Abstract: An expert system method is disclosed for analyzing window protocol-based data flows in a data communications network. The method includes the use of a data flow efficiency state variable S which is a binary number having at least three bits which reflect the number of packets transmitted by a node, the queuing of packets within a node, and the congestion of the packets within the node or in the node connected to the node of interest. After having assigned a value to the state variable, a knowledge base is accessed containing network problem determination recommendations for optimizing data flow efficiency within the network.