Core Issue
The show controllers command shows a repeating clock slip on the E1 or T1 interface, as shown in this command output:
Router#show controllers 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 occurrence of clock slips on the digital trunks can cause an audible clicking noise (or echo) during the conversation.
The Digital Signal Processor (DSP) resources on the 7200VXR series router reside on the PA-VXC-2TE1+ or PA-VXB-2TE1+ card, but DSP can be shared on the card E1 and T1 interfaces. DSP can also be shared with other E1 and T1 interfaces installed in other port adapter slots across the Time-Division Multiplexing (TDM) backplane architecture.
To allow all the interfaces and DSP resources to be correctly shared across the TDM backplane of the router chassis, the system clocking needs to be enabled. This allows the DSP resources to be synchronized to the clock signal coming in from the appropriate digital line.
Note: The default clocking configuration is for the port adapter 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 TDM backplane, its default clocking mode needs to be changed.
Resolution
To resolve the issues on 7200VXR series routers, issue the frame-clock-select command.
To confirm the 7200VXR system clocking, issue the show network-clocks command, as shown in this output:
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 clocking configurations, refer to Clocking Configurations On Voice-Capable IOS-Based Platforms.
Voice Gateway Hardware Components
PA-VXB-2TE1+
PA-VXC-2TE1+
PA-VXA-1TE1-24+
PA-VXA-1TE1-30+
Voice Gateways
7200 Series Multiservice Platform
