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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 T3/E3 CEM Interface Module |
1344 |
How to Configure ACR and DCR
Configuring ACR for T3/E3
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.
enable configure terminal controller t3/e3 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. |
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)
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
Router# show running-config | section recovered-clock recovered-clock 0 0 clock recovered 1 adaptive cem 1 0
Configuring DCR for T3/E3
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/e3 0/0/1 cem-group 0 unframed clock source recovered 1 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. |
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)
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
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
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.
enable configure terminal controller t3/e3 0/0/1 t1/e1 1 cem-group 0 unframed t1/e1 1 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 DS3-ds1 ADAPTIVE 0 ACQUIRED n/a 0/1 (Port/t1)
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
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
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.
enable configure terminal controller t3/e3 0/0/1 t1/e1 1 cem-group 0 unframed t1/e1 1 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 DS3-ds1 DIFFERENTIAL 0 ACQUIRED n/a 0/1 (Port/t1)
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
Router# show running-config | section recovered-clock recovered-clock 0 0 clock recovered 1 differential cem 1 0
The commands used to adaptive clock recovery and differential clock recovery on 48-Ports T3/E3 Interface Module.
Commands |
URL |
---|---|
clock recovered adaptive cem |
|
cem-group |
|
recovered-clock |
|
controller t3/e3 |
|
clock-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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