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Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide
OL-16506-17
Chapter 11 Network Synchronization Support
Network Synchronization Overview
Note This feature is supported only on the Cisco ASR 1002-X Router.
When this feature is enabled, the system clock is recovered from a GPS (10M) clock source.
• Line to External
Note This feature is not supported on the Cisco ASR 1002-X Router.
When this feature is enabled, the clock received from an Ethernet is forwarded to an external SSU.
The SyncE feature provides the clock cleanup functionality. When a router is in the middle of a
synchronization chain, the received clock may experience 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 then performs a cleanup and sends it back
to the BITS interface. The cleaned up clock is received from the SSU and is used as the Tx clock for
the SyncE ports. In the context of the Cisco ASR 1000 Series Aggregation Services Routers, the
interface from which the clock is recovered and the BITS port to the SSU must reside on the same
card.
A SyncE-enabled Cisco ASR 1000 Series Router provides the Squelching feature. In this feature, an
alarm indication signal (AIS) is sent to the Tx interfaces if the clock source goes down. When the
Line to External feature is configured, if the line source goes down at any point of time, an AIS is
transmitted through the external interface to the SSU. Squelching can be performed only on external
devices, such as SSUs and PRCs.
You can have a maximum of eight clock sources configured on a Cisco ASR 1000 Series Router. On a
router that supports the Network Synchronization feature, you can configure selection of the clock
source on the basis of the quality of the clock source. With this feature configured, the clock source that
offers the best quality is made the default clock source. If the highest level of quality is offered by more
than one clock source, the clock source with the highest priority is made the default clock source. You
can also manage synchronization by using the following management options:
• 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 milliseconds (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 selects a synchronization source irrespective of whether the source is
available or within the specified range.
• Manual Switch: Manually select a synchronization source, provided the clock source has a higher
quality level than the currently active clock.
Table 11-3 lists the SPAs that support network synchronization.
Ta b l e 11- 3 SPAs supporting Network Synchronization
SPA Type SPA Name
ASR 1001-X
Built-in SPA
BUILT-IN-2T+6X1GE
ASR1002-X
Built-in SPA
6XGE-BUILT-IN