Multi-frequency (MF) R1/R2 is an implementation of ITU-T Recommendations Q.320, Q.322, Q.323, and Q.441 for multi-frequency signal receiving equipment. Signaling systems R1 and R2 are used for inter-register signaling. The R1 signaling system is specified by the ITU-T as the North American code and the R2 signaling system is specified to be a European code.
Both signaling systems R1 and R2 consist of two parts: Line signaling and Register signaling. Line signaling is used to handle line and supervisory signals. Register signaling is used for address signals.
R1 and R2 line signaling operates in a digital transmission environment and operations are handled by signaling bits.
R1 Register signaling handles address signals using MF in-band pulse signaling at frequencies of 700Hz to 1700Hz, at 200Hz increments. The combination of two of these frequencies determines the signal. R2 Register signaling handles address signals also by sending a combination of two fundamental frequencies. The R2 system uses two different sets of six frequencies to combine for the forward and backward signals.
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