Danny H. K. Tsang

Performance analysis of IEEE 802.11e contention-based channel access

The new standard IEEE 802.11e is specified to support quality-of-service in wireless local area networks. A comprehensive study of the performance of enhanced distributed channel access (EDCA), the fundamental medium access control mechanism in IEEE 802.11e, is reported in this paper. We present our development of an analytical model, in which most new features of the EDCA such as virtual collision, different arbitration interframe space (AIFS), and different contention window are taken into account. Based on the model, we analyze the throughput performance of differentiated service traffic and propose a recursive method capable of calculating the mean access delay. Service differentiation functionality and effectiveness of the EDCA are investigated through extensive numerical and simulation results. The model and the analysis provide an in-depth understanding and insights into the protocol and the effects of different parameters on the performance.

The stochastic knapsack problem

The problem of packing a knapsack of integer volume F with objects from K different classes to maximize profit is studied. Optimization is carried out over the class of coordinate convex policies. For the case of K=2, it is shown for a wide range of parameters that the optimal control is of the threshold type. In the case of Poisson arrivals and of knapsack and object volumes being integer multiples of each other, it is shown that the optimal policy is always of the double-threshold type. An O(F) algorithm to determine the revenue of threshold policies is also given. For the general case of K classes, the problem of the optimal static control where for each class a portion of the knapsack is dedicated is considered. An efficient finite-stage dynamic programming algorithm for locating the optimal static control is presented. Furthermore, variants of the optimal static control which allow some sharing among classes are also discussed. >

Proportional QoS over OBS networks

Optical burst switching (OBS) is considered as an efficient switching technique for building the next generation optical Internet. An offset-time based scheme has recently been proposed in order to provide quality-of-service (QoS) in OBS networks. Unfortunately, the proposed service differentiation has several problems. The aim of this paper is to address these problems and introduce the concept of proportional QoS into this OBS paradigm. An intentional dropping scheme is proposed so as to give a controllable burst loss probability for different service classes. In order to achieve flexible packet delay differentiation, we extend the well-known waited-time-priority (WTP) scheduler to form a burst assembling scheme. Simulations are conducted to evaluate the performance of our proportional QoS provisioning within OBS networks in terms of burst loss probability and packet delay.

Optimal circuit access policies in an ISDN environment: a Markov decision approach

The problem of determining optimal access policies for circuit-switched networks that support traffic types with varying bandwidth requirements is addressed. The authors suppose that the network supports K classes of calls where each class is determined by a fixed route and a bandwidth requirement. A Markov decision process (MDP) approach is used to obtain optimal access policies for three models: the flexible scheme access-port model where a single link is shared; the contiguous scheme access-port model where wideband calls are required to occupy specific contiguous regions of the TDM frame; and the network-access model where a call holds several channels in different links simultaneously. Both linear programming and value-iteration MDP algorithms are coupled with a novel state descriptor in order to locate the optimal policy for reasonable-size problems (several T1 carriers in parallel for the access-port case, and small networks of T1 carriers for the network-access case). >

Large-scale cooperative caching and application-level multicast in multimedia content delivery networks

The Internet and multimedia technologies have greatly changed our lives. With the increasing popularity of multimedia entertainment applications over the Internet, innovative infrastructures and technologies are needed to efficiently distribute the surging amount of multimedia contents. Content delivery networks provide an intermediate layer of infrastructure that helps to deliver the contents from content providers to a large community of geographically distributed users. Cooperative caching and application-level multicast are two technologies that can be implemented in a multimedia content delivery network for delivering on-demand and live multimedia contents respectively. This article introduces the ideas and approaches of implementing cooperative caching and application-level multicast under a hierarchical architecture to achieve large-scale multimedia content delivery.

Algorithms to determine exact blocking probabilities for multirate tree networks

A circuit-switched network consisting of multiple-access links connected to a common link is considered. Each call requires circuits on one access link and on the common link. The network supports multiple classes of calls where each class specifies a bandwidth requirement, an arrival rate, and a holding-time distribution. Based on a product-form solution for these networks, four algorithms are developed to determine the exact blocking probability for each of the classes. The first two algorithms are based on convolution, the third on the fast Fourier transform, and the fourth on a recursion due to J.S. Kaufman (1981) and to J.W. Roberts (1981). Complexity bounds and numerical results demonstrate that these algorithms can determine blocking probabilities in reasonable CPU time for networks with thousands of circuits. >

Distributed Power Allocation Algorithm for Spectrum Sharing Cognitive Radio Networks with QoS Guarantee

In this paper we study the distributed multi-channel power allocation for spectrum sharing cognitive radio networks with QoS guarantee. We formulate this problem as a non- cooperative game G MCPA-C with coupled strategy space to address both the co-channel interference among secondary users and the interference temperature regulation imposed by primary systems. We investigate the properties of Nash equilibrium (N.E.) for our G MCPA-C , including the existence and QoS provisioning. Furthermore, we derive a layered structure by applying the Lagrangian dual decomposition to G MCPA-C and design a distributed algorithm to find the N.E. via this structure. Simulation results are presented to show both the validity of our game theoretic model and the performance of our proposed algorithm. Finally, we incorporate the Pigouvian taxation into our algorithm to improve the efficiency of N.E. when social optimality is considered.

Performance Study of Power Saving Classes of Type I and II in IEEE 802.16e

The IEEE 802.16e standard introduces two types of sleep modes which perform very differently under different traffic types: power saving classes of type I based on binary-increasing sleep window size and power saving of type II using constant sleep window size. This paper provides simple but accurate analytical models capable of calculating the power efficiency and packet access delay for the two power saving types. In addition, a comparison of the energy efficiency and delay performance between the two power saving types is reported. By means of the proposed model and evaluation, we point out the trade-off between these two types and suggest a power switching scheme to obtain optimal power efficiency under different traffic conditions. Numerical and simulation results are provided for validation of our models

A novel approach to estimating the cell loss probability in an ATM multiplexer loaded with homogeneous on-off sources

Estimating the cell loss probability in an ATM multiplexer is one of the most important problems concerning congestion control and bandwidth management in an ATM-based BISDN. We propose a new approach to estimating the cell loss probability in an ATM multiplexer. We use the Markov modulated deterministic process (MMDP) to approximate the actual arrival process and then model the ATM multiplexer as an MMDP/D/1/K queueing system. Using queueing analysis, we derive a formula for the cell loss probability expressed in terms of the limiting probabilities of a Markov chain. We propose two approximation methods based on the results of the analysis. The actual arrival process is approximated by an (M+1)-state MMDP in the first method and by a two-state MMDP in the second. The major advantages of both methods are simplicity, computational efficiency, and numerical stability. The most attractive feature of the second method is that the cell loss probability can be expressed in closed form. Numerical and simulation results show that the first method is sufficiently accurate for all cases in which burst-level congestion is the main contributing factor to cell loss, while the closed-form formula is sufficiently accurate for applications where the average burst length is large (such as large file transfers, image retrievals, etc.). >

Estimation of the cell loss ratio in ATM networks with a fuzzy system and application to measurement-based call admission control

An important parameter in asynchronous transfer model (ATM)-based network design and management is the cell loss ratio (CLR) in ATM multiplexers. It is a key parameter to many vital functions in the network such as call admission control (CAC), bandwidth allocation, etc. However, the CLR depends usually on many unknown and unpredictable traffic parameters such as input traffic correlations. In this paper, we propose a simple and robust fuzzy-based algorithm to predict the CLR in large-sized systems based on both a small amount of information from small-sized systems, and the asymptotic behavior for very large systems. Unlike the model-based approaches, our approximation avoids the problem of assuming any traffic parameters or arrival process. This algorithm is used with real-time traffic measurement to propose an effective measurement-based call admission control framework for ATM networks.