> 2.9.2 | CSD call handling – general instructions

> Basically, the steps to make voice or a data call are quite similar. The most significant difference is that during a voice call the module is always in command mode, but in a data connection it may either be in command mode (used to send AT commands) or in data mode (used to transfer data).
> Once a data connection is established, the ME first enters the data mode (online mode). With the escape sequence +++ you can switch from data to command mode without dropping the line. The command ATO returns from command to data mode.
> The escape sequence must be preceded and followed by a pause of at least 1000 ms. The +++ characters must be entered in quick succession, all within 1000 ms.
> To end a call, the caller or the called party may use the commands ATH or AT+CHUP. The response to ATH and AT+CHUP is “OK” while the remote party is given “NO CARRIER”.
> To verify the reason of call release, the command ATS18 can be used.