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In this dissertation, the traffic control functions involving the connection admission con-trol and the traffic policing for multimedia high-speed networks are studied by employing the neural/fuzzy intelligent techniques or a sophisticated computation algorithm, including a neural fuzzy connection admission controller, a power-spectrum-based neural-net connection admission controller, a fuzzy increment controller, a neural fuzzy increment controller and a enhanced traffic marker. Both ATM and IP networks which can be utilized to construct the multimedia high-speed networks are considered in this dissertation. The CAC schemes which make the admission control decisions according to the time-domain and frequency-domain traffic parameters are both discussed where the intelligent techniques are chosen to implement the CAC controllers. Also, the enhanced algorithms which implement the traffic policing function by incorporating the intelligent techniques and a elaborate compu-tation procedure into existing algorithms for ATM and IP networks respectively are both well explored.

In Chapter 3, a neural fuzzy connection admission control (NFCAC) scheme which based on the time-domain traffic parameters and provides QoS guarantees for ATM networks is proposed. The NFCAC scheme combines the linguistic control capability of a fuzzy logic controller and the learning ability of a neural network. This type of integrated neural fuzzy system can automatically construct a rule structure by learning from training examples

and can self-calibrate parameters of membership functions. It not only provides a robust framework to mimic experts’ knowledge embodied in existing traffic control techniques but also constructs intelligent computational algorithms for traffic control. It can be easily trained and enhances system utilization. Simulation results show that the proposed NFCAC scheme provides system utilization about 32% and 11% higher than the EBCAC and FLCAC schemes proposed in [10] and [18], respectively, and the NFCAC scheme requires only a fraction of the 103 order and the 101 order of training cycles, consumed by the NNCAC scheme proposed in [23] and RBFCAC scheme, respectively. An NFCAC scheme such as the one introduced here may be the answer to the problem of designing a coherent call admission controller for ATM systems.

In Chapter 4, we propose a power-spectrum-based neural-net connection admission con-trol (PNCAC) scheme for ATM networks. The PNCAC method adopts the converted power-spectrum parameters of traffic source to represent its traffic characteristics and uses neural network to implement the connection admission control. The frequency-domain power-spectrum parameters of traffic source possess additive property and can capture the cor-relation and burstiness behavior more than the time-domain parameters such as peak rate, mean rate, and peak rate duration. The neural network has the learning/adapting capabili-ties so that the boundary of the decision hyperplane for the connection admission control can be adjusted optimally and dynamically. Simulation results show that the proposed PNCAC enhances significantly the system utilization while fulfilling QoS requirements. Not only is it superior to the conventional equivalent capacity CAC scheme (ECCAC), it also obtains more flexibility and robustness than Hiramatsu’s NNCAC.

However, the practical traffic characteristics of multimedia services in broadband net-works may change very fast and abruptly with large volume. Also, several researches demon-strate that the multimedia traffic possesses self-similar or chaotic property, and present a

long-range dependence (LRD). The conventional traffic control algorithms based on current system performance measures may not perform well because of the fast varying dynamic traffic; the control decision would be obsolete and inappropriate due to delayed react to such a fast dynamic traffic. It is necessary to capture the next-step system performance, that is, the predicted information about the system status due to traffic change should be provided. Accordingly, a predictive intelligent traffic controller for broadband multimedia systems could be proposed as the future work for the CAC. It considers predicted system performance measures, instead of present ones, to well capture the oncoming effects in the future, besides also adopting the neural fuzzy network for the CAC decision making as well as the fuzzy logic controller for both of the equivalent capacity estimation of the new call and congestion estimation of the system. A pipelined recurrent neural network with extended recursive least square learning algorithm (PRNN/ERLS) [61], [62], which can efficiently re-duce the prediction error for the statistical fluctuations of the system, could be employed to implement the predictors to well attain the advance information of the system. It is expected that the predictive intelligent traffic controller with predicted system measured statistics would achieves better performances than that of the conventional CAC schemes without prediction.

In Chapter 5, we employ two intelligent techniques, the fuzzy logic systems and the neural fuzzy networks, to design two intelligent leaky bucket algorithms, respectively, for sustainable-cell-rate usage parameter control of multimedia transmission in ATM networks.

The first algorithm we proposed is the fuzzy leaky bucket algorithm, which as the name im-plies, employs a fuzzy increment controller (FIC) in conjunction with the conventional leaky bucket algorithm. The FIC monitors the long-term mean rate and the short-term mean rate of a connection and uses the fuzzification, inference rules and defuzzification to process them in order to derive the optimal increment value. The other intelligent leaky bucket

algorithm we proposed is the neural fuzzy leaky bucket algorithm, which utilizes a neural fuzzy increment controller (NFIC) to dynamically adjust the increment value. The NFIC is basically an FIC except that it further employs a neural network to optimize its fuzzy logic system through the reinforcement learning. Simulation results show that, regardless of the traffic sources chosen, both intelligent leaky bucket algorithms achieve better performances in terms of selectivity, responsiveness and mean queueing delay as compared to the conven-tional leaky bucket algorithm by responding about 160% faster when taking control actions against a non-conforming connection, while reducing as much as 50% of the queueing delay experienced by a conforming connection. The performance gain of the intelligent algorithms is a result of employing fuzzy logic and neural fuzzy controllers where the measured system statistics, the long-term and short-term mean rates, are introduced as the feedback infor-mation and served as the inputs of the intelligent controllers to form a robust and adaptive close-loop control system. Accordingly, both intelligent algorithms can adapt to the time-varying and non-stationary traffic, and thus enhance their performances. In addition, the simulation results also show that the neural fuzzy leaky bucket algorithm outperforms the fuzzy one by achieving better performance in all aspects especially the responsiveness.

In Chapter 6, we proposed an enhanced traffic marker (ETM) for the TRTCM-based traffic conditioner to perform the traffic policing function in DiffServ IP networks. The primary feature of the proposed ETM is that it can fairly allocate the color notations among connections within an aggregate one. It also enhances the throughput of each conforming level for the aggregate connection to achieve as high rate as possible by not only restore the conforming levels of the previously demoted packets, but also aggressively promote the packets to higher conforming levels if the network resource condition is available, so that the end-to-end QoS of the applications would be substantially improved while the traffic contract is still be respected. The operations of the ETM scheme as well as the computations of the

promotion/demotion probabilities are carefully defined. The performances of the proposed ETM scheme were verified via simulations and the simulation results were compared with the conventional TRTCM scheme. Simulation results show the ETM scheme outperform the TRTCM scheme in both aspects of marking fairness and traffic throughput of each conforming level under congested and under-loaded networks.

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Vita

Li-Fong Lin was born in Tainan, Taiwan, R.O.C., on June 10, 1974. He received B.E.

degree in communication engineering from the Department of Communication Engineering, National Chiao-Tung University, Taiwan, in 1996. Currently, he is a candidate and work-ing toward the Ph.D degree in the area of communication engineerwork-ing, in the Institute of Communication Engineering, National Chiao-Tung University. His current research inter-ests include performance analysis, traffic control over multimedia high-speed networks, and intelligent techniques involving fuzzy logic, neural networks and neural fuzzy systems. The principle considerations of his Ph.D dissertation are the analysis, simulation and optimal design of traffic control schemes in multimedia high-speed networks.