The worse soy on our Android phones is Google Play Services. For some magical reason when I firewall the Google Play Services I stop receiving ANY notifications (Signal, emails etc.). For some reason all these are routed through Google. I wonder how much of a coincidence/mishap is that in the architecture.

Does anyone know why, if I can bypass it?

That's intentional, push notifications are part of Google Play framework, not AOSP Android.

The reason is, that you won't get battery savings if random app can keep your radio busy. Since mobile carriers managed to kill WAP-Push some 15+ years ago, the only way to get push notifcations is to have a long-lived TCP connection open.

However, that opens another can of worms, there are multitude of timeouts on the way between your phone (including your phone) and the push messages server. Most apps would get this wrong, and they would have to cooperate together anyway (radio is global resource on your phone, it won't switch to low power if another app is busy chatting).

So on Android phones that come with Google apps, the task of managing push notifications is handled by Google Play framework (and also whatever Amazon is using), by single long-lived connection, used for all push messages, and not by apps themselves.

Exactly.

Anybody remember the way Blackberry handled this before proper push messaging? The data connection was completely dead, they just got the mobile companies themselves to do it over the phone call connection (SMS?) to indicate when there was something to read at which point the data layer came up. Really efficient in those days, except you obviously paid a fee for 'Blackberry service'

Play Services does handles all push notifications. The 'some reason' is battery life, because your phone shouldn't maintain 30 long lived connections.

From the privacy aspect, I believe all notifications are end to end encrypted actually. Same as Apple.

Sure, but there's no way to unbundle the very useful notifications service with... everything else. It's not the notifications service that's the problem, it's everything else you're required to run if you want it.

For this you may use microG. I have it installed for geolocation using Wi-Fi and cellular antennas but never tried to enable the notification service.

I would actually be interested in being able to choose the server used for this service, and would enable it without hesitation if I could use my own server for instance.

Encrypted, but that's on transit. Does Google read everything, or the only thing transfered is the alert and NOT the Signal/text/WhatsApp message itself?

Signal is e2ee so Google Cloud Messaging should only get the alert itself, then the encrypted message is downloaded from the server and decoded on device.

End to end encrypted to device, standard pub/private key crypto.

Push notifications require an intermediary server between the app service provider and the device push provider, that's GCM.

Your phone has a persistent connection to it so that the GCM can "notify" your device when you receive a push.

The alternative is to have a custom Android OS linked to your own push provider and then convincing app server developers to send pushes to that instead.

Unfortunately, whether we like it or not, it's hard to get away from.

Those apps are using "Google Play Services" for their notifications. For example, you can see it mentioned at https://support.signal.org/hc/en-us/articles/360027913252-Tr...