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MultiModemISDN User Guide
Using AT Commands to Operate the MTA128ST-USB
You can configure and operate the MTA128ST-USB entirely with AT commands if you like. But
remember, you can issue AT commands only from a terminal or from a computer running a
communications program in terminal mode. This section describes how to use AT commands for basic
operations, such as calling, answering a call, and hanging up.
Modes of Operation
The MTA128ST-USB has three modes of operation. They are:
• Offline Command Mode
—The MTA128ST-USB communicates with the terminal or computer
and responds to AT commands. There is no data communications link with a remote device.
• Data Mode
—The MTA128ST-USB enters data mode when it makes a successful data
communications link with a remote device. In data mode, the TA can send and receive data,
but it does not respond to AT commands. Instead it treats them as data and transmits them to
the remote device.
• Online Command Mode
—The MTA128ST-USB responds to AT commands while maintaining
a data communications link; however, transmission of data is suspended. To enter online
command mode from data mode, type the escape sequence +++AT<cr>. To return to data
mode from online command mode, type ATO<cr>.
Making a Call
Before you can place a data call, configure the MTA128ST-USB for the local switch type, serial port
speed, and the data type of the ISDN device you want to call. See Chapter 3, Software Installation
and Configuration.
Dialing
To dial a number using AT commands, you must first start a data communications program. In the
program’s terminal mode, type ATDxxxxxxx<cr>, where xxxxxxx is the telephone number you want
to dial, and <cr> is the carriage return character that is sent when you press the ENTER key, e.g.,
ATD7853500<cr>. The dial string can contain up to 80 characters.
To place an ML-PPP call, use an ampersand character (
&
) to join two telephone numbers, e.g.,
ATD7853500&7853502<cr>. The telephone numbers can be the same or different. Using this
method, two B-channels are activated to transmit data at an aggregate speed of 128 Kbps.
To make it easier to read the dial string, you can use hyphens, spaces or parentheses. These
characters are ignored by the MTA128ST-USB. For example, the MTA128ST-USB would read the
following dial strings the same way:
ATD17637853500 <
cr
>
ATD 1-763-785-3500 <
cr
>
ATD 1 (763) 785-3500 <
cr
>
Channel Bundling Flag Dialing
The command AT&Jn is used to indicate whether outgoing calls should be made on two B-channels
by default. The command AT&J1&W0<cr>, configures the TA to place a call, dialing on two B-channels
by default. If no second number is given in the dial string, that single number is dialed twice. This
compensates for the interworking issues with Windows 95. On the other hand, if the user explicitly
indicates two numbers in the dial string, then two numbers are dialed (e.g.,
ATD7853500&7853502<cr>). The command AT&J0&W0<cr>, disables automatic call bundling. Note
other valid characters joining two telephone numbers include a plus sign (+), and an exclamation mark
(!).