System Management
202
Basic System Configuration Guide
3HE 11010 AAAC TQZZA Edition: 01
For more information about ToD-1pps, see PTP Ordinary Slave Clock for Time of
Day/Phase Recovery.
6.1.2.6 GNSS
The 7705 SAR supports frequency synchronization via a Layer 1 interface such as
synchronous Ethernet, and ToD synchronization via a protocol such as NTP or PTP.
In cases where these methods are not possible, or where accuracy cannot be
ensured for the service, you can deploy a GNSS receiver as a synchronous timing
source. GNSS data is used to provide network-independent frequency and ToD
synchronization.
GNSS receivers on the following platforms support GPS reference only, or combined
GPS and GLONASS reference:
• 7705 SAR-Ax
• 7705 SAR-H with a GPS Receiver module
• 7705 SAR-Wx variants with a GPS RF port
• 7705 SAR-8 (CSMv2 only) with a GNSS Receiver card
• 7705 SAR-18 with a GNSS Receiver card
A 7705 SAR chassis equipped with a GNSS receiver and an attached GNSS
antenna can be configured to receive frequency traceable to Stratum-1 (PRC/PRS).
The GNSS receiver provides a synchronization clock to the SSU in the router with
the corresponding QL for SSM. This frequency can then be distributed to the rest of
the router from the SSU as configured with the ref-order and ql-selection
commands. The GNSS reference is qualified only if the GNSS receiver is
operational, has five or more satellites locked, and has a frequency successfully
recovered. A PTP master/boundary clock can also use this frequency reference with
PTP peers.
In the event of GNSS signal loss or jamming resulting in the unavailability of timing
information, the GNSS receiver automatically prevents output of clock or
synchronization data to the system, and the system can revert to alternate timing
sources.
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