REFERENCES
- Millman (J) and Taub (H). Pulse, Digital and Switching Waveforms. 1965. McGraw-Hill. New York.
- Atkinson (J). Telephony. Volume 1, 1950. Sir ISAAC Pitman and Sons, London.
- Atkinson (J). Telephony. Volume II. 1950. Sir ISAAC Pitman and Sons, London.