OSF DCE Administration Guide--Core Components

Chapter 26. Interoperation with Network Time
Protocol
Network Time Protocol (NTP) is an Internet-recommended standard. The NTP
synchronization subnetwork is represented by a tree-structured graph with nodes
representing time servers and edges representing the transmission paths between them.
The root nodes of the tree are designated primary servers that synchronize to a radio
broadcast or calibrated atomic clock. Remaining nodes are designated secondary servers
that synchronize to other servers (primary and secondary).
The number of subnetwork hops between a particular server and a primary server
determines the stratum of that server; that is, the smaller the number of hops, the lower
the stratum. A lower-stratum server always has a higher accuracy than a higher-stratum
server. All servers have identical functionality and can operate simultaneously as clients
of the next lower stratum and servers for the next higher stratum.
Servers, both primary and secondary, typically run NTP with several other servers at the
same or lower stratum. A selection algorithm attempts to select the most accurate and
reliable server or set of servers from which to actually synchronize the local clock.
NTP and DTS both can be used in large computer networks that have embedded local
nets (that is, those connected by routers, gateways, and bridges) and use both broadcast
and point-to-point transmission media. DTS and NTP can run simultaneously on the
same LAN.
The following sections describe how to give time to and get time from local and remote
NTP time sources, and how to prevent loops.
26.1 Getting the Time from NTP Time Sources
DTS provides two sample time-provider programs:
• dts_ntp_provider.c—Takes the time from an NTP server as it would from a radio
receiver. The user specifies the name of the NTP server and the inaccuracy.
• dts_null_provider.c—Used on a DTS server whose clock is already synchronized by
an external agent, such as NTP. It sets the inaccuracy, but it prevents DTS from
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