APNS, or Apple Push Notification Service, was the first mobile push notification service, debuting in 2009.
APNS is a cloud-based service that allows apps to send push notifications to iOS users via a secure connection from a distant server. You'll need an Apple p.12 certificate, which permits push sending through APNS before iOS users can see your messages. The system establishes an IP connection between your app and APNS when a user runs it. Subscribers receive push notifications from the APN servers after they are opt-in.