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Comment by hackthemack | Hacker News Reader

I have to wonder if the cap (theoretical) on the copper wires was more because of the technology standards in play at the time. Surely the copper wires could have handled more if they did not have to carry voice communication (with the old tech specs of the time) any longer?

Ok. Searched around. Here is an article that states old copper could have carried 1 gigabit.

https://www.newscientist.com/article/2317040-ordinary-copper...

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The practical implementation of this (at the time) was ADSL, HDSL, IDSL, and SDSL. Those technologies all took one or two copper pairs, and terminated them on a DSLAM (or similar device in the case of HDSL) instead of on a telephone switch. For physical pairs connected to an analog voice port on a telephone switch, between the band pass filtering and DSO coding, you were never going to get more than 56kbps. The xDSLs could get between 144kbps to a several mbps in practice, depending on the variant and line conditions.

Keep in mind that at the time, LAN speeds over controlled twisted copper pairs over short distances (100m) were 100mbps - 1gbps.

If you've ever seen the physical condition of the telephone company's outside subscriber wiring (what they call "outside plant") -- and particularly the intermediate splices between central office and subscriber -- you would quickly disabuse yourself of the notion that you could transmit anything close to 1gbps over a twisted pair.

If the copper isn't in good enough condition, you can always try with wet string instead:

https://www.revk.uk/2017/12/its-official-adsl-works-over-wet...

Those copper wires ran from your house to the local central office, the "last mile" of the connection. (which was sometimes 2-3 miles long)

A quick read of the linked article seems to indicate that it's BS, as it doesn't account for the real topology of the local loop. In particular, in older neighborhoods you had a bundle of pairs going down the street, and a new connection was made by patching in to a free pair, creating a "T" shaped circuit. When a house was disconnected, part of this "stub" might have been left attached; over time a single pair might accumulate multiple disconnected stubs. The capacity of that copper circuit is far lower than a straight run.

In addition in many cases corrosion and water cause noise, further reducing bandwidth - I can remember having noise so bad on rainy days that I had to call and get them to fix it. (I assume they patched us onto a free pair and abandoned the noisy one)

Of course none of this is related to the end-to-end bandwidth of the old telephone system. Starting in the 50s a longer-distance phone call would get a single-side-band channel on a microwave link, with about 3KHz allocated. Later on calls got sampled at 8KHz with 8-bit mu-law (logarithmic) encoding, or A-law in Europe, and transmitted digitally.

Of course ancient telephone wiring can carry 1 Gbps. The real question you always, always, always, need to be asking yourself is:

Over what distance?

Make that distance short enough, as has happened with FTTN, or FTTC deployments in a whole heap of places, you're basically building a network that's, and I'll keep this very brief, subpar.

Since you mentioned a UK context there, Openreach rolled out an upgrade that kept the last mile of copper but now just about a decade later they're rolling out Full fibre. Whatever argument copper had, it went out the window near enough a decade ago.

OK, had a look through the linked paper. The big graphs, on page 8, tell you that if you decrease the twist length - which would entail relaying all the copper in the entire network, at which point you may as well put down fibre instead - you will get -20 dB at 10 GHz over a distance of 0.5m, 50cm, less than two feet, instead of -25 dB in the worst case.

In other words, instead of losing 99.7% of the signal over that distance, it'll only lose 99% of the signal. Sure, it helps, but consider me underwhelmed.

Power, not signal, sigh.

Distance is the problem. The gauge is small so we can't throw a very strong signal down the wire. So you have repeaters on almost every span of any appreciable length.

The very first part of a dialup modem sound? Where it's playing a tone that reverses phase at regular intervals? That tone is actually designed to disable all the repeaters and echo cancelers that are in your switched circuit.

Also two parallel phone lines are prone to capacitive coupling. I had a case so bad once that one office could pick up the phone and nearly perfectly couple onto their neighbors line and hear all their conversations. It was a 50/50 which port on the PBX recognized the tones and started the call when either of them picked up to dial out.

They did it for efficiency. The observation was that the human voice doesn't use most of the audio spectrum, so they optimized everything for voice.

A reasonable decision at the time.

it can carry more, the whole value proposition of dsl was a high speed link over existing cabling, I think the dial up limitation is what speed can you sneak over the existing speech focused analog signal processing equipment. where as the article explained by making that analog link as short as possible it could improve speeds quite a bit. dsl was what you could achieve over the same lines when you were not forced to constrain your signal to speech frequencies

It can carry 1 gigabit, over a few metres. I.e. Not even the length from the street to your house.

Australia tried this, it's physically impossible.

https://en.wikipedia.org/wiki/G.fast

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