An AT&T standard for synchronous 9600 bps full-duplex modems using QAM modulation over four-wire leased lines or half-duplex operation over dial-up lines.
"Bell 209." YourDictionary, n.d. Web. 21 June 2018. <http://www.yourdictionary.com/bell-209>.
Bell 209. (n.d.). Retrieved June 21st, 2018, from http://www.yourdictionary.com/bell-209
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