Abstract: The processor 10 of the router 1a connects each of a plurality of adjacent routers 1b, . . . , 1n at a predetermined time specified by the timer 14 so as to collect line information of the communication line network A and execute an optimization processing for selecting an optimal communication route. This optimization enables data to be communicated via the communication route closest to a predetermined condition. Consequently, it is possible to improve the through-put of the whole communication line network A. Furthermore, it is possible to avoid imbalance of the local line access rate of the communication line network A, thereby improving the communication quality of the communication line network A.

Abstract: A reference voltage for an analog-to-digital (A/D) converting unit is converted into plural digital values through the effect of the A/D converting unit. A difference between an average value of the digital values and an ideal reference value is derived. If the different is larger than a predetermined allowable value, it is determined that a transient abnormality takes place in an A/D converter system. The last measured reference voltage and its related digital input signal are disallowed to be used as measured values. If detection of a transient abnormality serially takes place predetermined times, it is determined that a constant abnormality takes place in the A/D converter system.