| Modulations |
|---|
| V.34 |
| V.17 |
| V.29 |
| V.27ter |
| V.21 |
VOCAL offers a comprehensive and fully optimized Group 3 Fax solution for a wide variety of platforms. This includes complete and robust implementations for ITU-T modulations V.17, V.29, V.27ter, V.21 channel 2, and V.34.
All of the facsimile modulations and data streams can be controlled with VOCAL's T.30 library or with VOCAL's facsimile service Class 1 Command Set(EIA-578 and T.31). The T.30 library could in turn be controlled by VOCAL's facsimile service Class 2 Command Sets T.32 (Fax Class 2.1), EIA-592 (Fax Class 2.0), or industry standard (Fax Class 2). With Fax Class 1, most of the protocol is executed in software, with the advantage that any changes don't require hardware modifications. This is in contrast to Fax Class 2, where image processing is handled by the modem.
As an option, these modulations can be combined with VOCALs V.34Fax to provide image transfer rates of up to 33600 bps. The V.21 channel 2 and V.27ter are the minimum requirements for Group 3 Fax. For non V.34fax, V.21 channel 2 is used to transfer T.30 control frames. The "high speed" modulations V.27ter, V.29 and V.17 are used for the "compressed image" transfer. The term "compressed image" is used loosely here, as the high speed data may in actuality be other data, such as in the case of binary file transfer (BFT).
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 offers a direct binary and HDLC interface.