GCM application is based on the Google cloud communications platform, to inform the user of the current updates or product promotions, very rapidly replacing traditional SMS / text messaging services use data services (GPRS / 3G / CDMA / WIFI). Thus, it provides a cost-effective solution to keep your customers or users to be notified is almost free.
For inquiries, email: email@example.com
Google Cloud Communication (Google Cloud Message, GCM) Is to provide a free service by Google, developers can pass through servers in the service The information sent to Android application use. Transitive 4KB lightweight data message. 
GCM advantages and disadvantages:
GCM is advantage Free service offered by Google, you can simply send a message without the deployment wait SERVER can be used.
Disadvantages are: Use only receive messages App Android operating system. sent messages can be transmitted only 4KB size limit of messages. There throttling mechanism, once sent a message to a large number of Android devices too, the message will be directly Discarded.