Signal transmission control protocol sources with the objective of managing queue utilization and delay is actually a feedback control problem in active queue management (AQM) core routers. This paper extends AQM control design for single network systems to large-scale wired network systems with time delays at each communication channel. A system model consisted of several local networks is first constructed. The stability condition guaranteeing overall stability is subsequently derived using Lyapunov stability theory. The results developed have been successfully verified on a network simulator.
Random-early-detection (RED) is widely applied in network nodes for congestion control. It randomly drops packets to prevent congestion from occurring, while keeping high bandwidth utilization at the same time. Unfortunately, RED provides little protection against aggressive flows from consuming most of the bandwidth. BF-RED was introduced in the literature to address the problem, but it calculated packet drop history only in number, ignoring the sizes of the dropped packets. That is, BF-RED still suffers bandwidth unfairness when packet size varies. In this paper, we introduce a new algorithm named bandwidth-fair-considering-packet-size-RED (BF-PS-RED) to further improve bandwidth fairness. Similar to BF-RED, BF-PS-RED raises the dropping probability according to its drop-weight, but it further adjusts dropping probability according to its average packet size. The simulation shows that BF-PS-RED can effectively guarantee fairness not only in packet numbers but also packet sizes.
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