Support of incoming traffic differentiation and Quality of Service (QoS) assurance is very important for the development of high performance packet switches, capable of separating traffic flows. In our previous paper, we proposed the implementation of two buffers at each crosspoint of a crossbar fabric that leads to the Dual Crosspoint Queued (DCQ) switch. Inside DCQ switch, one buffer is used to store the real-time traffic and the other for the non-real-time traffic. We also showed that the static priority algorithms can provide the QoS only for the real-time traffic due to their greedy nature that gives the absolute priority to that type of traffic. In order to overcome this problem, in our paper we propose the DCQ switch with the Largest Weighted Occupancy First scheduling algorithm that provides the desired QoS support for both traffic flows. Detailed analysis of the simulation results confirms the validity of proposed solution.

A new expression for cell/packet loss probability in an ATM and packet switched queue system with a finite buffer is presented. Cell and packet loss analysis is based on the new concept of a "buffer overflow cluster" and the overflow probability for a queue with an infinite buffer. This approach holds for a wide variety of long-range dependent traffic sources typical of wide-area networks, as well as Internet and other communication traffics. The method is verified by simulations of two long-range dependent traffic scenarios: fractional Gaussian noise and multifractal wavelet model traffic with a beta marginal distribution.

Current literature on input buffer management reveals that, in representative ATM networks under highly bursty traffic conditions, the fuzzy thresholding approach yields lower cell loss rate at the cost of lower throughput. Also, under less bursty traffic, the traditional fixed thresholding approach achieves higher throughput at the expense of higher cell loss rate. The integration of these two properties into practice is termed adaptive dynamic buffer management (ADBM) approach for input buffers and its assessment is the objective of this paper. The argument is that, given that the traffic conditions are constantly changing, to achieve efficiency during actual operation, the network control must dynamically switch, at every ATM switch, under the call processor's control, between the two input buffer management techniques, dictated by the nature of the traffic at the inputs of the corresponding switch. The need to involve the call processor marks the first effort in the literature to dynamically configure input buffer management architectures at the switch fabric level under higher level call processor control. It stems from the fact that the switch fabric operates very fast and cannot engage in complex decision making without incurring stiff penalty. To achieve this goal, the network control needs knowledge of the burstiness of the traffic at the inputs of every ATM switch. The difficulties with this need are two-fold. First, it is not always easy to obtain the traffic model and model parameters for a specific user's call. Second, even where the traffic model and the model parameters are known for a specific user's call, this knowledge is valid only at the source switch where the user interfaces with the network. At all other switches in the network, the cells of the traffic in question interact asynchronously with the cells from other traffic sources and are subject to statistical multiplexing. Thus, to obtain the exact nature of the composite traffic at the inputs of any ATM switch, is a challenge. Conceivably, one may determine the burstiness by counting the number of cells incurred at the inputs of an ATM switch over a defined time interval. The challenge posed by this proposition lies in the very definition of burstiness in that the time interval must approach, in the limit, zero or the resolution of time in the network. To address this challenge, first, a 15-node representative ATM network is modeled in an asynchronous, distributed simulator and, second, simulated on a network of workstations under realistic traffic stimuli. Third, burstiness indices are measured for the synthetic, stochastic traffic at the inputs of every ATM switch as a function of the progress of simulation for different choices of time interval values, ranging from 20,000 timesteps down to 1,000 timesteps. A timestep equals 2.73 µs. Results reveal that consistent burstiness indices are obtained for interval choices between 1,000 and 5,000 timesteps and that a burstiness index of 25, measured at 3,000 timestep interval, constitutes a reasonable and practical threshold value that distinguishes highly bursty traffic that warrants the use of the fuzzy thresholding approach from less bursty traffic that can benefit from the fixed thresholding scheme. A comparative performance analysis of ADBM yields the following. For pure fixed and pure fuzzy thresholding schemes, the throughputs are at 73.88% and 71.53% while the cell drop rates are at 4.31% and 2.44%,respectively. For the ADBM approach, where the input buffer management alternates at each individual ATM switch between the fixed and fuzzy schemes, governed by measured burstiness index threshold of 25 for a 3,000 timestep interval, the throughput is 74.77%, which is higher than even the pure fixed scheme while the cell drop rate is 2.21% that is lower than that of the pure fuzzy scheme. In essence, ADBM successfully integrates the best characteristics of the fuzzy and fixed thresholding schemes.

In this paper, new integrated schemes of scheduling real-time traffic and cell loss control in high speed ATM networks are proposed for multiple priorities based on variable queue length thresholds for scheduling and the Partial Buffer Sharing policy for cell loss control. In our schemes, the queues for buffering arriving cells can be constructed in two ways: one individual queue for each user connection, or one physical queue for all user connections. The proposed schemes are considered to provide guaranteed QoS for each connection and cell sequence integrity for virtual channel/path characteristics. Moreover, these new schemes are quite flexible and can realize different scheduling algorithms. This paper also provides the Stochastic Petri Net models of these integrated schemes and an approximate analysis technique, which significantly reduces the complexity of the model solution and can be applied to real ATM switch models. From the numerical results, we can see that our schemes outperform those well-known schemes such as the head-of-line (HOL) priority control and the queue length threshold (QLT) policy.

A shared buffer ATM switch loaded with bursty input traffic is modeled by a discrete-time queueing system. Also, the unbalanced and correlated routing traffic patterns are considered. An approximation method to analyze the queueing system under consideration is developed. To overcome the problem regarding the size of state space to be dealt with, the entire switching system is decomposed into several subsystems, and then each subsystem is analyzed in isolation. We first propose an efficient algorithm for superposing all the individual bursty cell arrival processes to the switch. And then, the maximum entropy method is applied to obtain the steady-state probability distribution of the queueing system. From the obtained steady-state probabilities, we can derive some performance measures such as cell loss probability and average delay. Numerical examples of the proposed approximation method are given, which are compared with simulation results.

Cell loss is one of the most important metrics of quality of service in ATM mobile communication systems. This loss can be suppressed by introducing buffer memories in the network, but that sacrifices delay. This paper proposes a lossless handover scheme for ATM mobile communication networks that can suppress delay fluctuations, and presents a subjective evaluation of MPEG2 images with various buffer memory sizes.

Error performance as well as ATM cell transfer characteristics in a new category of wireless access systems is discussed. Relocatable wireless access with neutral feature between the fixed and mobile systems can convey Mbit/s-order capacity with fairly high quality under line-of-sight propagation. It is an important question for such wireless access systems whether they are able to form a part of wired networks satisfying performance objectives specified in ITU-T Recommendations. This paper analyzes the characteristics of relocatable systems under Gamma-distribution fading environments, and clarifies quantitative relations between Bit Error Rate (BER), Severely Errored Second (SES), Errored Second (ES) and Cell Loss Ratio (CLR) in a calculation model employing QPSK and typical HEC (Header Error Control). Thus it is demonstrated for the first time that in most cases the dominant parameter is the SES objective. Also it will be possible for a relocatable system with appropriate fade margin to meet the ITU-T performance specifications.

We propose a new approach to the exact performance analysis of a shared buffer ATM multiplexer, which is loaded with mixed correlated and uncorrelated traffic sources. We obtain the joint steady-state probabilities of both states of the input process and the buffer using a one-dimensional Markov chain. From these probabilities we calculate the loss probabilities and the average delays of the correlated and the uncorrelated traffic sources.

Input and output queueing two stage ATM switch model which is effective under variable hot-spot traffic is proposed. In order to prevent the degradation of performance due to hot-spot traffic, the hot-spot route is added in which cells destined to the hot-spot port bypass. The switch applies the backpressure mode basically. When the switch judges that the hot-spot port exists, it routes cells destined there to the hot-spot route and applies the queue loss mode on them. We evaluate both the cell loss probability and the mean system delay under the nonuniform traffic with variable hot-spot port by computer simulation. As the results, it is shown that our proposed switch can achieve better switching performance than those of conventional switches under variable traffic condition.

The asynchronous transfer mode (ATM) provides efficient switching capability for various kinds of communication services. To guarantee the minimum quality of services in the ATM networks, the bandwidth allocation setup procedure between the network nodes and users is very important. However, most of call admission control (CAC) methods which have been proposed so far are not fully appropriate to apply to real environments in terms of the complexity of the hardware implementation or the accuracy of assumptions about the cell-arrival processes. In addition, the success of broad bandwidth applications in the future multimedia environments will largely depend on the degree to which the efficiency in communication systems can be achieved, so that establishing high-speed CAC schemes in the ATM networks is an indispensable subject. This paper proposes a new cell-loss rate estimation method for the real time CAC in ATM networks. A neural network model using the Kalman filter algorithm was employed to improve the error minimizing process for the cell-loss estimation problem. In the process of optimizing the three-layer perceptron, the average, the variance, and the 3rd central moment of the number of cell arrivals were calculated, and cell-loss rate date based on the non-parametric method were adopted for outputs of the neural network. Evaluation results concerned with the convergence using the sum of square errors of outputs were also discussed in this paper. Using this algorithm, ATM cell-loss rates can be easily derived from the average and peak of cells rates coming from users. Results for the cell-loss estimation process suggest that the proposed method will be useful for high-speed ATM CAC in multimedia traffic environments.

Superposed ATM cell streams have burstiness and strong autocorrelation properties. This paper investigates traffic measurement-based modeling method for superposed ATM cell streams. We develop a new measurement method based on monitoring both the waiting time distribution in a monitoring queue and the autocorrelation of cell interarrival times. Through the monitoring queue, we directly observe the queueing effect of superposed cell flows on ATM multiplexers. The measured traffic is modeled as the two-state MMPP. With the measured traffic, we estimate the cell loss probability in ATM multiplexers from the MMPP/D/1/K queue. Our method successfully works with homogeneous and heterogeneous superposition of traffic sources including voice, data, and video. These results can be applied to the evaluation of ATM multiplexers, traffic engineering, and network performance monitoring.

Leaky Bucket based traffic parameters are widely used for traffic declaration and enforcing in an ATM network. In this paper, we investigate the characteristics of the system that every traffic source is policed by a dual leaky bucket before entering the network. In addition to mean cell rate, peak cell rate of traffic is also taken into consideration. We find the worst output pattern from the dual leaky bucket and derive the performance bound of maximum cell loss ratio encountered in the multiplexer. It is obtained as every source transmits cells according to the criteria for extreme synchronous transmission in a coincident token-generating condition.

Many ATM switching modules with high performance have been proposed and analyzed. A development of a large scale ATM switching system (e.g., used as a central switch) is the key to realization of the broadband ISDN. However, the dimension of ATM switching ICs is limited by the technological and physical constraints on VLSI. A multistage switching configuration is one of the promising configurations for a large scale ATM switch. In this paper, we treat a 3-stage switching configuration with no internal bufferes; i.e., bufferless switches are employed at the first and second stages, and output buffered switches at the third stage. A short-term cell loss probability is analyzed in order to examine the influence of bursty traffic on performance of the bufferless switch used at the first two stages. Furthermore, we propose a 4-stage switching configuration with traffic distributors added at the first stage. This switch provides more paths between a pair of input and output ports than the 3-stage switching configuration mentioned above. A few schemes to distribute cells are compared. It is shown that the distributor successfully reduces the deterioration of cell loss probability due to bursty traffic by splitting incoming cells into several switching modules.

The message level performance of error controls in data communication on ATM network is analyzed. Three layers, "a cell"(a unit of transmission), "a block"(a unit of error controls) and "a message"(a unit of transmission of user level) are considered. The error controls treated in this paper are GBN (Go-Back-N) and FEC+GBN. The cell loss process is assumed to be the two state Markov chain considering the cell loss process in ATM networks. Numerical results show that (1) the improvement of the message forwarding delay is saturated in some environments when the interface rate becomes high, (2) FEC is efficient when the burstiness of the cell loss process is small, the message length is large and the interface rate is high.

The connection admission control is one of preventive traffic control in ATM networks. The one objective of connection admission control is to keep the network load moderate so as to achieve a performance objective associated with quality of services (QOS). Because the cell loss rate is more sensitive to offered load than the average queuing delay in ATM networks, QOS requirement associated with cell loss rate is considered. The connection admission control acts as one of the major roles in traffic control. The job of connection admission control is to make an acceptance decision for connection set-up request to control the network load. This paper proposed and evaluated a connection admission control method. The proposed method is suitable for real time operation even in large diversity of connection types, because the amount of calculation for connection admission control is reduced remarkably compared to conventional algorithms. Moreover, the amount of calculation for the algorithm does not increase even when the number of connection types increases. The proposed method uses probability function for the number of cells transferred from multiplexed connections and uses recursive equations in estimating cell loss rate.

This letter describes the High-speed Statistical Retry switch (HSR switch) for high-speed ATM switching systems. The HSR switch uses a new matrix-shaped switching structure with buffers at input and ouptut ports, and a simple retry algorithm. The input buffers are very small, and no complicated arbitration function is employed. A cell is repeatedly transmitted from each input buffer at m times the input line speed until the input buffer receives an acknowledge signal from the intended output buffer. A maximum of one cell can be transmitted from each input buffer during the cell transmission time. The internal ratio (m) is decided according to the probability of cell conflict in the output line. Simulation results show that just a 10-cell buffer at each input port and a 50-cell buffer at each output port are required when m=4 to achieve a cell loss probability of better than 10-8, irrespective of the switch size. At each crosspoint, cells on the horizontal input line take precedence over those on the vertical input line. Only a very simple retry algorithm is employed, no complex arbitration is needed, and the arbitration circuit at the crosspoint can be reduced by about 90% in size. The proposed ATM switch architecture is applicable to high-speed (Gbit/s) ATM switches for B-ISDN because of its simplicity.

Cell losses due to statistical multiplexing of bursty traffic in ATM networks tend to be in clusters rather than uniformly scattered. Since the quality of service for users is quite sensitive to such bursty losses, it is necessary to characterize the temporal behavior of cell loss. This paper reports results obtained from investigating overload period and underload period in an ATM multiplexer with heterogeneous burst traffic input, using a bufferless model. The overload period is defined as the time interval when the instantaneous bit rate exceeds the output link capacity. With the bufferless model, we assume that all the instantaneous bit rate exceeding the link capacity is lost, and the loss rate is called "virtual cell loss probability". The virtual cell loss probability during the overload period, average overload period and underload period durations are analyzed. Numerical results show that the cell loss probability in overload periods and the average duration of overload periods (normalized by burst duration) are not very sensitive to link load or average rate/peak rate ratio of the burst, and that they are approximately on the order of peak bandwidth/link capacity ratio for the multiplexed burst. Furthermore, it is also shown that the mean underload duration is simply given as the inverse of the overall cell loss probability multiplied by the constant value inherently determined by peak bandwidth and link capacity. With these observations, applications to the call acceptance control using these measures are also presented.

This paper analyzes the performance of an ATM cell multiplexer with a two level MMPP input on a discrete-time basis. We approximated the input process as a simple MMPP model. We developed an MMPP/D/1/K queueing model for the ATM cell multiplexer, and employed an analytic approach for the evaluation of cell loss probability. We verified the accuracy of the results using computer simulation. We applied the above analytic method to connection admission control (CAC) of the ATM network. The resulting connection admission control scheme employs the concept of the "effective bandwidth" and table-look-up procedure. We confirmed through a computer simulation that the proposed connection admission control scheme outperforms the peak bandwidth allocation scheme with respect to link utilization.

In an ATM network, there are quality impairments particular to the ATM network such as cell loss and delay variation. During ATM network planning, therefore, various causes of quality impairments should be clarified. This paper overviews ATM network performance issues, and discusses performance requirements for the SDH network which will be applied as a physical layer of the ATM network. It also presents ATM network performance planning methods on cell loss and cell delay.