PRI Slips and Error

Unanswered Question
Mar 18th, 2008

We have a customer connecting their Nortel PBX via PRI to a 2851 router with VWIC2-2MFT-T1 on the Cisco CM side.

PRI is up and we are able to make calls bothways but the PRI is flapping (up and down every 10 mts). I checked ("sh controller t1") the router and saw just slip and error seconds go up but Line code and path code violation stays clean with 0 errors.

2851 router is providing clock to PBX here is the config

clock timezone AZ -7

network-clock-participate wic 0

ip subnet-zero



ip cef



no ip domain lookup


isdn switch-type primary-ni


voice-card 0

no dspfarm


controller T1 0/0/0

framing esf

clock source internal

linecode b8zs

pri-group timeslots 1-24 service mgcp


interface Serial0/0/0:23

no ip address

isdn switch-type primary-ni

isdn protocol-emulate network

isdn incoming-voice voice

isdn bind-l3 ccm-manager

no cdp enable


One thing I couldn't do is one of the clocking command "network-clock-select" if I try it comes back with an error "*** Controller T1 0/0/0 is NOT deriving Clock from Line".This is the only T1 PRI connected on this router and I have no other T1 to point for clocking.

How do I fix this slip error so the T1 won't flap anymore and stays clean.

Thanks for your help.

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4.7 (3 ratings)
Rick Morris Wed, 03/19/2008 - 07:56

I had a similar issue.

Make sure that the Framing and Coding are the same at both ends and what you ordered from the LEC.

If you ordered a point to point T ESF/B8ZS then you need to make sure that it is set up this way and not SF/AMI

Also make sure all the channels are set up.

The router should be providing clocking and the nortel should be getting clock from the network.

balukr Wed, 03/19/2008 - 15:00

We checked it is setup correct on both ends I upgrade the IOS to latest version just in case still no luck.

Rick Morris Thu, 03/20/2008 - 09:12

With this type of issue it could be the LEC causing the SLIP.

I would have them run some end to end testing with their T-Bird or like tester to see if it is a repeater, mux, or something else in "Telco Land"

I don't see any other way around it. At leas if they find nothing you can rule out the Telco portion.

Rick Morris Thu, 03/20/2008 - 09:13

Oh wait, is this going through telco or is it a direct cable from the Nortel to the 2811?

balukr Thu, 03/20/2008 - 09:28

It is a direct T1 crossover cable from nortel to 2851 ISR

molesworthcco Fri, 03/21/2008 - 00:25

set your clock source to external so you pull it from the telco provider...I had the same issue with setting my mgcp to internal...flopping and excessive slips.

molesworthcco Fri, 03/21/2008 - 08:15

It's just a generic term for a TDM system (telco could be a company, or in my case, I'm a telco because I administer the Nortel DMS-100). Anyway, if the nortel is not pulling timing from another source, it has to be configured to pull the time from the router...see below

>tb synclk

>lis all




0 STRAT3 SLAVE DTC 0 0 0 DTC 0 2 1



Your voice tech can point his time source to the router links. Then he can manage them via MAPCI;MTC;MS;CLOCK

balukr Fri, 03/21/2008 - 08:20

Sorry we misunderstood your term here, anyways they do have a T1 PRI coming from Telco (real Telco !!!) connected to there PBX and this is the second T1 for Tieline between Cisco 2851 and PBX.

Is this config still valid in that case or no?

I just want to check beofre I send this to him.

molesworthcco Fri, 03/21/2008 - 16:11

Hmmm...strange that he doesn't already have a timing source...especially since there is already a connection to another CO...if my clock drifts just a little, it throws my commercial links out of wack...this usually happens when I lose my timing source (pulled via ss7 from a distant multifunction switch). If the system is a DMS/MSL type switch, then yes the table listed is where he can datafill the timing links. However, if it is a Meridian1, the config will be quite different. I have the manuals for the Meridian1 and can find it out where to do it. I do know that LD 60 is the level for controlling synchronization on the time source, but it still has to be provisioned...possibly in LD 22.

anthony.king Fri, 03/21/2008 - 06:45

The Nortel PBX can only have one clock source. If there is already a PRI or T1 connected to the PBX from a Telco, then the clock controller on the PBX should be deriving the clock from that. In that case, the PBX is providing clock on the line to your router and you should set your clock source to 'line'.

balukr Fri, 03/21/2008 - 07:46

There is no Telco here it is a direct cable from PBX to 2851 router.I tried to configure router side as line for clocking then D channel never comes up.

I talked to the PBX tech he said if he needs to configure his side as master for clocking then he has to set his switch type as DMS-250 whcih I'm not sure why he can't do NI2.

I may move to a differnt card in the same router and see that helps.

I'll keep you posted.

balukr Fri, 03/21/2008 - 13:30

We replaced the cable didn't help , since we have two VWIC's on the router we moved the T1 to second VWIC card that didn't help either. I tried with MGCP and H323 both didn't work so I'm not sure what we are missing in the Nortel side. I'm sure it is a minor thing but we don't know what it is.

I'll keep you guys posted.

Paolo Bevilacqua Fri, 03/21/2008 - 15:04

Hi, the requirement that ties a given switchtype to clock source appears quite strange, anyway, have him do that, in reality all switchtypes are interoperable at least for basic calls.

Another thing you can try, although I'm not convinces, can you try to change "cablelenght" and gain under controller T1.

balukr Fri, 03/21/2008 - 15:24

I already tried both cable length "long" and "short" didn't help.

Paolo Bevilacqua Fri, 03/21/2008 - 16:11

I've posted a link to this in voice forum and I hope that my friend Rob will be able to help.

rob.huffman Sat, 03/22/2008 - 08:20

Hi Folks,

There are a few things here that we came across when first setting up our integration between CCM and our Nortel M61c.There are 4 PRI's configured between the two systems. The original config used Cisco 6608 blades but we now use 2x2811 ISR's with T1 VWIC's.

We tested using ESS5,NI2 and D100 (DMS-100).

All three interface protocols were available on the Nortel Meridian (maybe the Nortel Tech has not seen this).

The only one that has ever worked properly was DMS-100! It is a bit of a bear to change this on the Nortel as the whole PRI config has to be removed and re-programmed line by line when switching between IFC Types, so there may be a reluctance to change these. I know from first hand experience that this is not alot of fun, but this is the first thing that I would do. All of the rest of the changes that could be done would be pure speculation until the proper Interface between the two systems is setup.

Here are some great docs (have a close look at the White Paper);

Cisco Unified CallManager

Case Study: Nortel 61C PBX to Cisco IP Telephony Migration

From this good doc;

Nortel Meridian PBX and Cisco CallManager Integration

Hope this helps!


balukr Mon, 03/24/2008 - 07:48


Thanks for your prompt reponse and for the doc's. We were planning to try QSIG not only to fix this also it will pass caller id across the tie line.Can we try this or only DMS 100 will work ?

One more question on Nortel side

TKTP has to be configured as TIE or it doesn't matter . Since it is going to be a tie line I just want to make sure this is configured correct on that side.

Thank you so much again for your help.

rob.huffman Mon, 03/24/2008 - 08:38

Hi Balu,

You are most welcome :) Yes, QSIG will also work. We used DMS100 due to the fact that our Nortel release did not support QSIG.

For your second question, yes, this must be configured as TKTP TIE.

Hope this helps and best of luck!


balukr Tue, 03/25/2008 - 16:39


Sorry for the delayed update I have to work with PBX tech's schedule.We changed the switch type to QSIG today still had the same slip error so we changed to DMS-100 but this time Nortel side D channel was not coming up at all.He said he tried what ever he can on his side to troubleshoot this, since I'm not familiar with Nortel side I can't speak for him.

PBX tech has the same setup works fine with another customer site with QSIG so he is going to download that config and configure the same way here and try this again tomorrow.

If there are any other thoughts let me know if not I'll update tomorrow.

Thanks again for your help.

balukr Wed, 03/26/2008 - 17:06

Finally T1 is up and running clean now.PBX tech changed couple of settings in Nortel side (he got that config from working QSIG tieline and I'll try to get that setting from him if possible and post it ), it is setup as QSIG and we are getting clock from Nortel now because this time we were seeing LCV's and PCV's along with slips when we set clock on Cisco CM side as Master as soon as we changed it to User and added the "network-clock-select" command it is running clean now.

I wish PBX tech was able to make the clock setting on his side as master before so we don't have to go through all this anyways thanks for everyone's help on this.

Paolo Bevilacqua Wed, 03/26/2008 - 17:14

Good, like some people says, "router is (almost) never wrong". Now all what you've to do is refine the qsig config on the CM and you will be able to do certain sophisticated qsig things like calling name, inter-system transfers and forwards and some more that I don't even know about.

balukr Wed, 03/26/2008 - 17:17

Yeah I saw that too calling name already works ,I may play with other features later.


This Discussion