Patent ID: 7643544

Claim:
A communication quality controller for controlling a link speed to conduct data communication, comprising: means for monitoring, for a predetermined period of time during the data transmission at the link speed, whether or not an error occurs at a period shorter than a noise period changing periodically; means for checking to determine, according to presence or absence of the error taking place during the monitoring period, whether or not there exists a periodic noise period abruptly taking place; and wherein, when the checking means determines that there exists a periodic noise period abruptly taking place, disconnection of an associated communication line is avoided and the data communication is conducted at the link speed, wherein: if there is detected an error quantity exceeding a predetermined threshold value at a period shorter than a periodic noise period, occurrence of the error is determined; and otherwise, occurrence of the error is not determined, wherein the controller further comprises: a counter for counting a number of errors that occur during the predetermined period of time; and a timer for counting from zero up to a second predetermined period of time when an error has occurred during one of the predetermined periods of time, wherein the counter is cleared when no error has occurred during the second predetermined period of time as counted by the timer.