In this paper, we propose a new connection admission control (CAC) algorithm accommodating various classes of traffic, which can easily be implemented in mobile WiMAX system. The proposed CAC algorithm has three characteristics: first, the variation of air capacity is taken into account by measuring the distribution of modulation and coding scheme (MCS) levels offline; second, we estimate the mean and variance of frame occupancy ratio of each QoS flow based on declared traffic descriptors; and third, the admission region is determined to satisfy the target overflow probability in the bufferless model. Through numerical analysis, we show that the accuracy of the proposed CAC is satisfactory.

This paper studies a set of transport equations arising from stochastic models in congestion control. First, we introduce a general framework including both of mixed and extended Markovian loss models. Then we show that there is a unique density solving the general differential equation. For the first time, we provide an explicit form expression for this density and for its mean value. We propose a novel approach to solve a class of associated differential equations.

This paper analyzes the performance of a large population composed of several classes of long lived TCP flows experiencing packet losses due to random transmission errors and to congestion created by the sharing of a common tail-drop or RED bottleneck router. Each class has a different transmission error rate. This setting is used to analyze the competition between wired and wireless users in an access network, where one class (the wired class) has no or small (like BER in DSL) transmission error losses whereas the other class has higher transmission error losses, or the competition between DSL flows using different coding schemes. We propose a natural and simple model for the joint throughput evolution of several classes of TCP flows under such a mix of losses. Two types of random transmission error losses are considered: one where losses are Poisson and independent of the rate of the flow, and one where the losses are still Poisson but with an intensity that is proportional to the rate of the source. We show that the large population model where the population tends to infinity has a threshold (given in closed form) below which there are no congestion losses at all in steady state, and above which there is a stationary limiting regime in which we can compute both the mean value and the distribution of the rate obtained by each class of flow. We also show that the maximum mean value for the aggregated rate is achieved at the threshold.

This paper analyzes the performance of a large population of long lived TCP flows experiencing random packet losses due to both random transmission errors and congestion created by the sharing of a common tail drop bottleneck router. We propose a natural and simple model for the joint throughput evolution of the set of TCP sessions under such a mix of losses. For the case of Poisson transmission errors, we show that the asymptotic model where the population tends to infinity leads to a well defined and tractable dynamical system. In particular, we get the mean value of the throughput of each session as a function of the transmission error rate and the synchronization rate in the bottleneck router. The large population asymptotic model has two interesting and non-intuitive properties: 1) there exists a positive threshold (given in closed form) on the transmission error rate above which there are no congestion losses at all in steady state; 2) below this threshold, the mean throughput of each flow is an increasing function of the transmission error rate, so that the maximum mean value is in fact achieved when the transmission error rate is equal to this threshold. The finite population model and models based on other classes of point processes are also studied. In particular, a sufficient condition is obtained for the existence of congestion times in the case of arbitrary transmission error point processes.

In this paper, we investigate how to design AQM with a low-pass filter (average queuing) in supporting TCP based on the well-known AIMD dynamic model sharing a common bottleneck router. Since we formulate the AQM design problem for the given TCP as a state-space model, we get two interesting and important results: (1) we derive PD-type (proportional-derivative) AQM structure is derive in terms of queue length which supports the conjecture in the literature that the AQM RED is not enough to control TCP dynamic behavior, where RED can be classified as P-type AQM structure; (2) we propose a delay-dependent AQM structure to compensate for delays in congestion measure explicitly from the knowledge of RTT, capacity and number of sources, where the previous AQMs RED, REM/PI and AVQ are delay-independent controls. As one trial to obtain stabilizing gains of the proposed structures, we minimize a LQ (linear quadratic) cost of the transients on average-queue length, average-queue length rate, jitter in the rate and the loss probability. Finally, we illustrate the above theoretical results through ns simulations for TCP Reno.