[General Topics] RFZ:
Hey,

Germany is implementing EU-Alert (ETSI TS 102 900 [1]) at the moment and referring to the local News, it is a huge mess [2].

But let's start at the beginning.

CellBroadcast is a core component of each mobile network generation (2G,3G,4G,5G,...) and part of the 3GPP spec. CellBroadcast basically allows the network to send a simple SMS to all mobile phones connected to a specific base station. Thes SMS-CB are sent with a Message Identifier (aka Channel, aka Topic) which gives them a special purpose by convention. e.g. ID / Channel 50 is often used for area related information [3], while channel 207 might broadcast local weather information. Since not all Channels are standardized, there is also the option to broadcast an Index that lists all channels with a description. And since users probably don't want any message broadcasted, users have to subscribe to these channels.

Since decades now, CellBroadcast is also used for public Emergency Warnings. This means that, by definition of a country, a specific channel is used to broadcast Emergency Warnings. Long time ago, in many countries it looks like Channel 919 was used for this purpose. For this to work properly, mobile phones were instructed to subscribe to channel 919 by default and also use a special ringtone (even if muted) to alert such a message.

Later - over 12 years ago - additional channels from 4370-4399 were standardized in ETSI TS 123 041 [4] for public warning systems like CMAS, EU-Alert, KPAS. All using the same channels which is beneficial for global roaming.

Android of course supports these public warning systems specified in ETSI TS 123 041 [4] since at least Android 4.2.2 [5]. And nations that use these systems already, like CMAS in the US, report very high and reliable coverage.

However, referring to German news [2] and government, not many phones that are currently on the market will actually support EU-Alert in Germany, despite already supporting EU-Alert in Netherlands or CMAS in the US.

How is this possible when exactly the same SMS-CB is broadcasted, just in a different country?

Golem [2] says that Samsung and Google already confirmed that EU-Alert is currently not supported in Germany, but updates will be rolled out to recent devices.

This strongly suggests to me that OEMs like Samsung and Google actually added country specific filters/configurations for these public warning systems to their phones without deploying a reasonable fallback. Public warning systems based on ETSI TS 123 041 [4] thus may only work in countries that were known to use these systems when the phone was released.

Isn't this an obvious issue?

Google said, starting with Android 11+ it will be possible to update the CellBroadcastReceiver App via Google Play. So devices with Android 11+ will likely receive an update to support EU-Alert in Germany. For Android 10 and older, OEMs will have to supply updates.

What also confuses me is the fact that all Android Phones I own (Nexus 4 with Android 5, Nexus 5X with Android 8, Pixel 3a with Android 12) here in Germany do actually offer the setting for Emergency Warnings and they are already enabled by default. So I assume they would work? Did Google actually deploy a sane default configuration here already?

But if they did - why isn't it working on ALL Android 11+ Phones already? I'm pretty sure my Pixel 3a uses Googles CellBroadcastReceiver App which is provided through the Play Store. So all Android 11+ phones should already use the exact same App?! Or am I wrong here? So what is this update Google actually needs to provide?

And does this also mean that with Android 11+ OEMs are not allowed / cannot implement their own Emergency Warning CellBroadcastReceiver?

This topic is really confusing to me :(

Shouldn't it be really simple?

All phones, regardless of the OEM, should have a proper SMS-CB Application which allows you to subscribe to custom channels, view the index, and manage your SMS-CB Messages.

Phones should also be aware of special channels to apply special ringtones etc if needed, but they should have a sane fallbacks!

A phone that knows about NL-Alert and CMAS may call messages on Channel 4370 received in the Netherlands "NL-Alert". But when it receives the same message in Germany, it shouldn't just drop it! It should display it as warning and call it whatever it wants. And if it doesn't know about CMAS / EU-Alert, it should just receive it as regular SMS-CB.

Can't be that hard?

Interestingly enough, Samsung phones allow you to subscribe to custom channels. Google phones do not :/

Should there be a better / more enforced standard, so that a country that wants to implement CMAS/EU-Alert in the future doesn't have to rely on OEMs help?

And finally some technical Questions:

I found zero Apps for Android that would allow me to subscribe to custom CellBroadcast Channels on my Google Android phones. Is this even possible?

Also, is it possible to test these CellBroadcasts somehow? Is it possible to write an App that can inject SMS-CB into the system?

Sorry for the long post, but I think this an important Topic.

Let me know what you think ;)

Do you have experience with these Emergency Warnings already?

[1] https://www.etsi.org/deliver/etsi_ts/102900_102999/102900/

[2] https://www.golem.de/news/cell-broadcast-warum-es-am-warntag-ruhig-bleiben-koennte-2206-165822.html

[3] https://source.android.com/devices/architecture/modular-system/cellbroadcast#channel-50

[4] https://www.etsi.org/deliver/etsi_ts/123000_123099/123041/11.04.00_60/ts_123041v110400p.pdf

[5] https://cs.android.com/android/plat...ternal/telephony/gsm/SmsCbConstants.java;l=58