Performance of the revised routing metric in the ARPANET and MILNET

In the summer of 1987, a revised routing metric that makes better use of satellite lines and damps routing oscillations was introduced in the ARPANET and MILNET. The networks continue to use shortest-path-first routing, but the method of calculating link cost has changed. The revised metric changes its characteristics as the traffic level changes. Under light loads the metric behaves approximately the same as a delay-based metric and avoids satellite trunks. Under heavy loads the metric is based on available capacity and makes full use of satellite bandwidth. The revised metric substantially improves network performance by reducing delay and increasing the network effective capacity. These improvements are illustrated by a comparison of measurements taken before and after the revised metric was installed. For example, the round-trip delay was reduced by 35% for the European Peak hour on MILNET, and the number of dropped packets due to congestion decreased from around 1000 per day down to virtually zero