Notifications can be initiated in two ways:
With poll notifications, a client asks for notifications at regular intervals, such as every five minutes. This notification model reflects the standard client-server model, in which clients obtain information by initiating actions. One disadvantage of this notification model is that if an event occurs on the server that a client has interest in, the server must wait for the client to ask. Only by making frequent requests can clients receive information on a timely basis. This increases network traffic, which is a second disadvantage to the polling model.
With push notifications, if an event occurs on the server such as the arrival of new mail, the server can send a network packet that contains the relevant data to every registered client.
When an application registers for notifications, the information store activates push notifications if the network protocol installed on the client computer supports them. If push notifications are not possible for any reason, the information store activates poll notifications.
Push notifications are not used with the AppleTalk, NetBEUI, or Banyan Vines protocols , but they are supported for the TCP/IP and IPX/SPX protocols. If at least one client computer that has IPX/SPX installed is connected to a Microsoft Exchange Server computer, you need to install Gateway Services for Novell NetWare and the SAP agent on the Microsoft Exchange Server computer. For more information, see the Microsoft Exchange Server Concepts and Planning Guide and your operating system documentation.
The following table lists the protocols that, on a client computer, support push notifications.
Protocol Requirements for Push Notifications
| Network Client | Protocol for Push Notifications |
|---|---|
| Novell NetWare | NWLink (IPX/SPX) or LanWorkplace for DOS (TCP/IP) or Microsoft Windows for Workgroups TCP/IP 3.11A |
| Microsoft Windows for Workgroups, Microsoft Windows NT Workstation, MIcrosoft Windows 95 | IPX/SPX-compatible protocol or TCP/IP protocol |
The Named Pipes RPC protocol may be layered on top of the IPX/SPX or the TCP/IP protocol. This does not hinder the operation of push notifications.
If you are not using the Windows Internet Name Service (WINS), the IP addresses of all Microsoft Exchange Servers in the organization must be specified in the HOSTS file on client computers. This file can be found, for example, in the WINNT\SYSTEM32\DRIVERS\ETC directory on a client computer running Windows NT Workstation.