Architectural Overview

Architectural Overview

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This section gives an overview of how GCM works.
This table summarizes the key terms and concepts involved in GCM. It is divided into these categories:

• Components — The physical entities that play a role in GCM.
• Credentials — The IDs and tokens that are used in different stages of GCM to ensure that all parties have been authenticated, and that the message is going to the correct place.

Components
Mobile Device	The device that is running an Android application that uses GCM. This must be a 2.2 Android device that has Google Play Store installed, and it must have at least one logged in Google account if the device is running a version lower than Android 4.0.4. Alternatively, for testing you can use an emulator running Android 2.2 with Google APIs.
3rd-party Application Server	An application server that developers set up as part of implementing GCM in their applications. The 3rd-party application server sends data to an Android application on the device via the GCM server.
GCM Servers	The Google servers involved in taking messages from the 3rd-party application server and sending them to the device.
Credentials
Sender ID	A project ID you acquire from the API console, as described in Getting Started. The sender ID is used in the registration process to identify an Android application that is permitted to send messages to the device.
Application ID	The Android application that is registering to receive messages. The Android application is identified by the package name from the manifest. This ensures that the messages are targeted to the correct Android application.
Registration ID	An ID issued by the GCM servers to the Android application that allows it to receive messages. Once the Android application has the registration ID, it sends it to the 3rd-party application server, which uses it to identify each device that has registered to receive messages for a given Android application. In other words, a registration ID is tied to a particular Android application running on a particular device.
Google User Account	For GCM to work, the mobile device must include at least one Google account if the device is running a version lower than Android 4.0.4.
Sender Auth Token	An API key that is saved on the 3rd-party application server that gives the application server authorized access to Google services. The API key is included in the header of POST requests that send messages.