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ITU-T V.34 defines the modulation methods and operating sequences for a modem used on General Switched Telephone Networks (GSTNs) and on point-to-point 2-wire leased telephone-type circuits. Both full duplex and half-duplex modes are supported. Data rates in the range of 2400 bps to 33600 bps, in incremental steps of 2400 bps are supported. Symbol rates of 2400, 2743, 2800, 3000, 3200, and 3429 symbols per second are supported. Using QAM with synchronous line transmission, selectable mandatory rates are 2400, 3000, and 3200 symbols/s with optional rates of 2743, 2800 and 3429 symbols/s. Asymmetric symbol and data rates are also supported. Negotiation and training sequences at startup establish the data rate. Control channel rates are 1200 and 2400 bps, with an optional auxiliary channel with a synchronous data signalling rate of 200 bit/s.
Trellis coding for all data signaling rates and shell mapping permit satisfactory performance even over noisy channels. Adaptive techniques enable the modem to achieve close to the maximum data signalling rate a channel can support on each connection. VOCAL's V.34 software uses state-of-the-art line probing analysis to automatically determine maximum channel capacity. It also support MSE fallback/fallforward threshold control to adjust the tradeoff between higher data channel rates and symbol error rates. Channel separation is accomplished using echo cancellation techniques.
The line interface may be an analog front end (codec and DAA) or a digital interface such as T1/E1, Switched 56, and ISDN. The upper end of this software can provide a PPP, HDLC, V.14 or a direct binary framing layer. Higher data protocol layers, V.42 (including MNP 2-4), V.44, V.42bis and MNP 5, are also available.
This modulation family can be combined with other data modulations (V.92, V.90, V.32bis/V.32, and V.22bis/ V.22/V.23/V.21). Automatic modulation determination procedures (Automode) include those of V.8, V.8bis and PN-2330. All data modulation software is fully compatible with VOCAL’s facsimile, telephony, speech coder and multimedia systems.