Each PTP slave clock can be configured to receive timing from up to two PTP master clocks. If two PTP master clocks are configured, and if communication to the best master is lost or if the BMCA determines that the other PTP master clock is better, then the PTP slave clock switches to the other PTP master clock.
For a redundant or simple CSM configuration on the 7705 SAR-8 Shelf V2 and 7705 SAR-18, a maximum of two PTP slave clocks can be configured as the source of reference (ref1 and ref2) to the SSU. If a failure occurs between the PTP slave clock and the master clock, the SSU detects that ref1 or ref2 is unavailable and automatically switches to the other reference source. This switching provides PTP hot redundancy for hardware failures (on the 6-port Ethernet 10Gbps Adapter card, 8-port Gigabit Ethernet Adapter card, 10-port 1GigE/1-port 10GigE X-Adapter card, or Packet Microwave Adapter card) or port or facility failures (SFP or cut fiber). If a loopback address is used, PTP packets may arrive on any router network interface and the PTP clock remains up.
The 7705 SAR-M, 7705 SAR-H, 7705 SAR-Hc, 7705 SAR-A, 7705 SAR-Ax, 7705 SAR-Wx, and 7705 SAR-X support only one PTP slave clock. This slave clock can be configured as the source of reference (ref1 or ref2) to the SSU.