|Concepts and Planning||<<||>>|
When a message is sent, the Microsoft Exchange Server MTA determines the number of available routes and compares the routing cost of each connection.
You can influence the routing process by assigning costs to each connection, or by setting a schedule for desired connection times.
Microsoft Exchange Server considers the total cost of a path from end to end, and always chooses the lowest cost route available at the time. Cost values can be assigned from 1 to 100, as described in the following table:
|1||Used 100% of the time.|
|2 - 99||Lowest values are used first.|
|100||Used only if no other paths are available.|
The administrator evaluates these values to identify primary and backup paths for message transfer. Often these values are assigned based on the dollar cost of a specific network connection.
There are two types of routing costs in Microsoft Exchange Server: address space costs and connected site costs.
Address space costs are used to optimize message routing between sites or with foreign systems. If more than one address space is available, the address space with the lowest cost will be used. For example, a leased-line connection may be assigned a cost of 1, a frame-relay connection a cost of 5, and a satellite connection a cost of 50. You use the Address Space property page in the Administrator program to configure address space costs for connectors.
Connected site costs are configured only for connectors that connect Microsoft Exchange Server sites. The connected site costs may be based on the physical costs of sending messages between two sites. For example, a site connected by a Site Connector, on the same physical LAN and using remote procedure calls (RPCs), may be assigned a lower connected site cost than a site connected by an X.400 Connector using X.25. You configure connected site costs by using the Routing Address property page, which is accessed by using the Connected Sites property page.