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Consumer Electronics by S. P. Bali

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CCITT NO. 7

Until recently all such signalling was carried on or directly associated with the same speech path as was to be used for the call being established or supervised. Various terms are commonly used in connection with these speech-path-associated signalling systems.

  1. MF: Multi-frequency, i.e. using voice frequency tones.
  2. MFC: Multi-frequency compelled : this type of signal continues until the distant end acknowledges receipt and compels it to stop.
  3. 1 VF: One voice frequency : a single tone, sometimes pulsed in step with rotary dial impulses. 2600 Hz is a common 1VF tone.
  4. 2 VF: Two voice frequencies : two tones, sometimes used together, sometimes separately
  5. In band: A tone actually on the voice circuit itself, audible to any one using ...

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