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WAN - Troubleshooting for Layer1 and Layer2

Answered Question
Dec 2nd, 2006
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1. Can a Bert test be performed in a framed (n*64) circuit? If so, should it only test for physical layer problems on the whole line (i.e: T3, DS3) thus checking for bad circuitry, cabling problems, low light leveIs, etc?

2. Can a Bert provide indication about the layer 2 (framing ? ATM, Frame Relay, etc) health?

3. In the event that Bert can only test the Layer1, then what would be the best way to test the Layer2 of a framed/unframed circuit?

3.1 Perhaps, if I have ATM service, could a ?cell tester? accurately check the ATM layer for provisioning, AAL CRC, or other frame-level problems ?


Correct Answer by pciaccio about 10 years 8 months ago

To answer your questions:


1) Yes, a BERT test can be performed on a DS0 of a DS1 line. You would require a test set that can break out the DS0 so that it can be tested. Or you can demux to aggregate line to the DS0's and then throw a BERT tester on the DS0 of your choice. Such a DS0 test will test out the Nx64k pipe only. It will not test out the aggregate pipe as a whole. If you have an issue with your aggregate pipe then you may see issues with the Nx64k test. However if a timing issue where the more data on the pipe creates more errors then a DS0 test would probably not see any errors. If you have cabling problems, low light problems or bad circuitry on the aggregate then all sub-channels(Nx64k) will also see the problems.

2) A BERT will not see any issues with ATM or F/R health. The BERT is strictly a layer 1 test. However, some BERT testers do have layer 2 tests built in that allow you to test layer 2 protocols (ATM, F/R).

3)A Cell Tester can check the status of your ATM line. I have always worked with ATM test sets that generate their own cell and PCI/PVI interfaces....

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Correct Answer
pciaccio Sat, 12/02/2006 - 15:09
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To answer your questions:


1) Yes, a BERT test can be performed on a DS0 of a DS1 line. You would require a test set that can break out the DS0 so that it can be tested. Or you can demux to aggregate line to the DS0's and then throw a BERT tester on the DS0 of your choice. Such a DS0 test will test out the Nx64k pipe only. It will not test out the aggregate pipe as a whole. If you have an issue with your aggregate pipe then you may see issues with the Nx64k test. However if a timing issue where the more data on the pipe creates more errors then a DS0 test would probably not see any errors. If you have cabling problems, low light problems or bad circuitry on the aggregate then all sub-channels(Nx64k) will also see the problems.

2) A BERT will not see any issues with ATM or F/R health. The BERT is strictly a layer 1 test. However, some BERT testers do have layer 2 tests built in that allow you to test layer 2 protocols (ATM, F/R).

3)A Cell Tester can check the status of your ATM line. I have always worked with ATM test sets that generate their own cell and PCI/PVI interfaces....

mounir.mohamed Sat, 12/02/2006 - 15:11
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Dear,


The Bert can only test Layer1 or physical problems, regarding layer 2 protocols most of the layer 2 protocols show commands can give you a result to check Errors, drop frames/Cells..etc such commands like show frame-relay pvc, show frame-relay lmi, show atm pvc 1/1, also debug commands for layer 2 protocols could give you a very useful informations, regarding your last point, there is small devices acting as testers such devices can test or even capture the traffic and give you graphs for the type of traffic begin send over the link, delay, errors.


Best Regards,

Mounir Mohamed

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