Supervisory audio tone-signalling tone (SAT-ST) handling

Methods and systems allowing for the following two Supervisory Audio Tone-Signalling Tone (SAT-ST) qualifications: (1) when detecting a ST as being on, the signalling tone signal is accepted if the SAT strength value indicates that the SAT is on, in accordance with the IS-54-B standard; and (2) when detecting the ST as being on and a momentary or instantaneous SAT strength value indicates that the SAT is off, the signalling tone signal is not accepted at this stage. However, should the instantaneous SAT strength subsequently be detected as being on while the signalling tone is still on, the signalling tone signal is accepted, which is a deviation from the IS-54-B standard. In one embodiment, the measurements of the ST duration are not started until SAT and ST both on.