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U-90E Data/Fax Modem
11.2 Modem as Fax Machine
Modems can also be designed to include a fax transmitting and receiving function similar
to a fax card. Since the modem's interface with the computer is the standard serial RS-
232 interface, this interface is used for both modem and fax operations. Fax image coding
and decoding must be done in the computer. Modem/Fax, also called fax/modem, can be
either an external stand-alone unit or a plug-in card. External stand-alone units can be
connected to any computer with a standard RS-232 serial port.
Your modem supports Group 3 send and receive facsimile functions. For normal fax
operation, you must connect the modem to a computer, usually a PC. The computer
serves as the input/output device for the fax function. The RS-232 serial connection or the
ZyXEL serial port interface connects your modem to the computer. Your modem uses the
same interface for both data and fax applications. In fax operations, the modem performs
protocol handshaking and image data transfer. The computer handles image data
creation, capturing, conversion, compression, decompression, retrieval, and storage.
11.2.1 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.
You modem allows for fax speeds up to 14400 bps when transmitting to a fax machine
which complies with the V.17 fax standard. Speeds will fall back to 12000, 9600, or 7200
bps in poor line conditions. When connecting to a G3 fax device, your modem 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.
Special Functions
11-2
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