Some textbooks also consider passband data transmission using a digital modulation method such as ASK, PSK and QAM, i.e. a sinewave modulated by a digital bit-stream, as analog transmission and as an analog signal.
Telephony and voice communication was originally primarily analog in nature, as was most television and radio transmission.
The analog transmission method is still very popular, in particular for shorter distances, due to significantly lower costs with complex multiplexing and timing equipment that are unnecessary, and in small "short-haul" systems that simply do not need multiplexed digital transmission.
[2] However, in situations where a signal often has high signal-to-noise ratio and cannot achieve source linearity, or in long distance, high output systems, analog is unattractive due to attenuation problems.
Furthermore, as digital techniques continue to be refined, analog systems are increasingly becoming legacy equipment.