Pushy is a standalone push notification gateway, completely independent of GCM. It maintains its own background socket connection, just like GCM, to receive push notifications. The underlying protocol is MQTT, an extremely light-weight pub/sub protocol, utilizing very little network bandwidth and battery. We chose MQTT after comparing multiple protocols, including WebSockets and XMPP. Also, the fact that Facebook chose to implement its push notifications using MQTT is highly-convincing. A huge advantage of Pushy is that it's a drop-in replacement for Google Cloud Messaging. The code for sending a push notification (from the server) and receiving a registration ID is almost identical for GCM and Pushy. This makes it super easy to switch to Pushy after implementing GCM and having to ditch it for its instability. We charge $0.005 for each active device (number of devices connected to the service at least once during one month of period) every month. Do you have plans for iOS? A...
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