GCM (Google Cloud Messaging) allows third-party application servers to send lightweight messages to Android applications, eliminating the need for apps to continuously query servers for updates, and works by having an Android app register with the GCM connection server to receive messages sent via the internet from an app server that holds the API key credentials provided by Google. The document then outlines the architectural components involved, including the mobile device, third-party app server, GCM servers, and credentials like sender ID, application ID, registration ID, and sender auth token, before describing the implementation steps for enabling GCM, sending messages from a server, and receiving messages on Android.

1. GCM
Google Cloud Messaging for Android
Ahsanul Karim
karim.ahsanul@gmail.com

2. GCM: Introduction
-GCM (Google Cloud Messaging) is a free service that
helps developers send data from servers to their Android
applications on Android devices.
-Using GCM we can push
--lightweight message to applications telling that
there is new data to be fetched from the server or
--a message containing up to 4kb of payload data (e.g:
instant messaging apps).
-This can eliminate continuous query to server for
updates using background services

3. GCM: Characteristics
● Allows 3rd-party application servers to send messages to their
Android applications.
● GCM makes no guarantees about delivery or the order of
messages.
● Application on an Android device doesn't need to be running to
receive messages.
● Requires devices running Android 2.2 or higher (with Google Play
Store application installed), or or an emulator running Android 2.2
with Google APIs.
● Uses an existing connection for Google services. For pre-3.0
devices, this requires users to set up their Google account on their
mobile devices. A Google account is not a requirement on devices
running Android 4.0.4 or higher.

4. GCM: Architectural Overview
Key Terms:
key terms and concepts involved in GCM are 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.

5. GCM Architecture: Components
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 An application server that developers set up as part of
Application implementing GCM in their applications. The 3rd-party application
Server 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.

6. GCM Architecture: Components

7. GCM Architecture: Components
Credentials
Sender ID A project ID you acquire from the API console 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.
Registration ID An ID issued by the GCM servers to the Android application that
allows it to receive messages.
Google User For GCM to work, the mobile device must include at least one
Account Google account if the device is running a version lower than
Android 4.0.4.
Sender Auth An API key that is saved on the 3rd-party application server that
Token gives the application server authorized access to Google services.

8. GCM: Implementation
1. Enabling GCM: An Android application running on a
mobile device registers to receive messages.
2. Sending a Message: A 3rd-party application server
sends messages to the device. (we'll do it with php)
3. Receiving a Message: An Android application receives
a message from a GCM server.

9. GCM: Implementation Steps (1)
● Goto https://code.google.com/apis/console
● Create a project: GCM_test
● Browser link has changed as https://code.google.com/apis/console/?
pli=1#project:94384365614:services
● it contains project id (94384365614 in this example)
● We required that in our application as sender id.

10. GCM: Implementation Steps (2)
● In the main Google APIs Console page, select Services. Turn the Google Cloud
Messaging toggle to ON. In the Terms of Service page, accept the terms.

11. GCM: Implementation Steps (3)
● In the main Google APIs Console page, select API Access. Now you can see
there is API key if you use that key your application can receive messages from
any server & if you want to restrict servers you can generate new server key
using button there as “Create new server key…”.

12. GCM: Implementation Steps (3.1)
● Now we have Sender ID and API KEY
○ Sender ID: 94384365614
○ API KEY: AIzaSyBFhGpJswkvMxMTElfAQeMUskG13ii7s1Q

13. GCM: Implementation Steps (4)
Create new Android Project:

14. GCM: Implementation Steps (5)
Copy the gcm.jar file from: SDK~PATH/extras/google/gcm/gcm-client/dist
directory to your application classpath. As external jar.

15. GCM: Implementation Steps (6)
Permissions in Manifest

16. GCM: Implementation Steps (7)
Add GCM Receiver

17. GCM: Implementation Steps (8)
Add GCM Receiver

18. GCM: Implementation Steps (9)
Add GCMIntentService extending GCMBaseIntentService and add the service in
Manifest:

19. GCM: Implementation Steps (10)
Register:
Unregister:

20. GCM: Implementation Steps (11)
Receive Message

21. GCM: Implementation Steps (12)
Send Message from Server