Cisco ASR1006 Configuration Guide - Page 343

Network Synchronization Support Network Synchronization Overview Table 2 Framing Modes for a BITS Port on the Other Cisco ASR 1000 Series Aggregation Services Routers BITS or SSU Port Support Matrix E1 E1 E1 2048 kHz Framing Modes Supported E1 FAS E1 CAS E1 CAS CRC4 2048 kHz SSM or QL Support No No No No Tx Port No No No No Rx Port Yes Yes Yes Yes You can configure network synchronization on the Cisco ASR 1000 Series Routers by using one of the following features: • Clock Recovery from SyncE When the Clock Recovery from SyncE feature is configured, the system clock is recovered from the SyncE clocking source (SyncE-enabled interfaces only). The router uses this clock as the Tx clock for other supported SPAs. • Clock Recovery from an External Interface When the Clock Recovery from an External Interface feature is enabled, the system clock is recovered from a BITS clock source. • Clock Recovery from a GPS (10M) Source Note The Clock Recovery from a GPS (10M) Source feature is supported only on the Cisco ASR 1002-X Router. When the Clock Recovery from a GPS Source feature is enabled, the system clock is recovered from a GPS (10M) clock source. • Line to External Note The Line to External feature is not supported on the Cisco ASR 1002-X Router. When the Line to External feature is enabled, 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 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 is performed only on external devices, such as SSUs and PRCs. You can have a maximum of eight clock sources configured on the 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 Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide 3