As the name suggests, the Apple Push Notification Service is created by Apple Inc. and it was introduced for the first time as a part of iOS 3.0. The APNS is the centerpiece of the push notifications feature. It is definitely highly effective service for propagating information to devices such as iPhone,iPad and iPod touch devices.
Technically, it uses push technology through a constantly-open IP connection to forward notifications from the servers of 3rd party applications to the Apple devices. the notifications include badges, sounds as well as any custom text messages.
The service providers here originate the notifications in their server software. The provider connects with APNS through a secure channel while monitoring incoming data intended for their Client applications. Whenever some new data for the application arrives, the provider prepares and sends a notification through the channel to APNS, which pushes the notification to the target device. In addition to being a simple transport device, the APNS include a default quality-of-service component that provides store-and-forward capabilities.