ios - APNS (Apple Push Notification Service) reliability

Question

Our app uses APNS to receive Push Notifications. However, our client claims that some of their devices were not receiving notifications and argues to they 'must' make sure the notifications to be delivered 100%. But I have read somewhere that APNS is not 100% reliable and there should be cases which the notifications are not delivered.

I'm currently panic at how we could make sure APNS to received anytime. I have read that a case which may APNS not delivered (device may offline). But our test showing that even the device is online (Wifi or 3G), sometimes APNS were not delivered.

Is there any specific case which may APNS will not delivered? Or is there anything we (developers) can do with codes to make sure to receive all notifications? What I have done in the code is just registering the app to remote notification and write didRegisterForRemoteNotificationsWithDeviceToken, then throw the device token to our server.

Any help would be appreciated, for our client almost kill us if ALL of their devices not receiving APNS!

Answer 1

1. APNS is based on Apple Servers, and Apple doesn't give any guarantee on successful message delivery.
2. If the app is open (i.e. the user is using the app) while the notification arrives, iOS doesn't show a notification message, you need to handle it.
3. Notification shows up only when the app is backgrounded or killed.
4. Also implement feedback service on your server side; will help you get rid of old unwanted tokens (users who deleted the app or disabled notifications through settings).
5. Don't send too many notifications to a device within a short span of time, because APNS caches only 1 message/device (if the device is offline). So it can deliver the message when the device comes online. Am not sure how long the message is cached though.

Or just implement Pusher... http://pusher.com