the user-controlled test functions of fcd-2 consist of the following ioopbacks and tests:

    1 main link local analog loopback

    2 data channel remote digital loopback

    3 main link local digital loopback (debug mode only)

    4 main link remote analog loopback (debug mode only)

    5 main link remote digital loopback (debug mode only)

    6 data channel local digital loopback (debug mode only)

    7 bertesting.