Comment by chrismorgan
2 years ago
If talking about the US (though it’s not the only place that uses the number 911, and I would imagine that other countries’ numbers would be affected): all the major 3G networks have been shut down, so your current options for major networks are T-Mobile’s 2G network (which I successfully dialed 911 with a couple of months ago while in the US, but it’s only spottily available, and it’s being shut down next year), or 4G networks.
More generally, though, using different code paths for emergency dialing is the root of the problem in the first place—you want to minimise special handling of things like this, because less-tested paths are much more likely to be buggy. Consider also: error handling code is pretty much the buggiest out there, because it’s seldom tested.
At least 2 decades ago when I worked with phones the phone as a list of emergency numbers which could be updated to country-spefic values. Often 000, 112, and 911 were always present.
Once the software notices one of these numbers dialled call handling will go a completely different code path than normal calls.
I have no idea how things work in Android, where you obviously must have VoIP hooks?
>I have no idea how things work in Android, where you obviously must have VoIP hooks?
Yes, there's emergency IMS (basically volte/vonr version of SIP) profiles the phone is supposed to register to and all the carriers towers advertise emergency numbers in their signaling.
The problem with 4G (and 5G) is that it supports only internet traffic. Phone traffic is passed trough VoLTE that is VOIP on the network. Is something that is fairly new, few years ago only a couple of operators in my country even supported that, and thus phones had to drop to 3G to handle calls. Also VOIP is not that reliable and presents problems especially with different networks.
The problem is when the internet connection is not so stable, and thus VoLTE doesn't work that well. The safer option would be to drop to 3G or even 2G if available to complete emergency calls.
I think you missed the point in the post that you are replying to saying carriers have dropped 3G and the only remaining 2G network is also on its way out. Where I live all carriers are planning to phase out 3G by the end of 2025. All but one carrier have already phased out 2G.
We need to forget about falling back to 3G or 2G as that is not a viable solution in the long run. The carriers and phone manufactures have a responsibility to make emergencies calls work well over VoLTE.