Subscriber modems typically transport data within ATM cells or Ethernet packets. Therefore, chip makers often test for the passing of data using both protocols. Once ADSL chip sets are assembled into modems, modem makers perform similar tests to those performed by chip makers. An ADSL driver IC can supply as much as 400 mA of peak current. The system tests for both physical parameters and for data transport.
Tests begin through the chip set's loopback feature, which verifies modem functionality.
After the loopback tests, Alcatel performs several parametric tests. One such test is for multitone power ratio. In this test, a manufacturer compares the power that the UUT produced with all tones off to the power produced with all tones on. In an idle channel noise test. Each ADSL product manufacturer has to decide how much noise is acceptable.