User's Manual
V34bis Fax-modem - AJ 2885 P
AJ 2885 P - Page 10
1. Introduction
This chapter is to familiarize the user with the operation of a modem. Note: <CR> indicates that
the user must press the return key after a command sequence.
1.1. The
modem
A modem is a device that allows two terminals (DTE, PC...) to communicate via a
telecommunication line (phone line).
The data is converted by the modem into electrical signals adapted to the telecommunication
network. This conversion is called modulation and demodulation.
Various conversion techniques have been developed to speed-up the data flow. The different
speeds are particular to each type of modulation: 300 bps in V21, 2400 bps in V22bis, 14400
bps in V32bis, and 33600 bps in V34.
1.2. The
modem-fax
A fax device transmits scanned images via the telephone network.
In addition to traditional fax machines, the fax modem also allows transfer of computer data
such as:
•
ASCII files from a text processor,
•
PCX or TIF files from a graphic editor, etc.
The Fax mode operation is controlled by a fax software which:
•
Converts files to T4 format (fax graphic format),
•
Transmits and receives faxes,
•
Supervises fax modem operation.
Supervision of the fax modem is carried out by a standard protocol: "Asynchronous Facsimile
DCE Control Standard", Class 1 Service - TR 29.2188 or Class 2 Service - TR 29.2388.
The computer equipped with a fax modem will be able to transmit and receive fax in Group III
mode:
•
At about one A4 page per minute,
•
In fine or standard resolution.
See chapter 5 for the list of modem class 1 and 2 commands.
1.3.
Calling modes - dialing
The modem can be in 2 modes:
Send or calling,
Receive or answer.
1.3.1. Calling
Mode
The modem switches to originate mode when the dial command:
ATD 37487126
is sent
(example number).
The calling modem then waits for the remote modem to respond.
1.3.2. Answering
Mode
The modem switches to answer mode when it detects ringing on the phone line.
