Absrracr-The new ARPANET routing algorithm is an improvement test results. This paper is a summary of our conclusions only; over the old procedure in that it uses fewer network resources, operates on for more complete descriptions of our research findings, see more realistic estimates of network conditions, reacts faster to important our internai reports on this project [3]-[5]. network changes, and does not suffer from long-term loops or oscillations. In the new procedure, each node in the network maintains a database 11. PROBLEMS WITH THE ORIGINAL ALGORITHM describing the complete network topology and the delays on all lines, and uses the database describing the network to generate a tree representing the me original ARPANET routing algorithm and the new verminimum delay paths from a given root node to every other network node. sion both attempt to route packets along paths of least delay. Because the traffic in the network can be quite variable, each node The total path is not determined in advance; rather, each node periodically measures the delays along its outgoing lines and forwards this decides which line to use in forwarding the packet to the next information to all other nodes. The delay information propagates quickly through the network so that all nodes can update their databases and node. In the original approach, each node maintained a table continue to route traffic in a consistent and efficient manner. An extensive series of tests were conducted on the ARPANET, showing that line overhead and CPU overhead are 60th less than two percent, most nodes learn of an update within 100 ms, and the algorithm detects congestion and routes packets around congested areas. T I.