To everyone trying to speculate on the root cause, I haven't seen enough information in any of the comments to really draw any conclusions. Having worked on several nationwide cellular issues in Canada when I worked in telecom, we saw nationwide impacts based on any number of causes.

- A new route injected in the network caused the routing engines on a type of cellular specific equipment to crash nationwide. This took down internet access only from cell devices nationwide. But most people didn't notice because it happened at 2AM maintenance window and was fortunately discovered and reversed before business hours why the routing engine was in a crash loop.

- A tech plugged in some new routers, and the existing core routers crashed and rebooted. While the news worthy impact was just a regional outage for something like 20 minutes, we discovered bugs and side effects from the Pacific to Atlantic coasts over the next 12 hours. So when you say you're impacted at location x, that data point could be everyone is down in the area, many people are having issues, or only one or two people have issues spilled over to some other region. This is why seeing it does or doesn't work in location x is limited value, as almost every outage I've investigated could result in some people still having service for various reasons. The question is in a particular area is it 100% impact, 50% impact, or 0.001% impact.

- A messaging relay ran into it's configured rate limit. Retries in the protocol increased the messaging rate, so we effectively had a congestion collapse in that particular protocol. Because this was a congestion issue on passing state around, there were nationwide impacts, but you still had x% chance of completing your message flows and getting service.

And then there was the famous Rogers outage where I don't remember them admitting to the full root cause. It's speculated that they did an upgrade on change on their routing network, which also had the side effect of the problem booting all the technicians from the network. Then recovery was difficult because the issue took out the nationwide network and broke the ability for employees to coordinate (you know because they use the same network as all the customers who also can't get service). All the CRTC filings I reviewed had all the useful information redacted though, so there isn't much we can learn from it.

So it's fun to speculate, but here's hoping at the end of the day ATT is more transparent then we are in Canada, so the rest of the industry can learn from the experience.