"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
ITU communication standards V.27 V.29 V.17V.34 V.34bis
You can fin the specs here
from V.34...
10.1.2.1A Tone A is a 2400 Hz tone transmitted by the answer modem. Transitions between A and A, and similarly between A and A, are 180 degree phase reversals in the 2400 Hz tone. During the transmission of A and A, the answer modem sends a
1800 Hz guard tone without any phase reversals. Tone A is transmitted at
1 dB below the nominal transmit power while the guard tone is transmitted at the nominal transmit power. NOTE ? The bandwidth of a tone with phase reversals should not be constrained in a way that appreciably affects the accuracy of round trip delay measurements.
10.1.2.2B Tone B is a 1200 Hz tone transmitted by the call modem. Transitions between B and B, and similarly between B and B, are 180 degree phase reversals in the 1200 Hz tone. NOTE ? The bandwidth of a tone with phase reversals should not be constrained in a way that appreciably affects the accuracy of round trip delay measurements.
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