Juniper ACX2000 Configuration Guide

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 auto-select option at the [edit chassis synchronization] hierarchy level. You can also
configure the chassis to lock to the free-running local oscillator, which is the Stratum 3E
oscillator, by including the free-run option at the [edit chassis synchronization] hierarchy
level. The auto-select option enables the clock source selection algorithm to run. The
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 quality-mode-enable statement at
the [edit chassis synchronization] hierarchy level.
•
QL disabled—The default setting is disable, which means that when the
quality-mode-enable statement is not configured, QL is disabled. In this mode, the best
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.
Clock Source Selection Algorithm
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, QL must be configured for external clocks (gps or bits)
whether or not QL is enabled.
•
In the case of network-option option-2, the default QL for the external clocks is QL_STU,
whether or not QL is enabled.
227Copyright © 2017, Juniper Networks, Inc.
Chapter 9: Configuring Timing and Synchronization

Juniper ACX2000 Specifications

General

Brand	Juniper
Model	ACX2000
Category	Network Router
Language	English