Google Cloud Messaging for Android
Google Cloud Messaging for Android (GCM) is a service that allows you to send data from your server to your users' Android-powered device, and also to receive messages from devices on the same connection. 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.
Key Developer Features
Send data from your server to users' Android-powered devices
This could be a lightweight message telling your app 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). GCM Architectural Overview.
Send "send-to-sync" messages
A send-to-sync (collapsible) message is often a "tickle" that tells a mobile application to sync data from the server. For example, suppose you have an email application. When a user receives new email on the server, the server pings the mobile application with a "New mail" message. This tells the application to sync to the server to pick up the new email. Learn more »
Send messages with payload
Unlike a send-to-sync message, every "message with payload" (non-collapsible message) is delivered. The payload the message contains can be up to 4kb. Learn more »
New Features
Return Receipts
You can use upstream messaging to get receipt notifications, confirming that a given message was sent to a device. Your 3rd-party app server receives the receipt notification from CCS once the message has been sent to the device. Learn more »
Get Started
Get started with a tutorial that walks you through creating a GCM app. Learn more »