[jcims]

I know there are some telecom folks on here that may be provoked to correct me but pulp was standard before the advent of cheap plastic insulation in the 1950s on up. I live in the midwest and my brother is a lineman for AT&T. There is an astonishing amount of pulp-insulated phone line still in service today.

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.

[ComputerGuru]

> I know there are some telecom folks on here that may be provoked to correct me

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?

[BoorishBears]

http://www.airtalk.com/z_ref-4_1.html

[Johnythree]

The gas flow on each line was monitored with flow gauges, so any increase could be attended to before it became a problem.

[stefan_]

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.

[oasisbob]

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.

[kazen44]

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.

[stefan_]

Exactly. That all sounds infinitely easier than buried air pipes. Mind boggling physics are what gives us CPUs, but the final product is reliable bar none.

[NavinF]

Meh. Fiber has been cheaper than copper per mile for a long time and 10km optics are like $20.

[kazen44]

yes, but this does not scale if you want to build residential connectivity.

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.

[namibj]

Don't go for GPON, if you have a chance. Direct cabinet-to-apartment single-mode fiber (can be a pair that gets BiDi optics if one of the fibers fails, though only worth it if correlated failures aren't the bulk of issues) is future-proof. Also GPON tends to not get anywhere near the awesome pings 1G-LR and 10G-LR provide in sub-lightpseed regional situations.

[Johnythree]

It depends on the country, but originally our Telephone Companies were motivated by Quality of Service. However all that changed when the companies were privatised and profits became their only concern.

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.

[jcims]

I would bet this is a capex/opex thing.

[djweis]

There is still a lot of it in service. Sometimes you'll see a tank of nitrogen chained to a pole. It is there to put pressure through the cable to keep water out of a cut/nick on the lead sheath. The lines are pressurized normally from the central office and if the monitoring shows a drop in pressure (a cut in the sheath), they roll out cable maintenance.