V.32terbo: 19200 bit/s on V.32bis¶

V.32terbo is AT&T's extension of V.32bis from 1993. It keeps everything about V.32bis (the 2400 baud signal on an 1800 Hz carrier, the start-up, the trellis code) and adds two faster speeds, 16800 and 19200 bit/s, for clean lines. It came out while V.34 was still being written. AT&T's own modems had it, and so did others built on AT&T Microelectronics' modem chips (a business that became Lucent's and then Agere's). V.34 soon made it obsolete.

It was never an ITU standard and its specification was never published. D-Modem's version was rebuilt from a modem that has it: Agere's soft modem, which D-Modem's tests already run (see Interop). The two connect to each other at 19200 bit/s. For how it was found and how it works, see the technical details.

(There is no "V.34terbo". The name sometimes turns up as a mix of V.32terbo and V.34.)

Using it¶

AT+MS=V32T       (or AT+MS=232)

The modem then offers 19200 and 16800 bit/s on top of V.32bis's speeds. Each end measures the line during the start-up and the two agree on the fastest speed both can take; a modem that only does V.32bis just connects at 14400 or less. V.8 (the negotiation AT+MS=34 and up start with) has no code for V.32terbo, so it is used only when chosen with AT+MS.

Speeds in simulation¶

Two D-Modems back to back on a simulated phone line (pump_test):

Every one of these calls ran without a bit error.

Real phone lines in the 1990s seldom reached 19200 this way, which is part of why V.34 replaced it.