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PVC "dropping" intermittently

Unanswered Question
May 2nd, 2003
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Help...Cisco noob here...situation, frame relay circuit to remote site dropping intermittently throughout day. Outage 10-30 secs max. Telnet to router after circuit back up (Cisco 1600, WIC with Serial Interface to Adtran CSU/TSU, equipment in locked closet).... run command..sho frame pvc at router console, the PVC status change time corresponds to outage time. Router never loses power or boots. Had AT&T do numerous test off hours to try and isolate, of course the off hours tests show NTF. I do have some alarms on CSU related to phone company testing. Had local TCOM check from their switch into our equip overnight....no obvious trouble found. I haven't tried swapping WIC/Adtran yet but it appears this is where we are headed. How can I troubleshoot the WIC remotely. I have found some documentation about troubleshooting WIC using hardloopback, but that is only for WIC with female RJ-45...not the type we have. Sorry for the longwinded post. Any help is greatly appreciated.

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mark-obrien Fri, 05/02/2003 - 07:34
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1. Make sure that your Adtran CSU/DSU is configured to get its clocking from the T1 line. Clock slips can cause momentary outages.


2. Enter the command "show frame-relay lmi" and see if the number in the "Num Status Timeouts" field increments after one of your outages. If so, the carrier's line card may have problems.


3. Does the line protocol drop during the outages or just the PVC? Again, this could indicate problems in the line card of the carrier's frame relay switch.


Good luck.


Mark

Anonymous (not verified) Fri, 05/02/2003 - 09:05
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Thanks for the tips, Mark....I will try look at the line protocol status and the Num Status Timeout field after the next outage and I will get back.

Anonymous (not verified) Fri, 05/02/2003 - 10:32
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I just had another couple of momentary outages. The Num Status Timeouts counter incremented by 2 upon each occurance.

thisisshanky Fri, 05/02/2003 - 10:58
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Hello Robbie,


I guess u have an Adtran TSU IQ+ with you...Can you check if you get any type of alarms on the TSU when the outage occurs...?? Red, Yellow, AIS ??? You can notice it either by looking at the color of the ALM led on the front panel, or by logging into the TSU via hyperterminal. You will need to use the grey, flat cable and the DB-9 adapter, whch comes with the TSU. Let us know the results..



mark-obrien Fri, 05/02/2003 - 11:53
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I would add to Shanky's suggestions (all good ones) that you check the counters in the TSU and see if any clock slips are being registered.


Mark

michael-faust Fri, 05/02/2003 - 12:42
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Check the LMI timer. A good choice is to have your LMI timer set to 10 seconds. Most Frame Relay switches have the LMI timeout set to 15 seconds. The 5 second difference allows for the varience in the clocks (remember for the LMI timer you and the service providor are both using local timing). If your timer and the carrier's are set to the same value, variences in the clocks can cause an LMI failure. Of course, the router keeps trying, and LMI is re-established and the circuit comes back up. This may not be your problem, but it gives you something to check while you wait for the next crash.

Anonymous (not verified) Tue, 05/06/2003 - 06:13
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Everyone, thanks for the input. We are still trying to get to the root cause of the problem.

Anonymous (not verified) Mon, 05/19/2003 - 05:12
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The root of the problem turned out to be power related. All of the devices in the room are on UPS....a colleague visited the site and sat in the TCOM closet all morning. Right at the time when we were having the most occurances, the power spiked....all of the UPS's held except for the one the Adtran was connected to, the Adtran rebooted. Changed the UPS and haven't had a problem for over a week. Thanks to everyone for the input. This is the best forum on the Net.

mark-obrien Mon, 05/19/2003 - 06:07
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Don't thank us, thank the poor person who spent all morning in the closet.

:-).


Mark

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