OSF DCE Administration Guide--Core Components

Introduction to DCE Distributed Time Service
In order to build server lists and synchronize with the servers on the list, clerks need to
be able to locate servers automatically. They discover servers by using remote procedure
call (RPC) profiles. Recall that profiles are search tables that contain the following types
of entries:
• Server Entries—The CDS names of individual resource providers.
• Service Group Entries—A group of resource providers identified by a single CDS
name.
• Profile Entries—The names of other configuration profiles. These entries allow
hierarchical nesting of profiles.
Each DTS clerk node contains up to three profiles. When it attempts to locate servers, a
clerk first performs an RPC lookup of the entries in a base profile called the node initial
profile. The clerk then looks for the LAN profile entry. If the LAN profile entry is not
found, the clerk searches for the default profile entry; the default profile may contain the
LAN profile entry. When the clerk locates the LAN profile, it reads the server entries to
build a list of local servers. This process is repeated at set intervals.
If a clerk does not obtain enough server entries as dictated by the DTS management
attribute minservers, it attempts to locate additional servers, usually those outside the
LAN. To locate these servers, a clerk locates the cell profile, which has a well-known
CDS name. The cell profile contains global server entries; that is, servers that are
normally found outside the LAN. (See Section 23.3.2 for further information on servers.)
After building a server list with enough entries, a clerk can directly request time values
from several of the servers on the list. The clerk then receives these time values and uses
them to compute a new system time for its client system.
23.3.2 Servers
Servers provide many of the communications and synchronization functions for DTS.
Like clerks, they import information about other servers from LAN and cell profiles.
Servers, however, also export bindings to their own CDS namespace entries and export
their names to the LAN and cell profiles. (See the following subsections on the server
subtypes for further information on how servers are configured and located.)
External time-providers can be connected to servers, which propagate the precise time
intervals they obtain from the time-providers throughout the network.
Before one server can obtain time values from another, the servers must have the same
epoch number. Epochs divide the DTS implementation into logically separate areas.
Servers only synchronize with other servers that have the same epoch number. All
servers have the same epoch number when they are created. Infrequently, you may wish
to change a server’s epoch number, using the management interface, to isolate it from the
network in order to correct a problem.
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