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S12700 V200R010C00 Configuration Guide - Device Management

This document describes the principles and configurations of the Device Management features, and provides configuration examples of these features.
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Setting the Priority of a Clock Source

Setting the Priority of a Clock Source


When there are multiple clock sources, you can set different priorities for them. In normal situations, a clock board uses the clock source of the highest priority. If no clock source is specified forcibly or manually and the SSM quality level is not used in clock source selection, the clock board uses the clock source of the highest priority. If the clock source of the highest priority fails, the clock board uses the clock source of the second highest priority.

To implement clock synchronization on the entire network, you can set priorities of clock sources to ensure that the clock source on the input line of the primary reference clock has the highest priority on each device.

The primary reference clock must be stable. When configuring multiple clock sources, you need to configure a backup clock transmission path. When clock signals are lost on the original clock transmission path, a new clock source is selected and clock signals are transmitted on the backup path.

Pre-configuration Tasks

Before selecting the clock source based on the priority, complete the following tasks:

  • Set parameters of the link layer protocol and IP addresses for the interfaces to ensure that the link layer protocol on the interfaces is in Up state.
  • Configure the routing protocol to make the IP routes between the nodes reachable.
  • Disable the SSM from being used in clock source selection.
  • Cancel the configuration of forcible or manual clock source selection.
  • Ensure that the clock to be configured meets the following conditions:
    • All clock sources provide valid clock signals.
    • The result of frequency offset check does not affect clock source selection and the frequency offset of the clock sources is within the specified range.
    • The clock sources are not locked.


  1. Run:


    The system view is displayed.

  2. Run:

    clock priority priority source source { system | bits0 | bits1 }

    The priority is set for a clock source.

    By default, the priority of the inner clock source and system clock source is 254, and the priority of other clock sources is 255. A smaller priority value indicates a higher priority.

    • The number of the clock source for the system clock ranges from 0 to 8.
    • The number of the clock source for the BITS clocks ranges from 5 to 9.

    Table 6-10 shows the mappings between the clock source numbers and clock sources.

    Table 6-10  Mappings between the clock source numbers and clock sources

    Clock No.

    Clock Source


    Inner Clock






    Slave Board BITS0


    Slave Board BITS1


    Left Frame Clock


    Right Frame Clock


    FSU (reserved)


    Slave Board FSU (reserved)


    System Clock


  • Run the display clock mode [ slave ] command to view the clock source selection mode.
  • Run the display clock selection [ slave ] command to view the current clock sources of external clocks.
Updated: 2019-08-21

Document ID: EDOC1000142080

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