[giardini]

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"

https://forums.whirlpool.net.au/archive/9yzp5wr3

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

[DaiPlusPlus]

> 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).

[samwillis]

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!

[martinald]

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.

[samwillis]

Thanks, I figured it was something like that. One of the startups here is a bunch of former BT execs so I was assuming they were hoping to exit by selling either to BT or VM.

[rconti]

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.

[bcrl]

Your incumbent killed the local ISP's project. Fibre customers generally won't change ISPs in the first 2-3 years of having service, so being undercut by the incumbent makes it worthless to continue with the cost of construction when you'll only get a handful of customers. I know because the incumbent has done exactly the same thing to me. A project that planned on having 140 customers can't be supported by 5.

[rconti]

They're actually still rolling out, just slowly. Of course, this might well have caused the slowdown.

[aphrax]

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

[mattlondon]

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 :(

[ccakes]

Nit: if 70Mbps isn’t a typo, then you’re on VDSL not ADSL.

ADSL tops out at ~24Mbps while VDSL can go much higher, albeit over shorter distances than ADSL

[charcircuit]

Are you suggesting 70Mbps is slow ADSL? There are many places where not even a tenth of that speed is possible.

[SturgeonsLaw]

I had a chuckle at the 3.5Mbps that the wet string was getting in the article. When I first moved in to this house, I was getting around 3Mbps on ADSL. Thankfully now I'm on 100Mbps fibre (not amazing by global standards, but good by Australian standards).

That wet string would have been an upgrade for me.

[brokenmachine]

Knew you were from Australia as soon as you mentioned your old speed.

100Mbps isn't great for fibre. I'm on 100Mbps just on plain old HFC.

[tgpc]

BT have left a large number of people on ADSL. No VDSL upgrade.

[867-5309]

it's the UK average for urban ADSL. and those many places are where the FTTH startups are springing up

[ohyeshedid]

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?

[kazen44]

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.

[verve_rat]

Indeed. New Zealand has had a pretty successful fiber roll out over the last several years because the government awarded exclusive contracts to fiber providers that then have to provide access to their network to all ISPs.

Works great. Even my village of several hundred people has fiber now.

[unixhero]

Telenor

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

[hungryforcodes]

Meh

[zaphirplane]

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

[edude03]

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.

[namibj]

Yes, but at those wavelengths you can do substantial amounts of MU-MIMO/beamforming.

[zaphirplane]

I think you are answering “is it better bandwidth per household”, while I am talking mb/S per dollar and ROI.

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 ?

[edude03]

Personally I am yes, but I know that's not the case everywhere. I get that you mean in terms of ROI, but that's ROI for the business, not for you the customer. So I guess what I'm getting at is, why would you suggest the thing that's better for the business but worse for you?

[zaphirplane]

Because it’s not worse for me, it’s the same cost and value. To the other point, companies outside monopolies and prestige add a margin, if they do it cheaper it flows to the consumer, a company isn’t going to have low fiber margin if they can have better 5g margin, but I suppose the proof is in the pudding (and government incentives)

[Ancapistani]

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

[samstave]

>>...*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

[toast0]

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.

[djweis]

It was available in CenturyLink/Qwest areas. Not sure about now, a lot of the loop products have been grandfathered recently.

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.

[geofft]

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.)

[y04nn]

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

[Johnythree]

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.

[tiernano]

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...

[Terry_Roll]

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?

[hereforphone]

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

[Terry_Roll]

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.

[leoedin]

Radio waves down a wire are by definition AC. Otherwise they don't work. The voltage must change, thus the current must change, thus it is AC. Just because it's not 50/60Hz AC like a powerline doesn't change that.

There might be a DC component, but ultimately all the ADSL modem cares about is the AC part.

[Eelongate]

Couldn't you send an amplitude modulated signal down a DC line by modulating the voltage but keeping that voltage always above zero? If the current never actually reverses, it wouldn't be AC as I understand it. It would be PDC, pulsed direct current.

[goodpoint]

> modulating the voltage but keeping that voltage always above zero

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.

[hereforphone]

48VDC but yes. Sounds like we're agreed that the information is being transmitted via AC or another alternating signal.

[Terry_Roll]

I wasnt taught that radio waves were to be considered identical to AC power down a cable but when thinking about it, they probably are identical with waveform properties and the difference being the medium they are travelling through.

[jcrawfordor]

The exact details become confusing and get into some physics details, but in practice radio frequency on a cable is basically an AC voltage that needs special care to not be lost to inductance and other effects. This is of course part of the general trend that DC through gamma radiation are in many ways the same thing.

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.

[Terry_Roll]

> 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.

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.

[Johnythree]

The reason for your confusion is that the telephone exchange sends a constant Current, not a constant Voltage. There is 48V, but it's behind a 300+300Ohm relay which limits the current.

[Johnythree]

Phone lines use an AC signal which is superimposed on a DC current. The DC is used to power the phone.

[andoma]

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