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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) 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).
Effective Cisco IOS XE Everest 16.5.1, ACR is supported on the 8-port T1/E1 interface module.
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.
IM Card |
Pseudowires Supported (Number of Clocks Derived) |
---|---|
48-Port T1/E1 CEM Interface Module |
48 |
How to Configure ACR and DCR
Configuring ACR for T1/E1
Before configuring Adaptive Clock Recovery, CEM must be configured. Below are the guidelines to configure clock recovery:
The node (chassis) on which the DS1 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 64 bytes.
enable configure terminal controller t1/e1 0/0/1 cem-group 0 unframed clock source recovered 1 exit
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.
Router# show recovered-clock Recovered clock status for subslot 0/4 -------------------------------------- Clock Type Mode CEM Status Frequency Offset(ppb) Circuit-No 0 DS1 ADAPTIVE 0 ACQUIRED n/a 0 (Port)
Router# show running-config | section 0/0/1 controller T1/E1 0/0/1 framing unframed clock source recovered 1 linecode b8zs cablelength long 0db cem-group 0 unframed interface CEM0/0/1 no ip address cem 0
Router# show running-config | section recovered-clock recovered-clock 0 0 clock recovered 1 adaptive cem 1 0
Configuring DCR for T1/E1
Before configuring Differential Clock Recovery, CEM must be configured. Below are the guidelines to configure Differential clock recovery:
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 64 bytes.
enable configure terminal controller t1/e1 0/0/1 cem-group 0 unframed clock source recovered 1 exit
interface cem 0/0/1 cem 0 rtp-present
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. |
Router# show recovered-clock Recovered clock status for subslot 0/4 --------------------------------------- Clock Type Mode CEM Status Frequency Offset(ppb) Circuit-No 0 DS1 DIFFERENTIAL 0 ACQUIRED n/a 0 (Port)
Router# show running-config | section 0/0/1 controller T1/E1 0/0/1 framing unframed clock source recovered 1 linecode b8zs cablelength long 0db cem-group 0 unframed interface CEM 0/0/1 no ip address cem 0 rtp-present
Router# show running-config | section recovered-clock recovered-clock 0 0 clock recovered 1 differential cem 1 0
To configure a network clock, use the following commands:
enable configure terminal controller E1/T1 0/5/0 clock source line cem-group 0 unframed exit enable configure terminal network-clock input-source 1 controller E1/T1 0/5/0 exit
Use show run | sec network-cl command to verify the network clocking configuration.
network-clock synchronization automatic network-clock synchronization mode QL-enabled network-clock input-source 1 controller E1 0/1/0 network-clock wait-to-restore 10 global rtr1#sh netw 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 : 2048 (EEC-Option1) Clock Mode : QL-Enable ESMC : Enabled SSM Option : 1 T0 : E1 0/1/0 Hold-off (global) : 300 ms Wait-to-restore (global) : 10 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 *E1 0/1/0 NA NA/Dis 1 QL-SEC NA NA rtr1#
The commands used to configure adaptive clock recovery and differential clock recovery are:
Commands |
URL |
---|---|
clock recovered adaptive cem |
|
clock recovered differential cem |
|
cem-group |
|
recovered-clock |
|
controller t1/e1 |
|
clock-source |
|
network-clock input-source |
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
Standard/RFC |
Title |
---|---|
ITU -T G.8261 |
Timing and synchronization aspects in packet networks |
MIB |
MIBs Link |
---|---|
— |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
Description |
Link |
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