ZyXEL Communications COMET 336, User Manual

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42 Fax Operation
8
Fax Operation
The Comet 336 can be used as a fax machine, and this chapter explains how. In the
sections below, we will describe how the modem works as a fax machine, the ITU-T
T.30 fax protocol and the Class 1 and 2 fax commands. The instructions for using the
included modem/fax/voice utility program are included on the software disk. Some
distributors and dealers also include other software with the Comet 336. For help with
such software, refer to the documentation that came with it.
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.
The Comet 336 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 the Comet 336 to the computer. The Comet
336 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, 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 Comet 336 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, the
Comet 336 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 Comet 336 supports four command sets for fax operation:
•
Class 1 command set