T1/PRI Network Clocking Configuration Question

Unanswered Question
Apr 3rd, 2009

Hi Everyone,

I have a question regarding proper network clock configuration on a 2851 with a 4-port HWIC and a 2-port VWIC2-2MFT-T1/E1. There are 3 T1's (WIC 0 - 0/0/0, 0/0/1, and 0/0/2) and 2 PRI's (WIC 2 - 0/2/0 and 0/2/1).

The T1's are all taking slip secs errors at an increasing rate. The network clocking is currently configured with:

network-clock-participate wic 0

network-clock-participate wic 2

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

From this, I would infer that the T1's on WIC 0 are getting their clock information from the PRI on WIC 2 (0/2/0). All controller interfaces are set to 'line' which I have confirmed is correct.

Would it be best to remove the 'network-clock-participate wic 0' or add 'network-clock-select 2 T1 0/0/1'?

When I issue the show network-clocks command, I see no reference to a clock source for any WIC 0 interface(s).

Perhaps some insight in to T1/PRI best practices would help me understand and possibly answer this question myself.

Any and all help is MUCH appreciated!



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Collin Clark Fri, 04/03/2009 - 13:24

Hi Shane-

Are the T1's point-to-point or do they go to a provider (eg MPLS)?

s.clinard Fri, 04/03/2009 - 13:29

Hi Collin -

The T1's are straight internet T1's (no MPLS or point to point) with VPN back to our head end.

Collin Clark Fri, 04/03/2009 - 13:55

I've read your post a couple of times and I have a question. Are all 5 circuits for internet access? Do they all go to the same provider? I would have the PRIs get clocking from the PRI line and the T1's to get clocking from one of the T1 lines. I had a good link on this stuff once, I'll post it when I can find it.

s.clinard Fri, 04/03/2009 - 14:31

Only 3 circuits are for internet access, the other 2 circuits are for voice. They all go back to the same provider from what I am told. Ultimately I want clocking on the T1's to come from a T1 interface and clocking for the PRI's to come from a PRI interface, I just am not quite sure exactly how to go about this.

Thanks for your time!


viyuan700 Fri, 04/03/2009 - 23:13

"Ultimately I want clocking on the T1's to come from a T1 interface and clocking for the PRI's to come from a PRI interface, I just am not quite sure exactly how to go about this"

Certainly you have a problem but dont just confine your solution to deriving separate clock. Even cisco documentation says "If there are multiple T1s into an access server, only one can be the primary"


Are your all 5 circuits are comming from the same mux of service provider OR are they over copper as 5 separate links?

If all circuits are comming from the same mux then deriving clock source from 2 will not solve your problem.

Both PRI and Internet access are using the different T1 from the same mux, at service provider end PRI T1 is going to different equipment and internet T1 is going to different equipment. But the mux is providing the same clcok to all 5 circuits.

Even in case you have 5 circuits from 5 different equipment, each equipment of service provider is deriving clock from the same equipment of service provider.

Check if there is any problem with current clock etc,


This Discussion