Congestion control in BBN packet-switched networks

Introduction 1.1 The Origins of Congestion We define congestion in a packet network to be the state where performance degrades due to the saturation of a network resource. Resources required by packet networks encompass the communication links between packet switches and the switches' computational resources--processor cycles and buffer memory. The degradation arises when the network expends resources in doing work it can' t complete. Congestion arises for a number of reasons. The network may simply be underconfigured for the offered load. Underconfiguration can result from temporary failures elsewhere in the network, or it may be a busy-hour occurfence, hence not worthy of reconfiguration. In a network whose resources have different capacities, when all the capacity of a highspeed link is directed over a lower-speed link, that link cannot carry the offered load. Such over-demand can also arise due to the funnel- ing together or flows from several incoming links to an outgoing link.