To accommodate best-effort multimedia Internet protocol (IP) connections in mobile environments, we introduced new criteria for TCP-friendliness and developed a control algorithm for the transient response and stability in the packet transmission rate. We improved the maximum throughput and QoS guaranteed congestion control algorithm (MAQS) by using these two solutions, and solved the following problems that Reno and conventional congestion control algorithms have: (1) network congestion cannot be avoided when the round-trip time (RTT) is short and the holding time is long, (2) the packet transmission rate of a long-RTT connection is small when it is multiplexed with short-RTT connections, (3) the packet transmission rate cannot be adjusted quickly when the channel capacity changes according to hand-off.

In this letter, we evaluate the performance of several adaptive and non-adaptive AQM schemes for congestion control in a dynamic network environment with variable bandwidth links. The AQM schemes examined are RED, BLUE, Adaptive RED, REM, AVQ and PI controller. We compare their queueing performance and show that none of them can derive stable queue length and low packet drop rate simultaneously in networks where both input traffic and available output bandwidth are time varying. Adaptive and efficient algorithms should be designed and applied in order to improve the adaptiveness and robustness of congestion control in dynamic networks such as Internet.

Reliable multicast is an interesting application of distributing data to lots of clients at the same time. In heterogeneous environment, it is necessary to adjust the transmitting rate corresponding to the bandwidth of receivers. Placed at a network bottleneck point, an active server can buffer the multicast packets and control the transmitting rate to the downstream multicast receivers independently so as to absorb bandwidth differences. If wireless and wired receivers coexist, the best position for the active server is at the edge of the wired and wireless links because the bandwidth of wireless receivers are lower than that of wired receivers. However, it is not enough that an active server only controls the transmitting rate in such environment because wireless receivers tend to lose packet by the wireless transmission error. This paper proposes a scheme in which the active server independently controls a reliable multicast scheme that is robust against packet loss due to wireless transmission error. Simulation results show that rate-based reliable multicast congestion control is more appropriate than window-based control for wireless links. We also show that FEC applied only to the wireless link improves the throughput of wireless multicast receivers. Finally, we show that combining rate-based reliable multicast congestion control scheme with FEC only for the wireless link makes reliable multicast more practical and friendly with TCP even if packets are lost due to transmission errors.

We proposed a new buffer management scheme for GFR services through FIFO queuing discipline. Proposed scheme can provide minimum bandwidth guarantee for GFR VCs as well as improve the fairness among the competing GFR VCs on a single FIFO queue. From simulation result, we demonstrate the proposed scheme fulfills the requirements of GFR services as well as improves the TCP throughput

This paper proposes a gesture recognition method which uses higher order local autocorrelation (HLAC) features extracted from PARCOR images. To extract dominant information from a sequence of images, we apply linear prediction coding technique to the sequence of pixel intensities and PARCOR images are constructed from the PARCOR coefficients of the sequences of the pixel values. From the PARCOR images, HLAC features are extracted and the sequences of the features are used as the input vectors of the Hidden Markov Model (HMM) based recognizer. Since HLAC features are inherently shift-invariant and computationally inexpensive, the proposed method becomes robust to changes in the person's position and makes real-time gesture recognition possible. Experimental results of gesture recognition are shown to evaluate the performance of the proposed method.

In this paper, we propose a nonlinear control model to characterize the AQM algorithm-GREEN. Based on this model, we analyze its performance and prove that there exists a stable oscillation when in equilibrium. Furthermore, we also investigate the effects of the factors such as bandwidth, round trip time, and load level on the amplitude and frequency of the oscillation. Theoretical analysis and simulation results indicate that GREEN algorithm is insensitive to the network conditions when the link rate and the round trip time are relatively small and becomes more sensitive to the change of network conditions when the bandwidth delay product is relatively high. For GREEN the adaptability to a wide range of network conditions is based on the compromising of the efficiency.

As use of the Internet continues to spread rapidly, Traffic Engineering (TE) is needed to optimize IP network resource utilization. In particular, load balancing with TE can prevent traffic concentration on a single path between ingress and egress routers. To apply TE, we have constructed an MPLS (Multi-Protocol Label Switching) network with TE capability in the JGN (Japan Gigabit Network), and evaluated dynamic load balancing behavior in it from the viewpoint of control stability. We confirmed that with this method, setting appropriate control parameter values enables traffic to be equally distributed over two or more routes in an actual large-scale network. In addition, we verified the method's effectiveness by using a digital cinema application as input traffic.

Although TCP is widely used in the Internet, new specifications are still proposed and implemented. In the circumstance above, it is highly possible that some errors are detected on the communication between new and old implementations. Several test tools were developed so far. However, they do not have enough functions to allow test operators to modify test sequences suitable for their test purposes. We have developed a TCP tester which generates test sequence using test scenario. The tester performs exceptional TCP protocol behavior only when the condition specified in the test scenario is satisfied. Otherwise, it performs normal TCP behavior. The tester is implemented by modifying TCP module of NetBSD with SACK code developed by Pittsburgh Supercomputing Center. We have also evaluated implementations of congestion control and SACK algorithms using the tester.

Evolutionary learning methods have been applied to a variety of different problems. In this paper, a new algorithm for active queue management based on an evolutionary learning model is proposed. This novel algorithm generates packet marks for the purpose of improving robustness and responsiveness of congestion control in the Internet routers, while maintaining a reasonable degree of queueing performance such as utilization, delay, and packet drops due to buffer overflow. Simulation results demonstrate the effectiveness of the proposed algorithm and compare the performance of various algorithms.

In the Internet, flow analysis and network monitoring have been studied by various methods. Some methods try to make TCP (Transport Control Protocol) traces more readable by showing them graphically. Others such as MRTG, NetScope, and NetFlow read the traffic counters of the routers and record the data for traffic engineering. Even if all of the above methods are useful, they are made only to perform a single task. This paper describes an improved TCP Protocol Machine, a multipurpose tool that can be used for flow analysis, intrusion detection and link congestion monitoring. It is developed based on a finite state machine (automaton). The machine separates the flows into two main groups. If a flow can be mapped to a set of input symbols of the automaton, it is valid, otherwise it is invalid. It can be observed that intruders' attacks are easily detected by the use of the protocol machine. Also link congestion can be monitored, by measuring the percentage of valid flows to the total number of flows. We demonstrate the capability of this tool through measurement and working examples.

An adaptive congestion control scheme that can be applied to various random access protocols in mobile communication systems is proposed. Its main features are scalability for handling increasing numbers of mobile terminals and adaptability for coping with drastic changes in traffic load. These are achieved by controlling the traffic load adaptively to maintain maximum throughput even under overload conditions. Procedure for measuring and estimating offered traffic and a method of setting control thresholds that maximize the average throughput are analytically derived, and the algorithm for adaptively controlling the permission rate is described. This scheme was applied to both the slotted ALOHA and ICMA/CD protocols. For each protocol, three control parameters--the unsuccessful rate, optimal traffic, and control thresholds--were analytically derived. Then stationary throughput characteristics were numerically evaluated. We found that the scheme could achieve high throughput by regulating transmission adaptively depending on the offered traffic. The preferred range of the permission base rate that enables adaptive control and limits the amount of processing at terminals was also clarified. Since one of the main advantages of our scheme is its adaptability to drastic variations in traffic load, we simulated its transient characteristics with three types of time-variant input models. The results indicate that this control scheme achieved nearly theoretically optimal throughput even during an overload for each input model.

TCP congestion control is receiving increased attention in recent years due to their usefulness for network stability, robustness use of network buffer and bandwidth resources on an end-to-end per-connection basis. The RED scheme was designed for a network where a single dropped packet is sufficient to signal the presence of congestion to the TCP protocol. This paper applies matrix-analytic approach to analyze both the long-term and the short-term drop behaviors of a queue with RED scheme and uses this model to quantify the benefits brought about by RED. The result shows that the drop probability between RED and Drop-Tail is very close under heavy load conditions. This indicates that RED not only can resolve the synchronization problem but also has the same loss performance with Drop-Tail scheme under the heavy load circumstances. Our findings also show that the rate oscillation behavior of RED is better than Drop-Tail when TCP applies the additive-increase and multiplication-decrease mechanism. As a consequence, it can help reduce the required buffer capacity in the RED router.

Explicit Congestion Notification (ECN) supports the binary congestion information of the network for adjusting the window size. However, this results in the oscillation of the window size and the queue length due to the insufficient congestion information. In this paper, we propose the window-based congestion control mechanism with the modified ECN mechanism. The proposed scheme is based on extracting the network status from the consecutive binary congestion information provided by ECN. From the explicit network information, we estimate the allowable window size to achieve better performance. Through the simulations, the effectiveness of the proposed algorithm is shown as compared with the ECN algorithm.

We present a method to track and recognize shape-changing hand gestures simultaneously. The switching linear model using active contour model well corresponds to temporal shapes and motions of hands. However, inference in the switching linear model is computationally intractable, and therefore the learning process cannot be performed via the exact EM (Expectation Maximization) algorithm. Thus, we present an approximate EM algorithm using a collapsing method in which some Gaussians are merged into a single Gaussian. Tracking is performed through the forward algorithm based on Kalman filtering and the collapsing method. We also present a regularized smoothing, which plays a role of reducing jump changes between the training sequences of shape vectors representing complex-variable hand shapes. The recognition process is performed by the selection of a model with the maximum likelihood from some trained models while tracking is being performed. Experiments for several shape-changing hand gestures are demonstrated.

This paper proposes a stable rate allocation algorithm for ABR service in ATM networks. The main goals in designing this algorithm are to speed up the convergence according to the max-min fairness criterion and to maximize the network utilization while the switch queue length can be properly controlled. Importantly, the set goals should be achieved in a wide range of network conditions without the need for adjusting the algorithm parameters. The algorithm is targeted to work in various networking environments with additional criteria as extended from the work of E-FMMRA (Enhanced Fast Max-Min Rate Allocation) and ERICA+ (Explicit Rate Indication for Congestion Avoidance) . The additional design criteria include the ability to enhance a large number of ABR connections and staggered TCP connections as well as to perform an accurate traffic averaging. The algorithm is analytically proved to be convergent. Simulation results indicate that the proposed algorithm achieves the goals in all evaluated configurations. However, it has some limitations when working in the large-scale network due to its per-connection accounting. It is not recommended to implement the algorithm with a switch that has a small buffer size due to its relatively long averaging interval.

This paper chronicles the leaky-mode leakages in a corner-fed square patch. First, the measured peak RPA (relative power absorbed, 1-|S11|2-|S21|2) values of the two-port corner-fed square patch (two-port test circuit) are reported. These are 21.1%, 52.3%, 89.8% and 81.3% at 5.68 GHz, 11.76 GHz, 16.68 GHz and 22.29 GHz, respectively. Such periodicity of frequencies and the phenomenon of increasing losses at higher frequencies enable us to link these peak frequencies to leaky-mode excitations. The modal spectra of the higher-order leaky modes with a strip width of 630 mil, equal to the side length of the square patch, are obtained by the well-known space-domain integral equation method. The maximum available power gain (GA,max), obtained by simultaneously complex conjugate matched impedance at the referenced two ports of the test circuit, depicts that (1) nearly loss-free transmission parameter outside the leaky-mode regions and (2) substantial losses inside the leaky-mode regions. This result suggests that the leaky modes are the main sources causing losses for the two-port test circuit. Furthermore, the valley points of the measured and theoretical GA,max are about -7.5 dB, -9.7 dB and -12.0 dB at 10.13 GHz, 16.68 GHz and 22.29 GHz, respectively, and all are in the leaky-mode regions of the modal spectra. The one-port properties of the two-port patch with the second port opened are then investigated. The degenerated (0,N) and (N,0) modes (N=1, 2, 3 and 4), calculated by the cavity model method, fall into the strong leakage regions from the first to the fourth higher-order leaky modes. The well-known leaky line's frequency-scanning characteristics also appear in the one-port test circuit, with the angle of the main beam moving from θ=30 to θ=40 as the operating frequency is increased from 22.50 GHz to 23.75 GHz. Lastly, a two-dimensional (2-D) transmission-line model of the one-port test circuit is proposed. This model uses two orthogonal modal currents as excitations to stimulate the corner-fed square patch. At 22.60 GHz, in the fourth higher-order leaky mode (EH4) region, the current distributions obtained by the 2-D transmission-line model closely agree with those of the full-wave simulation. This consistency shows that the damped-oscillation current distributions of the corner-fed square patch at 22.60 GHz are caused significantly by the multiple reflections of the leaky mode. Furthermore, at the resonant frequencies of the patch, the tangled bound-mode resonance of the EH0 mode can enhance the leaky-mode leakages.

We developed a distributed control algorithm to solve the problem of a trade-off between transient response and stability. We applied it to a congestion control algorithm for transmitting best-effort packets such as transmission control protocol (TCP) packets over the Internet. A new transmission power control algorithm suitable for transmitting best-effort packets over the wireless Internet was also developed using the distributed control algorithm. We showed that in a steady state, TCP connections can use the bandwidth efficiently over both wired and wireless Internet when the proposed control algorithms are used. The transient response was also evaluated and it was found that the packet transmission rate and the transmission power adjusted by the proposed control algorithms converge to a steady state faster than when adjusted by conventional control algorithms while maintaining the stability of network systems.

Call demand suddenly and greatly increases in the aftermath of a major disaster, because people want to check on their families and friends in the stricken area. Many call attempts in mobile cellular systems are blocked due to the limited radio frequency resources. In this paper, as a solution to this problem, limiting the holding time of calls is investigated and a dynamic holding time limit (DHTL) method, which varies the holding time limit dynamically based on the number of call attempts, is proposed. The effect of limiting the holding time is investigated first using a computer simulation with a constant and heavy traffic load model. This simulation shows that the average holding time of calls is decreased as the holding time limit is reduced. But it also shows limiting the holding time decreases the number of calls blocked and forced call terminations at handover considerably. Next, a simple estimation method for the holding time limit, which reduces the blocking rate to the normal rate for increasing call demand, is described. Finally, results are given of a simulation, which show that the DHTL method keeps good performance for a sudden and great traffic load fluctuation condition.

We derived the design requirements that wireless systems and congestion control algorithms must satisfy to transmit best-effort Internet protocol (IP) packets over wireless systems. We proved that, if these requirements are satisfied, congestion control algorithms are robust against unfairness in the systems and can provide near-maximum throughputs in various environments. From the viewpoint of the design requirements, we investigated the effect of automatic repeat request (ARQ) on the throughputs of best-effort IP connections, and showed why ARQ can improve the throughputs while too large a number of retransmissions degrade them. We also investigated the effect of variance in packet transmission rates and clarified what kind of congestion control algorithm degrades the throughputs.

The skeleton and the skeleton function of an object are important representations for shape analysis and recognition. They contain enough information to recognize an object and to reconstruct its original shape. However, they are sensitive to distortion caused by rotation and noise. This paper presents another approach for binary object representation called a modified exoskeleton(mES) that combines the previously defined exoskeleton with the use of symmetric object whose dominant property is rotation invariant. The mES is the skeleton of a circular background around the object that preserves the skeleton properties including significant information about the object for use in object recognition. Then the matching algorithm for object recognition based on the mES is presented. We applied the matching algorithm to evaluate the mES against the skeleton obtained from using 4-neighbor distance transformation on a set of artificial objects, and the experimental results reveal that the mES is more robust to distortion caused by rotation and noise than the skeleton and that the matching algorithm is capable of recognizing objects effectively regardless of their size and orientation.