If you are using a single hand held ISDN tester to check the quality of an ISDN line by running a bit error rate test, then you are probably using a 'self call' function. The tester will ask you for your own telephone number and then make a call to itself which will arrive on the second available B channel. In reality this is only testing as far as the office PBX/switch and certainly not through the ISDN network.

To test from point to point between your local office and a remote site, you need an Astricom Loopback Device at the remote site to answer the call. It can be programmed to only answer the test call and to ignore any others. When the Loopback Device answers a call using either or both B channels it will loop any voice/data/tones received back to the sender for a true end to end quality test to be performed.