Not all iPHone push notifications delivered to iPhone

I am developing iPhone application, application registered for receive push notifications. I send push notification to gateway.sandbox.push.apple.com from server,all ok, but sometimes push notifications not delivered to iPhone (size of notification message is correct, < 256 bytes). Why? Maybe exists limitations for iPhone sandbox(for example count notifications in one hou开发者_Go百科r) ?

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There is no guarantee of delivery of push notifications. In addition to other potential causes consider this section of the Local and Push Notification Programming Guide

Quality of Service

Apple Push Notification Service includes a default Quality of Service (QoS) component that performs a store-and-forward function. If APNs attempts to deliver a notification but the device is offline, the QoS stores the notification. It retains only one notification per application on a device: the last notification received from a provider for that application. When the offline device later reconnects, the QoS forwards the stored notification to the device. The QoS retains a notification for a limited period before deleting it.

If a device is offline (either turned off or just unreachable) then it will receive at most a single push notification you attempt to send to your application during that time.

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Sometimes the fault is on your network provider which is unable to deliver notifications.same problem i was facing with my device when it was connected to wifi, When I connected it to 3g network all notifications were received instantly.