How do push notifications arrive on a smartphone?

Question

iPhone

For example, I turn on Wi-fi and applications with Push notifications establish permanent TCP or UDP connections with their servers and servers, when necessary, send notifications through these connections?
If so, then a little bit of traffic will go to maintain connections, and the number of connections is limited.

Answer 1

I won’t say about android, for iOS there is a special Notification Center (they sent you the first link, you obviously didn’t look)
in short: when a connection to the Internet appears, then all the notifications that have accumulated at the time of your inaccessibility are thrown off to your phone, according to those applications that interact with the specific provider of these notifications.
>The question is how do they work?
You just didn't read the links you were given. Even from the pictures you can see how everything works.

Answer 2

https://developer.apple.com/library/IOs/documentat...
https://developer.android.com/google/gcm/index.html

Answer 3

https://developers.google.com/cloud-messaging/
https://developers.google.com/cloud-messaging/andr...