This protocol enables a client to receive notifications about specific events that occur on the messaging server. The client can subscribe to certain events on the server, and when one of the events occurs, the server sends the client a notification. The notification sent by the server is commonly a two part operation. First, the server notifies the client about pending notifications. Then the server transmits the notification details.
The server supports three methods for notifying the client of pending notifications on the server:
Asynchronous RPC notifications. This method enables the client to make an asynchronous remote procedure call (RPC) call to the server; the server does not complete the RPC call until there is a notification for the session.
Push notifications. This method relies on a callback address being registered with the server, so that User Datagram Protocol (UDP) datagrams can be sent to the callback address when pending notifications exist.
The RopPending ROP ([MS-OXCROPS] section 22.214.171.124). This ROP is included in the EcDoRpcExt2 method call response if there are pending notifications on the server and the details of the notification do not fit in the response buffer.
Regardless of the means used to notify the client of the pending notification, the notification details are sent to the client by using the RopNotify ROP (section 126.96.36.199.1).