How does a push notification actually work? And what is that anyway? Microsoft has shut down its push servers for Windows Phone 7.5 and 8.0, so that no push notifications will be available on the affected systems.

Push notifications were introduced to the greater public by Apple in 2009 to solve the problem of wanting to receive messages in real time without having to run the entire app in the background. Until then, there were two predominant methods of sending notifications to applications. One is called polling, which is also used by the POP3 email standard. With this method, the app asks the server at fixed intervals if there is anything new. This requires the app to wake up from sleep every now and then to ask for something new. As a result, the CPU also has to wake up from power saving mode at certain intervals, which consumes battery power, and the notifications do not arrive in real time, but only when the app requests them.

Another solution would be for the app to run permanently in the background and keep a permanent TCP/IP connection to the web server open to receive real-time notifications. There’s no question that this puts even more load on the battery. Since both concepts are not practical for mobile devices that depend on a battery, Apple considered the push system.

Here, a server provided by the operating system developer is put between the service and the smartphone and takes over communication with the device. The device registers on the push server with a unique ID so that the right messages are sent to the right device. A small example:

A user uses Telegram to chat with his friends. As long as Telegram is open and active, the messages are sent directly from the Telegram server to the corresponding user account, the push system is not used. If the user now locks his smartphone and the app goes into sleep mode, the push system is used. In sleep mode, the smartphone keeps a single connection to the push server open in addition to various connections such as mobile telephony or the WLAN connection, so that each individual app does not need its own connection. If the user now receives a message in Telegram, the Telegram server informs the push server that a message is available for the user. The push server takes turn and sends the notification about the message to the smartphone, which then wakes up from sleep mode and displays the message.

This system mainly saves battery power, as the apps themselves can be terminated as long as the push service is running and only a single TCP/IP connection between the push server and the smartphone needs to be established.

The fact that Microsoft switched off the push servers for operating systems that are no longer supported does not mean that no more messages arrive on the smartphone. Nevertheless, users should consider whether they still want to use devices with such outdated systems, where good androids are already available from 150€.

Originally posted in German on WindowsUnited