The GCM service handles all aspects of queueing of messages and delivery to the target Android application running on the target device. GCM is completely free no matter how big your messaging needs are, and there are no quotas.
To learn more about GCM, you can join the android-gcm group and read the following documents:
- Getting Started
- Read this document to learn the basic steps involved in developing Android applications based on GCM.
- Architectural Overview
- Read this document for a description of the underlying concepts and architecture in GCM.
- Demo App Tutorial
- Read this document to walk through setting up and running the GCM demo app.
- Advanced Topics
- Read this document to get a more in-depth understanding of key GCM features.
- Migration
- Read this document if you are a C2DM developer moving to GCM.
- API Reference
- Helper libraries for client and server development.