UPnP Eventing
A UPnP control point can register for events to receive a notification if the state variable for a particular service description changes. The publication of such a change of state by the service is called eventing. In this context, then, evented variables, are those variables that send a notification to a control point regarding such a change of status. Non-evented variables, in contrast, send no such notification.
To subscribe to a particular event, the control point submits a SUBSCRIBE message to the service. The service of the event can accept the subscription and respond with a duration for the subscription by sending an OK message with a time-out value to the control point.
The control point can renew the subscription or cancel it when no longer needed. The control point can subscribe to a number of evented variables. When subscribed to a particular event, the device submits the complete state of all variables to the control point. After sending the complete set of information about all variables to the control point, the device keeps sending updates to the control point if any changes in the specific variables occur. The control point uses the General Event Notification Architecture (GENA) to format the URLs for event subscriptions. The URLS are transmitted between device and control point by means of TCP/IP.
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Last updated on Tuesday, May 18, 2004
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