OSF DCE Administration Guide--Core Components

Introduction to DCE Distributed Time Service

23.3.2.3 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 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.

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