Configuring Clocking
This section provides information about how to configure clocking on the SPA-24CHT1-CE-ATM or the
SPA-1CHOC3-CE-ATM, and contains the following topics:
BITS Clock Support Receive and Distribute CEM SPA
You can use the BITS Clock Support
—
Receive and Distribute
—
CEM SPA feature to select and configure a
clock and distribute it across the chassis to be used as the Transmit reference on all SPA ports.
The line card operates in three different modes, depending on the configuration and the configured source
state.
•
Free-running
—
A line card that is not participating in network clocking or a line card that is actively
sourcing the clock operates in the free-running mode. In this mode, the internal oscillator of the line
card generates the reference clock to the backplane.
•
Normal
—
In the normal mode, the module synchronizes with an externally supplied network timing
reference sourced from one of the chassis BITS inputs or recovered from a network interface. In this
mode, the accuracy and stability of the output signal is determined by the accuracy and stability of the
input reference.
•
Holdover
—
In the holdover mode, the network timing module generates a timing signal based on the
stored timing reference used when operating in the normal mode. The holdover mode is automatically
selected when the recovered reference is lost or has drifted excessively.
All the line cards operate in the free-running mode until the network clock is configured.
Note
Guidelines for Configuring the Network Clock
To configure the network clock, consider the following guidelines:
•
The Cisco ASR 1000 Series Aggregation Services Routers operate in the free-running mode until the
network clock is configured.
•
When the network clocking configuration is present in the startup configuration, the clocking configuration
is not applied until five minutes after the configuration has been parsed. This prevents clocking instability
on the backplane when the interfaces or controllers come up out of order.
•
Network clocking is enabled by default for the Cisco ASR 1000 Series Aggregation Services Routers.
•
If there is a source flap, an interval of 180 seconds exists before the source becomes valid and active.
•
In the event of an Out-of-Range (OOR) switchover (revertive mode), the source switchover occurs when
the clock offset crosses the -9.2 ppm or +9.2 ppm threshold. If OOR switchover occurs, you must
reconfigure the source.
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS XE
Everest 16.5
OL-14127-17
517
Configuring the Circuit Emulation over Packet Shared Port Adapter
Configuring Clocking