Cisco ASR 903 Router Chassis Software Configuration Guide
Configuring Synchronous Ethernet ESMC and SSM
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Table of Contents

Configuring Synchronous Ethernet ESMC and SSM

Understanding Synchronous Ethernet ESMC and SSM

Clock Selection Modes

QL-Enabled Mode

QL-Disabled Mode

Managing Clock Selection

Restrictions and Usage Guidelines

Configuring Synchronous Ethernet ESMC and SSM

Managing Clock Source Selection

Specifying a Clock Source

Selecting a Specific Clock Source

Forcing a Clock Source Selection

Disabling Clock Source Specification Commands

Disabling a Clock Source

Locking Out a Clock Source

Restoring a Clock Source

Verifying the Configuration

Troubleshooting

Sample Configurations

Configuring Synchronous Ethernet ESMC and SSM

Synchronous Ethernet is an extension of Ethernet designed to provide the reliability found in traditional SONET/SDH and T1/E1 networks to Ethernet packet networks by incorporating clock synchronization features. The supports the Synchronization Status Message (SSM) and Ethernet Synchronization Message Channel (ESMC) for synchronous Ethernet clock synchronization.

The following sections describe ESMC and SSM support on the Cisco ASR 903 Series Router.

Understanding Synchronous Ethernet ESMC and SSM

Synchronous Ethernet incorporates the Synchronization Status Message (SSM) used in Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) networks. While SONET and SDH transmit the SSM in a fixed location within the frame, Ethernet Synchronization Message Channel (ESMC) transmits the SSM using a protocol: the IEEE 802.3 Organization-Specific Slow Protocol (OSSP) standard.

The ESMC carries a Quality Level (QL) value identifying the clock quality of a given synchronous Ethernet timing source. Clock quality values help a synchronous Ethernet node derive timing from the most reliable source and prevent timing loops.

When configured to use synchronous Ethernet, the Cisco ASR 903 Series Router synchronizes to the best available clock source. If no better clock sources are available, the router remains synchronized to the current clock source.

The router supports two clock selection modes: QL-enabled and QL-disabled. Each mode uses different criteria to select the best available clock source.


Note The router can only operate in one clock selection mode at a time.


Clock Selection Modes

The Cisco ASR 903 Series Router supports two clock selection modes, which are described in the following sections.

QL-Enabled Mode

In QL-enabled mode, the router considers the following parameters when selecting a clock source:

  • Clock quality level (QL)
  • Clock availability
  • Priority

QL-Disabled Mode

In QL-disabled mode, the router considers the following parameters when selecting a clock source:

  • Clock availability
  • Priority

Note You can use override the default clock selection using the commands described in the “Managing Clock Source Selection” section.


Managing Clock Selection

You can manage clock selection by changing the priority of the clock sources; you can also influence clock selection by modifying modify the following clock properties:

  • Hold-Off Time: If a clock source goes down, the router waits for a specific hold-off time before removing the clock source from the clock selection process. By default, the value of hold-off time is 300 ms.
  • Wait to Restore: The amount of time that the router waits before including a newly active synchronous Ethernet clock source in clock selection. The default value is 300 seconds.
  • Force Switch: Forces a switch to a clock source regardless of clock availability or quality.
  • Manual Switch: Manually selects a clock source, provided the clock source has a equal or higher quality level than the current source.

For more information about how to use these features, see Managing Clock Source Selection.

Restrictions and Usage Guidelines

The following restrictions apply when configuring synchronous Ethernet SSM and ESMC:

  • To use the network-clock synchronization ssm option command, ensure that the router configuration does not include the following:

Input clock source

Network clock quality level

Network clock source quality source (synchronous Ethernet interfaces)

  • The network-clock synchronization ssm option command must be compatible with the network-clock eec command in the configuration.
  • To use the network-clock synchronization ssm option command, ensure that there is not a network clocking configuration applied to sychronous Ethernet interfaces, BITS interfaces, and timing port interfaces.
  • SSM and ESMC are SSO-coexistent, but not SSO-compliant. The router goes into hold-over mode during switchover and restarts clock selection when the switchover is complete.
  • It is recommended that you do not configure multiple input sources with the same priority as this impacts the TSM (Switching message delay).
  • You can configure a maximum of 4 clock sources on interface modules, with a maximum of 2 per interface module. This limitation applies to both synchronous Ethernet and TDM interfaces.

Configuring Synchronous Ethernet ESMC and SSM

Follow these steps to configure ESMC and SSM on the Cisco ASR 903 Series Router.

 

Command or Action
Purpose

Step 1

enable

 

Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

 

Router# configure terminal

Enters global configuration mode.

Step 3

network-clock synchronization automatic

 

Router(config)# network-clock synchronization automatic

Enables the network clock selection algorithm. This command disables the Cisco-specific network clock process and turns on the G.781-based automatic clock selection process.

Step 4

network-clock eec { 1 | 2 }

 

Router(config)# network-clock eec 1

Specifies the Ethernet Equipment Clock (EEC) type. Valid values are

  • 1—ITU-T G.8262 option 1 (2048)
  • 2—ITU-T G.8262 option 2 and Telcordia GR-1244 (1544)

Step 5

network-clock synchronization ssm option
{ 1 | 2 { GEN1 | GEN2 }}

 

Router(config)# network-clock synchronization ssm option 2 GEN2

Configures the G.781 synchronization option used to send synchronization messages. The following guidelines apply for this command:

  • Option 1 refers to G.781 synchronization option 1, which is designed for Europe. This is the default value.
  • Option 2 refers to G.781 synchronization option 2, which is designed for the United States.
  • GEN1 specifies option 2 Generation 1 synchronization.
  • GEN2 specifies option 2 Generation 2 synchronization.

Step 6

network-clock input-source priority { interface interface_name slot / card / port | ptp domain domain_num | { external { R0 | R1 [ { t1 { sf | esf } linecode { ami | b8zs } line-build-out length } | e1 [ crc4 | fas ] [ 125ohm | 75ohm ] linecode [ hdb3 | ami ] } | 2m | 10m ] }}

 

Router(config)# network-clock input-source 1 interface GigabitEthernet 0/0/1

Enables you to select an interface as an input clock for the router. You can select the BITS, Gigabit Ethernet 0/0, Gigabit Ethernet 0/1 interfaces, or GPS interfaces, or an external interface.

Step 7

network-clock synchronization mode ql-enabled

 

Router(config)# network-clock synchronization mode ql-enabled

Enables automatic selection of a clock source based on quality level (QL).

Note This command is disabled by default.

Step 8

network-clock hold-off { 0 | milliseconds }

 

Router(config)# network-clock hold-off 0

(Optional) Configures a global hold-off timer specifying the amount of time that the router waits when a synchronous Ethernet clock source fails before taking action.

Note You can also specify a hold-off value for an individual interface using the network-clock hold-off command in interface mode.

Step 9

network-clock wait-to-restore seconds

 

Router(config)# network-clock wait-to-restore 70

(Optional) Configures a global wait-to-restore timer for synchronous Ethernet clock sources. The timer specifies how long the router waits before including a restored clock source in the clock selection process.

Valid values are 0 to 86400 seconds. The default value is 300 seconds.

Note You can also specify a wait-to-restore value for an individual interface using the network-clock wait-to-restore command in interface mode.

Step 10

network-clock revertive

 

Router(config)# network-clock revertive

(Optional) Sets the router in revertive switching mode when recovering from a failure. Do disable revertive mode, use the no form of this command.

Step 11

esmc process

 

Router(config)# esmc process

Enables the ESMC process globally.

Step 12

network-clock external slot / card / port hold-off { 0 | milliseconds }

 

Router(config)# network-clock external 0/1/0 hold-off 0

Overrides the hold-off timer value for the external interface.

Step 13

network-clock quality-level { tx | rx } value { interface interface-name slot/card/port | controller [ E1 | BITS ] slot/card/port | external [ 2m | 10m ] }

 
Router(config)# network-clock quality-level rx qL-pRC external R0 e1 cas crc4

Specifies a quality level for a line or external clock source.

The available quality values depend on the G.781 synchronization settings specified by the network-clock synchronization ssm option command:

  • Option 1—Available values are QL-PRC, QL-SSU-A, QL-SSU-B, QL-SEC, and QL-DNU.
  • Option 2, GEN1—Available values are QL-PRS, QL-STU, QL-ST2, QL-SMC, QL-ST4, and QL-DUS.
  • Option 2, GEN 2—Available values are QL-PRS, QL-STU, QL-ST2, QL-TNC, QL-ST3, QL-SMC, QL-ST4, and QL-DUS.

Step 14

interface type number

 

Router(config)# interface GigabitEthernet 0/0/1

Router(config-if)#

Enters interface configuration mode.

Step 15

synchronous mode

 

Router(config-if)# synchronous mode

Configures the Ethernet interface to synchronous mode and automatically enables the ESMC and QL process on the interface.

Step 16

esmc mode [ ql-disabled | tx | rx ] value

 

Router(config-if)# esmc mode rx QL-STU

Enables the ESMC process at the interface level. The no form of the command disables the ESMC process.

Step 17

network-clock hold-off { 0 | milliseconds }

 

Router(config-if)# network-clock hold-off 0

(Optional) Configures an interface-specific hold-off timer specifying the amount of time that the router waits when a synchronous Ethernet clock source fails before taking action.

You can configure the hold-off time to either 0 or any value between 50 to 10000 ms. The default value is 300 ms.

Step 18

network-clock wait-to-restore seconds

 

Router(config-if)# network-clock wait-to-restore 70

(Optional) Configures wait-to-restore timer for an individual synchronous Ethernet interface.

Step 19

end

 

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

You can use the show network-clocks command to verify your configuration.

Managing Clock Source Selection

The following sections describe how to manage the selection on the Cisco ASR 903 Series Router:

Specifying a Clock Source

The following sections describe how to specify a synchronous Ethernet clock source during the clock selection process:

Selecting a Specific Clock Source

To select a specific interface as a synchronous Ethernet clock source, use the network-clock switch manual command in global configuration mode.


Note The new clock source must be of higher quality than the current clock source; otherwise the router does not select the new clock source.


 

Command
Purpose

network-clock switch manual external R0 | R1 {{ E1 { crc4 | cas | fas }} { T1 { d4 | sf | esf }} }

 

Router# network-clock switch manual external r0 e1 crc4

Manually selects a synchronization source, provided the source is available and is within the range.

network-clock clear switch { t0 | external slot/card/port [ 10m | 2m ]}

 

Router# network-clock clear switch t0

Disable a clock source selection.

Forcing a Clock Source Selection

To force the router to use a specific synchronous Ethernet clock source, use the network-clock switch force command in global configuration mode.


Note This command selects the new clock regardless of availability or quality.



Note Forcing a clock source selection overrides a clock selection using the network-clock switch manual command.


 

Command
Purpose

network-clock switch force external R0 | R1 {{ E1 { crc4 | cas | fas }} { T1 { d4 | sf | esf }} }

 

Router# network-clock switch force r0 e1 crc4

Forces the router to use a specific synchronous Ethernet clock source, regardless of clock quality or availability.

network-clock clear switch { t0 | external slot/card/port [ 10m | 2m ]}

 

Router# network-clock clear switch t0

Disable a clock source selection.

Disabling Clock Source Specification Commands

To disable a network-clock switch manual or network-clock switch force configuration and revert to the default clock source selection process, use the network-clock clear switch command.

 

Command
Purpose

network-clock clear switch { t0 | external slot/card/port [ 10m | 2m ]}

 

Router# network-clock clear switch t0

Disable a clock source selection.

Disabling a Clock Source

The following sections describe how to manage the synchronous Ethernet clock sources that are available for clock selection:

Locking Out a Clock Source

To prevent the router from selecting a specific synchronous Ethernet clock source, use the network-clock set lockout command in global configuration mode.

 

Command
Purpose

network-clock set lockout { interface interface_name slot/card/port | external { R0 | R1 [ { t1 { sf | esf } linecode { ami | b8zs }} | e1 [ crc4 | fas ] linecode [ hdb3 | ami ]}

 

Router# network-clock set lockout interface GigabitEthernet 0/0/0

Prevents the router from selecting a specific synchronous Ethernet clock source.

network-clock clear lockout { interface interface_name slot/card/port | external { R0 | R1 [ { t1 { sf | esf } linecode { ami | b8zs }} | e1 [ crc4 | fas ] linecode [ hdb3 | ami ] }

 

Router# network-clock clear lockout interface GigabitEthernet 0/0/0

Disable a lockout configuration on a synchronous Ethernet clock source.

Restoring a Clock Source

To restore a clock in a lockout condition to the pool of available clock sources, use the network-clock clear lockout command in global configuration mode.

 

Command
Purpose

network-clock clear lockout { interface interface_name slot/card/port | external external { R0 | R1 [ { t1 { sf | esf } linecode { ami | b8zs }} | e1 [ crc4 | fas ] linecode [ hdb3 | ami ] }

 

 

Router# network-clock clear lockout interface GigabitEthernet 0/0/0

Forces the router to use a specific synchronous Ethernet clock source, regardless of clock quality or availability.

Verifying the Configuration

You can use the following commands to verify your configuration:

  • show esmc—Displays the ESMC configuration.
  • show esmc detail—Displays the details of the ESMC parameters at the global and interface levels.
  • show network-clock synchronization—Displays the router clock synchronization state.
  • show network-clock synchronization detail—Displays the details of network clock synchronization parameters at the global and interface levels.

Troubleshooting

Table 10-1 list the debug commands that are available for troubleshooting the SyncE configuration on the Cisco ASR 903 Series Router:


Caution We recommend that you do not use debug commands without TAC supervision.

 

Table 10-1 SyncE Debug Commands

Debug Command
Purpose

debug platform network-clock

Debugs issues related to the network clock, such as alarms, OOR, active-standby sources not selected correctly, and so on.

debug network-clock

Debugs issues related to network clock selection.

debug esmc error

debug esmc event

debug esmc packet [interface <interface name>]

debug esmc packet rx [interface <interface name>]

debug esmc packet tx [interface <interface name>]

Verify whether the ESMC packets are transmitted and received with proper quality-level values.

Table 10-2 provides the information about troubleshooting your configuration

 

Table 10-2 Troubleshooting Scenarios

Problem
Solution

Clock selection

  • Verify that there are no alarms on the interfaces using the show network-clock synchronization detail command.
  • Ensure that the nonrevertive configurations are in place.
  • Reproduce the issue and collect the logs using the debug network-clock errors, debug network-clock event, and debug network-clock sm commands. Contact Cisco Technical Support if the issue persists.

Incorrect QL values

  • Ensure that there is no framing mismatch with the SSM option.
  • Reproduce the issue using the debug network-clock errors and debug network-clock event commands.

Alarms

  • Reproduce the issue using the debug platform network-clock command enabled in the RSP. Alternatively, enable the debug network-clock event and debug network-clock errors commands.

Incorrect clock limit set or queue limit disabled mode

  • Verify that there are no alarms on the interfaces using the show network-clock synchronization detail command.
  • Use the show network-clock synchronization command to confirm if the system is in revertive mode or nonrevertive mode and verify the non-revertive configurations.
  • Reproduce the current issue and collect the logs using the debug network-clock errors, debug network-clock event, and debug network-clock sm RSP commands.

Incorrect QL values when you use the show network-clock synchronization detail command.

  • Use the network clock synchronization SSM ( option 1 |option 2 ) command to confirm that there is no framing mismatch. Use the show run interface command to validate the framing for a specific interface. For the SSM option 1, framing should be SDH or E1, and for SSM option 2, it should be T1.
  • Reproduce the issue using the debug network-clock errors and debug network-clock event RSP commands.

Sample Configurations

Input Synchronous Ethernet Clocking

The following example configures the router to use the BITS interface and two Gigabit Ethernet interfaces as input synchronous Ethernet timing sources. The configuration enables SSM on the BITS port.

!
Interface GigabitEthernet0/0
synchronous mode
network-clock wait-to-restore 720
!
Interface GigabitEthernet0/1
synchronous mode
!
 
!
network-clock synchronization automatic
network-clock input-source 1 External R0 e1 crc4
network-clock input-source 1 gigabitethernet 0/0
network-clock input-source 2 gigabitethernet 0/1
network-clock synchronization mode QL-enabled

no network-clock revertive