Google Cloud Messaging for Android

from http://developer.android.com/intl/zh-CN/guide/google/gcm/index.html

Google Cloud Messaging for Android

Google Cloud Messaging for Android (GCM) is a service that helps developers send data from servers to their Android applications on Android devices. This could be a lightweight message telling the Android application
that there is new data to be fetched from the server (for instance, a movie uploaded by a friend), or it could be a message containing up to 4kb of payload data (so apps like instant messaging can consume the message directly). The GCM service handles all
aspects of queueing of messages and delivery to the target Android application running on the target device.
To learn more about GCM, read the following documents:
Getting StartedRead this document to learn the basic steps involved in developing Android applications based on GCM.Architectural OverviewRead this document for a description of the underlying concepts and architecture in GCM.Demo App TutorialRead this document to walk through setting up and running the GCM demo app.Advanced TopicsRead this document to get a more in-depth understanding of key GCM features.MigrationRead this document if you are a C2DM developer moving to GCM.
GCM also provides helper libraries for client and server development.