Clock Selection Algorithm - Cisco ASR 1000 Series Software Configuration Manual

Overview of the Ethernet SPAs

Clock Selection Algorithm

The clock selection algorithm selects the best available synchronization source from the nominated sources.
The algorithm has a non-revertive behavior among clock sources with the same QL value, and always selects
the signal with the best QL value. For clock option 1, the default is revertive, and for clock option 2, the
default is nonrevertive.
The clock selection process works in the QL-enabled and QL-disabled modes. When multiple selection
processes are present in a network element, all processes work in the same mode.
QL-Enabled Mode
In QL-enabled mode, the following parameters contribute to the selection process:
• Quality level
• Signal fail via QL-FAILED
• Priority
• External commands
If no external commands are active, the algorithm selects the reference (for clock selection) with the
Note
highest quality level that does not experience a signal fail condition. If multiple inputs have the same
highest quality level, the input with the highest priority is selected. For multiple inputs having the same
highest priority and quality level, the existing reference is maintained (if it belongs to this group), otherwise
an arbitrary reference from this group is selected.
QL-Disabled Mode
In QL-Disabled mode, the following parameters contribute to the selection process:
• Signal failure
• Priority
• External commands
If no external commands are active, the algorithm selects the reference (for clock selection) with the highest
priority that does not experience a signal fail condition. For multiple inputs having the same highest priority,
the existing reference is maintained (if it belongs to this group). Otherwise an arbitrary reference from this
group is selected.
Supported MIBs
The following MIBs are supported by the LAN/WAN Phy Gigabit Ethernet SPAs on the Cisco ASR 1000
Series Routers:
• ENTITY-MIB
• CISCO-ENTITY-SENSOR-MIB
OL-14127-17
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS XE
Supported MIBs
Everest 16.5
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