Recently researchers have proposed active queue management (AQM) mechanisms as a means of better managing congestion at the bottlenecks
inside the network. Random Early Detection (RED) mechanism has been
proposed to control the average queue size at the congested routers. It has been shown that the interaction between an RED gateway and TCP connections can lead to period doubling bifurcation and chaos. In this paper we extend this model and study the interaction of the RED gateway with TCP and UDP connections, using a discrete-time model.
First, we show that the presence of UDP traffic does much more than simply taking away the available capacity from the TCP connections. In fact it fundamentally changes the dynamics of the system. Second, with the help of bifurcation diagrams, we demonstrate the existence of nonlinear phenomena, such as oscillations and chaos, as the parameters of the RED mechanism are varied. Further, the presence of UDP traffic tends to stabilize the system in the sense that bifurcations and chaos are delayed in the parameter
region. We investigate the impact of various system parameters on the stability of the system, present numerical results, and validate our
analysis through ns-2 simulation.
The efficient management of the radio resource of a 3-G system is important from an operator's perspective. This, however, cannot be the only concern when quality of service (QoS) negotiations have been made for various users and the operator has to uphold these. This leads to a fairness objective that the operator has to keep in mind. In this paper we outline a scheme to perform packet-level scheduling and resource allocation at the wireless node that takes into account the notions of both efficiency and fairness and presents a means to explore the trade-off between these two notions. As a part of this scheme we see the scheduling problem as deciding not just the packet transmission schedule but also the power allocation, the modulation and coding scheme allocation and the spreading code determination since the latter three directly influence the radio resources consumed. Using a utility maximization formulation based on the data-rates that the mobiles can transmit at, we decide on the weights for a weighted proportionally fair allocation based scheduling algorithm. We also show how one can adapt the weights and the algorithm for a time-varying channel. We conclude with a simulation based performance analysis for infinitely-backlogged sources and TCP sources on an EDGE system.
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