Configuring Clock monitoring· 1

Clock monitoring module overview·· 1

Reference source level 1

Working mode of the clock monitoring module· 2

Working mode of the port clock· 2

Clock monitoring module configuration task list 3

Configuring working mode of the clock monitoring module of the SRPU·· 3

Configuring reference source priority· 4

Configuring SSM for reference sources 4

Setting the ways of deriving SSM level 4

Setting the bit position for transmitting bits clock source information· 4

Configuring SSM levels for the reference sources 5

Activating/deactivating SSM··· 5

Setting the input port of the line clock (LPU port) 5

Displaying and maintaining the clock monitoring module· 6

Clock monitoring module configuration example· 7

 

Clock monitoring module overview

Clock monitoring module provides highly-precise, highly-reliable synchronous digital hierarchy (SDH) line interface 38.88 MHz clock signals for different line processing units (LPUs). It implements such functions as input clock source automatic selection, software phase-lock, and real-time monitoring of the clock status of the interface card. The clock monitoring module supports hardware reset of the clock card.

The clock monitoring module supports 14 reference clock sources (referred to as reference source hereinafter), among which the first and the second are Bits clock sources and the others are line clock sources. The first and the second reference sources respectively correspond to external interfaces 1 and 2 for receiving clock signals on the active switching and routing processing unit (SRPU). Figure 1 shows the reference-slot relationship: On the SR8802, the clock in slot 2 corresponds to the fifth reference source, and the clock in slot 3 corresponds to the sixth reference source.

Figure 1 Relationship between reference source and slot

 

Classification of clock sources

Clock sources can be classified into three categories according to different sources of the clock source:

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

·           Bits clock source—Clock signals generated by a specific Bits clock device. The signals are sent to the clock monitoring module through a specific interface on the SRPU (switch and router processing unit) and then sent to all cards by the clock monitoring module.

·           Line clock source—Provided by the upper level device, whose precision is lower than that of the Bits clock source. The signals are derived from the specified WAN interface and sent to the clock monitoring module, which then sends the signals to all cards.

Reference source level

The reference source level is determined by the priority and the synchronization status marker (SSM) level of the reference source.

Priority of the reference source

You can set a high priority for the reference source with high-precision and high-reliability to make it be first selected as the clock source.

SSM level of the reference source

SSM, also known as synchronization quality marker, indicates the synchronization timing signal level on a synchronization timing transmission link.

The priority of SSM level of the reference source, ranging from high to low, includes:

·           PRC—G.811 clock signal.

·           TNC—G.812 transit node clock signal.

·           LNC—G.812 local node clock signal.

·           SETS—SDH device clock source signal.

·           unknown—Unknown synchronization quality.

·           DNU—Cannot be used as a clock source.

 

NOTE: The reference source whose SSM level is DNU cannot be used as a clock source.

 

Working mode of the clock monitoring module

The clock monitoring module can be configured to work in either of the following two modes:

Manual mode

In this mode, the clock source is configured manually. The clock monitoring module does not automatically switch the clock source, but just tracks the primary reference source. If the primary reference source is lost, the clock monitoring module enters a holdover state.

Auto mode

In auto mode, the clock source is automatically selected by the system. When the primary clock source is lost or not available, the clock monitoring module selects another clock source based on the following rules:

·           If SSM level is not activated, the clock source is determined by reference source priority. If two reference sources have the same priority, the clock source is selected according to the reference source number (1 to 18). When the reference source with the highest priority is lost, the next available reference source with the highest priority is selected. When the former clock source becomes available, the system switches to that clock again.

·           If SSM is activated, the clock source is decided by the SSM level. If two reference sources have the same SSM level, the reference source priority takes effect, in the way described above.

 

NOTE: The following clock sources are excluded in clock selection (when SSM is activated): ·       Clock sources whose signals are lost. ·       Clock sources whose priority is 255. ·       Clock sources whose SSM level is DNU (DoNotUse).

 

Working mode of the port clock

Depending on the source of the port clock, a port supports two modes of clocks:

Master mode

In this mode, the system uses the clock signals provided by the clock monitoring module. The signals include local clock signals and clock signals derived from LPU Port. If you have configured on the device to derive clock signals from LPU Port, these derived signals are adopted; otherwise, local clock signals are adopted.

Slave mode

In this mode, the system uses line clock signals. Only when you specify LPU Port of the device as the current port can the system derive the clock source from the line signals received on the current port and then send the clock source information to the clock monitoring module, which then sends the information to all cards.

 

IMPORTANT: When connected to SONET/SDH devices, a device should be set to work in slave clock mode, because the SONET/SDH clock is more precise than that of the device.

 

Clock monitoring module configuration task list

Complete these tasks to configure clock monitoring module:

 

Task		Remarks
Configuring working mode of the clock monitoring module of the SRPU		Optional
Configuring reference source priority		Optional
Configuring SSM for reference sources	Setting the ways of deriving SSM level	Optional
	Setting the bit position for transmitting bits clock source information	Optional
	Configuring SSM levels for the reference sources	Optional
	Activating/deactivating SSM	Optional
Setting the input port of the line clock (LPU port)		Optional

 

Configuring working mode of the clock monitoring module of the SRPU

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Set the working mode of the clock monitoring module.	clock { auto | manual source source-number }	Optional. auto by default.

 

NOTE: After you set the working mode of the clock monitoring module, it takes a period of time for device response. You can check whether your configuration takes effect through the display clock device command and the logging information.

 

Configuring reference source priority

In auto mode, the clock monitoring module selects and switches to a reference source with a higher priority based on SSM level and reference source priority. The smaller the value, the higher the priority.

To configure reference source priority:

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Configure the reference source priority.	clock priority value source source-number	255 by default.

 

Configuring SSM for reference sources

Setting the ways of deriving SSM level

You can use the following two ways to derive SSM level:

·           For bits clock source, SSM level can be derived from the interface card and reported to the SRPU, which then sends the SSM level to the clock monitoring module.

·           Or you can configure SSM level as needed, as shown in the following table:

To set the ways of deriving SSM level:

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Set the ways to derive SSM level.	clock forcessm { on | off } source source-number	Optional. By default, no SSM level is derived from any clock source, which means the SSM level is set by users.

 

Setting the bit position for transmitting bits clock source information

The bit position for transmitting Bits clock source information can be configured as sa4, sa5, sa6, sa7 and sa8. They are 5 bits in timeslot 0 of the even frame in a multi-frame as specified by ITU-TG.704 CRC4. You can choose one from the five bits to carry SSM information.

To set the bit for transmitting Bits clock source information:

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Set the bit for transmitting the Bits clock source information.	clock sa-bit { sa4 | sa5 | sa6 | sa7 | sa8 } source source-number	Optional. sa4 by default.

 

Configuring SSM levels for the reference sources

Follow these rules to manually set the SSM level for the clock source:

·           For the line clock source, the SSM level configured is that of the clock source.

·           For Bits clock source, if the input signal is a 2048 kbps (E1) signal and the clock forcessm off source source-number command is executed, the clock source adopts the SSM level derived from the input signals and the SSM configured is omitted.

·           For Bits clock source, if the input signal is a 2048 kHz signal or a 2048 kbps signal and the clock forcesssm on source source-number command is executed, the clock source adopts the SSM level configured.

To set the SSM levels:

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Set the SSM levels of the reference source.	clock ssm { dnu | lnc | prc | sets | tnc | unknown } source source-number	unknown by default.

 

NOTE: ·       The reference source with the SSM level DNU cannot be used as a clock source. Therefore, it does not participate in clock source switch when the clock monitoring module works in auto mode. ·       After you set the SSM levels of the reference source, it takes a period of time for device response. In this case, you can check whether your configuration takes effect through the display clock ssm-level command and the logging information.

 

Activating/deactivating SSM

Whether the SSM levels are obtained through clock signals or configured manually, you have to activate or deactivate them before they can take effect.

·           When SSM is activated, the reference source level is decided by the SMM level first and then the priority of the reference source in automatic clock source selection.

·           When SSM is not activated, you can still set and view the SSM levels, but they are ignored and the reference source level is decided by the priority of the reference source in automatic clock source selection.

To activate or deactivate SSM:

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Activate/deactivate SSM.	clock ssmcontrol { on | off }	Optional. By default, SSM is deactivated.

 

Setting the input port of the line clock (LPU port)

To set the input port of the line clock (LPU port):

 

Step	Command	Remarks
1.      Enter system view.	system-view	N/A
2.      Set the input port of the line clock.	clock lpuport  interface-type interface-number	Optional. By default, the clock input port is the first configurable port by port name in alphabetical order of the interface card.
3.      Enter interface view (ATM interface/POS interface/CPOS interface/E1 interface/T1 interface).	interface interface-type interface-number	N/A
4.      Set the input interface to work in Slave mode.	clock slave	Optional. By default, the input interface works in Slave mode.

 

NOTE: ·       For a POS interface card, if you set the port clock to work in Slave mode, you must use the clock lpuport command to set the input port of the card clock source. ·       For more information about the clock slave command, see Interface Command Reference.

 

Displaying and maintaining the clock monitoring module

 

Task	Command	Remarks
Display the current configuration of the clock monitoring module.	display clock config [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the detailed information of the clock monitoring module.	display clock device [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the input clock source port of the line card.	display clock lpuport [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the lock state of the clock monitoring module.	display clock phase-lock-state [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the priority of all reference sources.	display clock priority [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the self-test result of the clock monitoring module.	display clock self-test-result [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the state of all reference sources.	display clock source [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the SSM level of all reference sources.	display clock ssm-level [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the SSM level of the output clock signal.	display clock ssm-output [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the clock monitoring module version.	display clock version [ | { begin | exclude | include } regular-expression ]	Available in any view
Display the working mode of the clock monitoring module of the SRPU.	display clock work-mode [ | { begin | exclude | include } regular-expression ]	Available in any view

 

Clock monitoring module configuration example

Network requirements

·           Device A and Device B are connected through the POS interfaces. Device A is equipped with clock monitoring module on its SRPU.

·           The synchronized clock of Device A is provided by the clock monitoring module on its SRPU.

·           Device B adopts the line clock from Device A to synchronize with the SDH line of Device A.

Figure 2 Network diagram

 

Configuration procedure

1.       Configure Device A (master clock):

# Set the interface POS 3/1/1 to work in master clock mode, using local clock signals.

<DeviceA> system-view

[DeviceA] interface pos 3/1/1

[DeviceA-Pos3/1/1] clock master

2.       Configure Device B (slave clock):

# Set the LPU port on Device B to POS 3/1/1.

<DeviceB> system-view

[DeviceB] clock lpuport pos 3/1/1

# Set the interface POS 3/1/1 to work in slave clock mode.

[DeviceB] interface pos 3/1/1

[DeviceB-Pos3/1/1] clock slave

[DeviceB-Pos3/1/1] quit

# Enable the clock source from POS 3/1/1, set the clock to work in manual mode and adopt clock source 8, which corresponds to slot 3 on an SR8808 router (see Figure 1 for the relationship between reference source and slot).  

[DeviceB] clock manual source 3

Through the above configurations, all the other WAN interface cards get the same clock frequency derived by the clock card from the port 1 line clock of the POS interface card. In this way, all the service cards on the device can get precise, reliable, synchronized SDH line interface clock signals.