PubNub is more efficient than iOS APNS and Android FCM (formerly GCM) push notification services which are based on XMPP and is rather chatty with a default connection length of 60 seconds. In addition, XMPP is XML-based and is generally heavy weight in comparison to JSON-based PubNub. Due to the heaviness of the stock push notifications, additional limits are placed on message lengths (2KB for APNS, 4KB for FCM and 4KB for MPNS).