Facsimile Modulations
As an option, these modulations can be combined with VOCAL's 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).
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.
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.
Features
- Fully compliant with ITU recommendations
- Modular software suite available with controller code
- Optimized for high performance on leading edge DSP architectures
- Multi-tasking environment compatible
- Multichannel implementation
Configurations
- DAA interface using linear codec at 7.2 kHz, 8.0 kHz or 16.0 kHz sample rate
- Direct interface to 8.0 kHz PCM data stream (A-law or u-law)
- North American and International Dialing/Telephony dialing functions available
- Facsimile protocol layer (T.30 with ECM/BFT) available
- Facsimile service class 1 command sets (T.31 and EIA-578) available
- Facsimile service class 2 command sets (T.32, EIA-592 and industry standard fax class 2) available.
- System can be combined with V.34fax facsimile modulations and startup procedures (V.8 and V.8bis).
V.17
ITU-T V.17 defines the modulation methods and operating sequences for a modem used solely in high speed
facsimile applications. The data signaling connect rate is 14.4 kbps, with fallback to slower connect rates of 12 kbps,
9.6k bps, 7.2kpbs, 4.8 kbps, and 2.4 kbps for connection over noisy lines. For half duplex operation, signalling rates
of 14.4 kbps, 12kps, 9.6 kbps, 7.2 kpbs, 4.8 kbps synchronous line transmission are supported.
The modulation rate is 2400 symbols/second using
QAM with
synchronous line transmission. Training sequences at startup (long train) and synchronization (resync) are used during
negotiation to establish the data rate, coding, or additional parameters. The channel carrier frequency operates at 1800 Hz.
V.17 includes the use of data scramblers, adaptive equalizers, and trellis coding at rates from 7.2 kbps to 14 kbps.
Features
- Fully compliant with ITU recommendations
- Modular software suite available with controller code
- Optimized for high performance on leading edge DSP architectures
- Multi-tasking environment compatible
- Multichannel implementation
Configurations
- DAA interface using linear codec at 7.2 kHz, 8.0 kHz or 16.0 kHz sample rate
- Direct interface to 8.0 kHz PCM data stream (A-law or u-law)
- North American and International Dialing/Telephony dialing functions available
- Facsimile protocol layer (T.30 with ECM/BFT) available
- Facsimile service class 1 command sets (T.31 and EIA-578) available
- Facsimile service class 2 command sets (T.32, EIA-592 and industry standard fax class 2) available.
- System can be combined with V.34fax facsimile modulations and startup procedures (V.8 and V.8bis).
ITU Recommendation V.17
V.29
ITU-T V.29 defines the modulation methods and operating sequences for a 9600 bps modem used primarily
for use on point-to-point 4-wire leased telephone-type circuits.
This modem is intended to be used primarily on special quality leased circuits, e.g. Recommendation M.1020
[1] or M.1025 [2] circuits but this does not preclude the use of this modem over circuits of lower quality at the discretion
of the Administration concerned (see Notes 1 and 2).
On leased circuits, considering that there exist and will come into being many modems with features designed
to meet the requirements of the Administrations and users, this Recommendation in no way restricts the use of any other
modems.
The principal characteristics of this recommended modem for transmitting data at 9600 bits per second on
leased circuits are as follows:
a) fallback rates of 7200 and 4800 bits per second;
b) capable of operating in a duplex or half-duplex mode with continuous or controlled carrier;
c) combined amplitude and phase modulation with synchronous mode of operation;
d) inclusion of an automatic adaptive equalizer;
e) optional inclusion of a multiplexer for combining data rates of 7200, 4800 and 2400 bits per second (see
2 Line signals
2.1 The carrier frequency is to be 1700 ± 1 Hz. No separate pilot frequencies are provided. The power levels used
will conform to Recommendation V.2.
Features
- Fully compliant with ITU recommendations
- Modular software suite available with controller code
- Optimized for high performance on leading edge DSP architectures
- Multi-tasking environment compatible
- Multichannel implementation
Configurations
- DAA interface using linear codec at 7.2 kHz, 8.0 kHz or 16.0 kHz sample rate
- Direct interface to 8.0 kHz PCM data stream (A-law or u-law)
- North American and International Dialing/Telephony dialing functions available
- Facsimile protocol layer (T.30 with ECM/BFT) available
- Facsimile service class 1 command sets (T.31 and EIA-578) available
- Facsimile service class 2 command sets (T.32, EIA-592 and industry standard fax class 2) available.
- System can be combined with V.34fax facsimile modulations and startup procedures (V.8 and V.8bis).
ITU Recommendation V.29
V.27ter
ITU-T V.27ter defines the modulation methods and operating sequences for a 4800/2400 bps duplex modem designed for use on connections set up
by switching in the general telephone network.
(a) that there is a demand for data transmission at 4800 bits per second over the general switched telephone network;
(b) that a majority of connections over the general switched telephone network within some countries are capable of carrying data at 4800 bits per second;
(c) that a lower proportion of international connections in the general switched telephone network are capable of carrying data at 4800 bits per second;
(d) that other international connections in the general switched telephone network may still support operations at 2400 bits per second using a built-in fallback capability;
unanimously declares the view
that transmission at 4800 bits per second should be allowed on the general switched telephone network. Reliable transmission cannot be guaranteed on every connection or routing and tests should be made between the most probable terminal points before a service is provided. The CCITT expects that developments during the next few years in modern technology will bring about modems of more advanced design enabling reliable transmission to be given on a much higher proportion of connections. The provisions of this Recommendation are to be regarded as provisional in order to provide service where it is urgently required and between locations where it is expected that a reasonably satisfactory service can be given;
that the characteristics of the modem for transmission at 4800 bits per second over the general switched telephone network shall provisionally be the following:
1 Principal characteristics
a) Use of data signalling rate of 4800 bits per second with 8-phase differentially encoded modulation as described in Recommendation V.27.
b) Reduced rate capability at 2400 bits per second with 4-phase differentially encoded modulation as described in Recommendation V.26, Alternative A.
c) Provision for a backward channel at modulation rates up to 75 bauds, use of this channel being optional.
d) Inclusion of an automatic adaptive equalizer.
2 Line signals at 4800 and 2400 bits per second operation
2.1 Carrier frequency
The carrier frequency is to be 1800 ± 1 Hz. No separate pilot tones are provided. The power levels used will conform to Recommendation V.2.
Features
- Fully compliant with ITU recommendations
- Modular software suite available with controller code
- Optimized for high performance on leading edge DSP architectures
- Multi-tasking environment compatible
- Multichannel implementation
Configurations
- DAA interface using linear codec at 7.2 kHz, 8.0 kHz or 16.0 kHz sample rate
- Direct interface to 8.0 kHz PCM data stream (A-law or u-law)
- North American and International Dialing/Telephony dialing functions available
- Facsimile protocol layer (T.30 with ECM/BFT) available
- Facsimile service class 1 command sets (T.31 and EIA-578) available
- Facsimile service class 2 command sets (T.32, EIA-592 and industry standard fax class 2) available.
- System can be combined with V.34fax facsimile modulations and startup procedures (V.8 and V.8bis).
ITU Recommendation V.27ter
V.21
ITU-T V.21 defines the modulation methods and operating sequences for a 300 bps duplex modem designed for use on connections set up
by switching in the general telephone network.
A system of data transmission at a low data signalling rate, such that data could be transmitted over a telephone circuit operated alternatively for telephone calls and data transmissions, using simple input/output equipment and easy operating procedures, would be economical.
The data signalling rate must be such as to allow the use of current types of data sources and sinks, especially electromechanical devices.
The system for data transmission will be duplex, either for simultaneous two-way data transmission or for the transmission of signals sent in the backward direction for error-control purposes. The transmission must be such that use can be made of normal telephone circuits, and this applies both to the bandwidth available and to the restrictions imposed by signalling in the telephone networks.
The two correspondents are brought into contact by a telephone call, and the circuit is put into the data-transmission position:
a) manually by agreement between the operators, or
b) automatically.
For these reasons, the CCITT
unanimously declares the following view
1 Data transmission may take place at low data signalling rates on telephone calls set up on switched telephone circuits (or on leased telephone circuits).
2 The communication circuit for data transmission is a duplex circuit whereby data transmission in both directions simultaneously is possible at 300 bit/s or less.
The modulation is a binary modulation obtained by frequency shift, resulting in a modulation rate being equal to the data signalling rate.
Note - Attention is drawn to the fact that there may be in operation some old-type V.21 modems for which the maximum data signalling rate is 200 bit/s.
3 For channel No. 1, the nominal mean frequency is 1080 Hz.
For channel No. 2, it is 1750 Hz.
The frequency deviation is ± 100 Hz. In each channel, the higher characteristic frequency (FA) corresponds to a binary 0.
Features
- Fully compliant with ITU recommendations
- Modular software suite available with controller code
- Optimized for high performance on leading edge DSP architectures
- Multi-tasking environment compatible
- Multichannel implementation
Configurations
- DAA interface using linear codec at 7.2 kHz, 8.0 kHz or 16.0 kHz sample rate
- Direct interface to 8.0 kHz PCM data stream (A-law or u-law)
- North American and International Dialing/Telephony dialing functions available
- Facsimile protocol layer (T.30 with ECM/BFT) available
- Facsimile service class 1 command sets (T.31 and EIA-578) available
- Facsimile service class 2 command sets (T.32, EIA-592 and industry standard fax class 2) available.
- System can be combined with V.34fax facsimile modulations and startup procedures (V.8 and V.8bis).
ITU Recommendation V.21
