AT Commands Reference Manual - wireless netcontrol GmbH

Chapter 3: AT Commands Reference
Call Control
Managing a Circuit Switched Call
Basic managing of CS (Circuit Switched) calls in H24 follows the ITU V.25ter recommendation.
Specific details for each call control operations are found below in the Call Control AT
Commands section.
The D, A, and H basic AT commands are used for basic Dialing Answering and Releasing CS
calls.
The main behavior difference between established voice and data call is the working mode.
Once a voice call is established the working mode remains being command mode while once a
data call is established the working mode is data mode.
• Data Mode: In this mode, once the H24 has established a link with the remote modem, it does
not respond to any data passing through it (except for the Escape Sequence search). The H24
becomes a transparent link, connecting the terminal with the remote side.
• Command Mode: In this mode, the H24 responds to the AT commands issued by the
terminal. This is the default working mode.
In case of a data call, it is possible to switch between the working modes. Though the command
mode is now slight different and it behaves as “online command mode”. More of that is described
below and in the ITU V.25ter.
Learn mode on simultaneous working modes in the Multi channeling section.
Voice call allows extended features such as call manipulation multi party and sending DTMF
tones. See below the +CCWA and +CHLD AT commands.
Call status and information can be received by using the +CLCC command.
More information on fax calls in the Dial command and Fax sections.
Simple Circuit Switched Dialing
To dial a data call, send ATD for example ATD8765555
After issuing the Dial command, and if the remote modem answers the call, the two modems
negotiate to establish the transmission speed and other parameters for the data connection. After
successful negotiation process, the message, "CONNECT" is received. If the other phone line is
busy, the message "NO CARRIER" is received.
If the other modem does not answer, the message "NO CARRIER" is received.
Once a connection has been established, the modem is ready to immediately begin transmitting
and receiving data. This may vary from sending messages to each other, sending or receiving
files, logging on to an information service, or any other data communication task you wish to
perform.
To dial a voice call, send ATD; for example ATD8765555;
Once request is sent to the network the message, "OK" is received; once call is connected a 2nd
message "OK" is received. In case user wishes to receive “CONNECT” instead of “OK” in the
2nd message, it can be configured using the +MDC command. If the other phone line is busy, the
message "NO CARRIER" is received.
April 15, 2010 H24 - AT Commands Reference Manual 3-9