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Synchronization Status Message and Ethernet Synchronization Messaging Channel
You can implement SyncE on the Cisco ASR 1000 Series Routers, using three different configurations:
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A SyncE-enabled Cisco ASR 1000 Series Router provides the squelching functionality under which an
alarm indication signal (AIS) is sent to the Tx interfaces if the clock source goes down. The squelching
functionality is implemented in the following scenario:
Line to External: If the line source goes down, an AIS is transmitted through the external interface to the
SSU. Squelching is performed only on external devices such as SSU or PRC.
You can have a maximum of six clock sources for a Cisco ASR 1000 Series Router. The clock source
with highest priority is made the default clock source. You can manage the clock sources by changing
the priority of the clock sources. You can also manage synchronization using the following management
options:
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Synchronization Status Message and Ethernet Synchronization
Messaging Channel
Network clocking uses the following mechanisms to exchange the quality level of the clock between the
network elements:
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Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide
10-2
Clock Recovery from SyncE: The system clock is recovered from the SyncE clocking source
(gigabit interfaces only). The router uses this clock as the Tx clock for other SyncE interfaces or
ATM or CEoP interfaces.
Clock Recovery from External Interface: The system clock is recovered from a BITS clocking
source.
Line to External: The clock received from an Ethernet is forwarded to an external SSU. The SyncE
feature provides the clock cleanup functionality. For a router in the middle of a synchronization
chain, the received clock may have unacceptable wander and jitter. The router recovers the clock
from the SyncE interface, converts it to the format required for the BITS interface, and sends it to
an SSU through the BITS port. The SSU performs the cleanup and sends it back to the BITS
interface. The cleaned up clock is received back from the SSU. This clock is used as the Tx clock
for the SyncE ports. For Cisco ASR 1000 Series Router, the interface from which the clock is
recovered and the BITS port to the SSU should reside on the same card.
Hold-Off Time: If a clock source goes down, the router waits for a specific hold-off time before
removing the clock source from the clock selection process. By default, the value of hold-off time
is 300 ms.
Wait to Restore: If a SyncE interface comes up, the router waits for a specific period of time before
considering the SyncE interface for synchronization source. By default, the value is 300 seconds.
Force Switch: Forcefully select a synchronization source irrespective of whether the source is
available or within the specified range.
Manual Switch: Manually selects a synchronization source, provided the clock source has a higher
quality level than the currently active clock.
Synchronization Status Message, page 10-3
Ethernet Synchronization Messaging Channel, page 10-3
Chapter 10
Synchronous Ethernet Support
OL-16506-10
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