Method and apparatus for analyzing nodes on a computer network

Abstract

Disclosed is a system that monitors the signal strength of each transmission by a node on a LAN cable of a local area network and determines the location of the node sending the signal. This system has a monitor at each end of the LAN cable, with one of the monitors typically being located in a computer node attached to the cable. When an information frame is sent on the cable, each of the monitors records the signal strength of the frame preamble and the source address contained within the frame. The distance to the node from a first end of the cable is calculated based on the signal strengths. A LAN collision trap circuit transmits a pseudo frame signal, of maximum length, periodically and monitors any collision or jam signals that occur during the pseudo frame. If a collision or jam is detected, a collision/jam information bit and the signal strength and time of the collision or jam, relative to the beginning of the pseudo frame, is recorded in a FIFO. Software within the system reads this FIFO, and determines, based on the collision/jam information bit and time, if a valid early collision, an invalid late collision or a jam was detected. If a late collision or jam was detected, the software determines the defective node by comparing the signal strengths of the collision or jam signal to the strengths measured by the LAN level monitor and displays the address and location of the defective node that caused the late collision or invalid jam.