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Configuration Guide - Device Management

S2720, S5700, and S6720 V200R013C00

This document describes the configurations of Device Management, including device status query, hardware management, Stack, SVF, cloud-based management, PoE, monitoring interface, OPS, energy-saving management, information center, fault management, NTP, synchronous ethernet, PTP.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
PTP Fundamentals

PTP Fundamentals

Concepts of Clock Synchronization

Telecommunications services on modern communications networks require that the frequency offset or time difference between devices be within an acceptable range. This requirement must be met using network clock synchronization.

Clock synchronization includes frequency synchronization and phase synchronization.

  • Frequency synchronization

    Frequency synchronization, also called clock 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

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

In the following sections, time synchronization indicates phase synchronization, and clock synchronization indicates both phase synchronization and frequency synchronization.

Figure 14-1  Difference between time synchronization and frequency synchronization

Clock Synchronization Implementation

A network that implements clock synchronization between network devices is called a clock synchronization network. Such a network uses a two-level architecture, as shown in Figure 14-2. Level-1 nodes are level-1 clock synchronization devices, level-2 nodes are level-2 clock synchronization devices, and nodes below level-2 nodes are clients that require clock synchronization.

A client clock synchronization link connects a node and a client. Any transmission link can be used as a client clock synchronization link because multiple synchronization methods, including Ethernet clock synchronization and Network Time Protocol (NTP), are required between nodes and clients. A node clock synchronization link connects two nodes. Any transmission link except a link that runs NTP can be used as a node clock synchronization link.

PTP organizes all clocks into a master-slave synchronization hierarchy, with the grandmaster clock at the top of the hierarchy. PTP messages are used to implement clock synchronization. To synchronize its local clock with the master clock in the hierarchy, a slave clock uses the timestamp carried in PTP messages to calculate its offset and delay compared with the master clock.

Figure 14-2  Clock synchronization network hierarchy

Basic Concepts

  • PTP domain

    A PTP domain is a logical area that runs PTP. More than one PTP domains may exist on a network. Each PTP domain is an independent PTP clock synchronization system and has only one clock source. All devices in a PTP domain synchronize their clocks with the clock source.

  • 1588v2 clock nodes

    Clock nodes are nodes in a PTP domain. PTP defines the following types of clock nodes:
    • Ordinary clock (OC) device: provides only one physical port to participate in time synchronization in a PTP domain. An OC device uses this port to synchronize time with an upstream device or to send time to a downstream device.
    • Boundary clock (BC) device: provides two or more physical ports to participate in time synchronization in a PTP domain. One port synchronizes time with an upstream device, and the others send the time to downstream devices. A clock node is also a BC device if it functions as the clock source and sends time to downstream devices through multiple PTP ports.
    • Transparent clock (TC) device: forwards PTP messages between its PTP ports and measures the link delay of the messages. Different from an OC device and a BC device, a TC device does not synchronize time with other devices through ports.
  • 1588v2 clock types
    • OC: ordinary clock
    • BC: boundary clock
    • End to end transparent clock (E2ETC) for the delay mechanism: is a TC using a delay measurement mechanism in delay mode. A device that functions as an E2ETC does not need to have the delay measurement mechanism mode configured.
    • Peer to peer transparent clock (P2PTC) for the Pdelay mechanism: is a TC using a delay measurement mechanism in Pdelay mode. A device that functions as a P2PTC does not need to have the delay measurement mechanism mode configured.
    • End to end transparent clock (E2ETC) for the delay mechanism: is an ordinary TC in terms of time synchronization and a special TC that synchronizes the frequency with upstream devices based on PTP messages. For an E2ETCOC, the ports that function as a TC work in the delay measurement mechanism.
    • Peer to peer transparent clock and ordinary clock (P2PTCOC): is similar to an E2ETCOC. For a P2PTCOC, the ports that function as a TC work in the Pdelay measurement mechanism.
    • Transparent clock and boundary clock (TCandBC): For a TCandBC, some PTP ports function as a BC that synchronizes the clock with other devices, and other PTP ports function as a TC that transmits PTP messages and does not perform delay calculation.
  • G.8275.1 clock nodes

    The clock nodes supported by G.8275.1 are as follows:
    • Telecom grandmaster (T-GM): is a master-only clock that can have one or more PTP ports. It does not trace other PTP clocks.
    • Telecom boundary clock (T-BC): can be a master clock and trace other PTP clocks.
    • Telecom time slave clock (T-TSC): is a slave-only clock.
  • G.8275.1 clock type: T-BC

  • PTP port

    A PTP port is a port running PTP. PTP ports are classified into the following types based on roles:
    • Master port: is located on a BC, T-BC, or OC device and sends synchronization clock signals to a downstream port.
    • Slave port: is located on a BC, T-BC, or OC device and receives synchronization clock signals from an upstream port.
    • Passive port: is an idle port on a T-BC or BC device and does not send or receive synchronization clock signals.
  • Master-slave hierarchy

    Nodes in a PTP domain are organized into a master-slave hierarchy. Master nodes send synchronization clock signals, whereas slave nodes receive synchronization clock signals. A device may receive synchronization clock signals from an upstream node and then send the synchronization clock signals to a downstream device.

    If two clock nodes synchronize time with each other:

    • The node that sends synchronization clock signals is the master node, and the node that receives synchronization clock signals is the slave node.
    • The clock on the master node is the master clock, and the clock on the slave node is the slave clock.
    • The port that sends synchronization clock signals is the master port, and the port that receives synchronization clock signals is the slave port.
  • Grandmaster clock

    All clock nodes in a PTP domain are organized into a master-slave hierarchy. The grandmaster clock (GMC) is at the top of the hierarchy and serves as the reference clock. Clock nodes exchange PTP messages to synchronize the time of the GMC to the entire PTP domain. Therefore, the GMC is also called the clock source. The GMC can be statically configured or dynamically elected through the best master clock (BMC) algorithm.

  • PTP message

    Nodes exchange PTP messages to establish the master-slave hierarchy and implement time and frequency synchronization. PTP messages are classified into event messages and general messages depending on timestamps:
    • Event message: is tagged with a timestamp when reaching or leaving a port. PTP devices calculate the link delay based on the timestamps carried in event messages. Event messages include Sync, Delay_Req, Pdelay_Req, and Pdelay_Resp messages.
    • General message: is used to establish master-slave hierarchy, and to request and send time information. General messages are not tagged with timestamps. General messages include Announce, Follow_Up, Delay_Resp, Pdelay_Resp_Follow_Up, Management, and Signaling messages. Currently, devices do not support Management and Signaling messages.
    Message 1588v2 G.8275.1 Function
    Sync Supported Supported A Sync message is sent from the master to the slave and carries the t1 timestamp sent by the master.
    A Sync message can be sent in either one-step or two-step mode.
    • one-step: In this mode, a Sync message contains the transmit timestamp.
    • two-step: In this mode, a Sync message records the time when the message is sent, instead of containing the transmit timestamp. Such a transmit timestamp is carried in a Follow-Up message.
    Delay_Req Supported Supported A Delay_Req message is sent from the slave to the master during delay time synchronization and carries the t3 timestamp sent by the slave.
    Pdelay_Req Supported Not supported A Pdelay_Req message is sent from the slave to the master during peer delay time synchronization and carries the t3 timestamp sent by the slave.
    Pdelay_Resp Supported Not supported A Pdelay_Resp message is sent by the master to the slave during peer delay time synchronization and carries the t4 timestamp and interface ID sent by the master.
    Announce Supported Supported An Announce message is used to exchange time source information between clock nodes to determine the master-slave hierarchy.
    Follow_Up Supported Supported A Follow_Up message is sent from the master to the slave following a Sync message in two-way mode during delay time synchronization. A Follow_Up message carries the t1 timestamp sent by the master.
    Delay_Resp Supported Supported A Delay_Resp message is sent by the master to the slave during delay time synchronization and carries the t4 timestamp and interface ID sent by the master.
    Pdelay_Resp_Follow_Up Supported Not supported A Pdelay_Resp_Follow_Up message is sent from the master to the slave following a Sync message in two-way mode during peer delay time synchronization. A Pdelay_Resp_Follow_Up message carries the t1 timestamp sent by the master.
    Management Supported Not supported Currently, a switch does not support Management messages.
    Signaling Supported Not supported

Packet Encapsulation Modes

1588v2 message encapsulation modes

1588v2 messages can be encapsulated using the MAC or UDP encapsulation mode for transmission at Layer 2 or Layer 3, respectively.
  • MAC encapsulation

    This mode applies to 1588v2 messages that are transmitted over a Layer 2 link. In MAC encapsulation, the VLAN ID and 802.1p priority can be carried in 1588v2 messages, and the Ethernet type 0x88F7 is used.

    Figure 14-3  Untagged MAC-encapsulated messages

    Figure 14-4  Tagged MAC-encapsulated messages

  • UDP encapsulation

    This mode applies to 1588v2 messages that are transmitted over a Layer 3 link. In UDP encapsulation, the VLAN ID, 802.1p priority, and DSCP priority can be carried in 1588v2 messages, and the destination UDP port number is 319 (for non-Announce messages) or 320 (for Announce messages).

    Figure 14-5  Untagged UDP-encapsulated messages

    Figure 14-6  Tagged UDP-encapsulated messages

G.8275.1 packet encapsulation modes

G.8275.1 defines the packet encapsulation mode as Layer 2 multicast (without tags). The corresponding Ethernet Type is 0x88F7. There are two types of multicast destination MAC addresses: non-forwardable multicast MAC address (0180-C200-000E) and forwardable multicast MAC address (011B-1900-0000).

Figure 14-7  Untagged Layer 2 multicast encapsulation messages

Clock Synchronization Process

The clock synchronization process consists of three phases:

  1. Master-slave hierarchy establishment

    PTP selects the GMC and determines the master and slave ports.

  2. Frequency synchronization

    PTP synchronizes the frequency of the slave node with that of the master node.

  3. Time synchronization

    PTP synchronizes the time of the slave node with that of the master node.

Comparisons between synchronous Ethernet and other clock synchronization protocols

Clock Protocol Whether Frequency Synchronization Is Supported Whether Time Synchronization Is Supported Time Synchronization Accuracy Signal Transmission Mode
NTP No Yes Millisecond accuracy Time signals are transmitted using NTP packets.
Synchronous Ethernet Yes No - Clock signals are transmitted using serial data streams at the physical layer, without affecting upper-layer services and CPU performance.
PTP Yes Yes Sub-microsecond accuracy Clock and time signals are transmitted using PTP packets, and higher time accuracy is achieved with the assistance of hardware.
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Updated: 2019-04-20

Document ID: EDOC1100065674

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