A 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 POIN
This modem is intended for use on connections on General Switched Telephone Networks (GSTNs) and on point-topoint 2-wire leased telephone type circuits. The principal Characteristics of the modem are as follows: a) Framed Quadrature Audiornata Modulation (Framed QADM) transmission with simultaneous transmission of duplex audio information and a synchronous audio plus data signalling rate of 4800 bids; b) optional automatic switching between the data-only signalling rate and the audio plus data signalling rate to increase the data signalling rate to up to 14 400 bit/s during periods of audio silence; c) optional user controlled switching between the data-only signalling rate and the data plus audio signaling rate; d) independence of data plus audio and data-only modes in each direction of transmission; e) call establishment procedures from both the audio interface and the data interface; f) call establishment procedures from the data interface before or after voice connection establishment; g) separation of audio and data channels during audio plus data transmission via quadrature audioídata modulation; g) Quadrature Amplitude Modulation (QAM) transmission with the following synchronous data-only signalling rates implemented in the modem: 14400 bit/s; 12000 bit/s; 9600 bit/s; 7200bit/s; 4800bit/s; i) duplex mode of operation on GSTN and point-to-point 2-wire leased circuits; j) channel separation of both data and audio by echo cancellation techniques; k) quadrature amplitude modulation for each channel with synchronous line transmission at either 3000 symbolsís or 2800 symbolsís; l) exchange of symbol rate determination signals during start-up to establish the symbol rate; m) exchange of rate sequences during start-up to establish the data signalling rates; n) a procedure to change the data signalling rates without retraining; o) a duplex auxiliary control channel with a conditional signalling rate up to 342 bit/s.