GPS is used a a source for precision NTP servers such as these. Their industry solutions pages have a variety of situations where GPS is used behind the scenes.

This isn't from AT&T, it's from an outside analyst making wild guessimates. There are enough little errors throughout to make me doubt their big numbers. For example, AT&T installed their 145th 4ESS switch in 1999. There were few (if any) remaining 4ESS switches in SBC at the time they took over AT&T. Yet the PDF states that there are 5000 such offices.

The other point is that as older equipment has been removed, newer transport and local access equipment has taken up a good fraction of that freed space. This equipment tends to have higher heat output which either requires lower equipment densities or increased cooling or both. Given the existing HVAC systems and the building designs, this almost always results in more spread out equipment than in the past. Then there's the space for all of the new fiber terminations.

Which ones were those? Everyone I've seen has some requirements for preventive and corrective maintenance. Minor troubles can be ignored and they don't need someone on site full time or even regularly scheduled but the so did a community dial office from the '50's.

Take the phone switches for example. These things don't crash, ever. They just work. Great, but they only do one thing, yoy use only certified hardware, they've had like one major upgrade (5ESS to 7R/E) in the last couple decades, and they cost millions.

As other posters have already noted, telephone switches do crash, or much more frequently, have impairments short of a complete outage. Lucent's markteting boasts of five 9s availability, but thats based on aggregate FCC reporting data, not for any one switch.

And the claim that there has been only one major upgrade makes me laugh. Right now there have been about twenty generic releases (major software releases), although some of the recent ones (since about 5E16 or so) are supposed to be split between wireless & wireline. In between generics, there are numerous patch releases. That's just the software. On the hardware side, there have been many hardware changes since the No. 5 ESS came out in the 80's. Some of the changes have been optional, but many have required grafting new hardware onto an existing switch (like CM & AM retrofits.

7/RE was more of a collection of upgrades and marketing, than anything unique in it's own right. Lucent has since gone back to calling it 5ESS, just like they have with 5ESS-2000, and every other marketing name change they've tried. I can't wait to see what Alcatel tries.

There's redundancy and reliability built into most vendor's equipment, but it's far from perfect, especially when you start adding humans in to the mix.