NOTIFY Method
Topic Last Modified: 2006-06-13
This topic applies to Exchange 2000 Server SP2 or later.
The WebDAV NOTIFY method is called by the server whenever an event that the client has subscribed to fires. The NOTIFY method will send User Datagram Protocol (UDP) packets to the client until the subscription has timed out. The subscription to the resource will persist after the notification is sent by the server.
A NOTIFY method without a Subscription-ID Header is an unsolicited notification. This can be used if the server wants to notify all clients, for example, that the store was shut down and that notifications will not be working properly for some period of time. Call back responses may not occur in real time because the store may automatically coalesce events.
Because UDP packets sent by the NOTIFY method may be lost, the server will keep track of past events that have subscriptions. The server will maintain subscriptions for which events occurred until the client sends an acknowledgement (using the Subscription-ID Header in any method, typically the POLL Method) that it is refreshing the subscription.
Example
The following is an example UDP Request from a server. The Uniform Resource Identifier (URI) that is used was originally specified in the Call-Back Header of the SUBSCRIBE Method when the subscription was created. The Subscription-ID Header is the identifier of the subscription for the event being fired.
Request
NOTIFY httpu://www.fourthcoffee.com:8080/510 HTTP/1.1
Subscription-id: 15