Network Synchronization for the Cisco 4000 Series Integrated Services Routers

Network Efficiency

Most of the services that are provided over networks must be fully synchronized with one another in order to operate efficiently. If the network devices that constitute a network do not operate at the same clock rates, there is an overall decrease in the performance of the network and a consequent degradation in the quality of the services offered by the network.

Synchronization between the NIM and the Router

Network synchronization is supported for Cisco Fourth-Generation T1/E1 Voice and WAN Network Interface Modules (NIMs) on the Cisco 4000 Series ISR, by using the network-clock synchronization automatic global configuration command. By default, this command is disabled and user must configure it on Cisco 4000 Series ISR. This command is made ineffective for a particular NIM if you use the no network-clock participation slot / subslot command. See
Example 3: Disabling and Enabling a Module from Participating in the Backplane Clock. This causes the NIM to have its own separate clock domain.

Configuring Clock Recovery with a Primary Clock Source

This section describes how to configure clock recovery with a primary or secondary clock source.

SUMMARY STEPS

1. configure terminal

2. network-clock synchronization automatic

3. controller [t1|e1] slot/bay/port

4. clock source line primary

5. network-clock input-source priority controller [t1|e1] slot/bay/port

6. exit

DETAILED STEPS

Configuring the Deselection of a Primary Clock Source

This section describes how to deselect a clock source. This ensures that the clock source does not reappear after the router is rebooted.

SUMMARY STEPS

1. configure terminal

2. no network-clock input-source priority controller [ t1 | e1 ] slot / bay / port

DETAILED STEPS

 

Example: Deselection of a Clock Source

In this example, the 0/2/0 T1 controller, which has been deselected, does not appear in the list of clock sources shown by the show network-clocks synchronization command.

Configuring Participation of a Module in the Backplane Clock

By default, a NIM (module) participates in the backplane clock. In the first two examples below, the
show platform hardware subslot slot / subslot module device networkclock command verifies that a module participates in the backplane clock.

If you do not want clock synchronization with the backplane clock for a NIM, you can use the
no network-clock synchronization participate slot / subslot command shown in Example 3: Disabling and Enabling a Module from Participating in the Backplane Clock.

Example 1: Verifying that a Module Participates in the Backplane Clock

In this example, the show platform hardware subslot slot / subslot module device networkclock command shows:

“ntwk_clk_selected No”—none of the ports of the NIM 0/2 are configured as an input-source. To assign a controller to be an input clock source, see the command network-clock input-source priority controller [t1|e1] slot/bay/port in the “Configuring Clock Recovery with a Primary Clock Source” section.

“ntwk_clk_participate Yes”—the NIM 0/2 participates in the router’s backplane clock. This is the default for a NIM attached to the router.

Example 2: Verifying that a Module Participates in the Backplane Clock and is Selected as a Source

In this example, the network-clock input-source priority controller [t1 | e1] slot / bay / port command configures NIM 0/2/0 as an input clock source.

The show platform hardware subslot slot / subslot module device networkclock command shows:

“ntwk_clk_selected Yes”—a port on the NIM 0/2 T1 controller is selected as an input clock source.

“ntwk_clk_participate Yes”—the NIM 0/2 T1 controller participates in the router’s backplane clock.

Router# configure terminal

Router(config)# network-clock input-source 150 controller T1 0/2/0

Router(config)# end

Router# show platform hardware subslot 0/2 module device networkclock

primary clock 255, secondary clock 0, ntwk_clk_selected Yes, ntwk_clk_participate Yes, current clock = 0

PLL status= 1, and cntl = 17

Example 3: Disabling and Enabling a Module from Participating in the Backplane Clock

In the following example, NIM 0/2 is disabled from participating in the backplane clock, using the
no network-clock synchronization participate 0/2 command. This is displayed by the show platform hardware subslot slot / subslot module device networkclock command. ntwk_clk_participate = “No” indicates that module participation is disabled.

Router# configure terminal

Router(config)# no network-clock synchronization participate 0/2

Router(config)# end

Router# show platform hardware subslot 0 / 2 module device networkclock

primary clock 255, secondary clock 0, ntwk_clk_selected No, ntwk_clk_participate No, current clock = 0

PLL status= 2, and cntl = 6

Then NIM 0/2 is made to participate in the backplane clock, by using the
network-clock synchronization participate 0/2 command. This is verified by the show platform hardware subslot slot / subslot module device networkclock command. ntwk_clk_participate = “Yes” indicates that the module participation is enabled.

Router# configure terminal

Router(config)# network-clock synchronization participate 0/2

Router(config)# end

Router# show platform hardware subslot 0/2 module device networkclock

primary clock 255, secondary clock 0, ntwk_clk_selected No, ntwk_clk_participate Yes, current clock = 0

PLL status= 2, and cntl = 6

Configuring Network Clocking with Revertive Mode

Revertive mode can be set for a clock source or reference. For example, if an original source is set to be in revertive mode and there is a failure in the original source, the clock switches to using an alternate source. After the original clock source recovers from a failure, the clock source reverts back to this original source, independent of the condition of the alternate source.

The default value for network clock synchronization is non-revertive mode. In non-revertive mode, if a failure occurs for the original clock source, a switch to an alternate clock source occurs. This alternate clock source continues to be used, even after the original source recovers from the failure that caused the switch.

SUMMARY STEPS

1. network-clock revertive

2. show network-clocks synchronization

DETAILED STEPS

 

Example: Configuring Network Clocking with Revertive Mode

The following example starts by setting two clock sources:

• T1 0/3/0—secondary clock source (lower priority than T1 0/2/0)
• T1 0/2/0—primary clock source (higher priority than T1 0/3/0)

Revertive mode is set for network clocking using the network-clock revertive command for the primary clock source.

Because T1 0/2/0 has a higher priority than T1 0/3/0, T1 0/2/0 is selected as the clock source. The first
show network-clocks synchronization command in the example shows the T1 0/2/0 clock source selected and in revertive mode.

This example supposes that the primary clock source goes down after the first show network-clocks synchronization command. In this situation, T1 0/3/0 is selected as the clock source. The state of QL-IN is shown as “QL-FAILED” in the second show network-clocks synchronization command below.

Later, as a result of setting revertive mode, when clock source T1 0/2/0 comes back up again, the selected clock reverts to T1 0/2/0. This is shown by the third show-network-clocks synchronization command in the example. (If revertive mode had not been set, when T1 0/2/0 came back up, the clock source would stay as T1 0/3/0 and not revert to T1 0/2/0.)

(At this point, the primary clock source T1 0/2/0 becomes unavailable; for example, due to a signal failure.)

(At this point, the primary clock source T1 0/2/0 becomes available again.)

Configuring the Wait-to-Restore Timer

Use the network-clock wait-to-restore timer global command to specify how long the router waits before including a primary clock source in the clock selection process; for example, after a signal failure has affected the primary clock source.

SUMMARY STEPS

1. network-clock wait-to-restore timer global

2. show network-clocks synchronization

DETAILED STEPS

 

Example: Configuring the Wait-to-Restore Timer

The first part of this example is the same as shown in the “Configuring Network Clocking with Revertive Mode” section. The example starts after two clock sources have been set: T1 0/2/0 and
T1 0/3/0. T1 0/2/0 is the primary clock source—it has a higher priority than the T1 0/3/0 clock source.

Revertive mode is set for network clocking using the network-clock revertive command.

If a signal failure occurs, the system goes to hold-over (selects the “Internal” clock source) and waits for the period determined by the ‘wait-to-restore’ timer value, before switching back to the first clock source.

The show network-clocks synchronization command shows the timer to be 300 seconds. Next, the wait-to-restore timeout is changed using the network-clock wait-to-restore timer command. In this example, the wait-to-restore time is set to 500 seconds. You can configure the wait-to-restore time to any value between 0 to 86400 seconds. The default value is 300 seconds.

Entering the show network-clocks synchronization command now shows the wait-to-restore value of 500 seconds.

Configuring the Hold-Off Timer

Use the network-clock hold-off timer command to specify the length of time that the router waits when a primary clock source fails before removing the primary clock source from the clock selection process.

SUMMARY STEPS

1. network-clock hold-off timer global

2. show network-clocks synchronization

DETAILED STEPS

 

Example: Configuring the Hold-off Timer

The show network-clocks synchronization command shows the hold-off time to be 300 milliseconds (the default value). The hold-off timeout is changed using the command network-clock hold-off 500 global command. Entering the show network-clocks synchronization command shows that the hold-off value is now 500 milliseconds.

Configuring Lockout of a Clock Source

The network-clock set lockout controller command may be useful during testing and debugging.

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Note To clear the lockout on a source, use the network-clock clear lockout command.

SUMMARY STEPS

1. network-clock set lockout controller [t1 | e1] slot / bay / port

2. show network-clocks synchronization

DETAILED STEPS

 

Example: Configuring Lockout of a Clock Source

The following example starts with a configuration in which several clock sources have different priority levels.

To start with, T1 0/1/1 is the primary clock source as shown by the first show network-clocks synchronization command. T1 0/2/0 is then locked out using the network-clock clear lockout controller command. A show network-clocks synchronization command shows the primary clock source is now T1 0/1/1. In the example, T1 0/1/1 goes down at this point.

T1 0/2/0 is not selected as the primary clock source—Internal is selected instead, as shown by another show network-clocks synchronization command. The initial primary clock source is then cleared using the network-clock clear lockout controller command. Another show network-clocks synchronization command shows that the primary clock source is now T1 0/2/0 (T1 0/1/1 is still down).

Configuring Network Clocking with Force Switching

Instead of configuring using the set lockout controller command, you can force the network clock source to change to another clock source using the network-clock switch force controller command, irrespective of whether the source is available, and within range.

For example, this command is useful when you want to remove the module of the first controller for maintenance purposes. Use the network-clock switch force command to forcefully select another clock source.

Another command that performs the same function as network-clock switch force controller is the network-clock switch manual controller command. This command manually selects a synchronization source. The following example shows how to configure force switching:

You can later use the network-clock clear switch controller-id command to clear the effect of either a network-clock switch force controller command or network-clock switch manual controller command.

SUMMARY STEPS

1. network-clock force controller [t1|e1] slot / bay / port

2. show network-clocks synchronization

DETAILED STEPS

 

Example: Configuring Network Clocking with Force Switching

The following example starts with a configuration in which several clock sources have different priority levels.

The command network-clock switch force controller [ t1 | e1 ] slot/bay/port t0 switches the network clock source to a second priority clock source. You can verify that the primary clock source is now 0/3/0 T1 controller using the show network-clocks synchronization command. The switch is then cleared using the network-clock clear switch t0 command.

Example 1: Configuring Clock Recovery with a Primary Clock Source (Single Clock Source)

The following example shows how to configure clock recovery for controller T1 on the 0/2/0 slot/bay/port as the primary clock source.

In this example, the 0/2/0 T1 controller has a higher priority (value = 1) than the internal clock. T1 0/2/0 is the primary clock source as indicated by the asterisk “*” in the interfaces listed below (“*T1 0/2/0”).

Example 2: Configuring Clock Recovery with a Primary Clock Source (Two Clock Sources)

The following example shows how to configure clock recovery for controller T1 on the 0/2/0 slot/bay/port as the primary clock source.

In this example, the 0/2/0 T1 controller is shown to have a high priority (value = 1) which is higher than the priority of the 0/3/0 T1 controller (value = 2); therefore the 0/2/0 T1 controller is the primary clock source.

Example 3: Switchover from Primary Clock Source due to Loss of Signal

The following example shows how a primary clock source is affected by a signal failure which causes the primary clock source to change or switch to a different source.

Perform a signal failure of the primary clock source, by shutting down the remote end or causing an “Out of Resource” condition of the primary clock source, by disconnecting a cable.

After the above signal failure or “Out of Resource,” verify the feature using the following
show network-clocks synchronization command. Note that the output shows the primary clock source, T1 0/2/0, as having a QL_IN value of QL-FAILED and therefore the primary clock source has switched to the “Internal” clock (shown by an asterisk “*”).

Symbols: En - Enable, Dis - Disable, Adis - Admin Disable

NA - Not Applicable

* - Synchronization source selected

# - Synchronization source force selected

& - Synchronization source manually switched

Automatic selection process : Enable

Equipment Clock : 2048 (EEC-Option1)

Clock Mode : QL-Disable

ESMC : Disabled

SSM Option : 1

T0 : Internal

Hold-off (global) : 300 ms

Wait-to-restore (global) : 300 sec

Tsm Delay : 180 ms

Revertive : No

Nominated Interfaces

Interface SigType Mode/QL Prio QL_IN ESMC Tx ESMC Rx

*Internal NA NA/Dis 251 QL-SEC NA NA

T1 0/2/0 NA NA/Dis 2 QL-FAILED NA NA

Example 4: Switching of Input Source Clock

This example shows a primary clock source being affected by a signal failure, which then causes a different clock source to be selected.

Perform a signal failure of the primary clock source, by shutting the remote end or causing an “Out of Resource” condition of the primary clock source, by disconnecting a cable.

After the above signal failure or “Out of Resource”, verify the feature using the following show network-clocks synchronization command. Note that the output shows the primary clock source T1 0/3/0/. The controller T1 0/2/0 has a QL_IN value of QL-FAILED and therefore the primary clock source has switched to the controller T1 0/3/0 clock (shown by an asterisk “*”).

Configuring Clocking for Non-Facility Associated Signaling Voice

This example shows how to configure clocking for the Non-Facility Associated Signaling (NFAS) voice on Cisco 4000 Series ISRs:

 

Related Documents

 

Standards

 

MIBs

 

RFCs

 

Technical Assistance

 

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Table 1 F eature Information for Network Synchronization

Feature Name	Releases	Feature Information
Network Synchronization	Cisco IOS XE Release 3.12S	This feature was implemented on the Cisco ISR 4400 Series.

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