T1 CAS to Nortel version 17 with intermittent Line Code Violations

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Jun 14th, 2010
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I have a 2821 connected to a very old Nortel PBX running software version 17.  We have configured a T! CAS between the two using E&M Wink Start.  The circuit is clean while idle.  However, the errors start to increment when the Nortel side starts to talk.  The voice quality is fine.  No errors when we speak from the Cisco to Nortel Phone.  They see errors on their side, but it is hard for them to see any relationship between the errors and speech.  The physical layer is cross-connected over a 300 pair CAT 3 feeder.  The length is between 500 and 600 feet.


Please advise...

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Paolo Bevilacqua Mon, 06/14/2010 - 18:42
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Check that you are using the correct pairing, and that cisco supplies clock.

Jonathan Schulenberg Mon, 06/14/2010 - 19:39
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Two ideas come to mind for you:


  1. Ensure that the network side (preferrably Cisco) is providing clocking and the Nortel PBX is configured to get clocking from the circuit. Unless the clocks are matched up on both sides, you'll still be in trouble.
    Also, how many discrete clocking sources do you have here? I can't speak for the Nortel; however, it is not uncommon that PBX cards share a Cisco limitation where the DSPs can only deal with a single clock source. On Cisco ISR hardware this clocking domain is all circuits that share the same DSPs (ie. all VWIC/VICs on the motherboard). Does the PBX have a limitation with different clock sources (ie. the Cisco router vs. the telco)?
  2. If the total length of the cable is only a few hundred feet you can try using the cablelength short command.
jzapp Fri, 06/18/2010 - 13:48
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After several command changes on both sides including different E&M modes, we moved the router next to the PBX to isolate any cable issues.  No significant difference.  We decided to change to AMI and SF(D4).  We had to remove the line card from the Nortel to adjust the dip switches and reprogram the PBX.  They were down for about 30 minutes.


The Line Code Violations disappered with AMI and SF.  The old Nortel did not like b8zs and ESF.

Paolo Bevilacqua Sat, 06/19/2010 - 19:29
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Good to know, I've rated your post.

ryan_oconnell Sun, 10/03/2010 - 18:43
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Hi Jzapp,


I am about to do the same thing you just did with an old Nortel PBX to Cisco over T1-CAS. Now that yours is operational can you comment on the functionality. You mentioned the quality is voice quality is fine what about things such as Caller-ID, and Display or Putting a caller on hold and returning from on hold. Transfers etc.


In my situation I am thinking of using T1-CAS to replace some legacy tie-lines to other Nortel PBXs. I would like to know what functionality they are losing if I try to replace the current hub (nortel option 81c) with a Cisco 2921.


Also did you have a Cisco document you used for this integration. Any help you can provide would be great.




Cheers Ryno

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