ADSL works over wet string (2017)

ADSL works over wet string (2017)


·December 4, 2021


ADSL, being essentially a form of alternating current, will pass through an air gap. I was enlightened on this by an AT&T tech who pointed out that one of my ADSL lines had several breaks and could not carry DC but the ADSL signal still came through. The other line was dead so I was running essentially on one wire with an earth ground. Here is an interesting discussion:

"Phone line with 1 broken wire still gets ADSL2"

Anyway, my hat is off to the people who designed and implemented ADSL.


> Anyway, my hat is off to the people who designed and implemented ADSL.

It's a blessing-and-a-curse: too many incumbent ISPs in highly-developed nations used ADSL's ability to run on anything as an excuse to put-off FTTH deployments (looking at you, BT).


I think we (in Stamford Lincolnshire, UK) must be pretty unique right now with TWO competing FTTP startups both rolling out on the same streets. One day you will see Lightspeed Broadband pulling their fibre through the BT ducts and putting boxes on the top of telegraph polls. The next day Upp Brordband will be on the same street. So bizarre they they are doing the same town!

Apparently we are due to have BT put in their own fibre in the next few months too. Really don’t understand why they are doubling up the infrastructure.

Hoping for a local price war!


Basically there is an enormous amount of capital (at least £10bn from startup providers) out there going into UK FTTH builds. BT focussed too much of content (BT Sport) instead of FTTH and private equity now thinks there is an opp to steal marketshare from BT/VM.

However BT have now now committed £10-20bn, VM probably a few billion.

It will quickly consolidate like it always does.


Very strange! Mine was not quite as happy a story, but here in Silicon Valley (1mi from Facebook) I got a local ISP announcing fiber, and the very next week AT&T was running their own lines. This was back in 2019, and it felt like "everyone" had fiber before we did. 2 years later I guess it feels like old hat. And the local ISP has not yet run the fiber they promised. But one fast ISP is better than zero!

Good luck with your deployment. I'm still so happy about it.


How strange to see my hometown mentioned! Still not too far away and yes hoping for some local competition


Here in high-density London, we're stuck with ~70mbps ADSL and not even cable.

Not representative of all of London, but at least around my parts it is slow ADSL or nothing :(


From previous personal experience in building new plants, and expanding existing plants: Cost of deployment and slow roi are the primary drivers of stagnating local networks.

Complicated corporate accounting, carrier incumbency, and weak governments are the core causes. Carriers being publicly traded companies really screws up incentives to fix these problems. It seems to be mostly a binary decision at the top; more profit or better service?


also, the infra (which ADSL runs on) was build in a time when telephone companies used to be either state-owned or a single monopoly with heavy goverment involvement.

Doing the same thing with fiber is necessary, but will not happen without strong govermental involvement.



They also did the same, stalling and delaying, insisting on introducing ISDN 64/128kbit instead of going straight to DSL like Holland did.


In hind sight wouldn’t 5g have been a better investment than fiber to home, I mean companies will have to have 5g to stay competitive in mobile anyway


No, because 5g is a shared medium. It can deliver... 3 gigabit/s? or something like that? Let's say it's 10Gb. That's 10gb shared with everyone in the vicinity, which is not great especially in high density areas like apartment buildings.

Furthermore, you still need to run fiber to the actual base stations anyway.


Perhaps in densely-populated areas, but certainly not in sparsely-populated areas.


>>...*my hat is off to the people who designed and implemented ADSL.*

Maybe a few will recall: San Jose California, in the epicenter of Silicon Valley -- but for some reason Comcast (was previously called *COVID*) -- and you couldnt get DSL in San Jose at the time .... literally down the street from Netflix, and freaking home DSL took YEARS for it to reach our houses...

(My point is that it was ironic that in the heart of silicon valley we couldnt even get DSL due to COVID/Comcast


Are you thinking of COVAD? IIRC, they were a competitive local exchange carrier, unrelated to Comcast.

As a CLEC, they could place DSL equipment in the incumbent carriers (mostly Pacific Bell/ATT, but Los Gatos Telephone company was absorbed by GTE/Verizon and I think sold to Frontier) and use the existing wiring to run DSL. In silicon valley, this doesn't offer great coverage; to get reasonable line lengths, you need to be in the telephone company's remote terminals and that's not available to CLECs.


In some sense, that's "just" radio. An antenna is a wire... it's sending a signal and picking it up from a very nearby antenna. Radio transmissions are all AC.

(Arguably, the real insight here is that the very existence of radio is impressive / unintuitive.)


The gap on the line acts more as a capacitor than an antenna, AC pass through capacitors, but DC does not.


It's a differential signal using a center-tapped transformer to drive the signal. It's actually using three wires if you count the ground.

This means it's symmetrical about ground and thus cancels it's own radiated field (eg doesn't interfere with adjacent lines).

But with one side open there is still a path for AC, which is through the other side and using the ground return.


this explains a problem i had in Ireland... ADSL worked, but phone line had to dial tone... engineer had no idea how it was working... mind you, ISP had sent him out to get better internet... i was on 8mb and was promised closer to 24... after he "fixed" it, it went to 6... so they were really not happy with the "engineer" when i canceled 2 days later...




Its DC. If you had to imagine it, think of it as a range of radio stations being broadcast down a wire instead of over the air and your router can tune in to all the radio stations at the same time and then piece together the different bits of data being broadcast. Long Wave would be ADSL, ADSL2, Medium Wave ADSL2+, and FM would be higher forms of ADSL to give you your 40Mb, 80Mb, 100Mb download speeds.

With this broadcasting of signals down a wire now known, it becomes somewhat unsurprising anything capable of transmitting an electrical voltage & current would be capable of transmitting ADSL. Not knocking their effort though, Arnold and Arnold have always like to demonstrate their knowledge. One of them has a personal blog which can be quite interesting.

I wonder if they have considered trying to adapt an SDR dongle to become an ADSL transmitter?


What's DC? "Radio stations" communicate via alternating quantities (EM waves)


The telephone cable coming into the house is 50volts DC is not AC like a powerline. I know radio waves are just that, waves, its how things like noise cancelling headphones work. Different frequency's give you different ranges or distances for 1 watt, which is why you can bounce Long wave around the planet.


Same thing happened once at my parents house. Quite confusing for some :)


That fact that this delivers 3.5 MBit/s really makes you wonder how many low speed connections out in the wild are literally broken cables that still have some amount of coupling somewhere.


I lived in a forested area as a kid and the copper wire was always breaking for various reasons (falling branches, old deployment, temperature and humidity, etc). The ISP would always attempt to reduce the speed and leave it at that. It took a lot of effort as well as personally locating the breakage to get them to come and repair it properly (and it still took forever).


Potentially apocryphal, but Telstra's copper cable network supposedly had its insulation made of paper, not rubber. I remember when it rained the curbside pits fill with water, causing slowdowns and frequent ADSL dropouts (until things dried out).


It took over a year for Ziply to repair the land line of my 90-year-old parents. 30+ hours on the phone with support, multiple visits by techs who were simply not interested in doing any work. I had a tech tell me, literally to my face, "this line is working fine" when the line was stone dead. Another told me that I had to buy all new phones because the ones my parents had were "out of date". (To humor him, I bought a $15 phone from a local electronics store, plugged it in and showed the tech that it wasn't working. He did nothing).

I have now learned that the WA state utilities commission is pretty interested when providers try to pull stunts like this. You can also dig out useful company contact information from the commission's website.


> I have now learned that the WA state utilities commission is pretty interested when providers try to pull stunts like this.

A number of years ago I worked at a CLEC, during that short window of time when they could exist. One of the more useful things I learned is how much power the PUC has. Every phone company has a team that deals with complaints coming in via the PUC and they are eager to resolve them. Not something I'd necessarily use in lieu of regular old customer service for most issues, but when the first and second attempts fail, calling the PUC will work 100% of the time.


I think this is common in places where they don't expect moisture to reach, but then things change and it gets there anyway.

If your POTS lines are down and the telecom company is telling you a "wet pulp repair" is underway, your phones are going to be down for a while because a bunch of paper-insulated cables need to be manually rewired because they got wet and corroded.

I found this interesting: - guess it's standard practice to dry out the lines, wrap in cloth, put dessicant and then seal it.


I know there are some telecom folks on here that may be provoked to correct me but pulp was standard before the advent of cheap plastic insulation in the 1950s on up. I live in the midwest and my brother is a lineman for AT&T. There is an astonishing amount of pulp-insulated phone line still in service today.

In order to keep it dry, the conduit that the pulp lines are run through is pressurized to 5-10psi. Anyone that has worked with air compressors knows that pumping ambient pressurized air down into underground pipes is a recipe for condensation, so high capacity air driers are required to remove the water before it goes underground.

Any kind of outage on the compressor or dryer is effectively an emergency because water infiltration can happen almost immediately, creating an outage and extremely expensive repair.




Many parts of rural Prince Edward Island (PEI) has DSL running on a phone system that’s probably original from modernization initiatives in the 1960s - 1980s. Party lines were the norm in some areas up west until late-1980s.


Back when a whole family had the same number and you had to ask whoever answered that you want to talk to so and so. Now days everybody has their own number and with caller id you (sometimes) know who is calling.

My daughter is gonna grow up not knowing any of the “shared phone line” etiquette because it is largely obsolete.


You spelled Germany wrong... X_x


This not strictly true: The original pairs were paper insulated, but they were enclosed in a lead sheath which prevented water entry. Plus the cable was pressurised with dry nitrogen to keep out any water. Plus the flow of Nitrogen was monitored so that any pinholes could be detected before they caused a problem. Of course when Telecom was privatised all these quality control issues went out the window.

But there's a further point, the problem with moisture in the lines is the corrosion caused by electrolysis, which in turn is caused by the 50V DC on the lines. So even with modern plastic insulation, the copper would be corroded away by any electrolysis.

One last point: Rubber was almost never used as an insulator on phone lines.


Sums up my youth on ADSL in the hills of LA. Couldn't get a static IP address on coax/cable so I convinced my family to pay out the ears for DSL w/ a static IP. Performance was terrible!


I had a bonded DSL line for a while when I lived in the Bay Area with service coming from two different twisted pair lines. One line was consistently ~18Mbps, the other barely 3-5. It was pretty clear that one of the pairs was good and the other was broken somewhere alone the way. The lines were all in a bundle, with no way to discern what was what any individual strand was in the bundle (or which was broken or shorted). No one had any motivation to find the break and repair it. And because the line was technically “working”, ATT wouldn’t move it to a different pair. Sonic was the ISP with ATT handling the physical lines.

Still amazing that it worked at all.


You can do time domain reflectometry to find out where the breaks, sharp corners and reflections are in the cable.

Some modems have special debug modes in that can do this too - then you get to know exactly how many meters along the wire the break is. When you get close, you can hook a resistor to the line and rerun the test and it'll tell you how many meters forward or back you need to go to find the issue.

Pretty easy to track issues down that way.


Yeah, this was in a neighborhood bundle with many… many lines together. No one was going to dig into that to find which line a mouse or squirrel had chewed the insulation off of. I remember running a few diagnostics, but as it was “working”, no one was going to try to fix it. The ISP couldn’t even convince ATT to move the bad line to a different pair. Which was sad. I was supposed to be in the 40Mbps range, but could only get ~18-20. Also — this was enough bandwidth for us at the time, so I just ran off of the single line and was good. Given some of the dsl horror stories, we weren’t too and off.


A lot of the problem lies with distance.

10km of fiber (with transcievers made for that kind of fiber and distance)... gigabits without any issues.

10km of copper pairs for *dsl? Good luck.


Wet string? OK, fine.

But I defy ADSL to work over something really challenging. Like Telstra copper in Australia.


You think the outback’s bad? Try getting it to work over AT&T copper in heart of Silicon Valley!


Came here to make the same joke. Sure it isn't an insightful comment worthy of great praise. But consider my hat tipped to you.

3.5mb down is faster than my mother used to get from her farm north-west of Kempsey NSW. Though to be fair to Telstra she lived about 30km from the nearest town not 2m like the length of wet string.


When I lived in Perth about a decade ago, I had a DSL line from an exchange about 3-ish km away. If I remember correctly, I got 512kbps down, and 56k modem speeds up.

This was not outer-whoop-whoop either. Metro Perth.

Telstra. Ya gotta love 'em.


Related: ethernet over barbed wire:


There are IEEE standards for single-pair Ethernet:

> In addition to the more computer-oriented two and four-pair variants, the 10BASE-T1,[17] 100BASE-T1[18] and 1000BASE-T1[19] single-pair Ethernet physical layers are intended for industrial and automotive applications[20] or as optional data channels in other interconnect applications.[21] 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.[22] As of 2021, the P802.3cy Task Force is examining having 25, 50, 100 Gb/s speeds at lengths up to 11 m.[23]


Including power delivery:

> The IEEE 802.3bu-2016[12] amendment introduced single-pair Power over Data Lines (PoDL) for the single-pair Ethernet standards 100BASE-T1 and 1000BASE-T1 intended for automotive and industrial applications.[13] On the two-pair or four-pair standards, power is transmitted only between pairs, so that within each pair there is no voltage present other than that representing the transmitted data. With single-pair Ethernet, power is transmitted in parallel to the data. PoDL initially defined ten power classes, ranging from 0.5 to 50 W (at PD).

> Subsequently, PoDL was added to the single-pair variants 10BASE-T1,[14] 2.5GBASE-T1, 5GBASE-T1, and 10GBASE-T1[15] and as of 2021 includes a total of 15 power classes with additional intermediate voltage and power levels.[14]



Sadly, there's not much in the way of equipment for this. I could really use two small 10BaseT-1 to 10BaseT converters, preferably both powered from one end.


Since most of the 1000Base-T1 gear is still unreasonably expensive/effectively impossible to get quickly in small quantities, you can run 100mbps and 1gbps Ethernet over "reasonable" lengths of single twisted pair using MoCA adapters plus coax->twisted pair baluns. Achievable cable length will obviously depend on EMI conditions, but I've had reasonable success with this method on twisted pairs in industrial robots.


Seems to be mostly in the automative and industrial space, with some embedded stuff.

I could also see it being useful for door security (badge readers, latch control).


I remember in the 90s when we were deploying a business campus, we first used ADSL services from the local carrier, but not for long.

We discovered we can get "dry lines", basically just rent copper run from site-to-site, nothing on it from local carrier. Slap ADSL modems on each and we got max throughout, at a fraction of the cost. Then we upgraded to SDSL, and that was like hitting the jackpot.


I'm not sure if I'm reading this right. You got an unused copper line and stuck ADSL modems on both ends that talked to each other?


Almost. Search "dry loop DSL" or "naked DSL".


3.5Mbit!? Says a lot about my parents paltry 1Mbit. Perhaps their line was low on sodium.


The cable analyzer is showing about 55db of loss across 2 meters. That's about equivalent to the loss across 4km of "good" copper.


I kid, the issue was solved some time ago - a telecom engineer pinned it down to a soggy junction box.


That’s funny because my SO’s parents have 1.5Mbps DSL by contract. For only $100/mo they can jump up to 12Mbps. USA and 1 hour from me where I have gigabit docsis 3.1.

If they had 1Mbps because of a fault that would be more unfortunate than unfair.


3.5mbit over 2 metres


Personally I prefer a bit of garlic powder, say 1tsp, sprinkled over my router before any large downloads.

Although last year when I bought Cyberpunk I found that a bit of curry powder sped up the ~70GB download quite nicely.


Your parents’ ADSL noodle soup is a little bland.


I’ll go one better, ADSL doesn’t even need two continuous wires to work, one is good enough as long as the other is just barely electrically coupled. I had a 12 month epic journey to get a performance fault fixed on my line. In the end it took 6 technician visits, three senior technicians and finally one smart experienced technician to check the “not in the textbook” faults for a performance degradation and he discovered that my line had was actually mis-wired! I had one wire connected to the exchange and another was a barely connected lose joint (actually disconnected but still technically in the plastic joint housing) about half way to the exchange. I was still getting a few megabits with intermittent drop outs for months on what amounted to a single wire!


This thread is a good reminder to be very thankful for my £20/month unmetered 1gbit central London FTTH.


Can ADSL survive an acoustic coupler?

To give it a fair shot, assume the driver and microphone are studio quality rather than the kind you’d find on a 1970s telephone handset. I bet it’d work pretty well.

But the real question would then be: how much of an air gap could you create and still get a connection?

Could you post to HN on an ADSL signal that’s being screamed across the length of the room you’re sitting in?


ADSL upstream starts at 25kHz, downstream at >120kHz. So probably not. Purpose-designed ultrasonic hardware might be able to.


Or an acoustic coupler which also acts a little like an electrical coupler at higher frequencies because it has no electrical shielding...


Not sure if this is within the spirit of the question, but: The individual ADSL bands are only 4 kHz wide, so you could modulate 4 or 5 of them down into the audible range (20Hz - 20kHz) and back up again after the transmission through the acoustic coupler. In theory, ADSL should then pick those bands to transmit the data.


Most HDMI and Coaxial cables are little more than wet string

>only 10% of the HDMI RMCD met an acceptable EMC quality of at least 50 dB coupling attenuation


RMCD sure is an awkward way of spelling "cable". Especially when nobody else seems to use this acronym?


The miracle of modern signal processing!


Our homes' water supplies are untapped options for data connectivity.


joking aside, I remember a while back that there has at least been cursory investigation into running high-speed internet cables through water pipes.

Presuming you have water pipes to your property, could be easier than digging up roads etc.

Only issue might be if you have a leak and need to shut off your water!!


The linked article (and government push to do this) completely ignores the fact that this is done frequently now.

It's used to get the last few metres into the home, e.g. from the boundary to the inside of the house. You put a swept tee in at each end, after the stopcock. Water off, dig down adjacent to stopcock, cut pipe, shove a drinking water rated duct down the pipe through the small port on a swept tee. Shove some chlorine tablets in the pipe and couple up to the new swept tee. Repeat interception at other end outside or indoors, and then use standard fibre cable blowing through the inner microduct, and away you go.

There's a huge amount of disused water pipes in most developed nations which are frequently used, similarly using sub-ducting, and you can run cable through mains - but have to come out every time there's a valve, so practically it's usually cheaper to dig. Where it comes in handy is where there's areas you can't practically dig up, e.g. major roads with old pipes underneath.

Source: Have done a bunch of this for a major UK telco.


> I remember a while back that there has at least been cursory investigation into running high-speed internet cables through water pipes.



There is company in Czechia which provides optics via sewage. I guess it is cheaper to use existing infrastructure than to place new pipes under roads.


Sounds a bit like this "How TiSP Works"


"cheaper" is an understatement.


Discussed at the time:

ADSL over wet string - - Dec 2017 (88 comments)