In essence, push notifications involve a web service sending messages to an application. However, in actuality, the process is more complex. With push notifications, an application doesn't expose any kind of endpoint that your web service can communicate with directly. Even if the web service were to communicate directly, it wouldn't be able to talk to the application if it weren't running.
Rather than enabling direct communication in this way, the push notification architecture mediates communication between a web service and an application through a universal push cloud service that communicates with a push client on the Windows Phone 7 device on which the application exists. The device then communicates with the application and can start it up if necessary.
In this section, you'll look at how push notifications work in a little more detail, including the participating components, registration, notification channels, and the types of push notification that are available.
Four components participate in Windows Phone 7 push notifications:
In the following sections you'll learn ...