Testing the Business Modem using AT&Tn 14-5Digital LoopbackTesting (AT&T3)This test can help you locate a problem with a remote device or with thetelephone line. The figure below shows the data flow during DigitalLoopback (DL) testing.1 Send the command AT&M0&N3S14.0=0 to the modem to prepare fortesting.This command disables error control, fixes the connection rate at 2400bps, and makes the Business Modem return to command mode whenyou type +++.2 Establish a connection with the remote device.3 Send the Business Modem the escape code, +++, to bring it back toCommand mode.4 Send AT&T3 to the modem to enter Digital Loopback mode.5 Have the remote user type a short message. It will be looped back by yourBusiness Modem's transmitter for verification on the remote user'sscreen. You will not see the message or any other data.6 When the remote user has completed the test, send the escape code,+++, and then AT&T0 to end the test.Alternatively, you can end the test by sending ATH or ATZ. Be careful,because ATZ resets the modem in addition to ending the test.In any case, the Business Modem responds OK. If the modem sends anERROR message, you have issued an invalid command.7 Send AT&M4, unless you used ATZ.
