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 ?
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....