Clock Recovery System for SAToP

The Clock Recovery System recovers the service clock using Adaptive Clock Recovery (ACR) and Differential Clock Recovery (DCR).

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Information About Clock Recovery

Adaptive Clock Recovery (ACR)

Adaptive Clock Recovery (ACR) is an averaging process that negates the effect of random packet delay variation and captures the average rate of transmission of the original bit stream. ACR recovers the original clock for a synchronous data stream from the actual payload of the data stream. In other words, a synchronous clock is derived from an asynchronous packet stream. ACR is a technique where the clock from the TDM domain is mapped through the packet domain, but is most commonly used for Circuit Emulation (CEM). ACR is supported on unframed and framed modes of SAToP.

Note

Framing type should be maintained same in all routers end to end.

Effective Cisco IOS XE Everest 16.5.1, ACR is supported on the 8-port T1/E1 interface module.

Differential Clock Recovery (DCR)

Differential Clock Recovery (DCR) is another technique used for Circuit Emulation (CEM) to recover clocks based on the difference between PE clocks. TDM clock frequency are tuned to receive differential timing messages from the sending end to the receiving end. A traceable clock is used at each end, which ensures the recovered clock is not affected by packet transfer. DCR is supported on unframed and framed modes of SAToP.

Note

Framing type should be maintained same in all routers end to end.

Benefits of Clock Recovery

  • Customer-edge devices (CEs) can have different clock from that of the Provide-edge devices (PEs).

Scaling Information

IM Card

Pseudowires Supported (Number of Clocks Derived)

48-Port T3/E3 CEM Interface Module

1344

Prerequisites for Clock Recovery

  • The clock of interface modules must be used as service clock.

  • CEM must be configured before configuring the global clock recovery.

  • RTP must be enabled for DCR in CEM, as the differential clock information is transferred in the RTP header.

Restrictions for Clock Recovery

  • The reference clock source is used and locked to a single clock.

  • The clock ID should be unique for a particular interface module for ACR or DCR configuration.

  • When CEM group is configured, dynamic change in clock source is not allowed.

  • ACR clock configuration under each controller should be performed before configuring CEM group.

  • When ACR or DCR is configured and loopback network is applied on the same PDH (T1/E1), then the ACR or DCR mode configuration is removed to enable the loopback. The ACR or DCR should be configured again after the loopback maintenance activity.

Scale Restrictions

  • For the Cisco IOS XE Amsterdam 17.3.x release, a maximum of 5376 ACR and DCR session scale is supported on the Cisco 1-port OC-192 Interface module or 8-port Low Rate Interface Module (8-port SFP GE and 1-port 10GE IM with CEM, 10G). For releases before the Cisco IOS XE Amsterdam 17.3.1 release, only 2000 session are supported.

How to Configure ACR and DCR

Configuring ACR for T3/E3

Configuring ACR of T3/E3 Interfaces for SAToP

Before You Begin

  • The node (router) on which the 48-Port T3/E3 interface module is configured for ACR, must have its own clock derived from BITS/GPS/Stratum clock.

  • The minimum packet size of CEM pseudowires on the network that delivers robust clock recovery is 256 bytes.

To configure the clock on T3/E3 interfaces for SAToP in controller mode, use the following commands: 
 
enable
configure terminal
controller t3 0/0/1
clock source recovered 1
cem-group 0 unframed
exit
To configure the clock recovery on T3/E3 interfaces in global configuration mode, use the following commands: 
 
recovered-clock 0 0
clock recovered 1 adaptive cem 1 0
exit

Note

The clock configuration on controller must be done before configuring the clock recovery on global configuration mode.

Verifying Adaptive Clock Recovery Configuration of T3/E3 Interfaces for SAToP

Use the show recovered-clock command to verify the ACR on T3/E3 interfaces for SAToP: 

Router# show recovered-clock 

Recovered clock status for subslot 0/4
---------------------------------------
Clock    Type     Mode        CEM    Status       Frequency Offset(ppb)  Circuit-No

0        DS3      ADAPTIVE     0    	ACQUIRED   		n/a                    0 (Port)
Use the show running-config | section command to verify the configuration of adaptive clock of T3/E3 interfaces: 

Router# show running-config | section 0/0/1
controller MediaType 0/0/1
 mode t3
controller T3 0/0/1
  cem-group 0 unframed
 clock source recovered 1
 cablelength 224
interface CEM0/0/1
 no ip address
 cem 0
Use the show running-config | section recovered-clock command to verify the recovery of adaptive clock of T3/E3 interfaces: 

Router# show running-config | section recovered-clock
recovered-clock 0 0
 clock recovered 1 adaptive cem 1 0

Configuring DCR for T3/E3

Configuring DCR of T3/E3 Interfaces for SAToP

Before You Begin

  • Before you start configuring DCR, RTP must be enabled on the CEM interface. The RTP is used to carry the differential time.

  • The minimum packet size of CEM pseudowires on the network that delivers robust clock recovery is 256 bytes.

To configure differential clock recovery on T3/E3 interface for SAToP in controller mode, use the following commands: 

 
enable
configure terminal
controller t3 0/0/1
clock source recovered 1
cem-group 0 unframed
exit

To configure RTP header under interface, use the following commands: 

 
interface cem 0/0/1
cem 0
rtp-present

To configure differential clock recovery of T3/E3 interface in global configuration mode, use the following commands: 

 
recovered-clock 0 0
clock recovered 1 differential cem 1 0
exit

Note

The clock configuration on controller must be done before configuring the clock recovery on global configuration mode.

Verifying the DCR Configuration of T3/E3 Interfaces for SAToP

Use the show recovered-clock command to verify the DCR of T3/E3 interfaces for SAToP: 

Router# show recovered-clock 

Recovered clock status for subslot 0/4
----------------------------------------
Clock    Type     Mode        				CEM    Status       Frequency Offset(ppb)  Circuit-No

0        DS3      DIFFERENTIAL     0    	ACQUIRED   		n/a                    0 (Port)
Use the show running-config | section command to verify the configuration of differential clock of T3/E3 interfaces for SAToP: 

Router# show running-config | section 0/0/1
controller MediaType 0/0/1
 mode t3
controller T3 0/0/1
  cem-group 0 unframed
 clock source recovered 1
 cablelength 224
interface CEM0/0/1
 no ip address
 cem 0
  rtp-present
Use the show running-config | section recovered-clock command to verify the recovery of differential clock of T3/E3 interfaces: 

Router# show running-config | section recovered-clock
recovered-clock 0 0
 clock recovered 1 differential cem 1 0

Configuring ACR for Channelized T3/T1 or E3/E1

Configuring ACR of Channelized T3/T1 or E3/E1 Interfaces for SAToP

Before You Begin

  • The node (chassis) on which the T3/T1 or E3/E1 is configured for ACR, has to have its own clock derived from BITS/GPS/Stratum clock.

  • The minimum packet size of CEM pseudowires on the network that delivers robust clock recovery is 256 bytes.

To configure adaptive clock on a channelized T3/T1 or E3/E1 interfaces under controller for SAToP in controller mode, use the following commands: 
 
enable
configure terminal
controller t3 0/0/1
t1 1 clock source recovered 1
t1 1 cem-group 0 unframed
exit
To configure recovery of adaptive clock of channelized T3/T1 or E3/E1 interfaces in global configuration mode, use the following commands: 
 
recovered-clock 0 0
clock recovered 1 adaptive cem 1 0
exit

Note

The clock configuration on controller must be done before configuring the clock recovery on global configuration mode.

To remove the clock configuration in ACR and DCR, you must remove the recovery clock configuration in global configuration mode and then remove the controller configuration.

Verifying the ACR Configuration of Channelized T3/T1 or E3/E1 Interfaces for SAToP

Use the show recovered-clock command to verify the ACR of T3/T1 or E3/E1 interfaces for SAToP: 

Router# show recovered-clock

Recovered clock status for subslot 0/4
----------------------------------------

Clock    Type      Mode        CEM    Status      Frequency Offset(ppb)  Circuit-No
0        DS3-ds1  	ADAPTIVE     0     ACQUIRED 			n/a                    0/1 (Port/t1)
Use the show running-config | section command to verify the configuration of adaptive clock of channelized T3/T1 or E3/E1 interfaces: 

Router# show running-config | section 0/0/1
controller MediaType 0/0/1
 mode t3
controller T3 0/0/1
 framing c-bit
 cablelength 224
 t1 1 cem-group 0 unframed
 t1 1 clock source recovered 1
interface CEM0/0/1
 no ip address
 cem 0
Use the show running-config | section recovered-clock command to verify the recovery of adaptive clock of channelized T3/T1 or E3/E1 interfaces: 

Router# show running-config | section recovered-clock
recovered-clock 0 0
 clock recovered 1 adaptive cem 1 0

Configuring DCR for Channelized T3/T1 or E3/E1

Configuring DCR of Channelized T3/T1 or E3/E1 Interfaces for SAToP

Before You Begin

  • Before you start configuring DCR, RTP must be enabled on the CEM interface. The RTP is used to carry the differential time.

  • The minimum packet size of CEM pseudowires on the network that delivers robust clock recovery is 256 bytes.

To configure differential clock on a channelized T3/T1 or E3/E1 interfaces under controller in controller mode, use the following commands: 
 
enable
configure terminal
controller t30/0/1
t1 1 clock source recovered 1
t1 1 cem-group 0 unframed
exit
To configure RTP header under channelized T3/T1 or E3/E1 interfaces, use the following commands: 
 
interface cem 0/0/1
cem 0
rtp-present
To configure recovery of differential clock of channelized T3/T1 or E3/E1 interfaces in global configuration mode, use the following commands: 
 
recovered-clock 0 0
clock recovered 1 differential cem 1 0
exit

Note

The clock configuration on controller must be done before configuring the clock recovery on global configuration mode.

Verifying the DCR Configuration of Channelized T3/T1 or E3/E1 Interfaces for SAToP

Use the show recovered-clock command to verify the DCR of T3/T1 or E3/E1 interfaces for SAToP: 

Router# show recovered-clock 

Recovered clock status for subslot 0/4
---------------------------------------- 

Clock    Type         Mode        			CEM   	 Status     Frequency Offset(ppb)	Circuit-No

0        DS3-ds1      DIFFERENTIAL   0       ACQUIRED    n/a                  0/1 (Port/t1)
Use the show running-config | section command to verify the configuration of differential clock of channelized T3/T1 or E3/E1 interfaces: 

Router# show running-config | section 0/0/1
controller MediaType 0/0/1
 mode t3
controller T3 0/0/1
 framing c-bit
 cablelength 224
 t1 1 cem-group 0 unframed
 t1 1 clock source recovered 1
interface CEM0/0/1
 no ip address
 cem 0
  rtp-present
Use the show running-config | section recovered-clock command to verify the recovery of differential clock of channelized T3/T1 or E3/E1 interfaces: 

Router# show running-config | section recovered-clock
recovered-clock 0 0
 clock recovered 1 differential cem 1 0

Associated Commands

The commands used to adaptive clock recovery and differential clock recovery on 48-Ports T3/E3 Interface Module.

Commands

URL

clock recovered adaptive cem

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-c2.html#wp8894393830

cem-group

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-c1.html#wp2440628600

recovered-clock

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-o1.html#wp8262293900

controller t3/e3

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-c2.html#wp1921350260

clock-source

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-c2.html#wp6081785140

Additional References for Clock Recovery

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

Standards and RFCs

Standard/RFC

Title

ITU -T G.8261

Timing and synchronization aspects in packet networks

MIBs

MIB

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http://www.cisco.com/go/mibs

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