ISDN PRI clock slips

[webberr]

I have a 2911 that has two ISDN PRI's (T1's) that connect to a 3845 at my service provider:

2911 port 0/0/0 ------- SP 3845 port 0/3/1 

2911 port 0/0/1 ------- SP 3845 port 1/0

Whether I clock off 0/0/0 or 0/0/1, the other one takes clock slips:

c152conantr1>sho contr t1
T1 0/0/0 is up.
Applique type is Channelized T1
Cablelength is long 0db
Description: PRI-Voice VZ Ckt. ID
No alarms detected.
alarm-trigger is not set
Soaking time: 3, Clearance time: 10
AIS State:Clear LOS State:Clear LOF State:Clear
Version info FPGA Rev: 08121917, FPGA Type: PRK4
Framing is ESF, Line Code is B8ZS, Clock Source is Line.
CRC Threshold is 320. Reported from firmware is 320.
Data in current interval (267 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
Total Data (last 24 15 minute intervals):
0 Line Code Violations, 0 Path Code Violations,
0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins,
0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
T1 0/0/1 is up.
Applique type is Channelized T1
Cablelength is long 0db
Description: PRI-Voice VZ Ckt. ID
No alarms detected.
alarm-trigger is not set
Soaking time: 3, Clearance time: 10
AIS State:Clear LOS State:Clear LOF State:Clear
Version info FPGA Rev: 08121917, FPGA Type: PRK4
Framing is ESF, Line Code is B8ZS, Clock Source is Line.
CRC Threshold is 320. Reported from firmware is 320.
Data in current interval (267 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
11 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
11 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
Total Data (last 24 15 minute intervals):
0 Line Code Violations, 0 Path Code Violations,
864 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins,
864 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
c152conantr1>

My config is nearly identical to the config I have working successfully at other sites: 

network-clock-participate wic 0
network-clock-select 1 T1 0/0/0

network-clock-select 2 T1 0/0/1

!

controller T1 0/0/0
cablelength long 0db
pri-group timeslots 1-24
description PRI-Voice VZ Ckt. 
!
controller T1 0/0/1
cablelength long 0db
pri-group timeslots 1-24
description PRI-Voice VZ Ckt. 
!

My provider is set to “Clock Source is Internal” on both circuits and is clocking off the backplane:

C3845#show network-clocks

  Network Clock Configuration

  ---------------------------

  Priority      Clock Source    Clock State     Clock Type

    11          Backplane       GOOD            PLL

  Current Primary Clock Source

  ---------------------------

  Priority      Clock Source    Clock State     Clock Type

    11          Backplane       GOOD            PLL

Can’t figure out what the issue would be - any thoughts?

Thanks! Rob.

[mikeleebrla · Accepted solution]

Clocking domains on Cisco 2900 and 3800 routers is generally "per router" (4000 series are "per NIM" since each NIM has its own DSP chip by the way).

I bring this up b/c I noticed that on your carrier's 3845 they have your PRIs plugged into two different WICs from the config you shared (0/3/1  and 1/0).  There is an exception to the "per router" clock domain I mentioned above, and that is if the router has a service module with its own DSPs in it and then the PRI is plugged into that service module's WIC. In that config your carrier would have two clocking domains (one on the MOBO and one on the service-module) and it would explain your issue.  Can you verify if this is the case or not from your carrier?

If it is you need to look at "Scenario: Mixed Configuration" in the link below:

https://www.cisco.com/c/en/us/support/docs/wan/tdm/116050-trouble-tdm-clocking-00.html

[webberr]

Thanks for your reply! I noticed that also - one PRI is on the VWIC and one is on the service module. However I was not aware of the exception you mentioned, I thought it was indeed just one clocking domain. Let me check with them and I'll report back.

[webberr]

My service provider used a Cisco 3845 and one of my PRI's was coming off a VWIC and another off a Network Module (NM). Apparently they must have been in different clocking domains. We moved the "VWIC" PRI to the same NM and the clock slips immediately stopped.

Thanks for your help!

Rob.