When reading this object, system detects the quality of line connecting the port. Detect whether the line is broken or short circuit or not. The meaning of the obtained value: Return value=N*10000000+M N stands for the line state (0: perfect; 1: break; 2: short circuit) M stands for the location of the break or short circuit in the line(distance from the switch port, in metre) If the line is perfect, the value is zero.