Push Services (like GCM): How do they do it exactly?

From what I've heard during an Android developers conference in Israel:

There is simply a TCP socket waiting in accept mode on a cloud Google server. The TCP connection had been initiated by the Goggle Play application. That's why Google Play must be installed on the device for making Google Cloud Messaging (GCM) (formerly Android Cloud to Device Messaging Service - C2DM) work.

When this TCP client socket receives some message, the message contains information such as the package name of the application it should be addressed to, and of course - the data itself. This data is parsed and packed into an intent that is broadcast and eventually received by the application.

The TCP socket stays open even when the device's radio state turns into "idle" mode. Applications don't have to be running to receive the intents.

More information at http://developer.android.com/google/gcm/gcm.html

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Erel said:

The advantage of GCM is that the connection is maintained by the OS and can provide the push messages to many apps.

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Erel said:

It is not a "real" push solution. The device keeps an open connection to Google servers. The advantage of GCM is that the connection is maintained by the OS and can provide the push messages to many apps.

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Erel said:

Yes.
Custom WebSocket Based Push Framework

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somed3v3loper said:

What do google use to make sure their service is always running ?

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