Push Notification:

Push Notification allows an application to listen for messages being ‘pushed’ to it from the server.
Through Push Notification, our apps can provide uses even when they aren’t running.

Different techniques that could be used for push notifications in android:

1)  Polling:  In this technique device is polling the server on a regular basis to see if there is anything there.

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Polling that heavily just to check for notification is not a good idea,that would hurt battery life pretty badly after not too long.

2)  Creating a service: In this technique service create a persistent connection to your server.
This will also drain the phone’s battery and it will create problem on server side also if you had more users

3)  SMS: In this method clients gets notified by SMS.

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This technique is better as compare to other techniques because:

1) Transfer content as soon as available
2) Save device battery
3) Reduce data traffic for user

Way to implement push via SMS:

1) Your application should add permission in manifest :
Permission:  <uses-permission android:name=”android.permission.RECEIVE_SMS” />
2) and Registers a BroadcastReceiver, either in the manifest XML or in Java, and will get control when the events occur.
<receiver android:name=”.ReceiverClass”>
<intent-filter>
<action android:name=”android.provider.Telephony.SMS_RECEIVED” />
</intent-filter>
</receiver>
3) SMS Header may contain “app port” field that is dedicated range of free usable port numbers.Port handling not yet supported in Android 1.6.
4) You’d have to parse the PDU and get the port from there manually, you can listen to all SMS messages, parse the PDU of each incoming message and see if the destination port
matches the one that you are expecting. But so can other apps.so there’s no way to ensure that just one specific app gets to know about an incoming SMS to a specific port.
5) After matching ports appliaction can handle notification with the help of notification manager.
The problem with this method is that Android currently has no way to cancel the notification that is sent by the messaging app.So for every notification your app gets, the OS will also show a text message.