How often does APNS try to push message to devices?

If the target device is offline,

How often 开发者_如何学Cdoes APNS try to forward the message to device? Is it when just after the device gets online? How does it happen?

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You're not going to get a straight answer from Apple, so no one can really tell you. From anecdote, though, it appears to deliver push messages within 60 seconds if you're connected to 3G, and within 10 if you're in wi-fi range.