Network Synchronization Support

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. This document explains how to configure network synchronization on the Cisco 8500 Series Catalyst Edge Platform.

Contents

This guide covers the following topics:

Prerequisites for Network Synchronization Support

The following goals must be taken into account while designing the synchronization plan for a network:

  • Synchronize the greatest number of network elements to the smallest number of independent clock sources. Ideally, all the network elements should be synchronized to a single clock source.
  • Use clock sources of the highest quality (in terms of stability and long-term accuracy).
  • To ensure resiliency of synchronization, plan for possible failure of the clock sources, network elements, and network trunks.

Network Synchronization Overview

Synchronous Ethernet (SyncE), which is defined by the Telecommunication Standardization Sector (ITU-T) standards, such as G.8261 and G.8262, leverages the PHY layer of the Ethernet to transmit clock information to remote sites.

SyncE provides a cost-effective alternative to the Synchronous Optical Networking (SONET) networks. For SyncE to work, each network element along the synchronization path must support SyncE. To implement SyncE, the bit clock of the Ethernet is aligned to a reliable clock that is traceable to the Primary Reference Clock (PRC).

Synchronization Status Message and Ethernet Synchronization Messaging Channel

Network clocking uses the following mechanisms to exchange the quality level of the clock between the network elements:

Synchronization Status Message

Network elements use Synchronization Status Messages (SSM) to inform the neighboring elements about the Quality Level (QL) of the clock. Non-Ethernet interfaces, such as optical interfaces and T1 or E1 SPA frames, use SSM. The key benefits of SSMs are:

  • Prevents timing loops.Provides fast recovery when a part of the network fails.
  • Ensures that a node gets timing from the most reliable clock source.

Ethernet Synchronization Messaging Channel

In order to maintain a logical communication channel in synchronous network connections, Ethernet relies on a channel called the Ethernet Synchronization Messaging Channel (ESMC), which is based on the IEEE 802.3 Organization-Specific Slow Protocol (OSSP) standards. ESMC relays the SSM code that represents the quality level of the Ethernet Equipment Clock (EEC) in a physical layer.

The ESMC packets are received only for the ports configured as clock sources, and transmitted on all the SyncE interfaces in the system. These packets are then processed by the clock selection algorithm on route processors (RP) and are used to select the best clock. The Tx frame is generated based on the QL value of the selected clock source, and sent to all the enabled SyncE ports.

Clock Selection Algorithm

The clock selection algorithm selects the best available synchronization source from the nominated sources. This algorithm exhibits nonrevertive behavior among the clock sources with the same QL value, and always selects the signal with the best QL value. For clock option 1, the default is revertive, and for clock option 2, the default is nonrevertive.

The clock selection process works in the following modes:

When multiple selection processes are present in a network element, all the processes work in the same mode.

QL-Enabled Mode

In QL-enabled mode, the following parameters contribute to the selection process:

  • Quality level
  • Signal fail via QL-FAILED
  • Priority
  • External commands.

If no external commands are active, the algorithm selects the reference (for clock selection) with the highest QL that does not experience a signal fail condition. If multiple inputs have the same highest QL, the input with the highest priority is selected. For multiple inputs having the same highest priority and QL, the existing reference is maintained (if it belongs to the highest priority and QL group). Otherwise, an arbitrary reference from the highest priority and QL group is selected.

QL-Disabled Mode

In QL-disabled mode, the following parameters contribute to the selection process:

  • Signal failure
  • Priority
  • External commands

If no external commands are active, the algorithm selects the reference (for clock selection) with the highest priority that does not experience a signal fail condition. For multiple inputs having the same highest priority, the existing reference is maintained (if it belongs to highest priority group). Otherwise, an arbitrary reference from highest priority group is selected.

product="name=">Hybrid Mode

Restrictions for Network Synchronization

This section lists the restrictions for configuring network synchronization on a router.

  • If the network clock algorithm is enabled, use the system clock as the Tx clock (synchronous mode) for the Ethernet interfaces of the corresponding router. You cannot change the synchronous mode on a per-interface basis.
  • You can configure up to eight ports as clock sources on a router.
  • The SyncE feature coexists with SSO, but is not SSO-compliant. The clock selection algorithm is restarted on a switchover. During switchover, the router goes into holdover mode.
  • The SyncE interfaces in the WAN mode cannot be used for QL-enabled clock selection. You must either use them with the system in QL-disabled mode, or disable the ESMC on the interfaces, and use them as QL-disabled interfaces.
  • We recommend that you do not configure multiple input sources with the same priority because this impacts the TSM (switching message delay).
  • You cannot implement the network clock-based clock selection algorithm and the new algorithm simultaneously. Both these are mutually exclusive.
  • The Line to External feature for clock cleanup is supported only if the line interface and the external interface are on the same metronome SPA.

Note
The Line to External feature is not supported on the Cisco 8500 Series Catalyst Edge Platform.

Configuring Network Synchronization

You can configure network synchronization on the Cisco 8500 Series Catalyst Edge Platform by performing one of the following procedures:

Configuring Clock Recovery from SyncE

This section describes how to configure clock recovery by using the SyncE method.

SUMMARY STEPS

  1. configure terminal
  2. network-clock synchronization automatic
  3. network-clock synchronization ssm option {1 | 2 {GEN1 | GEN2}}
  4. interface gigabitethernet slot/card/port
  5. synchronous mode
  6. exit
  7. network-clock input-source priority {interface interface-name slot/card/port | {external slot/card/port }}
  8. exit

DETAILED STEPS

  Command or Action Purpose
Step 1

configure terminal

Example:


Router# configure terminal

Enters the global configuration mode.

Step 2

network-clock synchronization automatic

Example:


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 3

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

Example:


Router(config)# network-clock synchronization ssm option 2 GEN1

Configures the equipment to work in a synchronization network. The option_id value 1 refers to a synchronization network design for Europe. This is the default value. The option_id value 2 refers to a synchronization network design for the U.S.

Step 4

interface gigabitethernet slot/card/port

Example:


Router(config)# interface gigabitethernet 0/0/0

Specifies the Gigabit Ethernet interface to be configured:

slot/card/port—Specifies the location of the interface.

Step 5

synchronous mode

Example:


Router(config-if)# synchronous mode

Sets the mode to synchronous mode.

Step 6

exit

Example:

Example:


Router(config)# exit

Exits the global configuration mode.

Step 7

network-clock input-source priority {interface interface-name slot/card/port | {external slot/card/port }}

Example:

Example:


Router(config)# network-clock input-source 1 interface gigabitethernet 0/2/0

Example:

Example:


Router(config)# network-clock input-source 1 external R0 2048k

Enables clock recovery from SyncE.

The Cisco Catalyst 8500 Series Edge Platforms router supports two RP ports, one active and the other standby.
Step 8

exit

Example:


Router(config)# exit

Exits the global configuration mode.

Examples

The following example shows how to configure clock recovery from SyncE: 


Router# configure terminal
Router(config)# network-clock synchronization automatic
Router(config)# network-clock synchronization ssm option 2 GEN1
Router(config)# interface gigabitethernet 0/2/0
Router(config-if)# synchronous mode
Router(config)# exit
Router(config)# network-clock input-source 1 interface gigabitethernet 0/2/0
Router(config)# exit

Managing Synchronization

Manage synchronization on a Cisco 8500 Series Catalyst Edge Platform using the following management commands:

  • network-clock synchronization mode QL-enabled command

Use the network-clock synchronization mode QL-enabled command in the global configuration mode to configure the automatic selection process for the QL-enabled mode. This succeeds only if the SyncE interfaces are capable of sending SSMs.

The following example shows how to configure network clock synchronization (QL-enabled mode) in the global configuration mode: 


Router(config)# network-clock synchronization mode QL-enabled
  • esmc process command

Use the esmc process command in the global configuration mode to enable the ESMC process at system level. The no form of this command disables the ESMC process. The no form of this command fails if no SyncE-capable interface is installed on the platform.

The following example shows how to enable the ESMC process in the global configuration mode: 


Router(config)# esmc process
  • esmc mode [tx | rx] command

Use the esmc mode [tx | rx] command in the interface configuration mode to enable the ESMC process at the interface level. The no form of the command disables the ESMC process.

The following example shows how to enable ESMC in the interface configuration mode: 


Router(config-if)# esmc mode tx
  • network-clock quality-level command

Use the network-clock source quality-level command in the interface configuration mode to configure the QL value for ESMC on a gigabit Ethernet port. The value is based on global interworking options:

    • If Option 1 is configured, the available values are QL-PRC, QL-SSU-A, QL-SSU-B, QL-SEC, and QL-DNU.
    • If Option 2 is configured with GEN 2, the available values are QL-PRS, QL-STU, QL-ST2, QL-TNC, QL-ST3, QL-SMC, QL-ST4, and QL-DUS.
    • If Option 2 is configured with GEN1, the available values are QL-PRS, QL-STU, QL-ST2, QL-SMC, QL-ST4, and QL-DUS

The following example shows how to configure the network-clock source quality-level in the interface configuration mode: 


Router(config-if)# network-clock source quality-level QL-PRC rx

Use the network-clock quality-level command in the global configuration mode to configure the QL value for the SSMs on a BITS port.

The following example shows how to configure network-clock quality-level command in the global configuration mode: 


Router(config)# network-clock quality-level rx qL-pRC external R0 2048k
  • network-clock wait-to-restore command

Use the network-clock wait-to-restore timer global command to set the wait-to-restore time. You can configure the wait-to-restore time to any value between 0 to 86400 seconds. The default value is 300 seconds. The wait-to-restore timer can be set in the global configuration mode and the interface configuration mode.

The following example shows how to configure the wait-to-restore timer in the global configuration mode: 


Router(config)# network-clock wait-to-restore 10 global

The following example shows how to configure the wait-to-restore timer in the interface configuration mode: 


Router(config)# interface gigabitethernet 0/2/0
Router(config-if)# network-clock wait-to-restore 10
  • network-clock hold-off command

Use the network-clock hold-off timer global command to configure hold-off time. You can configure the hold-off time to either 0 or any value between 50 to 10000 ms. The default value is 300 ms. The network-clock hold-off timer can be set in the global configuration mode and the interface configuration mode.

The following example shows how to configure the hold-off timer: 


Router(config-if)# network-clock hold-off 50 global
  • network-clock switch force command

Use the network-clock switch force command to forcefully select a synchronization source irrespective of whether the source is available, and within range.

The following example shows how to configure a force switch: 


Router# network-clock switch force interface gigabitethernet 0/2/0
  • network-clock switch manual command

Use the network-clock switch manual command to manually select a synchronization source, provided the clock source has a higher quality level than the currently active clock.

The following example shows how to configure a manual switch: 


Router# network-clock switch manual interface gigabitethernet 0/2/0
  • network-clock clear switch controller-id command

Use the network-clock clear switch controller-id command to clear the manual, or switch it on by force.

The following example shows how to clear a switch: 


Router# network-clock clear switch t0
  • network-clock set lockout command

Use the network-clock set lockout command to lockout a clock source. A clock source flagged as lockout is not selected for SyncE. To clear the lock-out on a source, use the network-clock clear lockout command.

The following example shows how to lock out a clock source: 


Router# network-clock set lockout interface gigabitethernet 0/2/0

The following example shows how to clear the lock out on a clock source: 


Router# network-clock clear lockout interface gigabitethernet 0/2/0

Verifying the Network Synchronization Configuration

Use the following commands to verify the network synchronization configuration:

  • Use the show network-clock synchronization command to display the output: 

Router# show network-clock synchronization 
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 : 1544 (EEC-Option2)
Clock Mode : QL-Enable
ESMC : Enabled
SSM Option : GEN1
T0 : External R0 t1 esf
Hold-off (global) : 300 ms
Wait-to-restore (global) : 300 sec
Tsm Delay : 180 ms
Revertive : No
Force Switch: FALSE
Manual Switch: FALSE
Number of synchronization sources: 2
sm(netsync NETCLK_QL_ENABLE), running yes, state 1A
Last transition recorded: (src_rem)-> 1A (src_added)-> 1A (src_rem)-> 1A (src_added)-> 1A (ql_change)-> 1A (sf_change)-> 1A (force_sw)-> 1C (clear_sw)-> 1A (sf_change)-> 1A (sf_change)-> 1A
 
Nominated Interfaces
 Interface            SigType     Mode/QL      Prio  QL_IN  ESMC Tx  ESMC Rx
Internal             NA          NA/Dis       251   QL-ST3    NA        NA
Gi1/2/0              NA          Sync/En      1     QL-FAILED -         -
*External R0          T1 ESF      NA/En        2     QL-STU    NA        NA
  • Use the show network-clock synchronization detail command to display all the details of network clock synchronization parameters at the global and interface level, as shown in the following example: 

Router# show network-clock synchronization detail
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 : 1544 (EEC-Option2)
Clock Mode : QL-Enable
ESMC : Enabled
SSM Option : GEN1
T0 : External R0 t1 esf
Hold-off (global) : 300 ms
Wait-to-restore (global) : 300 sec
Tsm Delay : 180 ms
Revertive : No
Force Switch: FALSE
Manual Switch: FALSE
Number of synchronization sources: 2
sm(netsync NETCLK_QL_ENABLE), running yes, state 1A
Last transition recorded: (src_rem)-> 1A (src_added)-> 1A (src_rem)-> 1A (src_added)-> 1A (ql_change)-> 1A (sf_change)-> 1A (force_sw)-> 1C (clear_sw)-> 1A (sf_change)-> 1A (sf_change)-> 1A
 
Nominated Interfaces
Interface            SigType     Mode/QL      Prio  QL_IN  ESMC Tx  ESMC Rx
Internal             NA          NA/Dis       251   QL-ST3    NA        NA
Gi1/2/0              NA          Sync/En      1     QL-FAILED -         -
*External R0          T1 ESF      NA/En        2     QL-STU    NA        NA
Interface:
---------------------------------------------
Local Interface: Internal
Signal Type: NA
Mode: NA(Ql-enabled)
SSM Tx: Disable
SSM Rx: Disable
Priority: 251
QL Receive: QL-ST3
QL Receive Configured: -
QL Receive Overrided: -
QL Transmit: -
QL Transmit Configured: -
Hold-off: 0
Wait-to-restore: 0
Lock Out: FALSE
Signal Fail: FALSE
Alarms: FALSE
Slot Disabled: FALSE
Local Interface: Gi1/2/0
Signal Type: NA
Mode: Synchronous(Ql-enabled)
ESMC Tx: Disable
ESMC Rx: Enable
Priority: 1
QL Receive: QL-PRS
QL Receive Configured: -
QL Receive Overrided: QL-FAILED
QL Transmit: QL-DUS
QL Transmit Configured: -
Hold-off: 300
Wait-to-restore: 300
Lock Out: FALSE
Signal Fail: FALSE
Alarms: TRUE
Slot Disabled: FALSE
Local Interface: External R0
Signal Type: T1 ESF
Mode: NA(Ql-enabled)
SSM Tx: Disable
SSM Rx: Enable
Priority: 2
QL Receive: QL-STU
QL Receive Configured: -
QL Receive Overrided: -
QL Transmit: -
QL Transmit Configured: -
Hold-off: 300
Wait-to-restore: 300
Lock Out: FALSE
Signal Fail: FALSE
Alarms: FALSE
Slot Disabled: FALSE
  • Use the show esmc command to display the ESMC configuration output: 

Router# show esmc 
Interface: GigabitEthernet0/0/0
  Administative configurations:
    Mode: Synchronous
    ESMC TX: Enable
    ESMC RX: Enable
    QL TX: -
    QL RX: -
    Operational status:
    Port status: UP
    QL Receive: QL-PRC
    QL Transmit: QL-DNU
    QL rx overrided: -
    ESMC Information rate: 1 packet/second
    ESMC Expiry: 5 second
Interface: GigabitEthernet0/0/0
  Administrative configurations:
    Mode: Synchronous
    ESMC TX: Enable
    ESMC RX: Enable
    QL TX: -
    QL RX: -
    Operational status:
    Port status: UP
    QL Receive: QL-DNU
    QL Transmit: QL-DNU
    QL rx overrided: QL-DNU
    ESMC Information rate: 1 packet/second
    ESMC Expiry: 5 second
  • Use the show esmc detail command to display all the details of the ESMC parameters at the global and interface level, as shown in the following example: 

Router# show esmc detail 
Router#show esmc detail
Interface: GigabitEthernet0/0/0
  Administative configurations:
    Mode: Synchronous
    ESMC TX: Enable
    ESMC RX: Enable
    QL TX: -
    QL RX: QL-PRS
  Operational status:
    Port status: UP
    QL Receive: QL-DUS
    QL Transmit: QL-ST3
    QL rx overrided: QL-DUS
    ESMC Information rate: 1 packet/second
    ESMC Expiry: 5 second
    ESMC Tx Timer: Running
    ESMC Rx Timer: Running
    ESMC Tx interval count: 1
    ESMC INFO pkts in: 0
    ESMC INFO pkts out: 256
    ESMC EVENT pkts in: 0
    ESMC EVENT pkts out: 0

Troubleshooting the Network Synchronization Configuration


Note
Before you troubleshoot, ensure that all the network synchronization configurations are complete.

The following table provides information about troubleshooting scenarios that you may encounter while configuring network synchronization.

Table 1. Troubleshooting Scenarios

Problem

Solution

Incorrect clock selection

  • Verify that there are no alarms on the interfaces. Use the show network-clock synchronization detail command to check this.
  • Ensure that the nonrevertive configurations are in place.

Incorrect QL values

Ensure that there is no framing mismatch with the SSM option.

Incorrect clock limit set or queue limit disabled mode

  • Verify that there are no alarms on the interfaces. Use the show network-clock synchronization detail RP command to confirm.
  • Use the show network-clock synchronization command to confirm if the system is in revertive mode or nonrevertive mode and verify the nonrevertive configurations as shown in this example:

Router#show network-clock synchronization

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 : 1544 (EEC-Option2)

Clock Mode : QL-Enable

ESMC : Enabled

SSM Option : GEN1

T0 : External R0 t1 esf

Hold-off (global) : 300 ms

Wait-to-restore (global) : 300 sec

Tsm Delay : 180 ms

Revertive : No

Force Switch: FALSE

Manual Switch: FALSE

Number of synchronization sources: 2

sm(netsync NETCLK_QL_ENABLE), running yes, state 1A

Last transition recorded: (src_rem)-> 1A (src_added)-> 1A (src_rem)-> 1A (src_added)-> 1A (ql_change)-> 1A (sf_change)-> 1A (force_sw)-> 1C (clear_sw)-> 1A (sf_change)-> 1A (sf_change)-> 1A

Incorrect QL values observed 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 SSM option 1 , framing should be SDH or E1, and for SSM option 2 , it should be T1.

Mismatched Physical line coding mechanisms between clock source and input source on the router

To ensure that this feature works correctly, both the ends need to be configured with identical physical line coding mechanism and encapsulation values.