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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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Selecting the Clock Source Based on the SSM Quality Level

Selecting the Clock Source Based on the SSM Quality Level

Applicable Environment

If multiple clock sources can obtain their SSM quality levels, the system can select the reference clock source based on the SSM quality level. If no reference clock source is specified forcibly, the clock board uses the clock source of the highest SSM quality level. If this clock source fails, the clock source uses the clock source of the second highest SSM quality level. The SSM quality level of the external clock source will change to the SSM quality level of the clock source selected by the system.

The SSM quality level takes precedence over the priority in clock source selection; therefore, the SSM quality level of the primary reference clock source must be the highest so that clock synchronization can be implemented on the entire network.

The SSM quality levels, in descending order, are:
  • Primary Reference Clock (PRC)
  • Synchronization Supply Unit-T (SSU-T)
  • Synchronization Supply Unit-L (SSU-L)
  • SDH Equipment Clock (SEC)
  • Do Not Use (DNU)

If the SSM level of a clock source is DNU, and the SSM level is used in clock source selection, this clock source will not be selected as the reference clock source. The default SSM quality level of the inner clock and system clock (19.44 MHz) is SEC.

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 SSM quality level, 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.
  • Cancel the configuration of forcible 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.

Configuration Process

Complete the following tasks to configure clock source selection based on the SSM quality level.

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Updated: 2019-08-21

Document ID: EDOC1000142080

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