Couriers
Local servers called couriers request time values from one randomly selected global server at every synchronization. When DTS starts up, it automatically sets the server's courierrole attribute value to backup. You can change the server's courier role by manually changing this attribute value. To do this, you use the dcecp program's dts modify command with the -change option. If a server is connected to an external time-provider, you want to reconfigure it as a courier.
Couriers maintain lists of global servers whose bindings they import from the cell profile. At every synchronization, couriers use the responses of all local servers and one global server when synchronizing their own clocks. Couriers provide network-wide synchronization through the following procedure:
1. Couriers request time values from at least one global server in a remote area and request the balance of values from local servers up to the number determined by the minservers attribute.
2. Couriers use the global server times and local server times to synchronize the clocks that are in their respective systems.
3. Couriers relay newly computed clock times to other servers and clerks on the LAN during future synchronizations.
For a network containing multiple LANs or point-to-point links, one server on each LAN or segment needs to be configured as a courier. This configuration ensures that various portions of the network remain synchronized and are not isolated from each other.
Using the management interface, you can also designate one or more servers to be backup couriers. These local servers temporarily assume courier functions in the event that no courier servers are available on the LAN. In such a case, the backup courier with the lowest ordered Universal Unique Identifier (UUID) regularly synchronizes with global servers until a courier is again available.
If a courier cannot find any global server, then it uses local servers, and increments its no global server detected count.