What are the basic concepts behind "push" notifications / messaging?

Question

What are the key concepts that a developer should know when building an iPhone application that takes advantage of push notifications?

Answer 1

You may find this article, from Wikipedia of interest, since your question is very vague:

http://en.wikipedia.org/wiki/Push_technology

Are you talking about issues using a desktop app, or a browser application or a mobile phone app?

Answer 2

Number one most important thing, I think, is that your app can't depend on them. It's probably best to regard them as a nice thing for your user, rather than a part of your app's infrastructure. In particular:

• Apple doesn't guarantee delivery of the notices. Yes, their infrastructure is pretty good, but there's no promise.
• Only one alert can be up on the device at a time, and there's no log. So if the user has a bunch of push-enabled apps, you can't depend on them seeing your alerts.
• The only way that your app knows about a notice is if the user chooses to run it in response to an alert.
• The user can always turn push notices off, for your app, or for the whole device.

All of that also means: you can't cheat the "no background processes" restriction with the Push Notification Service. :-)