Cisco DNCS System Release 2.7 3.7 4.2 설치 가이드
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DBDS System Time Overview
78-4011510-01 Rev C
DBDS System Time Synchronization Overview
Introduction
This section provides an overview of system time synchronization on the DBDS.
DBDS System Time Overview
In the DBDS network, the DNCS functions as the timekeeper. The DNCS
automatically updates the time on each Quadrature Amplitude Modulation (QAM)
device when the DNCS processes start and then every 12 hours after that. The time
on a QAM device is also set when it reboots.
All time within the DNCS is measured as an offset from Greenwich mean time
All time within the DNCS is measured as an offset from Greenwich mean time
(GMT). GMT is the mean solar time of the meridian of Greenwich, England, and the
time standard against which all other time zones in the world are referenced. GMT is
not affected by DST. The actual amount of offset from GMT (time zone setting) and
the configuration for support of DST are part of the Solaris configuration and are
discussed later in this guide.
Note: The QAM devices use GMT and are not affected by DST.
Note: The QAM devices use GMT and are not affected by DST.
DBDS Time Synchronization Overview
The DNCS can use one of the following three methods for synchronizing time in the
DBDS environment:
•
Manually setting the DNCS internal (Solaris) clock
•
Global Position System (GPS) clock
•
Network Time Protocol (NTP) server.
This section provides a description of each of these time synchronization methods.
Important:
Important:
•
Manually setting the system clock is highly unreliable and is only suggested for
lab environments where the clock setting is not really significant. Systems that
provide services to subscribers should use one of the other methods listed (GPS or
NTP server) to keep the DNCS and DBDS network time properly set.
•
If you are using either an external (GPS) clock or an NTP server, the DNCS
maintains the time as directed by the GPS or the NTP server. However, you
should periodically verify that DNCS synchronization to the time source is
maintained.
Note: With either the GPS- or NTP-based solutions for maintaining accurate DBDS
system time, an outage or fault represents a minor issue. The clock in the SUN
Solaris workstation does drift over time, but not at such a rate that a failure to obtain
time from an external source represents an immediate issue.