ZyXEL U-1496S Plus User Guide - Page 10

V.25bis Command Set

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A leased-line phone service is also available from phone companies in a 4-wire form. Here the transmitting and receiving signal each uses a separate 2-wire pair and thus no echo problem will result. Normally, no DC current feeding, ringing, or dialing function is provided on a leased line. There is also the case of a 2-wire leased line which is a permanent 2-wire connection. INTELLIGENT MODEM In the old days, modem functions, settings, and operations were simple and everything was controlled by manual switches, either internal or external, or by wire-strapping settings. No computer control was provided. An intelligent modem has all its functions, including dialing and answering, controllable by the computer or terminal it is connected to, through the same RS-232 serial interface used for data connection. An intelligent modem operates in one of two states - the command state and the data state. In command state, the modem interprets data received from the serial interface as "commands" and send back an action result in response. In data state, the modem modulates the data received from the serial interface and sends the demodulated data to the serial interface as received data. The user needs to know whether the modem is in the command state or data state and how to switch it. AT COMMAND SET The AT command set is the industry de facto standard used to control a modem in command state. It got its name from the fact that every command line has a prefix "AT". AT commands were first used in the Hayes Smartmodem (R) and hence adopted by other modem manufacturers and communication software writers. The original set of AT commands such as dialing, answering, etc., is used by everyone else and is standardized. The AT command set is extended by each modem manufacturer for control of ever-increasing modem functions and capabilities. This "extended" or "enhanced" command set is not standardized whatsoever. The AT command set is used only with an asynchronous serial data interface. ZyXEL has defined a set of extended AT commands to support many of its unique functions and features. V.25bis COMMAND SET V.25bis is a set of auto-dialing commands defined by the CCITT. V.25bis supports both synchronous and asynchronous data

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A leased-line phone service is also available from phone companies in a 4-wire form. Here the
transmitting and receiving signal each uses a separate 2-wire pair and thus no echo problem will
result. Normally, no DC current feeding, ringing, or dialing function is provided on a leased line.
There is also the case of a 2-wire leased line which is a
permanent 2-wire connection.
INTELLIGENT MODEM
In the old days, modem functions, settings, and operations were
simple and everything was controlled by manual switches, either
internal or external, or by wire-strapping settings. No computer
control was provided.
An intelligent modem has all its functions, including dialing and
answering, controllable by the computer or terminal it is
connected to, through the same RS-232 serial interface used for
data connection.
An intelligent modem operates in one of two states - the command
state and the data state. In command state, the modem interprets
data received from the serial interface as "commands" and send
back an action result in response. In data state, the modem
modulates the data received from the serial interface and sends
the demodulated data to the serial interface as received data.
The user needs to know whether the modem is in the command state
or data state and how to switch it.
AT COMMAND SET
The AT command set is the industry de facto standard used to
control a modem in command state. It got its name from the fact
that every command line has a prefix "AT".
AT commands were first used in the Hayes Smartmodem (R) and hence
adopted by other modem manufacturers and communication software
writers. The original set of AT commands such as dialing,
answering, etc., is used by everyone else and is standardized.
The AT command set is extended by each modem manufacturer for
control of ever-increasing modem functions and capabilities. This
"extended" or "enhanced" command set is not standardized
whatsoever.
The AT command set is used only with an asynchronous serial data
interface.
ZyXEL has defined a set of extended AT commands to support many
of its unique functions and features.
V.25bis COMMAND SET
V.25bis is a set of auto-dialing commands defined by the CCITT.
V.25bis supports both synchronous and asynchronous data