19 ms·

A deep dive into Single Pair Ethernet

237 points by killcoder 3y ago

killcoder 3y ago
We built a Power over Data Line (PoDL) compliant device and power supply as part of a one-month 'sink or swim' approach to designing and testing new hardware, and getting to look at maturity of the 10Base-T1 ecosystem. The board was enclosed a submersible sensor node and field tested at a popular dive reef, SCUBA diving down and mounting it to the jetty. It was also a nice excuse to get some macro shots of the PCB assembly process, including some nice footage of solder paste melting and the interesting surface tension interactions. (I can't seem to get the videos to render in a format that iOS Safari will play, if anyone knows the ffmpeg incantation, please let me know, nothing I've tried has worked on my iPhone...)
- fanf2 3y ago
  Interesting write-up with some very nice pictures! The videos worked for me on my iPhone. Always nice to see a bit of solder reflow :-)
  - killcoder 3y ago
    Turns out it might just be my phone, what a weird bug.
- maaarghk 3y ago
  my shell history has this in it, but it might have been for android firefox ~ `-c:v vp8 -b:v 2000k -pix_fmt yuv420p`
- Timon3 3y ago
  Might I suggest using an ffmpeg frontend like HandBrake? It has a bunch of presets, the Apple ones will surely work for this.
- doctorpangloss 3y ago
  The amount of expertise that went into this 1 month project is crazy and it's all really cool and well put together. I don't comprehend how you made no mistakes on the journey after drafting the PCBs and writing drivers. From my POV as a software developer, C has so many pitfalls that it is incomprehensible to me that things will Just Work, especially in the context of something that is meant to run for a very long time and not be "restarted." Why do sensor things at all? What is the ROI for the person who needs that stuff? I mean this in no derogatory sense, I really admire this work. But the academics who need something something hardware are either so rich they use something commercial / the paid core or so poor they'll use someone else's refuse or a grad student to do it 10x worse & 10x slower for free. Lab equipment, sensors, whatever. If it's for an industrial purpose, the ultimate consumer for hardware 2 guys can make is the government, as far as the eye can see. Like the people who have a business stake in e.g. the ocean ecosystem are fishermen, oil people, shippers, whatever, and they're only doing this because of a government regulation or threat thereof or whatever. I view government needs as worthwhile, they are a worthy customer, it's that the ROI is essentially imaginary, it's whatever the payer values government compliance and that can be infinitely large or small. My background in this is very limited, I didn't take "How to Make," I don't know how to use anything in a fablab, but in an intellectually honest way, the audience for "polished, well working gizmo with bug-free firmware" is 1,000,000x larger when it's a coffee machine than any academic or industrial purpose. Why not make "the perfect espresso machine" or "the perfect bike" or whatever? There are $3m Kickstarters for coffee machines whose #1 actual obstacle to successful execution is writing firmware. There are e-bikes that are 10x expensive or 10x crappier because ultimately it's too challenging to make a single firmware and controller to make disparate commodity parts work together cohesively. I am not at all raining on this parade, because this little blog post was so mind numbingly impressive; and I'm not saying there aren't 10,000 people toiling on dead-on-arrival consumer hardware, be it Oculus peripherals or connected emotive robots or whole divisions at Google. My question is: why? Why not, with your skills, make a thing and fucking sell it?
  - CuriousCosmic 3y ago
    Not OP but > I don't comprehend how you made no mistakes on the journey after drafting the PCBs and writing drivers. From my POV as a software developer, C has so many pitfalls that it is incomprehensible to me that things will Just Work, especially in the context of something that is meant to run for a very long time and not be "restarted." You aren't meant to make no mistakes, just only make recoverable mistakes. In a lot of cases you can rely on your hardware for this. Watchdog Timers are specifically intended for this. You set up a watchdog when you deploy the device and your software has to periodically "pet" the watchdog or the system triggers some action. In practice this is used to verify that the software never gets stuck or else it triggers a recovery/restart sequence and maybe sends out an alert. The end goal shouldn't be bug free but "even with bugs it eventually recovers and keeps working unless the hardware physically dies". > Why do sensor things at all? What is the ROI for the person who needs that stuff? I mean this in no derogatory sense, I really admire this work. Once again not the OP but I could see this being useful. They are recording wave patterns on or around a reef. That could be used for modelling how reefs can buffer water conditions (ex: for the purpose of constructing man made analogues) or as part of a greater sensor suite for documenting how "weather" impacts reef ecosystems. And you would want a system you can deploy and leave unattended for long periods of time since every trip out costs money and depending on what you are specifically researching, simply returning to the site could interfere with/disrupt the experiment.
h2odragon 3y ago
> Single Pair Ethernet supports long range >1km cable runs That's going to introduce a lot of people to the joys of outdoor long wires and their interaction with lighting. I've seen the induction current from ground surge turn 25 pair cat3 into vapor ... there's fun to be had there.
- FfejL 3y ago
  Lighting? Or lightning? I'm hoping the latter!
  - lostlogin 3y ago
    Surely lightning. I’m in New Zealand and our sun just destroys everything. The UV eats everything up and I’d not expose a cable to sunlight. Plenty of places are hotter or have more UV but also have air pollution which blocks UV. Our relatively clear air lets the UV come ripping through. At least sunlight won’t toast my switch though.
    - sgt 3y ago
      Is this why NZ streets, roads, towns generally look a bit "tired"? Hard to explain what I mean, but if UV light fades all the colors and makes things look neglected, it would be one explanation.
      - lostlogin 3y ago
        New concrete or even clean concrete is actually hard to be near and squinting is the norm. The difference just so striking when I go to Europe - it's like soft focus has been applied.
- mschuster91 3y ago
  Or with wildlife. Moles, mice, rats, rabbits, if your cable is not shielded with solid metal it will get eaten through. Other common issue with novices running outdoor cabling are people running belowground cables strung outdoors on poles in the open air - UV degradation can take such cables (or rather, their insulation) apart in a matter of less than a year. Or silicone cables that end up in stagnant water, which can dissolve them (don't ask me about specifics, but it's a hotbed of issues in PV power plants). Or people not burying their cables deep enough, i.e. below the frost line, and the ground freezing over killing the cables. Outdoor wiring is fun for everyone involved. If anyone here wants to deal with that crap, please read up on using the correct cable for the job, and FFS have a certified electrician sign off on the grounding of such cables and surge arrestor designs and installation.
myself248 3y ago
But there are several types of ethernet that run over a single pair now. There's 802.3bu, 802.3cg, 802.3da, 802.3bw, and possibly more. And I can't tell if any of them are compatible. I think da is compatible with cg, but the others are all little islands, all serving very similar needs in mutually-frustrating ways. Whyyyyyyyyyyyyyyyyyyy?
- coder543 3y ago
  This is nowhere near as confusing as you're making it out to be. - 802.3bu specifies PoDL (power over data lines). - 802.3bp specifies 1000Mb/s over SPE (single pair ethernet) - 802.3bw specifies 100Mb/s over SPE - 802.3cg specifies 10Mb/s over SPE - 802.3da is an enhancement of 802.3cg. In fact, you've had most of this explained to you before[0], including your long "whyyyyyy". Modern WiFi has a very long list of 802.11 standards attached to it... My WiFi access point supports all of these: - 802.11a - 802.11b - 802.11g - 802.11n - 802.11ac - 802.11ax I rarely hear anyone complain about the alphabet soup involved there, but relatively recently, they've been rebranding it as WiFi 5, WiFi 6, WiFi 7 since it is something consumers run into more frequently than things like SPE. SPE is not intended for home users. The SPE standards are designed to make things easier for automotive and industrial applications, and they seem fine. Automotive needs are not the same as industrial needs, so flexibility in the standards allows them to meet the specific needs of each application better. It also allows them to remove unnecessary weight and complexity. Weight reduction is one of the main reasons automotive is interested in SPE. SPE has no obvious advantages for home users over something like Monoprice's Micro SlimRun cables, which are extremely thin and flexible, for example. So, it makes sense that they haven't put effort into giving it cool branding like "WiFi 7". [0]: https://news.ycombinator.com/item?id=35074023 https://news.ycombinator.com/item?id=35074023
  - addaon 3y ago
    > SPE has no obvious advantages for home users over something like Monoprice's Micro SlimRun cables, which are extremely thin and flexible, for example. PoDL does have real advantages over PoE. I agree that there's no home-user-ready products at this point, but I could see future exploration of this space for that reason alone.
addaon 3y ago
Two things I've learned working with SPE in its 100 Mb and 1 Gb configurations for a few years: 1) PoDL is substantially lighter, smaller, and simpler (though not necessarily cheaper) at 1 Gb than at 100 Mb, due to the increased frequency separation. Just like with other Ethernet protocols, the lowest frequency of comms is basically DC; it's only statistically brought above that by the scrambler, but there's no useful true lower bound. Having an order of magnitude more separation, such as it is, allows a more reasonably sized filter to stomp over less (ideally, approximately none) of the data. 2) Only the 1 Gb protocol includes FEC, 100 Mb is a simpler, non-error-correcting encoding. This means that even though the maximum frequency on the twisted pair goes up by an order of magnitude to ~660 MHz, requiring better cabling, better twist spacing, etc... it allows a "sloppier" job at both high and low frequencies, since the FEC really does hide a few errors. This can be spent on even worse filters for PoDL, on frequency-specific interference (e.g. an RF amp running nearby), etc. Basically, I was surprised to find that 1 Gb was not only not more challenging at the system design level, it was often simpler. (I haven't played with 10 Mb in either of its two incarnations seriously yet.)
- wmf 3y ago
  PoDL = Power over Data Line. I guess this is similar but incompatible to PoE.
  - addaon 3y ago
    Similar in purpose, extremely different in implementation, since PoE-supporting Ethernets (e.g. 100base-TX) are magnetically coupled, but PoDL-supporting Ethernets (e.g. 100base-T1) are capacitively coupled.
    - monocasa 3y ago
      I mean, isolation transformers like in regular amd PoE Ethernet are a form of capacitive coupling.
      - unsung 3y ago
scohesc 3y ago
As a side project I'm looking at making an autonomous vehicle of some kind, starting with a ground vehicle and eventually moving to something on or under the water. It's mindboggling how many different ways there are to communicate with microcontrollers, sensors, etc. So many different standards with different data rates, capabilities, features, etc. It's cool to see something like ethernet be able to be used in rough situations like this. I'm sure this is done already with some technology, but I'd love to see a buoy with solar/wind and batteries for power, with a tether going down into the water to supply power and data for sensor arrays underwater. Trying to communicate through water is tough - I even looked at acoustic modems to try and transfer data but it looks like they haven't gotten down to consumer/tinkerer level of electronics yet. Single Pair ethernet with power seems very complicated for a fairly ignorant but interested hobbyist haha
- bb88 3y ago
  Canbus seems like the easy solution here. It's used in cars in engine's and other noisy environments. https://discourse.odriverobotics.com/t/can-bus-signal-noise/6810 https://discourse.odriverobotics.com/t/can-bus-signal-noise/... I understand there's even linux drivers for some hardware for the RPi. As they say, motors and engines cause a lot of local noise....
throw0101a 3y ago
802.3cy recently added support for 25 Gb/s: > In addition to the more computer-oriented two and four-pair variants, the 10BASE-T1,[20] 100BASE-T1[21] and 1000BASE-T1[22] single-pair Ethernet physical layers are intended for industrial and automotive applications[23] or as optional data channels in other interconnect applications.[24] The single pair operates at full duplex and has a maximum reach of 15 m or 49 ft (100BASE-T1, 1000BASE-T1 link segment type A) or up to 40 m or 130 ft (1000BASE-T1 link segment type B) with up to four in-line connectors. Both physical layers require a balanced twisted pair with an impedance of 100 Ω. The cable must be capable of transmitting 600 MHz for 1000BASE-T1 and 66 MHz for 100BASE-T1. 2.5 Gb/s, 5 Gb/s, and 10 Gb/s over a 15 m single pair is standardized in 802.3ch-2020.[25] In June 2023, 802.3cy added 25 Gb/s speeds at lengths up to 11 m.[26] * https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Single-pair https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Sin... 802.3dg is going for 100M and 1000M over distances of 500m
- LinuxBender 3y ago
  Are there any consumer devices supporting 802.3dg? The reason I ask is that I often push the limits of current gigabit ethernet distances and have found that actual limits are much shorter than theoretical limits meaning some network cards have a hard time negotiating at full speed and often fall back to 100mb unless forced
  - throw0101a 3y ago
    > Are there any consumer devices supporting 802.3dg? Given that it's not even ratified yet… no.
  - ilyt 3y ago
    > The reason I ask is that I often push the limits of current gigabit ethernet distances and have found that actual limits are much shorter than theoretical limits meaning some network cards have a hard time negotiating at full speed and often fall back to 100mb unless forced Does it have problems on single unbroken cable like that or it just has few patch-panels along the way ? IIRC the standard was for 100m unbroken cable, not the usual of device -> cable -> patchpanel -> cable ->patchpanel -> cable -> patchpanel -> cable -> device
Dylan16807 3y ago
Also, since this doesn't really talk about the ethernet data, the signalling for 10Base-T1L is PAM3, 4B3T, 7.5 megabaud. So 4 bits of data get turned into 3 symbols, each symbol being either negative voltage, positive voltage, or zero voltage, and then the symbols are transmitted at 7.5MHz. Something to note is that it has a much lower bandwidth requirement than 10BASE-T, because 10BASE-T uses manchester encoding with two symbols per bit (either 01 or 10). So 3.75MHz of bandwidth versus 10MHz of bandwidth.
TrueDuality 3y ago
Great write up. Looks like the GitHub repo with the project hasn't been posted yet. Look forward to poking through that!
- joezydeco 3y ago
  Agreed. This writeup is beautiful. And I learned a bunch about SPE in the meantime.
inamberclad 3y ago
I just started a job using PoDL and so far I'm quite impressed with it as a technology. I'd like to see consumer devices start to use it too.

237 points by killcoder 3y ago

We built a Power over Data Line (PoDL) compliant device and power supply as part of a one-month 'sink or swim' approach to designing and testing new hardware, and getting to look at maturity of the 10Base-T1 ecosystem. The board was enclosed a submersible sensor node and field tested at a popular dive reef, SCUBA diving down and mounting it to the jetty. It was also a nice excuse to get some macro shots of the PCB assembly process, including some nice footage of solder paste melting and the interesting surface tension interactions. (I can't seem to get the videos to render in a format that iOS Safari will play, if anyone knows the ffmpeg incantation, please let me know, nothing I've tried has worked on my iPhone...)

fanf2 3y ago
Interesting write-up with some very nice pictures! The videos worked for me on my iPhone. Always nice to see a bit of solder reflow :-)
- killcoder 3y ago
  Turns out it might just be my phone, what a weird bug.
maaarghk 3y ago
my shell history has this in it, but it might have been for android firefox ~ `-c:v vp8 -b:v 2000k -pix_fmt yuv420p`
Timon3 3y ago
Might I suggest using an ffmpeg frontend like HandBrake? It has a bunch of presets, the Apple ones will surely work for this.
doctorpangloss 3y ago
The amount of expertise that went into this 1 month project is crazy and it's all really cool and well put together. I don't comprehend how you made no mistakes on the journey after drafting the PCBs and writing drivers. From my POV as a software developer, C has so many pitfalls that it is incomprehensible to me that things will Just Work, especially in the context of something that is meant to run for a very long time and not be "restarted." Why do sensor things at all? What is the ROI for the person who needs that stuff? I mean this in no derogatory sense, I really admire this work. But the academics who need something something hardware are either so rich they use something commercial / the paid core or so poor they'll use someone else's refuse or a grad student to do it 10x worse & 10x slower for free. Lab equipment, sensors, whatever. If it's for an industrial purpose, the ultimate consumer for hardware 2 guys can make is the government, as far as the eye can see. Like the people who have a business stake in e.g. the ocean ecosystem are fishermen, oil people, shippers, whatever, and they're only doing this because of a government regulation or threat thereof or whatever. I view government needs as worthwhile, they are a worthy customer, it's that the ROI is essentially imaginary, it's whatever the payer values government compliance and that can be infinitely large or small. My background in this is very limited, I didn't take "How to Make," I don't know how to use anything in a fablab, but in an intellectually honest way, the audience for "polished, well working gizmo with bug-free firmware" is 1,000,000x larger when it's a coffee machine than any academic or industrial purpose. Why not make "the perfect espresso machine" or "the perfect bike" or whatever? There are $3m Kickstarters for coffee machines whose #1 actual obstacle to successful execution is writing firmware. There are e-bikes that are 10x expensive or 10x crappier because ultimately it's too challenging to make a single firmware and controller to make disparate commodity parts work together cohesively. I am not at all raining on this parade, because this little blog post was so mind numbingly impressive; and I'm not saying there aren't 10,000 people toiling on dead-on-arrival consumer hardware, be it Oculus peripherals or connected emotive robots or whole divisions at Google. My question is: why? Why not, with your skills, make a thing and fucking sell it?
- CuriousCosmic 3y ago
  Not OP but > I don't comprehend how you made no mistakes on the journey after drafting the PCBs and writing drivers. From my POV as a software developer, C has so many pitfalls that it is incomprehensible to me that things will Just Work, especially in the context of something that is meant to run for a very long time and not be "restarted." You aren't meant to make no mistakes, just only make recoverable mistakes. In a lot of cases you can rely on your hardware for this. Watchdog Timers are specifically intended for this. You set up a watchdog when you deploy the device and your software has to periodically "pet" the watchdog or the system triggers some action. In practice this is used to verify that the software never gets stuck or else it triggers a recovery/restart sequence and maybe sends out an alert. The end goal shouldn't be bug free but "even with bugs it eventually recovers and keeps working unless the hardware physically dies". > Why do sensor things at all? What is the ROI for the person who needs that stuff? I mean this in no derogatory sense, I really admire this work. Once again not the OP but I could see this being useful. They are recording wave patterns on or around a reef. That could be used for modelling how reefs can buffer water conditions (ex: for the purpose of constructing man made analogues) or as part of a greater sensor suite for documenting how "weather" impacts reef ecosystems. And you would want a system you can deploy and leave unattended for long periods of time since every trip out costs money and depending on what you are specifically researching, simply returning to the site could interfere with/disrupt the experiment.

h2odragon 3y ago

> Single Pair Ethernet supports long range >1km cable runs That's going to introduce a lot of people to the joys of outdoor long wires and their interaction with lighting. I've seen the induction current from ground surge turn 25 pair cat3 into vapor ... there's fun to be had there.

FfejL 3y ago
Lighting? Or lightning? I'm hoping the latter!
- lostlogin 3y ago
  Surely lightning. I’m in New Zealand and our sun just destroys everything. The UV eats everything up and I’d not expose a cable to sunlight. Plenty of places are hotter or have more UV but also have air pollution which blocks UV. Our relatively clear air lets the UV come ripping through. At least sunlight won’t toast my switch though.
  - sgt 3y ago
    Is this why NZ streets, roads, towns generally look a bit "tired"? Hard to explain what I mean, but if UV light fades all the colors and makes things look neglected, it would be one explanation.
    - lostlogin 3y ago
      New concrete or even clean concrete is actually hard to be near and squinting is the norm. The difference just so striking when I go to Europe - it's like soft focus has been applied.
mschuster91 3y ago
Or with wildlife. Moles, mice, rats, rabbits, if your cable is not shielded with solid metal it will get eaten through. Other common issue with novices running outdoor cabling are people running belowground cables strung outdoors on poles in the open air - UV degradation can take such cables (or rather, their insulation) apart in a matter of less than a year. Or silicone cables that end up in stagnant water, which can dissolve them (don't ask me about specifics, but it's a hotbed of issues in PV power plants). Or people not burying their cables deep enough, i.e. below the frost line, and the ground freezing over killing the cables. Outdoor wiring is fun for everyone involved. If anyone here wants to deal with that crap, please read up on using the correct cable for the job, and FFS have a certified electrician sign off on the grounding of such cables and surge arrestor designs and installation.

myself248 3y ago

But there are several types of ethernet that run over a single pair now. There's 802.3bu, 802.3cg, 802.3da, 802.3bw, and possibly more. And I can't tell if any of them are compatible. I think da is compatible with cg, but the others are all little islands, all serving very similar needs in mutually-frustrating ways. Whyyyyyyyyyyyyyyyyyyy?

coder543 3y ago
This is nowhere near as confusing as you're making it out to be. - 802.3bu specifies PoDL (power over data lines). - 802.3bp specifies 1000Mb/s over SPE (single pair ethernet) - 802.3bw specifies 100Mb/s over SPE - 802.3cg specifies 10Mb/s over SPE - 802.3da is an enhancement of 802.3cg. In fact, you've had most of this explained to you before[0], including your long "whyyyyyy". Modern WiFi has a very long list of 802.11 standards attached to it... My WiFi access point supports all of these: - 802.11a - 802.11b - 802.11g - 802.11n - 802.11ac - 802.11ax I rarely hear anyone complain about the alphabet soup involved there, but relatively recently, they've been rebranding it as WiFi 5, WiFi 6, WiFi 7 since it is something consumers run into more frequently than things like SPE. SPE is not intended for home users. The SPE standards are designed to make things easier for automotive and industrial applications, and they seem fine. Automotive needs are not the same as industrial needs, so flexibility in the standards allows them to meet the specific needs of each application better. It also allows them to remove unnecessary weight and complexity. Weight reduction is one of the main reasons automotive is interested in SPE. SPE has no obvious advantages for home users over something like Monoprice's Micro SlimRun cables, which are extremely thin and flexible, for example. So, it makes sense that they haven't put effort into giving it cool branding like "WiFi 7". [0]: https://news.ycombinator.com/item?id=35074023 https://news.ycombinator.com/item?id=35074023
- addaon 3y ago
  > SPE has no obvious advantages for home users over something like Monoprice's Micro SlimRun cables, which are extremely thin and flexible, for example. PoDL does have real advantages over PoE. I agree that there's no home-user-ready products at this point, but I could see future exploration of this space for that reason alone.

addaon 3y ago

Two things I've learned working with SPE in its 100 Mb and 1 Gb configurations for a few years: 1) PoDL is substantially lighter, smaller, and simpler (though not necessarily cheaper) at 1 Gb than at 100 Mb, due to the increased frequency separation. Just like with other Ethernet protocols, the lowest frequency of comms is basically DC; it's only statistically brought above that by the scrambler, but there's no useful true lower bound. Having an order of magnitude more separation, such as it is, allows a more reasonably sized filter to stomp over less (ideally, approximately none) of the data. 2) Only the 1 Gb protocol includes FEC, 100 Mb is a simpler, non-error-correcting encoding. This means that even though the maximum frequency on the twisted pair goes up by an order of magnitude to ~660 MHz, requiring better cabling, better twist spacing, etc... it allows a "sloppier" job at both high and low frequencies, since the FEC really does hide a few errors. This can be spent on even worse filters for PoDL, on frequency-specific interference (e.g. an RF amp running nearby), etc. Basically, I was surprised to find that 1 Gb was not only not more challenging at the system design level, it was often simpler. (I haven't played with 10 Mb in either of its two incarnations seriously yet.)

wmf 3y ago
PoDL = Power over Data Line. I guess this is similar but incompatible to PoE.
- addaon 3y ago
  Similar in purpose, extremely different in implementation, since PoE-supporting Ethernets (e.g. 100base-TX) are magnetically coupled, but PoDL-supporting Ethernets (e.g. 100base-T1) are capacitively coupled.
  - monocasa 3y ago
    I mean, isolation transformers like in regular amd PoE Ethernet are a form of capacitive coupling.
    - unsung 3y ago

scohesc 3y ago

As a side project I'm looking at making an autonomous vehicle of some kind, starting with a ground vehicle and eventually moving to something on or under the water. It's mindboggling how many different ways there are to communicate with microcontrollers, sensors, etc. So many different standards with different data rates, capabilities, features, etc. It's cool to see something like ethernet be able to be used in rough situations like this. I'm sure this is done already with some technology, but I'd love to see a buoy with solar/wind and batteries for power, with a tether going down into the water to supply power and data for sensor arrays underwater. Trying to communicate through water is tough - I even looked at acoustic modems to try and transfer data but it looks like they haven't gotten down to consumer/tinkerer level of electronics yet. Single Pair ethernet with power seems very complicated for a fairly ignorant but interested hobbyist haha

bb88 3y ago
Canbus seems like the easy solution here. It's used in cars in engine's and other noisy environments. https://discourse.odriverobotics.com/t/can-bus-signal-noise/6810 https://discourse.odriverobotics.com/t/can-bus-signal-noise/... I understand there's even linux drivers for some hardware for the RPi. As they say, motors and engines cause a lot of local noise....

throw0101a 3y ago

802.3cy recently added support for 25 Gb/s: > In addition to the more computer-oriented two and four-pair variants, the 10BASE-T1,[20] 100BASE-T1[21] and 1000BASE-T1[22] single-pair Ethernet physical layers are intended for industrial and automotive applications[23] or as optional data channels in other interconnect applications.[24] The single pair operates at full duplex and has a maximum reach of 15 m or 49 ft (100BASE-T1, 1000BASE-T1 link segment type A) or up to 40 m or 130 ft (1000BASE-T1 link segment type B) with up to four in-line connectors. Both physical layers require a balanced twisted pair with an impedance of 100 Ω. The cable must be capable of transmitting 600 MHz for 1000BASE-T1 and 66 MHz for 100BASE-T1. 2.5 Gb/s, 5 Gb/s, and 10 Gb/s over a 15 m single pair is standardized in 802.3ch-2020.[25] In June 2023, 802.3cy added 25 Gb/s speeds at lengths up to 11 m.[26] * https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Single-pair https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Sin... 802.3dg is going for 100M and 1000M over distances of 500m

LinuxBender 3y ago
Are there any consumer devices supporting 802.3dg? The reason I ask is that I often push the limits of current gigabit ethernet distances and have found that actual limits are much shorter than theoretical limits meaning some network cards have a hard time negotiating at full speed and often fall back to 100mb unless forced
- throw0101a 3y ago
  > Are there any consumer devices supporting 802.3dg? Given that it's not even ratified yet… no.
- ilyt 3y ago
  > The reason I ask is that I often push the limits of current gigabit ethernet distances and have found that actual limits are much shorter than theoretical limits meaning some network cards have a hard time negotiating at full speed and often fall back to 100mb unless forced Does it have problems on single unbroken cable like that or it just has few patch-panels along the way ? IIRC the standard was for 100m unbroken cable, not the usual of device -> cable -> patchpanel -> cable ->patchpanel -> cable -> patchpanel -> cable -> device

Dylan16807 3y ago

Also, since this doesn't really talk about the ethernet data, the signalling for 10Base-T1L is PAM3, 4B3T, 7.5 megabaud. So 4 bits of data get turned into 3 symbols, each symbol being either negative voltage, positive voltage, or zero voltage, and then the symbols are transmitted at 7.5MHz. Something to note is that it has a much lower bandwidth requirement than 10BASE-T, because 10BASE-T uses manchester encoding with two symbols per bit (either 01 or 10). So 3.75MHz of bandwidth versus 10MHz of bandwidth.

TrueDuality 3y ago

Great write up. Looks like the GitHub repo with the project hasn't been posted yet. Look forward to poking through that!

joezydeco 3y ago
Agreed. This writeup is beautiful. And I learned a bunch about SPE in the meantime.

inamberclad 3y ago

I just started a job using PoDL and so far I'm quite impressed with it as a technology. I'd like to see consumer devices start to use it too.