.
- gumby 8y ago
  and more silicon. These cables are more than just wire.
- metaphor 8y ago
  It's more the process of qualifying technology that's increasingly faster with every generation than the cost of raw materials.
starpilot 8y ago
Why not turn them on all at once?
- NullPrefix 8y ago
  Crosstalk with other pairs.
Dylan16807 8y ago
Not 'just' at all. USB 2 has a single twisted wire pair, specced for moderate speed. USB 3 replaces that with two pairs with much tighter requirements, one for transmit and one for receive. This involves a tenfold speed boost (.5Gbps to 5Gbps), with much more modern transceivers using much higher frequencies on much better wires. But it also drops the length a single passive cable can be from about 5 to 2 meters. USB C doubled the number of pins while making the plug reversible, so they went ahead and made the special case of C-to-C cables connect to all the pins and have four pairs of wires. But that's only a doubling from 5Gbps to 10Gbps. How are we getting up to 20 or 40? It's mostly coming from restricting cable length even further, down to 1 meter or only half a meter. But on the bright side you can get an active cable, with chips inside, that can get you back up to 1 meter or 2 meters or 60 meters. As long as you're willing to pay enough.
- kondro 8y ago
  Now, if only someone would actually ship a USB-C 3.2 (or Thunderbolt) active cable. :( I have a couple of situations I would like a 7m-ish Thunderbolt 3 cable but can’t seem to find one, even for the multiple-hundreds it would probably cost.
  - Dylan16807 8y ago
    Corning has several lengths of optical thunderbolt 2 cable, do you need it to be thunderbolt 3 specifically?
    - kondro 8y ago
      This is for 5K and docking station specifically.
      - Dylan16807 8y ago
        Ah, so just barely more than thunderbolt 2 or USB 3.2 can handle at 60Hz. It's really disappointing that Display Stream Compression hasn't been built into everything for the last 5+ years, and is only now barely getting into equipment. 2:1 or 3:1 compressed display data looks fine, and being able to add more pixels or bit depth or refresh rate far more than makes up for the tiny losses. Without it, tons of screens are stuck at significantly reduced framerates or 4:2:0 subsampling.
xxs 8y ago
I still wonder why the 'S' in the name - USB has stopped being serial (or bus) for quite some time.

pkaye 8y ago

I'm no means an expert but up to USB 2.0 there were 4 pins (2 for power and 2 differential signals for bidirectional data) With USB 3.0 they added 4 more signals for separate transmit/receive. Initially they used 8b/10b encoding and then switched to 128b/132b encoding. They also increased the signaling rate with each generation. Also in the USB 2.0 and earlier the higher level protocols were kind of inefficient with lots of back and forth. So they improved upon that. And I'm sure they also tightened up on the cable and connection specs to increase the signaling rates. So a lot of little improvements added up.

chrisseaton 8y ago
> With USB 3.0 they added 4 more signals for separate transmit/receive So is it not actually serial any more?
- _wmd 8y ago
  Transmit and receive previously shared pins, USB 3 split transmit and receive into separate pairs, which are still serial edit: yikes, looks like USB C doubled the number of those separate pairs, for a total of 6 data pins (2x RX, 2x TX, 2x USB 2.0 RX/TX)
  - projektfu 8y ago
    It’s better to say they were mirrored to make the connector work the same upside down, and then they expanded the spec to allow simultaneous use, effectively doubling the throughput.
- TOGoS 8y ago
  Multiple serial connections in parallel.
- matthewmacleod 8y ago
  It's more like… multiple serial connections over the same cable – kind of like PCI-E, SATA etc.
- 8y ago

baybal2 8y ago

> At the physical layer, is it the materials in the cables are getting better? Yes, and more expensive on that. Laptop makers totally hate usb 3.0+ for that. The industry standard for internal digital connectivity was the FPC - flexible printed circuit board, a very economical and ergonomic solution, but then came USB 3.0. Regular polyimide FPC can't reliably handle the high frequency signalling. Still, many laptop makers still use it, to regrettable results. The few solutions left are the micro coax cable, running twisted pair inside the case, or passing it over a hard pcb bridge. All are very expensive, and hard on assembly lines. This is why in most budget laptops manufacturers do a following trick – they put all usb 3.0 ports on one side, and 2.0 on the opposite. This way they only have to run the low frequency, low lane count usb 2.0 to other side of the laptop. Only very recently, there came an FPC maker that makes custom cabling with some proprietary dielectric that can handle 3.0. And they charge more for it than for hard pcb bridge. Even if the cable material issue is solved, you still have to find way to connect it to PCB. High frequency connectors are not cheap either.

metaphor 8y ago
Thanks for sharing and interesting industry perspective. Color me unconvinced on one point though: > Only very recently, there came an FPC maker that makes custom cabling with some proprietary dielectric that can handle 3.0. A brief glance at IPC-4203A (which has been around since 2013) tells me this is a consequence of market cost sensitivity, not one driven by the inherent performance limitations of available material. The latest IPC-4203B was just published circa March 2018 last year. Is there something new worth looking into here, or is this "recent advancement" just a manufacturing process-driven one which has made high-performance FPC more viable in the throwaway consumer electronics market?
- baybal2 8y ago
  It's more to finding FPC factories dealing with anything amounting to a "specialty product," and finding somebody who can engineer that FPC with all attention needed to signal integrity and fickleness of high frequency circuits.
- baybal2 8y ago

deleted 8y ago

[deleted]

KSS42 8y ago

Others have mentioned tighter tolerance in the cable and PCB parameters. Each successive frequency increase has required more complex PHY design. On the digital side : more sophisticated bit encoding schemes On the analog side : tighter tolerances for clocking and signal jitter, more sophisticated transmitter and receiver technology (better emphasis/deemphasis, better equalization) Here's taste of the PHY changes : https://www.chipestimate.com/Type-C-USB31-PHY-Challenges-in-Analog-and-Digital-Design/SilabTech/Technical-Article/2016/02/23 https://www.chipestimate.com/Type-C-USB31-PHY-Challenges-in-...