During the past few years, the study of internetworking systems has been a very active research area. There is an increasing need for novel protocol mechanisms capable of ensuring proper interwork operation for high-speed systems. These systems consist of a high-speed network which internetworks a few low-speed LANs. Proper coupling of subnetworks having a large difference in transmission speeds has been identified as one of the major challenges to overcome. In this paper, we propose a novel congestion control mechanism, specially designed for high-speed internetwork systems. The design of this control mechanism is done, by keeping in mind that a fair and simple control mechanism is necessary when dealing with high-speed communications systems. A performance evaluation of this mechanism is carried.