Abstract: The present invention utilizes hardware and/or software, in combination with a personal computer and its peripheral devices (i.e., storage media, peripheral control, video display and the like) to monitor communication links. The personal computer, to operate properly, must operate in an interactive communication mode. But, to avoid "lock-up" of a communication link which is being monitored, the personal computer must be "invisible" to equipment on the communication link. Hardware is disclosed which permits the personal computer to operate in its interactive communications mode while being "invisible" (non-interactive) to equipment on a communication link being monitored.