What is GCM (Google Cloud Messaging)?
Google Cloud Messaging is a free service that enables developers to send messages between servers and client apps. This includes downstream messages from servers to client apps, and upstream messages from client apps to servers. It was launched in 2012 with a goal of making it the best mobile messaging platform to help marketers reach their users, notify them of important events and keep the data in their applications fresh. GCM is being used by marketers and developers to send messages to their users with the help of GCM Sender ID and the Server Key.
Google Cloud Messaging (GCM) Sender ID: A unique numerical value which is created when you configure your Project in the Google Developers Console/ Google Cloud Console. The Project Number is GCM Sender ID and this is used in the registration process to identify an app server that is permitted to send messages to the client app.
GCM, while showing an amazing growth, is an integral part of any application these days. Messaging is a feature that almost every developer needs and uses for engaging with his users. Push notifications enabled have almost 3X higher attention and 88% more app launches, which means more user engagement.
Two main aspects of any messaging platforms are Reliability and Low Latency.
Firebase Cloud messaging (FCM)