What is specified in a modem recommendation?
nData signaling rates, symbol rates, carrier frequencies pre-emphasis, scrambler, framing, encoder
nInterchange circuits
nStart-up signals and sequences
nOperating procedures
nTesting facilities
nThere are two kind of modems specified by ITU-T:
nDigital modems: Generates G.711 signals and receives V.34 signals passed through a G.711 encoder. Connected to a digital switched network through a digital interfacenAnalog modems: Generates V.34 signals and receives G.711 signals that have been passed through a G.711 decoder in an analog PSTN local loop
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G.711 (11/88) - Pulse code modulation (PCM) of voice frequencies
V.34 (02/98) - A modem operating (up to 33 600 bit/s) for use in 2-wire analog PSTN