Precision Time Protocol (PTP) provides time synchronization among devices with submicrosecond accuracy. It provides also precise frequency synchronization.

Basic concepts

PTP profile

PTP profiles (PTP standards) include:

· IEEE 1588 version 2—1588v2 defines high-accuracy clock synchronization mechanisms. It can be customized, enhanced, or tailored as needed. 1588v2 is the latest version.

· ITU-T G.8275.1—G.8275.1 is introduced based on IEEE 1588. It is a precision time protocol telecom profile for phase and time synchronization with full timing support from the network.

PTP domain

A PTP domain refers to a network that is enabled with PTP. A PTP domain has only one reference clock called "grandmaster clock (GM)." All devices in the domain synchronize to the clock.

Clock node and PTP port (IEEE 1588 version 2)

A node in a PTP domain is called a clock node. A port enabled with PTP is called a PTP port. IEEE 1588 version 2 defines the following types of basic clock nodes:

· Ordinary Clock (OC)—A PTP clock with a single PTP port in a PTP domain for time synchronization. It synchronizes time from its upstream clock node through the port. If an OC operates as the clock source, it sends synchronization time through a single PTP port to its downstream clock nodes.

· Boundary Clock (BC)—A clock with more than one PTP port in a PTP domain for time synchronization. A BC uses one of the ports to synchronize time from its upstream clock node. It uses the other ports to synchronize time to the relevant downstream clock nodes. If a BC operates as the clock source, such as BC 1 in Figure 1, it synchronizes time through multiple PTP ports to its downstream clock nodes.

· Transparent Clock (TC)—A TC does not keep time consistency with other clock nodes. A TC has multiple PTP ports. It forwards PTP messages among these ports and performs delay corrections for the messages, instead of performing time synchronization. TCs include the following types:

¡ End-to-End Transparent Clock (E2ETC)—Forwards non-P2P PTP messages in the network and calculates the delay of the entire link.

¡ Peer-to-Peer Transparent Clock (P2PTC)—Forwards only Sync, Follow_Up, and Announce messages, terminates other PTP messages, and calculates the delay of each link segment.

Figure 1 shows the positions of these basic clock nodes in a PTP domain.

Figure 1 Clock nodes and PTP ports in a PTP domain (IEEE 1588 version 2)

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In addition to these basic types of clock nodes, PTP introduces hybrid clock nodes. For example, a TC+OC has multiple PTP ports in a PTP domain. One port is the OC type, and the others are the TC type.

A TC+OC forwards PTP messages through TC-type ports and performs delay corrections. In addition, it synchronizes time through its OC-type port. TC+OCs include these types: E2ETC+OC and P2PTC+OC.

Clock node and PTP port (ITU-T G.8275.1)

A node in a PTP domain is a clock node. A port enabled with PTP is a PTP port.

ITU-T G.8275.1 defines the following types of basic clock nodes:

· Telecom boundary clock (T-BC)—A clock node with more than one PTP port in a PTP domain for time synchronization. It uses one of the ports to synchronize time to its upstream clock node and uses the other ports to distribute time to the downstream clock nodes. If a T-BC operates as the clock source, it distributes time through multiple PTP ports to its downstream clock nodes.

· Telecom transparent Clock (T-TC)—A clock code that forwards non-P2P PTP messages in the network. The forwarding duration will be included in calculation of the entire link delay.

· Telecom time slave clock (T-TSC) —An OC clock node (as defined in IEEE 1588 version 2 and IEEE 802.1AS) that can act only as a member clock.

Figure 1 shows the positions of these basic clock nodes in a PTP domain.

Figure 2 Clock nodes and PTP ports in a PTP domain (ITU-T G.8275.1)

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Technical standard

A PTP profile uses the parameters including time accuracy, time class, time source, and clock offset (log variance) to describe PTP clock source signals. Users can customize and supplement a PTP profile based on the network conditions to develop their own PTP technical standard.

Four PTP technical standards are available: the default technical standard, OAM technical standard and Unicom technical standard. The default parameter values, the elected clock source, and PTP message processing vary by technical standard.

Only the ITU-T G.8275.1 PTP profile supports the OAM standard and Unicom standard. The default values for clock source-related parameters such as accuracy, time class, time source, and offset (log variance) differ between OAM and Unicom standards.

Master-member/subordinate relationship

The master-member/subordinate relationship is automatically determined based on the Best Master Clock (BMC) algorithm. You can also manually specify a role for the clock nodes.

The master-member/subordinate relationship is defined as follows:

· Master/member node—A master node sends a synchronization message, and a member node receives the synchronization message.

· Master/member clock—The clock on a master node is a master clock (parent clock) The clock on a member node is a member clock.

· Master/subordinate/passive port—A master port sends a synchronization message, and a subordinate port receives the synchronization message. The master and subordinate ports can be on a BC or an OC. A port that neither receives nor sends synchronization messages is a passive port.

Clock source type

A clock node supports the following clock sources:

· Local clock source—38.88 MHz clock signals generated by a crystal oscillator inside the clock monitoring module.

· External clock source—Clock signals generated by an external clock device. The signals are received and sent by a 1PPS/ToD port on the MPU. It is also called a ToD clock source.

Grandmaster clock

As shown in Figure 1, the grandmaster clock (GM) is the ultimate source of time for clock synchronization in a PTP domain. It is elected automatically by the clock nodes in the PTP domain. The clock nodes exchange PTP messages and elect the GM by comparing the clock priority, time class, and time accuracy carried in the PTP messages.

You can also specify a GM manually.

Grandmaster clock selection and master-member/subordinate relationship establishment

IEEE 1588 version 2

A GM can be manually specified. It can also be automatically elected through the BMC algorithm as follows:

1. The clock nodes in a PTP domain exchange announce messages and elect a GM by using the following rules in descending order of precedence:

a. Clock node with higher priority 1.

b. Clock node with higher time class.

c. Clock node with higher time accuracy.

d. Clock node with higher priority 2.

e. Clock node with a smaller port ID (containing clock number and port number).

The master nodes, member nodes, master ports, and subordinate ports are determined during the process. Then a spanning tree with the GM as the root is generated for the PTP domain.

2. The master node periodically sends announce messages to the member nodes. If the member nodes do not receive announce messages from the master node, they determine that the master node is invalid, and they start to elect another GM.

ITU-T G.8275.1

A GM can be manually specified. It can also be automatically elected through the BMC algorithm as follows:

1. The clock nodes in a PTP domain exchange announce messages and elect a GM by using the following rules in descending order of precedence:

a. Clock node with higher time class.

b. Clock node with higher time accuracy.

c. Clock node with higher priority 2.

d. Clock node with higher local priority.

You can use the ptp priority clock-source command to set the local priority for the local node.

To set a local priority for the peer node, use the ptp local-priority command to set a local priority for the PTP interface connected to the peer node. This priority will be used as the local priority of the peer node.

e. Whether the time class values of the clock nodes are smaller than or equal to 127.

- If the time class values of the clock nodes are smaller than or equal to 127, two or more clock nodes are elected GMs in the PTP domain. A member node selects the GM nearer to it as its master node. Two or more spanning trees are generated. No PTP messages are exchanged between the trees.

- If the time class values of the clock nodes are greater than 127, the clock node with a smaller port ID (containing clock number and port number) will be the GM.

The master nodes, member nodes, master ports, and subordinate ports are determined during the process.

Synchronization mechanism

After master-member relationships are established between the clock nodes, the master and member clock nodes exchange PTP messages and record the message transmit and receive time. Based on the timestamps, each member clock calculates the path delay and time offset between them and the master clock and adjusts their time accordingly for time synchronization with the master clock.

PTP defines two path delay measurement mechanisms: Request_Response_ and Peer Delay, both of which are based on network symmetry.

Request_Response

The Request_Response mechanism measures the average path delay between the master and member clock nodes by using the PTP messages as shown in Figure 3. A TC between master and member clock nodes does not calculate the path delay. It forwards PTP messages and makes residence time correction on the Sync messages.

This mechanism can be implemented in one of the following two modes:

· Two-step mode—t1 is carried in the Follow_Up message as shown in Figure 3.

· Single-step mode—t1 is carried in the Sync message, and no Follow_Up message is sent.

Figure 3 shows the Request_Response mechanism in two-step mode.

1. The master clock sends a Sync message to the member clock, and records the sending time t1. Upon receiving the message, the member clock records the receiving time t2.

2. After sending the Sync message, the master clock immediately sends a Follow_Up message that carries time t1.

3. The member clock sends a Delay_Req message to the master clock, and records the sending time t3. Upon receiving the message, the master clock records the receiving time t4.

4. The master clock returns a Delay_Resp message that carries time t4.

After this procedure, the member clock obtains all the four timestamps and can make the following calculations:

· Round-trip delay between the master and member clocks: (t2 – t1) + (t4 – t3)

· One-way delay between the master and member clocks: [(t2 – t1) + (t4 – t3)] / 2

· Offset between the member and master clocks: (t2 – t1) – [(t2 – t1) + (t4 – t3)] / 2 or [(t2 – t1) – (t4 – t3)] / 2

Figure 3 Request_Response mechanism (two-step node)

Protocols and standards

· IEEE Std 1588-2008, IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems, 2008

· ITU-T G.8275.1, Precision time protocol telecom profile for phase/time synchronization with full timing support from the network

Restrictions and guidelines: PTP configuration

Before configuring PTP, determine the PTP standard and define the scope of the PTP domain and the role of every clock node.

PTP tasks at a glance

Configuring PTP (IEEE 1588 version 2)

1. Specifying PTP for obtaining the time

2. Specifying a PTP profile

Specify the IEEE 1588 version 2 PTP profile.

3. Configuring clock nodes

¡ Specifying a clock node type

¡ (Optional.) Configuring an OC to operate only as a member clock

4. (Optional.) Specifying a PTP domain

5. (Optional.) Enabling the PTP clock state feature

6. Enabling PTP on a port

7. (Optional.) Configuring PTP ports

¡ (Optional.) Configuring the role of a PTP port

¡ Configuring the mode for carrying timestamps

¡ Specifying a delay measurement mechanism

8. (Optional.) Configuring PTP message transmission and receiving

¡ Setting the interval for sending announce messages and the timeout multiplier for receiving announce messages

¡ Setting the interval for sending Sync messages

¡ Setting the minimum interval for sending Delay_Req messages

9. (Optional.) Configuring parameters for PTP messages

¡ Configuring the destination MAC address for PTP messages

¡ Disabling PTP path tracing

10. (Optional.) Disabling PTP path tracing

11. (Optional.) Specifying the maximum number of removed steps (clock nodes) from the GM to the device

12. (Optional.) Enabling the device to notify the downstream nodes of its time synchronization state

13. (Optional.) Adjusting and correcting clock synchronization

¡ Setting the delay correction value

¡ Calculating the TAI based on the UTC time

¡ Configuring ToD input or output

¡ Enabling the device to ignore the synchronizationUncertain flag

¡ Synchronizing the TAI time and UTC time

14. (Optional.) Setting clock source parameters

15. (Optional.) Configuring a priority for a clock (IEEE 1588 version 2)

16. (Optional.) Configuring PTP logging

17. (Optional.) Enabling SNMP notification for the PTP module

Configuring PTP (ITU-T G.8275.1)

1. Specifying PTP for obtaining the time

2. Specifying a PTP profile

Specify the IEEE 802.1AS PTP profile.

3. Specifying a clock node type

4. (Optional.) Specifying a PTP domain

5. (Optional.) Specifying a PTP technical standard

6. (Optional.) Enabling the PTP clock state feature

7. Enabling PTP on a port

8. Configuring PTP ports

¡ (Optional.) Configuring the role of a PTP port

¡ Configuring the mode for carrying timestamps

¡ Enabling NotSlave on a PTP port

9. (Optional.) Configuring PTP message transmission and receiving

¡ Setting the interval for sending announce messages and the timeout multiplier for receiving announce messages

¡ Setting the interval for sending Sync messages

¡ Setting the minimum interval for sending Delay_Req messages

10. (Optional.) Configuring parameters for PTP messages

¡ Configuring the destination MAC address for PTP messages

11. (Optional.) Disabling PTP path tracing

12. (Optional.) Specifying the maximum number of removed steps (clock nodes) from the GM to the device

13. (Optional.) Enabling the device to notify the downstream nodes of its time synchronization state

14. (Optional.) Adjusting and correcting clock synchronization

¡ Setting the delay correction value

¡ Calculating the TAI based on the UTC time

¡ Configuring ToD input or output

¡ Enabling the device to ignore the synchronizationUncertain flag

15. (Optional.) Setting clock source parameters

16. (Optional.) Configuring a priority for a clock (ITU-T G.8275.1)

17. (Optional.) Configuring PTP logging

18. (Optional.) Enabling SNMP notification for the PTP module

Specifying PTP for obtaining the time

1. Enter system view.

system-view

2. Specify PTP for obtaining the time.

clock protocol ptp

By default, the device uses NTP to synchronize the system time.

For more information about the clock protocol command, see device management commands in Fundamentals Command Reference.

Specifying a PTP profile

Restrictions and guidelines

You must specify a PTP profile before configuring PTP settings. Changing the PTP profile clears all settings under the profile.

Procedure

1. Enter system view.

system-view

2. Specify a PTP profile.

ptp profile { 1588v2 | g8275.1 }

By default, no PTP profile is specified for the device.

Configuring clock nodes

Specifying a clock node type

Restrictions and guidelines

· You can specify only the BC, OC, T-BC, or T-TSC clock node type for the device.

· You can specify a PTP clock node type only after you specify a PTP profile.

· When the PTP profile is IEEE 1588 version 2, you cannot specify the T-BC or T-TSC clock node type.

· When the PTP profile is ITU-T G.8275.1, you can specify only the T-BC or T-TSC clock node type.

· Changing or deleting the clock node type restores the default settings of the PTP profile.

Procedure

1. Enter system view.

system-view

2. Specify a clock node type.

IEEE 1588v2 PTP profile:

ptp mode { bc | oc }

ITU-T G.8275.1:

ptp mode { t-bc | t-tsc }

By default, no clock node type is specified.

Configuring an OC to operate only as a member clock

About this task

An OC can operate either as a master clock to send synchronization messages or as a member clock to receive synchronization messages. This task allows you to configure an OC to operate only as a member clock.

If an OC is operating only as a member clock, you can use the ptp force-state command to configure its PTP port as a master port or passive port.

Restrictions and guidelines

This task is applicable only to OCs.

Procedure

1. Enter system view.

system-view

2. Configure the OC to operate only as a member clock.

ptp slave-only

By default, an OC operates as a master or member clock.

Specifying a PTP domain

About this task

Within a PTP domain, all devices follow the same rules to communicate with each other. Devices in different PTP domains cannot exchange PTP messages.

Procedure

1. Enter system view.

system-view

2. Specify a PTP domain for the device.

ptp domain value

The default settings of this command depends on the PTP profile.

¡ The device is in PTP domain 0 When the PTP profile is IEEE 1588 version 2.

¡ The device is in PTP domain 24 when the PTP profile is ITU-T G.8275.1.

Specifying a PTP technical standard

Restrictions and guidelines

This task is available only for the ITU-T G.8275.1 PTP profile.

The ptp technical-standard command is mutually exclusive with the ptp clock-state enable command.

Procedure

1. Enter system view.

system-view

2. Specify a PTP technical standard.

ptp technical-standard { oam | unicom }

By default, the default PTP technical standard applies.

Enabling the PTP clock state feature

About this task

The PTP clock state feature defines and clarifies the following PTP clock states:

· Free-Run—The PTP clock has never been synchronized to a time source and is not in the process of synchronizing to a time source.

· Acquiring—The PTP clock is in the process of synchronizing to a time source.

· Locked—The PTP clock has been synchronized to a time source within the acceptable accuracy.

· Holdover—The PTP clock is no longer synchronized to a time source and is using information obtained when it was previously synchronized.

Restrictions and guidelines

This task is available only for the IEEE 1588 version 2 and ITU-T G.8275.1 PTP profiles.

The ptp technical-standard command is mutually exclusive with the ptp clock-state enable command.

Procedure

1. Enter system view.

system-view

2. Enable the PTP clock state feature.

ptp clock-state enable

By default, the PTP clock state feature is disabled.

Enabling PTP on a port

About this task

A port enabled with PTP becomes a PTP port.

Restrictions and guidelines

You can enable PTP on only one port on an OC or T-TSC clock node.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Enable PTP on the port.

ptp enable

By default, PTP is disabled on a port.

Configuring PTP ports

Configuring the role of a PTP port

About this task

You can configure the master, passive, or slave role for a PTP port.

For an OC that operates in slave-only mode, you can perform this task to change its PTP port role to master or slave.

Restrictions and guidelines

By default, the PTP port roles are automatically negotiated based on the BMC algorithm. If you use the ptp force-state command to change the role of one PTP port, all the other PTP ports in the PTP domain stop working. For these PTP ports to function, you must specify roles for each of them by using the ptp force-state command. As a best practice, enable automatic negotiation of PTP port roles based on the BMC algorithm.

You can configure only one subordinate port on a device.

After you change the role of a PTP port, you must execute the ptp active force-state command to activate the port role configuration.

This task is not available for a T-TSC clock node.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view.

interface interface-type interface-number

3. Configure the role of the PTP port.

ptp force-state { master | passive | slave }

By default, the PTP port role is automatically calculated through BMC.

4. Return to system view.

quit

5. Activate the port role configuration.

ptp active force-state

By default, the port role configuration is not activated.

Configuring the mode for carrying timestamps

About this task

Timestamps can be carried in either of the following modes:

· Single-step mode—The Sync message in the Request_Response mechanism carries its own sending timestamp.

· Two-step mode—The Sync message in the Request_Response mechanism does not carry its own sending timestamp which is carried by the subsequent message.

Restrictions and guidelines

Single-step mode is not supported in FlexE physical interface view.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Configure the mode for carrying timestamps.

ptp clock-step { one-step | two-step }

By default, two-step mode is used for carrying timestamps.

Specifying a delay measurement mechanism

Restrictions and guidelines

PTP defines two transmission delay measurement mechanisms: Request_Response and Peer Delay. For correct communication, ports on the same link must share the same delay measurement mechanism.

When the PTP profile is IEEE 1588 version 2, you can configure this task only for a BC or OC clock node.

The ITU-T G.8275.1 PTP profile supports only the request-response delay measurement mechanism and does not support this task.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Specify a delay measurement mechanism.

ptp delay-mechanism { e2e | p2p }

The e2e keyword specifies the Request_Response mechanism, and the p2p keyword specifies the Peer Delay mechanism.

By default, the request-response delay measurement mechanism applies.

Enabling NotSlave on a PTP port

About this task

The NotSlave feature is supported only by the ITU-T G.8275.1 profile., enables a PTP port to select the clock node where it resides as the master node. You can use this feature to control master/member role of the clock nodes. For automatic master/member clock node selection in a PTP domain under the ITU-T G.8275.1 or ITU-T G.8275.2 PTP profile, you must disable NotSlave on all PTP ports.

Restrictions and guidelines

When the PTP profile is ITU-T G.8275.1, you can configure this task only on a T-BC clock node.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Disable NotSlave.

ptp notslave disable.

Configuring PTP message transmission and receiving

Setting the interval for sending announce messages and the timeout multiplier for receiving announce messages

About this task

A master node sends announce messages to the member nodes at the specified interval. If a member node does not receive any announce message from the master node after the timeout expires, it determines that the master node is invalid. The timeout = timeout multiplier × interval at which the master node sends announce messages.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Set the interval for sending announce messages.

ptp announce-interval interval

The default varies by PTP profile:

¡ IEEE 1588 version 2—The interval argument value is 1 and the interval for sending announce messages is 2 (21) seconds.

¡ ITU-T G.8275.1—The interval argument value is –3 and the interval for sending announce messages is 1/8 (2-3) seconds.

4. Set the number of intervals before a timeout occurs.

ptp announce-timeout multiple-value

By default, a timeout occurs when three intervals are reached.

Setting the interval for sending Sync messages

About this task

This task allows you to configure the interval at which the master node sends Sync messages to the member nodes. You must configure this task on the master node.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Set the interval for sending Sync messages.

ptp syn-interval interval

The default varies by PTP profile:

¡ IEEE 1588 version 2—The interval argument value is 0 and the interval for sending Sync messages is 1 (20) second.

¡ ITU-T G.8275.1—The interval argument value is –4 and the interval for sending Sync messages is 1/16 (2-4) seconds.

Setting the minimum interval for sending Delay_Req messages

About this task

When receiving a Sync or Follow_Up message, an interface can send Delay_Req messages only when the minimum interval is reached.

Restrictions and guidelines

In PTP multicast transport mode, this setting takes effect only when configured on the master clock. The master clock sends the value to a member clock through PTP messages to control the interval for the member clock to send Delay_Req messages. To view the value on a member clock, execute the display ptp interface command on the member clock.

In PTP unicast transport mode, this setting takes effect when configured on member clocks. It does not take effect when configured on the master clock.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Set the minimum interval for sending Delay_Req messages.

ptp min-delayreq-interval interval

The default setting varies by PTP profile.

¡ IEEE 1588 version 2—The value of the interval argument is 0 and the minimum interval for sending delay request messages is 1 (20) second.

¡ ITU-T G.8275.1—The value of the interval argument is –4 and the minimum interval for sending delay request messages is 1/16 (2-4) seconds.

Configuring parameters for PTP messages

Configuring the destination MAC address for PTP messages

About this task

IEEE 802.3/Ethernet-encapsulated PTP messages can be sent through multicast or unicast. The destination MAC address for PTP messages can be as follows:

· Any unicast MAC address in unicast mode.

· In multicast mode:

¡ 0180-C200-000E or 011B-1900-0000 for non-Pdelay messages, including delay_Req, delay_Resp, delay_Resp_Follow_Up, Announce, Sync, and FollowUp messages.

¡ 0180-C200-000E for Pdelay messages, including Pdelay_Req, Pdelay_Resp, and Pdelay_Resp_Follow_Up messages.

Restrictions and guidelines

You must specify the PTP profile and a PTP mode before configuring this feature.

This feature takes effect only when PTP messages are encapsulated in IEEE 802.3/Ethernet packets.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Configure the destination MAC address for PTP messages.

ptp destination-mac mac-address

By default, the destination MAC address for non-Pdelay messages is 011B-1900-0000 and the destination MAC address for Pdelay messages is 0180-C200-000E.

Disabling PTP path tracing

About this task

PTP path tracing traces the clock nodes that the clock signals traverse from the GM to the device. The system can obtain complete path tracing information only when all clock nodes on the path are enabled with PTP path tracing. If a device on the path does not support PTP path tracing, disable this feature to prevent PTP intercommunication issues.

Procedure

1. Enter system view.

system-view

2. Disable PTP path tracing.

ptp path-trace disable

By default, PTP path tracing is enabled.

Specifying the maximum number of removed steps (clock nodes) from the GM to the device

About this task

If the number of removed steps from the GM to the device on the PTP synchronization path is too large, the time synchronization accuracy will decrease. After you specify the maximum number of removed steps from the GM to the device, the device cannot synchronize time through PTP if the number of the removed steps exceeds the maximum value.

Procedure

1. Enter system view.

system-view

2. Specify the maximum number of removed steps from the GM to the device.

ptp max-steps-removed step-removed-value

By default, the maximum number of removed steps from the GM to the device is 255.

Enabling the device to notify the downstream nodes of its time synchronization state

About this task

The task enables the device to notify its downstream nodes of its time synchronization state.

By default, the device transfers only the locked and unlocked status of the upstream node to the downstream nodes, and does not transfer its locked or unlocked status to the downstream nodes.

After this task is configured, the device notifies the downstream nodes of its locked and unlocked status through the synchronizationUncertain flag in the announce messages. The downstream nodes do not synchronize to the device when they receive information that the device time is unlocked and synchronize to the device when they receive information that the device time is locked.

Restrictions and guidelines

This task is available only for the IEEE 1588 version 2 and ITU-T G.8275.1 PTP profiles.

Procedure

1. Enter system view.

system-view

2. Enable the device to notify the downstream nodes of its time synchronization state.

ptp sync-uncertain enable

By default, the device does not notify the downstream nodes of its time synchronization state.

Adjusting and correcting clock synchronization

Setting the delay correction value

About this task

PTP performs time synchronization based on the assumption that the delays in sending and receiving messages are the same. However, this is not practical. If you know the offset between the delays in sending and receiving messages, you can set the delay correction value for more accurate time synchronization.

Procedure

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Set a delay correction value.

ptp asymmetry-correction { minus | plus } value

The default is 0 nanoseconds. Delay correction is not performed.

Calculating the TAI based on the UTC time

About this task

International Atomic Time (TAI) is a high-precision atomic coordinate time scale. Coordinated Universal Time (UTC) is based on TAI and adjusted by leap seconds for synchronization with astronomical time.

UTC is constantly compared with UT1 (astronomical time, reflecting the earth's rotation). The International Bureau of Weights and Measures (BIPM) will notify to add or subtract one second from the UTC time scale at the last minute on a specific date (typically June 30 or December 31) to ensure that the difference between UTC and UT1 is within one second.

The BIPM publishes the difference between UTC and TAI periodically. Till now, UTC is 37 seconds behind TAI.

Internet devices typically use the UTC time. To provide more accurate time, PTP also uses TAI. If the device acts as a subordinate clock node, it uses the UTC time and TAI time of the clock reference. If the device acts as the clock reference, it will calculate the TAI time based on the UTC time, and synchronize the UTC and TAI time to the subordinate clocks. This task is used to calculate the TAI time based on the UTC time.

TAI = UTC + cumulative offset. To get the correct TAI time from the UTC time:

· Set the accurate UTC time on the device.

· Use the ptp utc offset command to set the cumulative offset of UTC relative to TAI as published by BIPM. This command takes effect immediately.

· If the BIPM notifies to add or subtract one second from the UTC time scale on a specific data after you use the ptp utc offset command to configure the cumulative offset of TAI relative to UTC, use the ptp utc { leap59-date | leap61-date } date command to change the UTC time. The TAI time will be changed accordingly.

Restrictions and guidelines

This setting takes effect only when it is configured on the master clock node and the local clock of the master clock node is the GM.

Configure this feature on both the master and member nodes for the new master clock to provide accurate TAI time after a master/member node switchover.

Procedure

1. Enter system view.

system-view

2. Set the cumulative offset of UTC relative to TAI.

ptp utc offset utc-offset

The default is 0 seconds.

3. Add or subtract one second from the UTC time scale at the last minute on the specified date.

ptp utc { leap59-date | leap61-date } date

By default, no second is added or subtracted from the UTC time.

Configuring ToD input or output

About this task

To use a ToD clock, you must configure ToD input or output:

· ToD input—The device obtains clock signals from an external ToD clock and synchronizes ToD to all cards on the device.

· ToD output—The device operates as a ToD clock to synchronize ToD to other devices in the PTP network.

To implement more accurate time synchronization, you can specify a delay correction value.

Procedure

1. Enter system view.

system-view

2. Configure ToD input or output.

ptp tod0 { input [ delay input-delay-time ] | output [ delay output-delay-time ] }

By default, whether to receive or transmit ToD clock signals is not configured. The transmit and receive delay correction value is 0 nanoseconds.

Enabling the device to ignore the synchronizationUncertain flag

About this task

By default, the device reads the value of the synchronizationUncertain flag in the announce message it receives.

· A synchronizationUncertain bit value of 1 indicates that synchronization information from the upstream node is unlocked.

· A synchronizationUncertain bit value of 0 indicates that synchronization information from the upstream node is locked.

If synchronization information from the upstream node is unlocked, the device will not use that information for time synchronization. Only if synchronization information from the upstream node is locked, the device uses that information for time synchronization.

Typically, you are not required to configure this task. If the upstream clock is very reliable, you can configure this task to enable the device to ignore the synchronizationUncertain flag. After this task is configured, the device will synchronize the time directly with synchronization information from the upstream clock without reading the synchronizationUncertain bit value.

Restrictions and guidelines

Only the IEEE 1588 version 2 and ITU-T G.8275.1 PTP profiles support this task.

Procedure

1. Enter system view.

system-view

2. Enable the device to ignore the synchronizationUncertain flag.

ptp ignore sync-uncertain

By default, the device does not ignore the synchronizationUncertain flag.

Synchronizing the TAI time and UTC time

About this task

When the device acts as the GM clock on the network and services that rely on PTP clock synchronization (such as iFIT measurement and deterministic network technology) exist on the network, a PTP time jump might affect the operation of these services. This task helps reduce PTP time jumps, and consequently minimize the impact of PTP time jumps on services.

Operating mechanism

The device has two local clock sources: one is UTC time (generated by the local crystal on the MPU), and the other is TAI time (also known as PTP time, generated by the clock daughtcard/PTP chip). After this task is configured, the device synchronizes the TAI time and UTC time as follows by default if the device acts as the GM clock on the network:

1. The device uses the UTC time as the reference clock source for the entire network.

2. After the network administrator enables PTP in interface view, the device synchronizes the clock daughtcard/PTP chip with the UTC time.

3. After synchronizing with the UTC time, the clock daughtcard/PTP chip uses its own frequency for timekeeping. The device synchronizes downstream devices with the TAI time.

4. The device automatically synchronizes the PTP-enabled clock daughtercard/PTP chip with the UTC time every 6 hours.

5. If the network administrator changes the UTC time (for example, execute the clock data-time, ptp utc offset, or ptp utc { leap59-date | leap61-date } command, the device will instantly and automatically synchronize the clock daughtercard and PTP chip with the UTC time.

Finally, devices on the network are synchronized with the UTC time of the device.

After the TAI time and UTC time are synchronized, they are counted separately based on their own frequencies. As a result, there might be extremely subtle deviations between the TAI time and UTC time. Synchronizing the TAI time with the UTC time every 6 hours might cause the TAI time to jump, leading to network-wide time jumps, and consequently affect services that rely on PTP clock synchronization.

To avoid this situation, you can execute the undo command undo ptp refclock-master sync-utc. After executing the undo command, the device will automatically synchronize the UTC time with the TAI time every 6 hours, preventing time jumps from affecting the entire network.

Restrictions and guidelines

This task takes effect only after the clock protocol ptp command is configured.

Procedure

1. Enter system view.

system-view

2. Configure the device to synchronize the TAI time with the UTC time at 6-hour intervals to ensure consistency between the TAI and UTC time when it acts as the GM

ptp refclock-master sync-utc

By default, when the device acts as a GM clock, it synchronizes the TAI time with the UTC time at 6-hour intervals to ensure consistency between the TAI and UTC time.

Setting clock source parameters

Restrictions and guidelines

The clock's time class is an inherent attribute of the device. For a local clock source, keep and do not change the default time class of a local clock source.

Procedure

1. Enter system view.

system-view

2. Set clock source parameters. Choose the options to configure as needed:

¡ ptp clock-source local { accuracy acc-value | class class-value | time-source ts-value }

¡ ptp clock-source tod0 { accuracy acc-value | class class-value | time-source ts-value | grandmaster-clockid clock-id | offsetscaled-logvariance value }

The default settings for clock source parameters vary by PTP profile and PTP technical standard.

· The clock ID of a GM clock is 000000-0000-000000.

· ITU-T G.8275.1 PTP profile

¡ T-TSC clock node type

- Local clock source—The accuracy value is 254, the time class value is 255, the offset (log variance) value is 65535, and the time source value is 160. The four values are fixed, not configurable.

- ToD clock source—The accuracy value is 254, the time class value is 255, the offset (log variance) value is 65535, and the time source value is 32.

¡ T-BC clock node type

- Default PTP technical standard

Local clock source—The accuracy value is 254, the time class value is 248, the offset (log variance) value is 65535, and the time source value is 160.

ToD clock source—The accuracy value is 32, the time class value is 6, the offset (log variance) value is 65535, and the time source value is 32.

- PTP OAM technical standard

Local clock source—The accuracy value is 254, the time class value is 165, the offset (log variance) value is 65535, and the time source value is 160. The offset (log variance) value is not configurable.

ToD clock source—The accuracy value is 254, the time class value is 165, the offset (log variance) value is 65535, and the time source value is 160.

- PTP Unicom technical standard

Local clock source—The accuracy value is 254, the time class value is 248, the offset (log variance) value is 65535, and the time source value is 160. The offset (log variance) value is not configurable.

ToD clock source—The accuracy value is 33, the time class value is 6, the offset (log variance) value is 20061, and the time source value is 32.

· IEEE 1588 version 2 PTP profile

¡ Local clock source—The accuracy value is 254, the time class value is 255, the offset (log variance) value is 65535, and the time source value is 160. The offset (log variance) value not configurable.

¡ ToD clock source—The accuracy value is 32, the time class value is 6, the offset (log variance) is 65535, and the time source value is 32.

Configuring clock priorities

Configuring a priority for a clock (IEEE 1588 version 2)

About this task

Priorities for clocks are used to elect the GM. The smaller the priority value, the higher the priority.

Procedure

1. Enter system view.

system-view

2. Configure the priority for a clock .

ptp priority clock-source { local | tod0 } { priority1 priority1 | priority2 priority2 }

When the PTP profile is IEEE 1588 version 2, the default value of priority 1 and the default value of priority 2 are both 128.

Configuring a priority for a clock (ITU-T G.8275.1)

About this task

When the PTP profile is ITU-T G.8275.1, you can configure priorities for the local clock node and the peer clock node.

Priorities for clocks affect the GM election. The smaller the priority value, the higher the priority. For more information about GM election, see "Grandmaster clock selection and master-member/subordinate relationship establishment."

Restrictions and guidelines

Only the ITU-T G.8275.1 PTP profile supports this task.

Configuring priorities for the local clock node

1. Enter system view.

system-view

2. Configure the priority for a clock.

ptp priority clock-source { local | tod0 } { priority2 priority2 | local-priority local-priority }

By default, the priority 2 value is 128 for a T-BC clock node and 255 for a T-TSC clock node. The local priority value is 128.

Configuring a priority for the peer clock node

An announce message does not carry the local priority of the clock node. Each PTP interface on a clock node has a local priority. You can use the ptp local-priority command to configure a local priority for a PTP interface. This priority will be used as the local priority of the peer node in BMC selection and is one of the factors that determine whether the peer node can be elected as the GM.

To configure a priority for the peer clock node:

1. Enter system view.

system-view

2. Enter Layer 3 Ethernet interface view or FlexE physical interface view.

interface interface-type interface-number

3. Configure a priority for the peer clock node.

ptp local-priority local-priority

By default, the clock priority of the peer clock node is 128.

Configuring PTP logging

About this task

PTP logs help monitor the clock source status. The following PTP logs are available:

· PTP log that indicates a lower time class

Each PTP clock source has a class value. For a ToD clock source, you can set its class value by using the ptp clock-source command. The higher the value, the lower the class. When the class value of the clock source crosses the class threshold, the system outputs a log for notification.

· PTP log that indicates a higher time offset between the external reference clock and the PTP clock

If the device uses an external reference clock, it periodically calculates the time offset between the external reference clock and the PTP clock. When the offset exceeds the threshold, the device outputs a log for notification

· PTP logs that indicate a higher time-offset-sum peak-to-peak value

The PTP module calculates the time-offset-sum peak-to-peak value at specific intervals and compares the value with the threshold configured by this command. If the value is larger than the threshold, the system outputs a log for notification.

· PTP logs that indicate the time-locked or time-unlocked state

When the time offset of the PTP reference clock crosses the PTP time locking threshold, the PTP time is put into unlocked state. The system outputs a time-unlocked log for notification. When the time offset of the PTP reference clock drops to or below the PTP time locking threshold, the PTP time is put into locked state. The system outputs a time-locked log for notification.

Restrictions and guidelines

Only the IEEE 1588 version 2 and ITU-T G.8275.1 PTP profiles support this task.

Procedure

1. Enter system view.

system-view

2. Configure the class threshold for the clock source.

ptp alarm-threshold clock-source-class class-value

By default, the class threshold for the clock source is 6.

3. Configure the time-offset threshold between the external reference clock and the PTP clock.

ptp alarm-threshold time-offset time-offset-value

By default, the time-offset threshold is 500 ns between the external reference clock and the PTP clock.

4. Set the time-offset-sum peak-to-peak threshold.

ptp alarm-threshold time-offset-sum pk-pk threshold-value

By default, the time-offset-sum peak-to-peak threshold is 500 ns.

5. Set the PTP time locking and unlocking thresholds.

ptp alarm-threshold { time-lock lock-value | time-unlock unlock-value } *

By default, the PTP locking threshold is 10 ns and PTP unlocking threshold is 3000 ns.

Enabling SNMP notification for the PTP module

About this task

To get informed of important events of the PTP module, enable SNMP notification for the PTP module. The notifications generated for the PTP module will be sent to the SNMP module of the device. Configure SNMP notification parameters on the device for the SNMP module to output the notifications as required.

For information about SNMP configuration and SNMP notifications, see SNMP configuration in Network Management and Monitoring Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enable SNMP notification for the PTP module.

snmp-agent trap enable ptp

By default, SNMP notification is enabled for the PTP module.

Display and maintenance commands for PTP

Execute display commands in any view and the reset command in user view.

Task	Command
Display PTP clock information.	display ptp clock
Display the delay correction history.	display ptp corrections
Display information about foreign master nodes.	display ptp foreign-masters-record [ interface interface-type interface-number ]
Display PTP information on an interface.	display ptp interface [ interface-type interface-number \| brief ]
Display parent node information for the PTP device.	display ptp parent
Display brief information about the PTP synchronization path from the GM to the device.	display ptp path-trace
Display historical role change information for PTP ports.	display ptp port-history [ interface interface-type interface-number ]
Display PTP statistics.	display ptp statistics [ interface interface-type interface-number ]
Display PTP clock time properties.	display ptp time-property
Clear PTP statistics.	reset ptp statistics [ interface interface-type interface-number ]

PTP configuration examples

Example: Configuring PTP (ITU-T G.8275.1, IEEE 802.3/Ethernet transport, multicast transmission)

Network configuration

As shown in Figure 4, configure PTP (ITU-T G.8275.1, IEEE 802.3/Ethernet transport, multicast transmission) to enable Device A to synchronize Device B.

· Specify the ITU-T G.8275.1 PTP profile for Device A and Device B.

· Assign Device A and Device B to the same PTP domain. Specify the T-BC clock node type for Device A and T-TSC clock node type for Device B.

· Use the default Request_Response delay measurement mechanism on Device A and Device B.

Figure 4 Network diagram

‌

Procedure

IMPORTANT:

The ITU-T G.8275.1 PTP profile transports PTP messages over IEEE 802.3/Ethernet rather than IPv4 UDP and in multicast rather than unicast mode.

1. Configure Device A:

# Configure the use of SSM quality level in automatic reference selection.

<DeviceA> system-view

[DeviceA] network-clock ssmcontrol on

# Extract the SSM level from the signals received on the GigabitEthernet 2/0/0 line clock port.

[DeviceA] network-clock source lpuport gigabitethernet 2/0/0 forcessm off

# Set the priority of the GigabitEthernet 2/0/0 line clock to 1.

[DeviceA] network-clock source lpuport gigabitethernet 2/0/0 priority 1

# Enable the synchronous mode and ESMC on GigabitEthernet 2/0/0.

[DeviceA] interface gigabitethernet 2/0/0

[DeviceA-GigabitEthernet2/0/0] synchronous mode

[DeviceA-GigabitEthernet2/0/0] esmc enable

[DeviceA-GigabitEthernet2/0/0] quit

# Specify the ITU-T G.8275.1 PTP profile.

[DeviceA] ptp profile g8275.1

# Specify the T-BC clock node type.

[DeviceA] ptp mode t-bc

# Specify PTP for obtaining the time.

[DeviceA] clock protocol ptp

# Enable PTP on Ten-GigabitEthernet 2/0/0.

[DeviceA] interface ten-gigabitethernet 2/0/0

[DeviceA-Ten-GigabitEthernet2/0/0] ptp enable

[DeviceA-Ten-GigabitEthernet2/0/0] quit

2. Configure Device B:

# Configure the use of SSM quality level in automatic reference selection.

<DeviceB> system-view

[DeviceB] network-clock ssmcontrol on

# Extract the SSM level from the signals received on the GigabitEthernet 2/0/0 line clock port.

[DeviceB] network-clock source lpuport gigabitethernet 2/0/0 forcessm off

# Set the priority of the GigabitEthernet 2/0/0 line clock to 1.

[DeviceB] network-clock source lpuport gigabitethernet 2/0/0 priority 1

# Enable the synchronous mode and ESMC on GigabitEthernet 2/0/0.

[DeviceB] interface gigabitethernet 2/0/0

[DeviceB-GigabitEthernet2/0/0] synchronous mode

[DeviceB-GigabitEthernet2/0/0] esmc enable

[DeviceB-GigabitEthernet2/0/0] quit

# Specify the ITU-T G.8275.1 PTP profile.

[DeviceB] ptp profile g8275.1

# Specify the T-TSC clock node type.

[DeviceB] ptp mode t-tsc

# Specify PTP for obtaining the time.

[DeviceB] clock protocol ptp

# Enable PTP on Ten-GigabitEthernet 2/0/0.

[DeviceB] interface ten-gigabitethernet 2/0/0

[DeviceB-Ten-GigabitEthernet2/0/0] ptp enable

[DeviceB-Ten-GigabitEthernet2/0/0] quit

Verifying the configuration

When the network is stable, perform the following tasks:

· Use the display ptp clock command to display PTP clock information.

· Use the display ptp interface brief command to display brief PTP running information for all PTP interfaces.

# Display PTP clock information on Device A.

[DeviceA] display ptp clock

PTP profile : ITU-T G.8275.1

PTP mode : T-BC

Slave only : No

Sync uncertain : Disabled

Clock state : Disabled

Lock status : Unlocked

Clock ID : 24881D-FFFE-F20100

Clock type : Local

Clock domain : 24

Number of PTP ports : 1

Priority1 : 128

Priority2 : 128

Local priority : 128

Clock quality :

Class : 248

Accuracy : 254

Offset (log variance) : 65535

Offset from master : 0 (ns)

Mean path delay : 0 (ns)

Steps removed : 0

Local clock time : Fri Dec 7 00:59:44 2018

Clock source info:

Clock Pri1 Pri2 Accuracy Class TimeSrc Direction In-Status Offset(log variance)

-------------------------------------------------------------------

Local 128 128 254 248 160 N/A N/A 65535

ToD0 128 128 32 6 32 In Inactive 65535

# Display brief PTP running information for all PTP interfaces on Device A.

[DeviceA] display ptp interface brief

Name State Delay mechanism Clock step Asymmetry correction

XGE2/0/0 Master E2E Two 0

# Display PTP clock information on Device B.

[DeviceB] display ptp clock

PTP profile : ITU-T G.8275.1

PTP mode : T-TSC

Slave only : No

Sync uncertain : Disabled

Clock state : Disabled

Lock status : Unlocked

Clock ID : 2461E3-FFFE-A20200

Clock type : Local

Clock domain : 24

Number of PTP ports : 1

Priority1 : 128

Priority2 : 255

Local priority : 128

Clock quality :

Class : 255

Accuracy : 254

Offset (log variance) : 65535

Offset from master : 50 (ns)

Mean path delay : 5000 (ns)

Steps removed : 1

Local clock time : Fri Dec 7 14:52:54 2018

Clock source info:

Clock Pri1 Pri2 Accuracy Class TimeSrc Direction In-Status Offset(log variance)

-------------------------------------------------------------------

Local 128 128 254 248 160 N/A N/A 65535

ToD0 128 128 32 6 32 In Inactive 65535

# Display brief PTP running information for all PTP interfaces on Device B.

[DeviceB] display ptp interface brief

Name State Delay mechanism Clock step Asymmetry correction

XGE2/0/0 Slave E2E Two 0

The output shows that Device A is elected as the GM, and Ten-GigabitEthernet2/0/0 on Device A is the master port.

12-Network Management and Monitoring Configuration Guide

Basic concepts

PTP profile

PTP domain

Clock node and PTP port (IEEE 1588 version 2)

Clock node and PTP port (ITU-T G.8275.1)

Technical standard

Master-member/subordinate relationship

Clock source type

Grandmaster clock

ITU-T G.8275.1

Request_Response

Specifying PTP for obtaining the time

Specifying a PTP profile

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Configuring an OC to operate only as a member clock

About this task

Restrictions and guidelines

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Enabling NotSlave on a PTP port

About this task

Restrictions and guidelines

Procedure

Configuring PTP message transmission and receiving

Setting the interval for sending announce messages and the timeout multiplier for receiving announce messages

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Operating mechanism

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Configuring a priority for a clock (IEEE 1588 version 2)