Chapter 9 - Fax Operation
9-2
image data transfer. The computer handles image data creation, capturing,
conversion, compression, decompression, retrieving, and storing.
ITU-T T.30 Fax Protocol
The ITU-T T.30 fax protocol is known as the G3 fax handshake signals and
procedures. The modem takes full control of this protocol - initiating and
terminating fax calls, managing the communication session, and transporting the
image data. Therefore, the modem relieves the computer fax software of the T.30
protocol handling.
The Omni 288S allows for fax speeds up to 14400 bps when transmitting to a fax
machine which complies with the G3 fax standard. Speeds will fall back to
12000, 9600, or 7200 bps in poor line conditions. When connecting to a non-G3
fax device, the Omni 288S allows for fax speeds up to 9600 bps and will
automatically fall back to 7200, 4800, and 2400 bps if the line quality is poor.
Fax Command sets
The Omni 288S supports four command sets for fax operation:
Class 1 command set
TIA PN-2388 Class 2 command set
TIA 592 Class 2.0 command set
ZyXEL Extended Fax AT command set
Defining the Fax Command Sets
The EIA Class 1 and Class 2 fax commands are a set of AT fax commands
defined by EIA/TIA (Telecommunications Industry Association) for controlling
fax/modems from a computer through the serial RS-232 interface. All fax/modems
and fax software supporting this standard will be compatible with each other.
Class 1 commands control how the modem does on-line negotiation while Class 2
commands allow the modem to do many negotiations at once. The Class 1
protocol uses the modem to transmit fax data only. The complete organizational
overhead for this protocol is handled by the connected computer. The Class 1
command set is also called the TIA-578 standard.
Several revisions of the class 2 standard exist. Implementations conforming to
different revisions may not work together. A formally approved version is the
Class 2.0 command set, also called the TIA-592 standard.
