In the past few years, there has been an increasing need for novel protocol mechanisms capable of ensuring the proper operation of internetwork systems consisting of a high-speed MAN linking together lower-speed LANs. The proper coupling of subnetworks having a big difference in transmission speed has been identified as one of the main challenges to overcome. Due to the LAN to MAN speed disparity, the buffer space of the internetworking units is more likely to be overflowed during periods of high inter-LAN traffic activity. In this paper, we propose a novel congestion control scheme specially designed for LAN/MAN internetwork systems. The scheme aims to control the use of the buffer space of the internetworking units. The mechanism is based on the definition of a virtual partitioning of the buffer space among all the communicating inter-LAN traffic streams. This scheme therefore allows for a flexible and efficient sharing of the critical system resources, i.e. the buffer space of the internetworking units. We have conducted a performance study to evaluate the quality of service provided to the various streams, as well as the overhead needed for the scheme to operate. © 1995.