Simultaneous Voice Plus Data Modem, Operating at a Voice Plus Data Signalling Rate of 4800 Bit/s, with Optional Automatic Switching to Data-Only Signalling Rates of up to 14 400 Bit/s, for Use on the General Switched Telephone Network and on Leased Point-to-Point 2-Wire Telephone Type Circuits - Series V: Data Communication over the Telephone Network Interfaces and Voicband Modems