Clock Source Selection Algorithm - Juniper ACX1000 Configuration Manual

Clock Source Selection Algorithm

Copyright © 2017, Juniper Networks, Inc.
NOTE: Automatic clock selection does not apply to the IEEE 1588v2 recovered
clock.
Automatic clock selection is supported on the ACX Series routers. Automatic clock
selection of the best quality clock source is based on the Ethernet Synchronization
Message Channel (ESMC) Synchronization Status Message (SSM) quality level, the
configured quality level, and the priority. To configure automatic clock selection, include
the option at the [
auto-select
configure the chassis to lock to the free-running local oscillator, which is the Stratum 3E
oscillator, by including the
level. The option enables the clock source selection algorithm to run. The
auto-select
clock source selection algorithm is triggered by the following events:
Signal failure detected on the currently selected source
Changes in the received Ethernet Synchronization Message Channel (ESMC)
Synchronization Status Message (SSM) quality level (QL)
Configuration changes. For example, the addition or deletion of a clock source, a change
to the QL mode, and so on.
Automatic clock selection supports two modes on the ACX Series router: QL enabled
and QL disabled. To configure QL mode, include the
the [ edit chassis synchronization
QL disabled—The default setting is disable, which means that when the
statement is not configured, QL is disabled. In this mode, the best
quality-mode-enable
clock is selected based on the configured ESMC SSM QL. If the QL of the best clocks
are equal, the clock selection is based on the configured priority. If both the configured
QL and priority are equal, one of the sources is randomly selected.
QL enabled—In this mode, the best clock is selected based on the incoming ESMC
SSM QL as long as the incoming QL is at least as good as the source's configured QL.
If the QLs are equal, the clock selection is based on the configured priority. If both the
received QL and the priority are equal, one of the sources is selected randomly.
The clock source selection algorithm uses the following logic and restrictions:
QL must be configured for non-external clocks, whether or not QL is enabled.
For
network-option option-1
whether or not QL is enabled.
In the case of network-option option-2
whether or not QL is enabled.
Chapter 9: Configuring Timing and Synchronization
edit chassis synchronization
free-run option at the [ edit chassis synchronization
quality-mode-enable
] hierarchy level.
, QL must be configured for external clocks (
, the default QL for the external clocks is QL_STU,
] hierarchy level. You can also
] hierarchy
statement at
or
gps bits
)
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