Congestion control in interconnected LANs

The reasons why congestion control is more difficult in interconnected local area networks (LANs) than in conventional packet nets are examined. The flow and congestion control mechanisms that can be used in an interconnected LAN environment are reviewed. The focus is on congestion control (that is, prevention of internal congestion); however some of the proposed schemes require the interaction of flow and congestion control. The schemes considered are dropping packets; input buffer limit, i.e. a limit on the number of input packets (i.e. packets from local hosts) that can be buffered in the packet switch; the use of choke packets, in which, whenever a bridge or router experiences congestion, it returns to the source a choke packet containing the header of the packet traveling in the congested direction and the source, on receiving the choke packet, declares the destination congested, and slows (or stops altogether, for a period of time) traffic to that destination; backpressure, which is the regulation of flow along a virtual connection; and congestion prevention, whereby a voice or video connection is accepted only if there is enough bandwidth (in a statistical sense) in the network to support it.<>