OSF DCE Administration Guide--Core Components

Introduction to DCE Distributed Time Service
23.1.1 Applications Support
Operating systems and distributed applications require synchronized time measurements
to coordinate their processes. DTS synchronizes the system clocks in a network with
each other and, in the presence of an external time-provider, to the UTC time standard.
Any distributed application that reads the system clock, which is the majority of
applications, needs DTS. As the number of distributed applications and systems in a
network increases, DTS becomes increasingly vital to process coordination.
There are several types of existing applications that use the synchronized time DTS
provides to system clocks. These applications must reference synchronized system
clocks in order to coordinate the events that occur throughout the network. Applications
use synchronized clocks for the following functions:
• Event Measurement—Applications can read the system clock to start and stop timers
and to measure the elapsed time between events.
• Event Reporting—Applications can read the clock when an event occurs and append
a timestamp to the event report.
• Event Scheduling—Applications can read the system clock and add a relative time to
determine the occurrence of a future event.
• Event Sequencing—Applications can determine the order of events by reading the
event report timestamps that are derived from the synchronized system clock.
For new applications, DTS provides an API. This API provides routines that new
applications can use to obtain and manipulate binary timestamps. The DTS API supports
ANSI C language constructs. (See the
for further information on the DTS API.)
23.1.2 External Time-Provider Support
For most networks, it is desirable to synchronize the system clocks with the UTC time
standard. Many commercial devices are available for obtaining the UTC time that is
provided by standards organizations; these devices receive signals by short-wave radio,
satellite, and telephone. If your network or cell is larger than a single LAN, it is
recommended that you use at least one external time-provider in combination with the
DTS software. (See Appendix C for a list of suppliers of time-provider hardware.
Sample time-provider programs are available online in dcelocal/usr/examples/dts.)
DTS servers can synchronize with time-providers by means of the TPI, which is
described in the communications between the DTS server process and the time-provider
process.
When a DTS server attempts to synchronize, it uses the TPI to check for a time-provider
process. If one is available, the server synchronizes only with the time-provider. If no
time-provider is present, the server synchronizes with other servers in the network.
By using a time-provider with a DTS server, you can ensure that the server is closely
synchronized with UTC. When other servers request a time from the server with the
124243 Tandem Computers Incorporated 23−3