Core Issue
The show controller command shows a repeating clock slip on the E1 or T1 interface, as shown in this example:
Router#show controller e1 0/0
E1 0/0 is up.
Applique type is Channelized E1 - balanced
No alarms detected.
alarm-trigger is not set
Version info Firmware: 20020812, FPGA: 11
Framing is CRC4, Line Code is HDB3, Clock Source is Line.
Data in current interval (97 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
4 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
4 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
Total Data (last 14 15 minute intervals):
1 Line Code Violations, 4 Path Code Violations,
425 Slip Secs, 0 Fr Loss Secs, 1 Line Err Secs, 0 Degraded Mins,
427 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
The digital errors cause the call to be dropped, or the fax transmissions to be incomplete or corrupted. The problem occurs with all fax machines.
In the above example, a fax passthrough is used between a skinny-based Analog Telephone Adaptor (ATA) 186 registering with the Cisco CallManager 3.3(2). The Cisco IOS Software gateway at the other end of the Voice over IP (VoIP) network is 2621. However, this issue could apply to other situations as well.
Note: The default clocking configuration is for the Advanced Integration Module (AIM) to source clock from the router backplane. On the other hand, the digital interface defaults to clocking from the line. In situations such as these, where digital interfaces need to source clock across the Time-Division Multiplexing (TDM) backplane, its default clocking mode needs to be changed.
If clocking is not correctly configured, clock slips result.
Resolution
To resolve the issue, perform these steps:
- Issue the clock source line command under the appropriate controller. The Voice and WAN Interface Card (VWIC) controller configuration defaults to clock source line. However, the recovered clock is not used to drive the AIM module. Therefore, this configuration is not sufficient to resolve the clock slip problem.
- To allow the router to recover the clock from the E1 and T1 VWIC and pass it across the backplane to the AIM, issue the network-clock-participate command in global configuration mode. If multiple VWICS are installed, the command is appropriately repeated.
- To allow the AIM modules in a Cisco 3700 or 2691 to participate in system clocking, issue the network-clock-participate command for each AIM module.
- Specify the network clock source and priority. Issue the network-clock-select command in global configuration mode.
This is an example configuration:
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#network-clock-participate wic 0
Router(config)#network-clock-participate aim 0
Router(config)#network-clock-select 1 t1 0/0
Router(config)#^Z
Issue the show network-clocks command to confirm the system clocking, as shown in this example:
Router#show network-clocks
Network Clock Configuration
---------------------------
Priority Clock Source Clock State Clock Type
0 T1 0/0 Good T1
5 Backplane Good PLL
Current Primary Clock Source
---------------------------
Priority Clock Source Clock State Clock Type
0 T1 0/0 Good T1
For more information on synchronized clocking, refer to the NAS Clocking Commands section of Clock Synchronization for AS5xxx Network Access Servers.
For further background information on clocking configurations, refer to Clocking Configurations On Voice-Capable IOS-Based Platforms.
Also refer to DSP on NM-HDV2 Functionality Verification for 2600XM/2691/2800/3700/3800 Platforms.
