Toshiba V.90 - Manual (Page 80)

Test Function
Testing procedure
61
2 Enter the following AT commands to select the local/analog/
loopback test:
AT&T1
You are now in the online state.
3 Enter characters from the keyboard as desired.
The characters you enter should be displayed on the screen.
4 Enter the escape code as follows to return to the command
state from the online state.
+++
Receive OK.
5 Enter the following AT commands to terminate the test:
AT&T0
Receive OK.