Monitoring the audio on my at&t (swbt) landline without going offhook, each day at approx. 1:15am I record an automated test:
I don't have a dso to record exactly what's happening, but a VOM across the line shows a momentary voltage drop from the usual -48v similar to going off hook. In addition, another test occasionally is performed-- this one with three tones similar (or identical) with some combination of SIT tones.
Any idea of the purpose or scope of these tests?? I believe the line is served by 5ESS.
Regards,***** Moderator's Note *****
I've never heard those tones, or anything like them, before.
Bill Horne Moderator