Google says you can reach over a billion devices with this free cloud messaging service – CBR gives you the main features of GCH.
Google Cloud Messaging (GCM) is a free mobile service that enables third party app developers to send messages between servers and client apps. Google pitches GCM as a way to engage users across Android, iOS and Chrome with simple messaging.
GCM allows information to be sent to users’ devices, while also receiving messages from devices on the same connection.
GCM allows for versatile messaging targets, enabling the distribution of messages to a client app in any of three ways – to single devices, to groups of devices, or to devices subscribed to topics.
GCM allows for both downstream and upstream messaging. Enabling a reliable and battery-efficient connection between server and devices, downstream messaging can be used for purposes such as alerting users, chat messaging or starting background processing before a user opens the client app. Upstream messaging allows the sending of acknowledgements, chats and other messages from devices back to the server.