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Configuration Guide - Device Management

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, PIM (IPv4), PIM (IPv6), MSDP, multicast VPN, multicast route management (IPv4), multicast route management (IPv6), IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN, multicast network management.

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Basic Concepts of Synchronous Ethernet

Basic Concepts of Synchronous Ethernet

Clock Synchronization

On a modern communications network, most telecommunications services require that the frequency deviation or time difference between devices be within an acceptable range. This requirement must be met using network clock synchronization.

Network clock synchronization includes frequency synchronization and phase synchronization.

  • Frequency synchronization, also called clock synchronization

    Frequency synchronization indicates that signals have the same frequency and a fixed phase difference. That is, signals are sent or received at an average rate. All devices on a communications network operate at the same rate.

  • Phase synchronization, also called time synchronization

    Phase synchronization indicates that both frequencies and phases of signals are consistent. That is, the phase offset between signals is always 0.

Figure 5-1 illustrates the difference between frequency synchronization and phase synchronization. If Watch A and Watch B show different time but they keep a constant time difference, this is called frequency synchronization. If Watch A and Watch B always keep the same time, this is called phase synchronization.

Figure 5-1 Difference between frequency synchronization and phase synchronization

Clock Source

The device that provides clock signals for another device is called the clock source. A device may have multiple clock sources:
  • External clock source

    A device is connected to an external clock of a higher level through Ethernet interfaces.

  • PTP clock source

    A device extracts clock signals from 1588v2 messages using 1588v2.

  • Line clock source

    A device extracts clock signals from the Ethernet line bit stream through Ethernet interfaces.

  • Internal clock source

    A device uses its reference clock (for example, the clock provided by the clock chip) as the working clock of its interfaces.

These clock sources are listed in descending order of clock accuracy: external clock source, PTP clock source, line clock source, and internal clock source.

Updated: 2020-01-07

Document ID: EDOC1100075362

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