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25. Loop-back Connections: Essential Tests for ISDN & Source-Connect    10/11/12 by Dave Immer

Being able to confirm your codec system is operating properly or to identify the source of a problem is a basic procedure we should all have in our back pockets.  A network loop-back test can accomplish this easily and provide valuable insight:

1.) It shows you that your signal path is set up correctly. You should hear the signal that you are feeding to the codec input “slap back” to your codec output.
2.) It confirms your network is passing the bit-stream in both directions.
3.) For ISDN users it confirms your long distance carrier is cooperating.
4.) For Source-Connect  it confirms your bit-rate and receive buffer are set at usable values.

Source-Connect users can connect to one of the “echo” sites on the contacts list.

ISDN users can dial an AT&T ISDN number set up for this purpose: 732-758-9999. This number can be dialed multiple times depending on your codec bit-rate. For instance if your codec is in L2Mono128 mode you would make 2 calls to this same number. If you need to test an APTX codec at 384kbs you would make 6 calls. If the calls don’t go through (meaning you either have no long distance carrier or your long distance carrier is failing to complete the calls) try dialing from one line to another. These would be local calls.

Doing this test prior to your first session of the day is a quick, easy way to confirm all is well.

Let me know if you have questions about loop-back test connections.   Thanks,

-Dave