The network clock monitoring module provides network clock synchronization for all interface cards in the system. It ensures that all ports on the interface cards operate at the same clock rates for network synchronization.

The network clock monitoring module provides the following functions:

· Provides highly precise, reliable timing signal to all interface cards.

· Constantly monitors the signaling status on the interface cards.

· Selects a clock reference from available clock sources, and then distributes its timing signal to all interface cards.

· Performs phase lock to maintain a deterministic relationship between the input and output signals in frequency and phase.

Clock sources

The device supports the following clock sources:

· BITS—Building integrated timing supply (BITS) clock. The MPU has BITS ports to receive and send timing signals.

· Line clock—Timing signal extracted from the signal received on a WAN port from a higher-level device. The WAN port is called a line processing unit (LPU) port. Line timing signal is less precise than BITS timing signal.

· PTP—Timing signal obtained through PTP. PTP timing signal is less precise than BITS timing signal.

· Local clock source—38.88 MHz timing signal generated by a crystal oscillator on the clock daughter card. The local clock signal has the lowest precision.

Clock source levels

The level of a clock source is determined by its SSM quality level and priority.

SSM quality levels

The synchronization status message (SSM) is transmitted in a synchronization distribution trail to indicate the quality of the clock source. The following are the SSM quality levels supported by the device, from the highest to the lowest:

· PRC—G.811 primary reference clock.

· SSU-A—G.812 primary-level SSU.

· SSU-B—G.812 second-level SSU.

· SEC—SDH equipment clock.

· Unknown—Synchronization quality unknown.

· DNU—Do not use for synchronization.

Clock source priority

For a clock source to be selected as the clock reference, assign it a lower priority value than other clock sources. The lower the priority value, the better the clock source. For example, the clock source with a priority of 1 is better than the clock source with a priority of 3.

Clock reference selection

The network clock monitoring module supports automatic and manual clock reference selection.

Automatic reference selection

In an automatic reference selection process, the network clock monitoring module uses the SSM quality level, clock source priority, and clock source number to make a selection decision. The use of SSM in the automatic reference selection process is user configurable.

The selection process is as follows:

1. If SSM is enabled for automatic reference selection, the module selects the clock source with the highest SSM quality level.

2. If SSM is disabled for automatic reference selection, or clock sources have the same SSM quality level, the module selects the clock source with the lowest priority value. (A lower priority value indicates a better clock source.)

3. If the clock sources have the same priority, the module selects the clock source that has the lowest slot-number/subslot-number/port-number sequence.

After selecting the best reference, the network clock monitoring module distributes the selected timing signal to all interface cards, and locks the timing to the reference signal. When the traced timing signal is lost, the network clock monitoring module selects the next optimal clock reference. When the signal of the best clock source can be traced again, the module selects the best clock source to replace the less optimal clock source as the reference.

NOTE:

A clock source will not be selected as the reference if the clock source is in one of the following situations:

· The timing signal cannot be detected.

· The clock source priority is 255 and SSM levels are ignored in automatic reference selection.

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Manual reference selection

If you specify a clock source as the reference, the network clock monitoring module does not change the clock reference automatically. When the signal of the specified clock reference is lost, the module changes to the holdover state. In this state, the module continues to distribute the signal of the clock reference to the interface cards.

Clock mode on a port

IMPORTANT:

Set the clock mode to slave on the port connected to a SONET/SDH device, because the SONET/SDH clock is more precise.

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A port can operate in one of the following clock modes:

· Master—The port provides timing to the peer end. The timing signal is derived from the network clock monitoring module.

¡ If automatic reference selection is used, the timing signal is derived from the reference clock selected by the network clock monitoring module.

¡ If manual reference selection is used, the timing signal is derived from the manually specified clock reference.

¡ If the manually specified clock reference is not available, the port outputs the timing signal generated by the local clock.

· Slave—The port uses the timing signal received from the peer end. For the network clock monitoring module to extract timing signal from a port, you must place the port in slave clock mode. If the port is in master clock mode, the module does not extract the timing signal from the incoming traffic on the port.

Restrictions and guidelines: Network synchronization configuration

All the commands in this chapter are configurable on the default MDC. The network-clock ssmcontrol command is not configurable on non-default MDCs.

For a detailed description of MDCs, see Virtual Technologies Configuration Guide.

Network synchronization tasks at a glance

To configure network synchronization, perform the following tasks:

4. Configuring clock reference selection

Enable automatic clock reference selection or manually select a clock reference.

5. (Optional.) Configuring automatic reference selection parameters

¡ Controlling the use of SSM in automatic reference selection

Configuring clock reference selection

Restrictions and guidelines

If you specify a line clock as the reference, you must perform the task on the MDC that contains the line clock input port.

If manual reference selection is used, the SSM levels and priorities configured for the clock sources do not take effect.

Procedure

6. (Optional.) Verify that the clock source you want to select is in Normal state.

display network-clock source

Skip this step if you use automatic reference selection.

7. Enter system view.

system-view

8. Enable automatic reference selection or manually select a reference.

In standalone mode:

network-clock work-mode { auto | manual source { bits0 | bits1 | lpuport interface-type interface-number | ptp } }

In IRF mode:

network-clock chassis chassis-number work-mode { auto | manual source { bits0 | bits1 | ptp } }

network-clock work-mode manual source lpuport interface-type interface-number

By default, automatic reference selection is enabled.

9. (Optional.) Verify that the configuration is effective.

display network-clock status

It takes time for the clock reference selection mode change to take effect. To verify the effectiveness of the change, you can also check the logs.

Configuring automatic reference selection parameters

Controlling the use of SSM in automatic reference selection

Restrictions and guidelines

In an MDC environment, you must perform this task on the default MDC. However, the setting takes effect on all MDCs.

Procedure

10. Enter system view.

system-view

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

In standalone mode:

network-clock ssmcontrol { off | on }

In IRF mode:

network-clock chassis chassis-number ssmcontrol { off | on }

To ignore the SSM quality level in clock reference selection, specify the off keyword. To use the SSM quality level in clock reference selection, specify the on keyword.

By default, SSM quality level is ignored in the automatic reference selection process.

Display and maintenance commands for network clock monitoring module

‌Execute display commands in any view.

Task	Command
(In standalone mode.) Display the operating state of the network clock monitoring module.	display network-clock status
(In IRF mode.) Display the operating state of the network clock monitoring module.	display network-clock status [ chassis chassis-number ]
(In standalone mode.) Display the states of clock sources.	display network-clock source
(In IRF mode.) Display the states of clock sources.	display network-clock source [ chassis chassis-number ]

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Network synchronization configuration examples

Example: Configuring network synchronization

Network configuration

As shown in Figure 1, Device A obtains its timing signal from an external BITS clock.

Configure Device B to derive its timing from Device A through XGE 3/0/50.

Figure 1 Network diagram

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Procedure

1. Configure Device A (master clock).

# Specify the master clock mode on XGE 3/0/50.

<DeviceA> system-view

[DeviceA] interface ten-gigabitethernet 3/0/50

[DeviceA-Ten-GigabitEthernet3/0/50] clock master

2. Configure Device B (slave clock).

# Specify XGE 3/0/50 as a line clock input port.

<DeviceB> system-view

[DeviceB] network-clock lpuport ten-gigabitethernet 3/0/50

# Sepcify the slave clock mode on XGE3/0/50.

[DeviceB] interface ten-gigabitethernet 3/0/50

[DeviceB- Ten-GigabitEthernet3/0/50] clock slave

[DeviceB- Ten-GigabitEthernet3/0/50] quit

# Specify XGE3/0/50 as the source to provide clock reference.

[DeviceB] network-clock work-mode manual source lpuport ten-gigabitethernet 3/0/50

[DeviceB] quit

Verifying the configuration

# Verify that XGE3/0/50 provides the network clock reference for Device B.

<DeviceB> display network-clock status

Mode : Manual

Reference : N/A

Traced reference : XGE3/0/50

Lock mode : Locked

OSC state : Normal

SSM output level : SSUB

SSM control enable: Off

Configuring synchronous Ethernet

About synchronous Ethernet

Synchronous Ethernet (SyncE) provides high-quality frequency synchronization on Ethernet at the physical layer. It can provide the same level of clock precision as SONET/SDH.

Transferring frequency signals at the physical layer, SyncE functions regardless of the network conditions such as congestion, packet loss, and delay.

Quality levels of clocks

SyncE devices use an Ethernet synchronization messaging channel (ESMC) to transmit the quality level (QL) of their system clocks. A SyncE device uses QL information to select the optimal clock reference from all available timing sources for its system clock.

The following are the QLs supported by the device, from the highest to the lowest:

· PRC—G.811 primary reference clock.

· SSU-A—G.812 primary-level SSU.

· SSU-B—G.812 second-level SSU.

· SEC—SDH equipment clock.

· DNU—Do not use for synchronization.

· UNK—Synchronization quality unknown.

DNU clock sources cannot participate in clock reference selection.

Clock reference selection

The system clock uses the clock reference selected with the highest QL from the following sources. If these sources have the same QL, the system clock selects the clock reference by priority, from the highest to the lowest:

· External clock sources.

· Line clock sources input from interfaces.

· Internal clock sources.

The system clock uses the QL of the selected reference. Clock reference selection process starts each time the QL of a source is updated.

NOTE:

If QLs are the same on two interfaces, the clock source input from the lower-numbered interface has priority.

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System clock QL distribution and SyncE port input QL updating

Distribution of the system clock QL

When distributing the QL of the system clock, the system uses the following rules:

· If the clock reference is not from a SyncE port, the system distributes the QL out of all SyncE ports.

· If the clock reference is from a SyncE port, the system distributes the QL out of all SyncE ports except for the reference input port. To prevent timing loops, the sent QL is DNU on the timing reference input port.

Input QL updating on SyncE ports

The default input QL is Unknown on a SyncE port. The port updates its input QL when it receives a quality level higher than Unknown. The Unknown level will be restored if the port does not receive ESMC packets within 5 seconds after the update.

Protocols and standards

· ITU-T G.781, Synchronization Layer Functions

· ITU-T G.813, Timing characteristics of SDH equipment slave clocks (SEC)

· ITU-T G.823, The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy

· ITU-T G.8261, Timing and Synchronization Aspects in Packet Networks

· ITU-T G.8262, Timing Characteristics of a Synchronous Ethernet Equipment Slave Clock (EEC)

· ITU-T G.8264/Y.1364, Distribution of Timing Information through Packet Networks

Restrictions: Hardware compatibility with SyncE

Copper ports on SD interface modules and 10G ports installed with a GE fiber transceiver module or fiber-to-copper transceiver module do not support SyncE.

Configuring SyncE on an Ethernet interface

3. Enter system view.

system-view

4. Enter Layer 2 Ethernet interface view or Layer 3 Ethernet interface view.

interface interface-type interface-number

5. Enable the synchronous mode.

synchronous mode

By default, Ethernet interfaces are in the non-synchronous mode. An interface can participate in the clock reference selection only when it is in the synchronous mode.

6. Enable ESMC to transmit QL information.

esmc enable

By default, ESMC is disabled on Ethernet interfaces.

Setting the clock mode on a copper SyncE GE port

‌About this task

Configure the clock mode for a copper SyncE GE port based on its time synchronization direction.

Restrictions and guidelines

By default, a copper SyncE GE port automatically negotiates its clock mode with the remote end. To avoid a negotiation result that conflicts with your clock synchronization trail design, manually set the clock mode.

· To derive timing from the upstream clock, set the clock mode to slave.

· To provide timing for the downstream clock, set the clock mode to master.

Procedure

7. Enter system view.

system-view

8. Enter Layer 2 Ethernet interface view or Layer 3 Ethernet interface view.

interface interface-type interface-number

9. Set the clock mode.

synce state { master | slave }

By default, the clock mode of a copper SyncE GE port is automatically negotiated.

Display and maintenance commands for SyncE

Execute display commands in any view.

Task	Command
Display ESMC information.	display esmc [ interface interface-type interface-number ]

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Synchronous Ethernet configuration examples

Example: Configuring synchronous Ethernet

Network configuration

As shown in Figure 2, configure SyncE between the devices.

Figure 2 Network diagram

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Procedure

# On Device A, enable the synchronous mode and ESMC on Ten-GigabitEthernet 3/0/1.

<DeviceA> system-view

[DeviceA] interface ten-gigabitethernet 3/0/1

[DeviceA-Ten-GigabitEthernet3/0/1] synchronous mode

[DeviceA-Ten-GigabitEthernet3/0/1] esmc enable

[DeviceA-Ten-GigabitEthernet3/0/1] quit

# On Device B, enable the synchronous mode and ESMC on Ten-GigabitEthernet 3/0/1.

<DeviceB> system-view

[DeviceB] interface ten-gigabitethernet 3/0/1

[DeviceB-Ten-GigabitEthernet3/0/1] synchronous mode

[DeviceB-Ten-GigabitEthernet3/0/1] esmc enable

[DeviceB-Ten-GigabitEthernet3/0/1] quit

Verifying the configuration

# Verify that ESMC is enabled on both Device A and Device B when they are connected to their respective clock references. The clock QLs of Device A and Device B are QL-PRC and QL-SEC, respectively. Device A provides more precise timing than Device B.

[DeviceA] display esmc

Interface : Ten-GigabitEthernet3/0/1

Mode : Synchronous

ESMC status : Enable

Port status : Up

Duplex mode : Full

QL received : QL-SEC

QL sent : QL-PRC

ESMC information packets received : 2195

ESMC information packets sent : 6034

ESMC event packets received : 1

ESMC event packets sent : 1

ESMC information rate : 1 packets/sec

ESMC expiration : 5 seconds

[DeviceB] display esmc

Interface : Ten-GigabitEthernet3/0/1

Mode : Synchronous

ESMC status : Enable

Port status : Up

Duplex mode : Full

QL received : QL-PRC

QL sent : QL-SEC

ESMC information packets received : 6034

ESMC information packets sent : 2195

ESMC event packets received : 1

ESMC event packets sent : 1

ESMC information rate : 1 packets/sec

ESMC expiration : 5 seconds

# Verify that QL information is exchanged correctly after synchronization between Device A and Device B. Ten-GigabitEthernet3/0/1 on Device B becomes a reference input port. The clock QL sent from Device B to Device A changes to QL-DNU.

[DeviceA] display esmc

Interface : Ten-GigabitEthernet3/0/1

Mode : Synchronous

ESMC status : Enable

Port status : Up

Duplex mode : Full

QL received : QL-DNU

QL sent : QL-PRC

ESMC information packets received : 2573

ESMC information packets sent : 6412

ESMC event packets received : 1

ESMC event packets sent : 1

ESMC information rate : 1 packets/sec

ESMC expiration : 5 seconds

[DeviceB] display esmc

Interface : Ten-GigabitEthernet3/0/1

Mode : Synchronous

ESMC status : Enable

Port status : Up

Duplex mode : Full

QL received : QL-PRC

QL sent : QL-DNU

ESMC information packets received : 6412

ESMC information packets sent : 2573

ESMC event packets received : 1

ESMC event packets sent : 1

ESMC information rate : 1 packets/sec

ESMC expiration : 5 seconds

12-Network Management and Monitoring Configuration Guide

SSM quality levels

Clock source priority

Automatic reference selection

Manual reference selection

Restrictions and guidelines

Procedure

Configuring automatic reference selection parameters

Controlling the use of SSM in automatic reference selection

Restrictions and guidelines

Procedure

Display and maintenance commands for network clock monitoring module

Network configuration

Procedure

Verifying the configuration

Distribution of the system clock QL

Input QL updating on SyncE ports

‌About this task

Restrictions and guidelines

Procedure

Network configuration

Verifying the configuration

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