Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

ADSL works over wet string (2017)

revk.uk

Post reply on HN
Print view View original

91–100 of 157 posts

Re: ADSL works over wet string (2017)

#91

Post by ohyeshedid »

DaiPlusPlus wrote: post #45
giardini wrote: post #23

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. 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).

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?

Re: ADSL works over wet string (2017)

#92

Post by spookthesunset »

xattt wrote: post #57
someperson wrote: post #8

Earlier quoted context omitted.

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).

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.

Re: ADSL works over wet string (2017)

#93

Post by mattlondon »

samwillis wrote: post #61
DaiPlusPlus wrote: post #45

Earlier quoted context omitted.

> 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 th…

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 :(

Re: ADSL works over wet string (2017)

#94

Post by Terry_Roll »

hereforphone wrote: post #86
Terry_Roll wrote: post #83

Earlier quoted context omitted.

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 bro…

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.

Re: ADSL works over wet string (2017)

#95

Post by techdragon »

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!

Re: ADSL works over wet string (2017)

#96

Post by kazen44 »

ohyeshedid wrote: post #91
DaiPlusPlus wrote: post #45

Earlier quoted context omitted.

> 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).

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…

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.

Re: ADSL works over wet string (2017)

#98

Post by hereforphone »

Terry_Roll wrote: post #94
hereforphone wrote: post #86

Earlier quoted context omitted.

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.

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

Re: ADSL works over wet string (2017)

#99

Post by kazen44 »

oasisbob wrote: post #89
stefan_ wrote: post #77

Earlier quoted context omitted.

The more you learn about this ancient cable technology the more absurd it becomes. We shower these fuckers with money but they would rather keep their paper insulated phone lines with permanent compressors and dryer running than braindead simple fiber. No wonder it is permanently broken and they can't keep a single 9 of reliability.

Fiber may be simple, but the way we use it is not. Unlike copper, a GPON fiber install is going to have active electronics and splice trays for every several dozen subscribers. Plenty of opportunities for water ingress to still cause problems.

Also, sending a singal across fiber is definitely not easy.

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.

Re: ADSL works over wet string (2017)

#100

Post by NavinF »

hereforphone wrote: post #97

I think this relies on the particular string being a linear time-invariant channel. There is some limit where the string won't react accordingly (at a certain low or high frequency). What is that later phenomenon called, anyone know?

Hmm the author had to use salt water to get it working. Maybe resistance is the limiting factor rather than dispersion. In which case a higher power modem or some sort of amplifier would get this working over >2m distances.
Post reply on HN