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New Member

Nortel passport DCD down


I have an international circuit. I am trying to analyze this fault whereby my WAN equipment(Nortel passport) shows DCD down. It was a downtime of 4minutes, without any reset of equipment serial interface and the carrier CSU/DSU. I further confirm with the carrier there is no alarms detected on the carrier's international and local access portions -- meaning nothing was done at the carrier portion too.

I was puzzled what could have cause the line to auto-up and what could be the possible causes of the initial DCD down.

I really appreciate if you can share your analysis for the above scenario. Much thanks in advance as this was a very critical international circuit.

Thank you.

(ps: I am borrowing this CCO a/c from a friend. )

New Member

Re: Nortel passport DCD down

With some DSU/CSUs, DSR needs to be set to properly reflect DCD properly. This will vary depending on DSU/CSU manufacturers. Check the DSU/CSU documentation.

New Member

Re: Nortel passport DCD down

No sure answer here - but some things to consider. When the CSU/DSU is able to detect carrier form the remote end it will raise DCD. If there is a fault between you and your carrier on your receive, the carrier won't detect it but you will (the trouble is leaving here fine!). That said, you may have had an actual outage on your receive for four minutes.

The problem that I have with that answer though is that you don't metion CTS. In the most common configuration, CTS will either follow DCD or it will follow RTS if DCD is high. In other words, if your CSU/DSU detected a loss of carrier, it probably would have dropped DCD and CTS. You may have your CSU/DSU optioned for CTS always on. This didn't cause your problem, but it does sometimes make it more difficult to troubleshoot.

Were you able to determine if the CSU/DSU showed any problems? The CSU/DSU may have had DCD high all of the time but the Nortel had a problem. The situation is the same as with your carrier. If the CSU/DSU is sending DCD and the Nortel is not seeing it, the CSU/DSU would still be happy.

So what are the possible causes? 1) trouble between the carrier and you on your receive 2)bad CSU/DSU 3) trouble with cable between the CSU/DSU and the Nortel 4) trouble with the Nortel. A four minute outage that has cleared itself is very difficult to troubleshoot. Your time may be better spent checking every detail of the hardware and software so it doesn't re-occur. Also, be ready with a game plan to check and troubleshoot if it should happen again. Good Luck.