Use the LOOP LINE command to initiate loopback testing of X25 lines
 only.  The parameters are optional and can be entered in any order.
 Before beginning loopback testing of an X25 line, use the SET LINE
 command to set the STATE SERVICE and CONTROLLER LOOPBACK parameters
 for internal loopback testing or the STATE SERVICE and CONTROLLER
 NORMAL for all other loopback testing.

 LOOP    LINE line-id        COUNT number
                             LENGTH number
                             WITH
                               MIXED
                               ONES
                               ZEROS