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by 188201 2661 days ago
FCM is integrated in kernel, so it cannot be killed. And it starts a persistent TCP connection to Google server. If all apps uses FCM, then all notification would route through this connection, and this significantly reduce battery consumption than the alternative, where each app uses its own web socket server.

So, assume using a degoogled android, can this notification replaced FCM if more apps use this notification server? This server uses web socket, so what does FCM use for its connection? Does web socket battery efficient enough?
2 comments
gruez 2661 days ago
>FCM is integrated in kernel, so it cannot be killed.

What do you mean it's "integrated in kernel"? Are you saying google play services includes a kernel module?

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londons_explore 2661 days ago
It does not.

It's a plain-old TCP connection in GMSCore, but has special permissions to ignore various power save modes.

I personally wish Google would work with mobile networks to replace it with something lower level (eg. Based on the same thing used to initiate phone calls), because a hanging TCP connection open for many hours gets unreliable as NAT drops it and as the phone migrates from one mobile network to another (eg. Across country boundaries)

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sofaofthedamned 2661 days ago
That was how BlackBerry worked wasn't it?
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nimrody 2661 days ago
It's handled by Play services which is whitelisted to allow network access when the device is in light/deep doze mode.

Play services can also instruct Google's servers to stop sending notifications when the device is in deep doze and re-open the connection when the device is active again -- thus saving power (messages are queued at Google's servers)

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qwertox 2661 days ago
FCM uses XMPP

https://firebase.google.com/docs/cloud-messaging/xmpp-server...

I really like the idea of Google providing a single, efficient connection for push-notifications, but having it bundled with Firebase (and therefore with Google Play Services) is an unfriendly approach.

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damian2000 2661 days ago
XMPP is only one option for communicating with the FCM server. The most popular method is using HTTP/REST. XMPP is only needed when you have bidirectional messages - server to client app (downstream) and client app to server (upstream).
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