ADSL works over wet string (2017)(revk.uk) |
ADSL works over wet string (2017)(revk.uk) |
"Phone line with 1 broken wire still gets ADSL2"
https://forums.whirlpool.net.au/archive/9yzp5wr3
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).
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!
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?
They also did the same, stalling and delaying, insisting on introducing ISDN 64/128kbit instead of going straight to DSL like Holland did.
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
(Arguably, the real insight here is that the very existence of radio is impressive / unintuitive.)
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.
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?
But I defy ADSL to work over something really challenging. Like Telstra copper in Australia.
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.
This was not outer-whoop-whoop either. Metro Perth.
Telstra. Ya gotta love 'em.
> 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]
* https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair#Sin...
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]
Although last year when I bought Cyberpunk I found that a bit of curry powder sped up the ~70GB download quite nicely.
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.
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?
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!!
https://www.theguardian.com/technology/2021/aug/09/uk-launch...
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.
Oblig:
https://ec.europa.eu/docsroom/documents/46433
>only 10% of the HDMI RMCD met an acceptable EMC quality of at least 50 dB coupling attenuation
ADSL over wet string - https://news.ycombinator.com/item?id=15908107 - Dec 2017 (88 comments)
The next step would be to mandate fibre cables in all new housing. Along with ONT and Router in one solution.
- https://www.quora.com/Is-cellulose-fibre-conductive?share=1
- https://duckduckgo.com/?t=ffab&q=conducting+polymers+example...
In some cases I would be forced to use a cat-5 or even poor quality cat-3 where two pairs are for ethernet , one pair for A/VDSL and the blue pair for voice/POTS (voip to pots converted)
And of course, if the interference can get out, it can also get in. Which is why Powerline Ethernet can work just fine one day, then suddenly stop working.
Plus the big problem with any ODFM system is that it is incredibly intolerant of wideband interference, eg a series of sparks. The reason being that the band of ODFM channels are fed straight into an A/D converter without channel filters. So each time that wideband interference takes out the system, the modem has to stop and renegotiate each channel from the start.
To any experienced RF engineer, Ethernet over Powerline (or any ADSL system) is a disaster waiting to happen.
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.
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: http://etler.com/docs/bsp-archive/629/629-295-300_I3.pdf - guess it's standard practice to dry out the lines, wrap in cloth, put dessicant and then seal it.
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.
Still amazing that it worked at all.
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.
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.
Doing the same thing with fiber is necessary, but will not happen without strong govermental involvement.
Works great. Even my village of several hundred people has fiber now.
Furthermore, you still need to run fiber to the actual base stations anyway.
Where I am 5g is same price as fixed broadband but faster for my plan.
Are you paying and using 1g/s have no caps ?
If they had 1Mbps because of a fault that would be more unfortunate than unfair.
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.
https://www.centurylink.com/wholesale/pcat/fcp.html
I was one of two providers in their 13 state region that used it. It was really successful and let us put in ADSL and then Ethernet over Copper in business parks.
Thanks a lot for the link though. Are you into green electronics by any means ?
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.
My daughter is gonna grow up not knowing any of the “shared phone line” etiquette because it is largely obsolete.
Some of the first-hand accounts I’ve read talked about neighbours listening in on conversations. People could tell a snooper was on the line because the volume of the other caller would drop. There was a social aspect to the whole enterprise because you could tell the one nosy neighbour to get off the line and the volume would magically raise.
I could also see it being useful for door security (badge readers, latch control).
That’s true. But very slowly in electrical terms. If I remember right the actual electronics in a reasonable circuit I read about was something like 1” per second. The vast majority of work done is an electron shuffle of bouncing into the next one in space.
That model isn't right; think about a transformer - energy is transferred between conductors that are not physically connected at all.
Watch the video. Like waves in the ocean, are water molecules pushing each other and making the wave? Or is the wave carrying the molecules with itself? Or both things at the same time?
There might be a DC component, but ultimately all the ADSL modem cares about is the AC part.
It's common parlance to say "DC component" to refer to any offset from zero in the AC waveform. So, for example, a typical analog telephone line when in use could be described as having a DC component of around 5 volts (referred to as the battery voltage for historic reasons), and then an AC component of around a few volts (varying by signal amplitude) is superimposed. Someone else mentioned the case of an AC signal with its center point not at zero actually being a pulsed DC signal... but both are correct in their own ways. An AC signal with a DC component will have its "neutral" voltage wherever the DC component puts it. This isn't usually referred to as pulsed DC because the AC signal usually starts out that way---as AC, and the DC component gets added. To receive the signal, the DC component is essentially removed. A lot of real systems end up this way either intentionally (in the case of phones) or unintentionally. Much of the time people talk about a DC component its in the sense of an undesirable one induced for some reason. Many people who use SDRs are familiar with this as common direct-conversion SDRs virtually always pick up a spurious DC voltage in the down-converter used to bring the selected frequency band into the range of the ADC. This results in the so-called "DC spike" in the middle of the tuned band.
Now, others have said, and elsewhere you have probably read, that telephone battery voltage is 48-ish volts (varies somewhat by central office equipment and line loss, phones are expected to tolerate a wide range). That's true, but when a phone is taken off hook it closes the loop (while presenting some resistance) and the voltage drops much lower. One of the odd things about DSL from a telephony perspective is that, unlike normal telephone applications, it is designed to function whether the phone is on or off hook. As a result, DSL devices do not make assumptions about the battery voltage, which during DSL operation can vary from off-hook of a few volts to ringing of around 100 volts.
Another odd detail of telephone circuits is that typical local loops use two wires, one pair, for audio both directions. The telephone, though, needs an "in" and an "out" to connect to the microphone and speaker. Similarly, the telephone network itself predominantly operates using pairs of two separate signal circuits, one for each direction, as this greatly simplified analog telephone systems and is required for digitization for digital ones. This is achieved by the use of a hybrid on each end of the phone line, which historically was a type of matching transformer that used some clever electrical tricks to provide three taps. One has signals both directions, the other two have one of each signal cancelled out based on matching or mismatching the impedance of the telephone line. It's a bit hard to wrap your head around and rather clever. Unfortunately hybrids, being analog devices, are never perfect and introduce some oddities on the line. DSL devices must use DSP methods to contend with phase shifts and other issues caused by hybrids. Today, it is increasingly common for not just telco equipment but also consumer phones to also use DSP instead of a hybrid to isolate the directions, since the DSP can self-tune to achieve a more perfect result. Amusingly, so-called "sidetone" in telephones (being able to hear yourself in the speaker) is an undesired result of imperfect performance of the hybrid but turns out to be an important comfort to humans, so DSP-based systems usually intentionally mix the outbound audio into the inbound at a low level.
All of this adds up to DSL being surprisingly robust. Unfortunately, there is a downside to the fact that DSL relies on frequencies beyond what telephone circuits were originally designed to convey: line loss of DSL signals is very high, which results in a rather short practical range for DSL, typically only a few miles even with a local loop in good condition. DOCSIS is able to achieve tens of miles, even at the very high speeds it supports, because coaxial cable and the fittings and amplifiers used are designed to carry high frequencies with minimal loss. Even so, the push to greater-than-gigabit speeds has required outside plant upgrades for cable networks, just as the push to expand DSL coverage (and less so, but in some markets, speed) has lead to outside plant improvements to the telephone network, such as heavy use of remote DSLAMs that "convert" most of the subscriber loop to a longer-range medium like fiber.
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.
Aka Cunningham’s law
> Any kind of outage on the compressor or dryer
I’m confused: isn’t a bigger concern any physical damage to the conduit anywhere in the run that is too large for the compressor to overcome? Or are we talking football-field-sized compressors here?
Plenty of opportunities for water ingress to still cause problems.
Historically there was a continuous upgrade of equipment as the technology improved. Manual exchanges became automatic, step-by-step gave way to cross-bar which gave way to electronic exchanges. Analog phones were replaced with digital and ADSL. And had that steady improvement continued, ADSL would have routinely been replaced with Optical fiber.
What stopped the perpetual upgrades was the arrival Thatcher/Regan/Howard and the advent of Neoliberalism. Which meant that anything which provided a Public Service (gasp Socialism!) was completely abandoned. We are only now starting to realise the long term cost of their vandalism.
However BT have now now committed £10-20bn, VM probably a few billion.
It will quickly consolidate like it always does.
Good luck with your deployment. I'm still so happy about it.
Not representative of all of London, but at least around my parts it is slow ADSL or nothing :(
ADSL tops out at ~24Mbps while VDSL can go much higher, albeit over shorter distances than ADSL
That wet string would have been an upgrade for me.
100Mbps isn't great for fibre. I'm on 100Mbps just on plain old HFC.
In signal transmission theory people almost always think in terms of frequency ranges.
Any DC component is simply a frequency set to 0 - that can be ignored.
Similar to the earth magnetic field when talking about radio transmission in air.
I wonder if the circuit lag from sidetone is something that affects hearing aid users, considering they have another circuit in which audio has to go through before the user gets to hear, but I wonder if the sidetone passes through their skull or jaw bone instead, totally bypassing their hearing aid. I guess the speed of electrical circuits, the speed of electricity passing through a circuit, is a bonus for our slower nervous system and brain which is only running at speeds of up to the old 286's/386's/486's iirc.
>DOCSIS >coaxial cable and the fittings and amplifiers used are designed to carry high frequencies with minimal loss So the old Token Ring network never died out it just morphed into Cable networks?
>heavy use of remote DSLAMs that "convert" most of the subscriber loop to a longer-range medium like fiber. And then there is Deep Packet Analysis (DPA) which can not only be used as a firewall like solution, but also used for compression/decompression to increase the bandwith of fibre by virtue of using compression algo's that give high rates of compression for different types of packet streams based on the type of data and also the way its delivered.
May be Youtube's delivery of packets from a variety of servers in a co-ordinated manner could negatively affect the compression algos, that could then be used to deliver over fibre and other networks, because we cant assume all network traffic for a service comes from one server. At the same time, this method of delivery can also be used to work out where compression of packet data is taking place on a "hop" or number of hops on the network to the end user, by virtue of packets arriving out of order. I think that method could be used to work out physical layouts of telephone networks between their servers and the end user. I then wonder are the spooks/telco providers in some country's using crypto currency like "tumblers" to make the telephone network change so no route is ever the same.
Its interesting but frustrating when looking back at some of the ways things were explained when at school, education can be used for so much more intelligence gathering than meets the eye.
All this results in 40-50v being considered a normal on-hook line voltage, but it can vary more in the real world. Of course modern SAIs or RLCs or what have you tend to use solid-state regulators that keep a very tight 48v, so I'm sure the variation is much lower in like modern suburban neighborhoods than it is in cities or with older exchanges.
When off-hook, current starts flowing and the line relays and local loop come into play. The line relays are not tightly standardized and range from say 400-700 ohm, but unless you're pretty close to the exchange the line resistance of the local loop is greater, which can be 1kohm or more. Then the actual telephone instrument has a resistance due to the current it uses for operation, 200 ohm is perhaps average but it varies plenty, I think the WECo phones were usually 180 ohm nominal. Both line resistance and telephone resistance vary widely. A total loop resistance of 2400 ohm could be called a maximum because it allows the phone the 20 mA that's considered a minimum for reliable telephone operation, but lots of equipment will work out of that range, especially since so many newer phones have an independent power supply and digital voice circuit. On older switches, where "older" includes plenty that are still in wide service like 5ESS, the line cards have a couple of jumper options to adjust the relay resistance in order to bring loop current up or down depending on length of the loop. That's mostly because high loop currents due to a short loop can shorten the service life of equipment.
Nothing is really regulated (on older equipment and per specs, newer equipment tends to have voltage regulation as a result of using more advanced transistorized power supplies), neither voltage nor current, and so it can all vary within a fairly wide range. This is surprising from the modern perspective but not so much when you consider that the "standards" here are a hundred years old. Newer switches, RLCs, etc often measure the current on lines and raise trouble alarms when it's too high or low, which does impose certain tighter bounds.
ADSL is basically modulating a radio wave over a cable directly to another device. Fiber requires high quality optics, high quality lasers, tons of active hardware if you want to do it at scale. (not to mention the mind boggling physics and manufacturing required for things like DWDM, optical path switching etc).
Fiber optics have existed since the 80's yes, but prices of high quality fiber solutions have only dropped massively in the last decade or so.
GPON makes this scalable and affordable, but at the cost of technical complexity. Fiber (as in, the cables themselves) is far cheaper to produce compared to copper, but this has mostly to do with the price of copper and not manufacturing techniques.