Difference between voip push and regular push when waking app from background
I have a messaging service that I use for regular push notifications. For example, when one user sends a message, the other user receives a push notification with that message. I have noticed if the phone is on wifi and 3g / 4g, and the app is killed (and the screen is locked), the notification will be received. If the device is only on wifi and the app is killed (and the screen is locked), the notification is not received.
My assumption is that in order to conserve battery, the device disconnects from wifi after a certain time, and that is why push notifications are not received.
But when I use VOIP push notifications, the situation is different. Even if the app is killed and the device is on wifi (and the screen is locked), the notification will be received. So what does this mean? How is phone receiving this notification, if it disconnects from wifi?
What am I missing here?
Answer
Furthermore, to add to Sivajee Battina's answer, this is what you can read in the guidelines:
There are many advantages to using PushKit to receive VoIP pushes:
The device is woken only when VoIP pushes occur, saving energy.
Unlike standard push notifications, which the user must respond to before your app can perform an action, VoIP pushes go straight to your app for processing.
VoIP pushes are considered high-priority notifications and are delivered without delay.
VoIP pushes can include more data than what is provided with standard push notifications.
Your app is automatically relaunched if it’s not running when a VoIP push is received.
Your app is given runtime to process a push, even if your app is operating in the background.
So the third point confirms that your standard push notifications can be delayed in certain circumstances, while VoIP push notifications will always be delivered instantly.
Also, have a look at this question for reasons why standard push notifications are delayed or dropped.