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Comment by dr_dshiv | Hacker News Reader

It is the same kind of format as the Amber Alert things I used to get in the states. How do they push that out? Based on location, cell tower usage, sim card?

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It's not as disruptive and open to abuse as an Orange Alert.

https://boingboing.net/2018/10/03/orange-alert.html

All of these kinds of alerts (amber, tornado, flood, fire, and presidential test) that I've received on the west coast of the USA have been based on very coarse regions e.g. entire cities, counties, or districts. Whether that is cell tower or not I can't tell, but I've always assumed it was.

Yes, amber alerts are one class of alert that uses WEA. It's based on the mobile station (phone's) location. The rules used to be written allowing per-tower granularity, but new FCC rules require 0.1 mile accuracy to whatever geo-bounding the author of the alert sets. The bounding can be specified as a circle, polgyon, or by geocode. Geocodes specify a state (or all), county (or all). Geocodes for EAS (the alert system on FM radio) allowed for county subdivisions drawn by the NWS. I don't actually know if those made it into WEA.

It's like wifi broadcasts. It transmits to all devices in cell. It might do this for many cells and many operators/physical networks at the same time.

I didn't get them on my cellphone which was connected through the KPN mobile network, appearently there is some provider dependency here

Yes, access to the base stations in the network still goes through the provider and apparently that is the layer that has problems with interfacing to the outside world. Intra KPN traffic works just fine, including SMS.

Each provider uses a different cell tower (or at least their own antennas on a shared mast), with their own independent radio frequencies.

"All devices in cell" is still accurate. Each cell belongs to a single provider.

It's up to the network backend to make sure all providers get the emergency message at the same time to forward.

> Each provider uses a different cell tower

This is incorrect. A lot of providers share infrastructure, there are even providers without infrastructure.

You are of course correct. But getting into the details behind MVNOs and roaming is a much more complicated topic than I'd want to type into a small comment box, and not really relevant to the issue at hand. :)

My point is just that CMAS-style cell broadcasts need to be repeated by each cell site, and cell sites aren't universally shared by all carriers.

It appears the problem here was at a higher level, the signalling fabric that transports the data for call setup, teardown, roaming and SMS, and to complicate matters even further apparently the 4G network is where the problem originated but it had effects far outside that. That's also why the whole thing appeared so patchy from outside.

You might not have it enabled? Do you have a recent Android/iOS device?

Probably some form of cell, as me and my colleagues got them at the same time with different operators (different network operators, not virtual).

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