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ADSL over wet string (revk.uk)
337 points by tomkap 37 days ago | hide | past | web | favorite | 88 comments

I linked this to my dad (who's been a network engineer and CIO-type for nearly thirty years) and his response kind of floored me: "yeah, we did this with ARCNET. Brine-soaked twine." So, one, this is Older Than It Looks, and two, apparently my dad might be a wizard?

Also reminds me of ethernet over barbed wire. Seems like similar things have been done for a long time...


>Brine-soaked twine.

reminded about other sodium ion transmission channels - our nerves.

Man, I wish my dad was technical. Treasure that relationship.

My dad did CS in the 70s then got into sales. So our tech talks usually go right to, "do your languages do recursion? That was a big deal when I was doing Cobol on UW's PDP8" or something along those lines.

Always with the recursion.

"Does this conversation?"

I've often wondered if Ethernet can be ran over brine or wet string, if even only just a few inches. I played with the idea once unsuccessfully but never put more than five minutes into it.

I wouldn't expect modern 100BaseT or such to work, but probably the older 10Base2 over coax type ethernet i'd expect to work.

"The standard on copper twisted pair is IEEE 802.3ab for Cat 5e UTP, or 4D-PAM5; four dimensions using PAM (pulse amplitude modulation) with five voltages, −2 V, −1 V, 0 V, +1 V, and +2 V."

if you can rig the equipment to provide five voltages over four dimensions...

Years ago, I tried the same thing on ham radio - made an antenna from a piece of wet string and tried to call cq.

It worked a charm, though I had to continously wetten the string as I applied RF power to it.

(21MHz ground plane antenna; eased the top end of the string through a hole pierced in an empty beer can, suspended it from a tree and filled the can with salt water.

Losses were huge, so antenna was easy to tune. Not the best of radiators, though, but I did work twelve or thirteen countries with it.

Cost of string and beer - $4.

"Antenna this end is the proverbial piece of wet string - literally. Back to you." -Priceless.

A garden hose filled with salt water is superior technology. It does not dry out and has a good size diameter. Better bandwidth performance than a thin wire.

Just got my HAM license and callsign. Gonna try this out.

Just make sure not to use too much power - ten watts is plenty to start with.

Oh, and congratulations. You're in for a treat. (Though I would suggest not using wet string as your only antenna. :-))

73 de LB1LF /OddE

You really do not want to use too much power because when that string dries up you'll end up frying your end stage if the stars don't align.

Stick a SWR meter inline and keep your eye on it.

I've used some pretty dicey end-fed half waves but that takes the cake!

Probably harder now that we're in a solar minimum but you'd have decent luck on CW.

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For context, this is Adrian Kennard's blog. He's the CEO of AAISP (which I'd highly recommend for UK residents, they're extremely ethical and transparent; although I would not recommend their mobile service for different reasons).

I recently switched to AA from Virgin Media due to the unreliability of Virgin's service, but have found AA's to be no improvement.

I currently subscribe to both services and toggle back and forth whenever one of them stops working.

I recommend AA for their philosophy, and the debugging tools in their web interface are second to none, but in my brief experience the quality of their actual service is no better than anyone else's.

In my experience (been using them for a few years now), the difference is that if you contact them (via phone, e-mail or IRC) then they are significantly more likely to provide useful support vs. "Hmm, I don't see a problem. Have you tried turning it off and on again?"

They are still beholden to Openreach, but they will actively manage them vs. just take them at face value/accept what they are being told.

If you're seeing frequent drops in connection, contact their support. [0] They're very good at getting openreach to fix problems.

Another option for you in particular (if you're willing to keep paying for both virgin and AAISP) is to set up a router with multi-WAN support which can load balance between both wans and handle failures, instead of swapping manually.

[0]: http://aa.net.uk/support.html

You probably already know this, but I think it should be pointed out for others: this is not a true fail-over. The connection still gets dropped and needs to be reestablished.

So, an online game will disconnect and a video stream will stop. You will however be able to reconnect or refresh right away.

AA provide true fail-over if you buy multiple lines from them with different backhaul providers, and have a separate solution that will provide true fail-over with lines from other ISPs(!!)

I had it for 2 odd years: you get a few dropped packets before the system realises a line has become unavailable

if it hadn't been for the email telling me I'd never have noticed that a line dropped: connections remained established and downloads continued (at a lower speed)

yes, you can get true failover if you get two lines from the same provider. This will rarely give you an improvement of service though. To visualize it, this is (simplified) how the network looks on the ISP site.

    WAN County ---- WAN City ---- WAN Street ---- HOUSE
                                       |--------- HOUSE
The problems are mostly on the WAN Street level, were both failover lanes would end. This isn't always the case! just most of the time. And if both Uplinks are connected to the faulty device, they'll both have the same problem and cant failover.

let me repeat: it is possible to get real failover from the same ISP. It will however be extremely costly, and just getting two lanes from the same Street Router only gives you marginal improvements in uptime

So in the UK it's a bit weird: all the lines from the cab or exchange are owned by OpenReach, but carriers can set up their own backhaul from the exchange. Thus, if you have an upstream issue with one provider, your other provider may be still unaffected. I would have drawn the diagram like this:

   Network    //   Carrier     //    OpenReach    // Network
   Provider1 Internet <-->                   <--|
                           Exchange <--> Cab    |-> CPE    
   Provider2 Internet <-->                   <--|
BT and TalkTalk operate their own carrier networks for back haul, and networks like AAISP can let you choose which carrier to use for a line, hence why they offer the dual WAN CPE.

it is not extremely costly, it cost me an extra £20/month

the only shared infrastructure is the cable under the street being in the same physical duct, the copper wire electrically terminates in physically different equipment owned by a different company

they also offer a 3g backup on top of those two independent lines, which is completely independent of the physicality of the path of the copper pairs

they'll even let you announce BGP if you want to multi-home your (existing) PI address space yourself

it's not a normal ISP

we're very lucky in the UK that the way the telecoms industry is regulated allows a small techie focused ISP to operate on a national scale, instead of in one town

and you can use the same IP across different providers?

they would need to be on the same subnet... I don't see how its technologically feasible to implement across ISPs. (though strictly speaking possible with several routing protocols, just extremely unlikely)

TCP Packet Streams are always directed at an IP, and if that IP changes, a new Stream needs to be established. This will cause a disconnect and its no longer a true failover once that has happened.

Applications can be developed to gracefully handle IP changes, but a lot of them aren't.

yes, you can use the same IP across multiple providers; I this mentioned previously (AA will allow you to announce PI address space)

as for "I don't see how it is technically feasible": read up about BGP and multi-homing: they form the backbone of the internet

(just somewhat unusual on a consumer home connection...)

> in my brief experience the quality of their actual service is no better than anyone else's.

It'll be better simply because they're better at finding issues and following up on them, but like most ISPs in the UK, they do not have their own infrastructure.

There are three networks in the UK: British Telecom (BT, copper), TalkTalk (TT, copper) and Virgin Media (cable). Virgin Media, in my experience, is the most reliable network but unlike BT it is not available everywhere. AAISP use both the BT and TT networks, and will offer you what is available, or let you choose.

But if there are issues with BT/TT, you're outta luck. You can get, if you like, two lines and have a failover or whatever, AAISP will in my experience support you way, way more than any other ISP.

> There are three networks in the UK:

It’s getting better though. Various smaller towns have access to Gigabit internet at home now, but it’s still a tiny percentage of the population (around 1.67%). https://www.ispreview.co.uk/index.php/2017/09/ultrafast-fibr...

BT & TalkTalk both use OpenReach's infrastructure for last-mile; they have separate backhaul networks but the limiting factor is always the copper from the cabinet or exchange.

I would say, the UK has 2 major infrastructure networks (OpenReach, split off from BT, formed from the GPO; Telewest:NTL, now absorbed into Virgin Media) + some minor, growing networks (CityFibre).

There are way more than three networks in the UK, but BT, TalkTalk and Virgin Media are by some measures the most popular and broad in reach... Vodafone and Sky are two other common ISPs that have unbundled the local loop in the same way as TalkTalk (i.e. they have equipment in BT exchanges so that no BT backhaul is needed).

See https://availability.samknows.com/broadband/ for what is available in your area (may not include other mobile, satellite, fibre providers)

Can't wait for CityFibre & Vodafone to get busy blowing cable everywhere and leaving OpenReach in the dust behind.

Coming from SF & Sonic's tremendous quest to run fibre in Sunset, the state of broadband in the UK is atrocious. There's 4 street cabs between my house and the exchange, which is 200 metres away, and none of them have fibre (BT are planning to build 2 more).

I once had an issue where my phone line was completely dead, but I was still getting ADSL, just at very slow speeds. In the order of 1mbit.

After the technician came he told me that one of the two phone line wires had been broken off at the exchange.

In other words, there wasn't a complete electrical circuit.

The phone was dead but ADSL still works without even having a complete circuit.

I don't even understand how that can work at all.

Everything about a POTS operates completely from DC to audio band, from the DTMF tones [1] when you press a number to the signal that makes the phone ring (~90V@25Hz AC) [2], to the -48VDC power that makes the keypad light up and any electronics operate, backed up by massive battery banks and generators, in case of power outage.

ADSL operates completely beyond the audio band[2]. Since it's entirely a high frequency AC signal, with no DC component whatsoever, a break in a wire will just act as a capacitor, reducing the AC signal strength. Since a broken wire is a terrible capacitor, the signal strength will be reduced tremendously, but in your case, not enough to drop the link.

[1] http://www.etsi.org/deliver/etsi_es/201200_201299/20123502/0...

[2] https://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_...

Hmm, should have read your post first... Thanks for the more detailed explanation, and with that, my guess above, is on the money, interesting communication tech.

The most fascinating thing about any of these high-speed-over-crappy-wire technologies is that they all have very cool signal processing going on, with echo cancellation, crosstalk compensation, and even trading of signal response, all in an effort to design and transmit a sort of "anti distortion" distorted signal that, once passed through the distortion caused by the crappy wire, will results in the desired clean signal.

For a funny example of how sensitive some of these links are, just flick a 100m ethernet cable, running at 10G, with your finger. If you're of normal luck, this will cause a temporary changed in the electrical characteristics of the wire, and that "anti distortion" distortion to be temporarily incorrect, causing a interruption in the data!

I had the same experience, except it was my fault. I crimped a cable poorly. But I had no idea anything was wrong. I didn't even bother testing it because it Just Worked.

The phone company (Centurylink) just one day called me, "Hey, we think we see a problem with your line, and we're sending someone over to check it. Is Saturday okay?"

It's the most proactive I've ever seen a huge ISP be, and it really impressed me. Almost as much as getting nearly my full rated speed out of a single wire.

I'm guessing they called you because the connection was so bad the compensation for your line was interfering with other lines that ran parallel to yours. It is nice that they called you, the standard procedure is to disconnect you and when you call to complain, come out and fix it (and bill you for it)

I think you're probably right. I was fully expecting to be billed, especially when the tech ended up climbing under my desk. Normally, they draw a bright line at the dmarc.

But I cynically wonder if it didn't have something to do with my contract ending and the price nearly doubling, leaving me free to jump to the other provider.

It worked, though. I'm still with them. It doesn't hurt that the other provider is Comcast...

HF will jump that small gap easily enough due to capacitive coupling, POTS is a DC current to begin with as long as you're on-hook and very low frequency when off-hook so you're out of luck.

Interesting, I had a similar problem, suddenly no land line, and crippled Internet, then after a week, dead, I had nothing.

I used to work for a private TelCo, so checked all my inside wiring, then had a friend call in a trouble report, and it took the damn company 3 weeks! to clear the trouble, because their line test equipment indicated the line was fine.

After reading your post, I'm guessing it was a barely broken/corroded part of a pair in an outside "B" (connection) box, as I live within 1/4 Mile of the ocean.

Did the dog bark just before an e-mail came in?

I head that story years ago from my father, who's a network engineer.

I've always wondered if it's real, or one of those funny stories with a technical punchline. It seems feasible.

What story is that? Google didn't return anything.

>What story is that? Google didn't return anything.

I'm not able to find a definitive source, but it could be the following, which I have also heard from a retired BT employee:

"It's common practice in England to ring a telephone by sending extra voltage across one side of the two wire circuit and ground (earth in England). When the subscriber answers the phone, it switches to the two wire circuit for the conversation. This method allows two parties on the same line to be signaled without disturbing each other.

Anyway, an elderly lady with several pets called to say that her telephone failed to ring when her friends called; and that on the few occasions when it did ring her dog always barked first. The telephone repairman proceeded to the scene, curious to see this psychic dog.

He climbed a nearby telephone pole, hooked in his test set, and dialed the subscriber's house. The phone didn't ring. He tried again. The dog barked loudly, followed by a ringing telephone.

Climbing down from the pole, the telephone repairman found:

a. The dog was tied to the telephone system's ground post via an iron chain and collar.

b. The dog was receiving 90 volts of signaling current.

c. After several such jolts, the dog would start barking and urinating on the ground.

d. The wet ground now completed the circuit and the phone would ring."

I'll bet it was a German dog. German dogs 'bell'.


Search for "Berkeley Biff Dog"


1mbit is my usual throughput.. I hope I'll get the fiber soon

"As a bonus, fit tin cans to both ends and you get voice as well as broadband on the same wet string!"


I'm sure Australia's NBN will add this to their 'multi technology' mix any day now.

Every time it rains, my local copper pit fills with water and my internet drops out.

Maybe they should replace the copper with Damp Twine to the Node.

Take a net, dip it in water, boom! Mesh networking.

You're joking, but that was the first application I thought of.

It would be really interesting to create a low-throughput fallback network for neighborhoods using something like this. Though I suppose RF or optical are still quite a bit more practical.

Or copper.

You'll never justify your choice of "wet string" as medium of choice when things go south.

Hot dogs are also conductive, since they are also filled with salt water. I wonder if you could do ADSL-over-hotdog. Obviously the length would be limited by the length of a frankfurter, so you wouldn't be able to get more than a foot or so, but it would be an interesting experiment.

A pickle might work too.

So, now that the concept has been proven, are we going to see a proper RFC proposal to standardize this? There's still 110 days left for submissions. That should be plenty of time to test what string types and electrolytes work best for various applications, to and improve the distance limit.

After another 10 ADSL iterations, I think someone will accidentally forget to connect the wires and discover that it works just fine over the air.

You kid but this is literally what is being proposed in industry conferences: https://www.assia-inc.com/wp-content/uploads/2017/05/TDSL-pr... -- sending ~200GHz [sic] RF into the dielectric spaces between copper conductors and using the copper wires as guide (same principle as Sommerfeld-Goubau lines, except massively MIMO). (the same principle is also quite interesting to apply to above-ground power lines, btw, people have worked on that too)

People will do literally anything to avoid pulling fibre and "sending multi-hundred-gigahertz surface waves along rotten old voice copper" is apparently one of them.

Broadband without wires? Preposterous.

Yeah, how would we charge money for it?

Anyone have a link that explains (ideally with some math) how this works?

How it adapts to poor line characteristics? Seems that ADSL uses multiple frequency bins, probing each for signal-to-noise ratio and choosing parameters accordingly, because different lines have different attenuation/noise on different frequency ranges.

This article might be helpful: http://www.kitz.co.uk/adsl/adsl_technology.htm

The pair of parallel conductors (wet string) forms a balanced transmission line[1] just like the copper pair in traditional phone line. The ADSL transceivers at each end automatically adapt to the available transmission line; you'll note that instrument reports that this 2 meter line looks like 4.5km of copper; it is a very poor conductor, so the ADSL transceivers fall back to lower frequency operation, which is apparently sufficient for low speed communication.

I do wonder about impedance matching here. Traditional phone lines apparently have a characteristic impedance of either 600 or 900 ohms. That pair of wet strings look to be separated by about the right distance to produce impedance in that neighborhood, or maybe the line length is tuned to eliminate reactance. It isn't mentioned but I suspect that RevK understood this.

[1] https://en.wikipedia.org/wiki/Transmission_line

Whilst the impedance of the line under yesterday's test conditions wasn't measured, it was replicated again this morning, and from memory it was around the 900 ohm mark. I'll be testing again tomorrow (trying to run bonded data across two of them) so I'll try and get a recorded measurement of the line's impedance at some point rather than just something from memory.

Great! That will be very interesting. It was just guesstimation on my part but the diameter and separation of the strings looked similar to high impedance lines used in SW amateur equipment typically in the 400-600 ohm range. A couple sites I've read state that ASDL actually experiences about 100 ohms impedance as opposed to voice (600 ohms) due to the large frequency difference. If all that is true then bringing the strings closer together will lower impedance which should improve the match.

String wet with salt water conducts electricity similarly to wire.

I was curious about this line in particular.

> One of the key aspects of the technology is its ability to adapt to the length and characteristics of the line on which it is deployed.

DSL transfers data over specific frequencies. Certain frequencies will resonate better than others over certain lines. Here is an image of a line test conducted for a VDSL2 customer: http://wut.nz/images/spm/1027296.jpg. The redder the graph, the faster (up to the maximum VDSL2 speed) the connection is.

The vertical line is when the connection spontaneously resynced, and a new speed was attained based on the new conditions of the line.

For this particular customer, you can see that tones 410-460 show no transfer at all. This causes a reduction in speed, since those frequencies couldn't be used.



As I understand it, the endpoints test a range of frequency blocks (or "bins") and only use the ones where there is sufficient signal-to-noise. This is dependent on line conditions.

Heh, "line". That has a very different connotation in this case.

Saltwater conducts electricity.

It seems to conduct dsl frequencies pretty poorly - the first attempt had 56db loop loss, equivalent to that of a 4.5 kilometre copper line for just two metres of wet salty twine. Detailed line stats from the testset here: https://twitter.com/0x47DF/status/940634277967990784

It's only a ratio of 2250 estimated metres for each actual metre of wet string, perfect for low cost broadband needs! :p

I'm still amazed that it works at all, but I guess that does show how fault tolerant ADSL is...?

Sounds to me like they just need to tune their electrolyte balance!

The last mile approximator.

Perhaps some Australian NBN (National Broadband Network) customers would get improved speeds with wet string over their fibre to the node installations

I wish more science were taught using this kind of thing as a starting demo to provoke a lot of wonderment.

"salty wet twisted pair", lovely.

I once did this with HPNA 1.0

Not sure if science or another pro net neutrality piece.

"He got some proper string, and made it wet..."

idk what people thought i was alluding to here, i just thought it was a fun/funny way to talk about the experimental setup. get your minds out of the gutter!

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