Users Guide

QL-enabled mode
In the QL-enabled mode, the switch considers the following factors when selecting a clock source on the SyncE-enabled
interfaces:
● Clock quality level (QL)
● Clock availability or signal fail through QL-FAILED
● Priority
● External commands (SyncE force switch or manual switch)
In this mode, the switch always selects the clock source with the best QL value. SSM codes indicate the QL values, which are
defined for the different regions such as Europe and America (see sync-e ssm-network-option). When multiple clock
sources are available on the network, a clock source is selected according to the following rules:
● If no external switch commands are active, the switch selects the clock source with the highest QL that does not experience
a signal fail condition.
● If multiple clock sources have the same highest QL, the clock source with the highest priority is selected.
● If multiple clock sources have the same highest priority and QL, the switch remains synchronized to the current clock source
or an arbitrary clock source from the group is selected.
QL-disabled mode
In the QL-disabled mode, the switch considers the following factors when selecting a clock source on the SyncE-enabled
interfaces:
● Clock availability or signal fail through QL-FAILED
● Priority
● External commands (SyncE force switch or manual switch)
When multiple clock sources are available on the network, a clock source is selected according to the following rules:
● If no external switch commands are active, the switch selects the clock source with the highest priority that does not
experience a signal fail condition.
● If multiple clock sources have the same highest priority, the switch remains synchronized to the current clock source or an
arbitrary clock source from the group is selected.
Manage clock selection
Clock synchronization depends to a large extent on QL or priority of the clock sources. However, you can influence clock
selection by modifying the following clock properties:
● Force switch—The switch forcibly selects a clock source regardless of its availability or quality. Use the sync-e switch
force command to override the currently selected synchronization source. Ensure that the new source clock is enabled and
is not locked out. Use the clear sync-e switch command to clear the force switch command.
● Manual switch—The switch selects a synchronization source that is in enabled state, not locked out, not in signal fail
condition, and has a QL better than Do Not Use (DNU) in QL-enabled mode. In QL-enabled mode, a manual switch is
performed only to a source that has the highest available QL. Use the sync-e switch manual command to initiate a
manual switch. Use the clear sync-e switch command to clear the manual switch command.
● Lockout—The clock source is locked and it is not available for the selection process. Use the sync-e lockout command
to lock a clock source on an interface. Use the clear sync-e lockout command to clear the lockout state of an
interface so that the clock source on that interface can be considered for selection process.
● Hold-Off Time—When a clock source goes down, the switch waits for the configured hold-off time period before removing
the clock source from the clock selection process. The default time period is 300 milliseconds. Use the sync-e hold-
off-time command to configure the hold-off time.
● Wait-to-Restore Time—The amount of time that the switch waits before considering a previously failed synchronization
source as available for the selection process, if it is fault free for the configured time period. The default time period is 300
seconds. Use the sync-e wait-to-restore-time command to configure the wait-to-restore time. Use the clear
sync-e wait-restore-time command to stop the remaining timer and allow the ports to participate in clock selection.
254
System management