Comment by user_7832
2 years ago
It's really absurd how such a problem still exists. Couldn't a separate method be used for emergency calling? For example drop to 3g, don't use the dialer app but a separate "emergency" app.
2 years ago
It's really absurd how such a problem still exists. Couldn't a separate method be used for emergency calling? For example drop to 3g, don't use the dialer app but a separate "emergency" app.
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.
It would be great if when 911 is dialed the phone dropped into a “black box” state where all unnecessary functionality is suspended to maximize battery and signal. It could alert emergency contacts w/ location pings, start recording voice and video, and go into a heightened security mode to avoid tampering.
No you definitely don't want the phone doing confusing and weird things during an emergency. You want it to behave in the way the user is accustomed.
I thought 3G networks have been shut down in the US? (Not living there but I remotely maintain some devices with cellular modems over there, so the topic has somewhat of professional interest.)
They have not. 2G networks have been shut down, however.
Incorrect, T-Mobile's 2G network is active until this coming April. Both their 3G networks (theirs and the Sprint legacy one) are shut down as they used more spectrum. Keeping GSM going the spectrum use is minimal.
Having dedicated code path for 911 is literally the problem. It makes it legally almost impossible to test in many countries (since in many countries you're not allowed to dial 911 if you don't have an emergency)
Which countries? Where I live, in the US, if you want to make a callback to a police detective, you have to call 911 and ask to be transfered. It's clearly not an emergency, and the detective will tell you to do it. This police department doesn't have a phone system that allows the public to call a non-emergency number and have their calls routed.
But most places I've lived in the US had a non-emergency police number, and non-emergency 911 calls were very discouraged. If you have a good reason to make them for network or device testing, you'd just need to schedule a time to make a test call, stay on the line and tell the operator, etc.
Device development would be well served by using a tower simulator in a Faraday cage, as a sibling suggested. But a responsible developer would do a few tests on live networks during release acceptance testing.
Just call nearest Rohde & Schwarz office and get a signaling tester... If you're doing phone firmware, there should be couple extra briefcases of cash for that. No need to call actual 911 just to test a dev branch build.
The article explains how to schedule a test call to 911.
Test in a Faraday cage with an isolated base station.
Probably not exactly what you are looking for, but when one is in such a situation and they happen to have an app like Skype, people can use it for emergency calls (support in the US)