Leaky Bucket Scheme Research Articles

Analysis of the State-Dependent Queueing Model and Its Application to Battery Swapping and Charging Stations

This study analyzes the performance of a queue length-dependent overload control policy using a leaky bucket (LB) scheme. This queueing model is applied to the operation of a battery swapping and charging station for electric vehicles (EVs). In addition to the LB scheme, we propose two congestion control policies based on EV queue length thresholds. With these policies, the model determines both EV-arrival and battery-supply intervals, and these depend on the number of EVs waiting in the queue. The queue length distributions, including those at arbitrary epochs, are derived using embedded Markov chain and supplementary variable methods. Performance measures such as blocking probability and mean waiting time are investigated using numerical examples. We study the characteristics of the system using numerical examples and use a cost analysis to investigate situations in which the application of each congestion control policy is advantageous.

On the packet allocation of multi-band aggregation wireless networks

The use of heterogeneous networks with multiple radio access technologies (RATs) is a system concept that both academia and industry are studying. In such system, integrated use of available multiple RATs is essential to achieve beyond additive throughput and connectivity gains using multi-dimensional diversity. This paper considers an aggregation module called opportunistic multi-MAC aggregation (OMMA). It resides between the IP layer and the air interface protocol stacks, common to all RATs in the device. We present a theoretical framework for such system while considering a special case of multi-RAT systems, i.e., a multi-band wireless LAN (WLAN) system. An optimal packet distribution approach is derived which minimizes the average packet latency (the sum of queueing delay and serving delay) over multiple bands. It supports multiple user terminals with different QoS classes simultaneously. We further propose a packet scheduling algorithm, OMMA Leaky Bucket, which minimizes the packet end-to-end delay, i.e., the sum of average packet latency and average packet reordering delay. We also describe the system architecture of the proposed OMMA system, which is applicable for the general case of the multi-RAT devices. It includes functional description, discovery and association processes, and dynamic RAT update management. We finally present simulation results for a multi-band WLAN system. It shows the performance gains of the proposed OMMA Leaky Bucket scheme in comparison to other existing packet scheduling mechanisms.

QUEUEING ANALYSIS FOR TRAFFIC CONTROL WITH COMBINED CONTROL OF DYNAMIC MMPP ARRIVALS AND TOKEN RATES

We analyze the queueing model for leaky bucket (LB) scheme with dynamic arrivals and token rates. In other words, in our LB scheme the arrivals and token rates are changed according to the buffer occupancy. In telecommunication networks, the LB scheme has been used as a policing function to prevent congestion. By considering bursty and correlated properties of input traffic, the arrivals are assumed to follow a Markov-modulated Poisson process (MMPP). We derive the distribution of system state, and obtain the loss probability and the mean waiting time. The analysis is done by using the embedded Markov chain and supplementary variable method. We also present some numerical examples to show the effect of our proposed model.

A Policy-Based Admission Control Scheme for Voice over IP Networks

Problem statement: In Voice Over IP (VOIP) network, when more calls are admitted to the network, more voice packet traffic is created. Since bandwidth is always limited, this may result network congestion and/or may affect voice quality. Thus, we needed a mechanism for improving the Quality of Service (QoS) by controlling VOIP calls admission. Approach: Given a specified bandwidth and a constant background data rate, we attempted to explore the effect of Open Window and Leaky Bucket admission schemes on VoIP calls quality. These policy-based admission controls were simulated using NS-2 Simulator. The inter-arrival time distribution for the network background data traffic was assumed to be deterministic with a Constant Bit Rate (CBR). Voice packets traffic inter-arrival time is assumed to have an exponential distribution. Each voice call has a rate of 64 kbps for duration of 120 min. Results: Various performance measures of VoIP calls and packet traffic were evaluated including: packet loss, packet drop rate, delay, jitter and call rejection rate. Performance results of the experiment are summarized in a power ratio index which presented the impact of a collection of performance parameters on VoIP service quality. Conclusion: Implementing a policy based admission scheme on VoIP network will improve its QoS and the degree of improvement depends on the network setting parameters. If threshold rate for call admission is set above network ceiling bandwidth, leaky bucket will result a higher and unacceptable jitter. Overall, leaky bucket scheme was considered inferior when compared to open window for improving QoS of VoIP.

PERFORMANCE ANALYSIS OF THE LEAKY BUCKET SCHEME WITH QUEUE LENGTH DEPENDENT ARRIVAL RATES

In this paper, we analyze a leaky bucket (LB) scheme with queue length dependent arrival rates. In other words, if the queue length exceeds an appropriate threshold value on buffer, the arrivals need to be controlled. In ATM networks, if the congestion occurs, the input traffics must be controlled (reduced) for congestion resolution. By the bursty and correlated properties of traffics, the arrivals are assumed to follow a Markov-modulated Poisson process (MMPP). We derive the loss probability and the waiting time distribution for arbitrary cell. The analysis is done by using the embedded Markov chain and supplementary variable method. We also present some numerical examples to show the effects of our proposed LB scheme.

Efficient Transmission of MPEG-2 Coded Video Traffic over ATM Networks

Video traffic is expected to account for a significant share of the traffic volume in the future asynchronous transfer mode (ATM) networks. MPEG-2 proposed by Moving Picture Expert Group is one of the most promising compression techniques for such applications. One of the critical issues in MPEG-2 is to realize effective variable bit rate (VBR) video transfer thorough ATM networks. The Leaky Bucket (LB) scheme has been widely accepted as the usage parameter control (UPC) mechanism to police the VBR sources. We proposed a new Adaptive Dynamic Leaky Bucket (ADLB) congestion control mechanism, which is based on the LB scheme. Unlike the conventional LB, the leak rate of the ADLB is controlled using delayed feedback information of available bandwidth sent by the network. This scheme allows sources to get varying amounts of bandwidth over time, while reserving a minimum guaranteed bandwidth (MCR) for the entire duration of the connection. At the time of congestion, the leak rate of the ADLB is adjusted according to the feedback indicating the currently available bandwidth to the connection. The simulation results show that the end-to-end cell transfer delay and cell loss of each source has been improved significantly.

An effective congestion control scheme for ATM networks

Congestion control is considered one of the most challenging issues of ATM. Simulation results are presented which show the performance superiority of the proposed scheme as compared to the conventional leaky bucket scheme. © 1998 John Wiley & Sons, Ltd.

Performance analysis of priority leaky bucket scheme with queue-length-threshold scheduling policy

The leaky bucket scheme is a promising method that regulates input traffic for preventive congestion control in ATM networks. One of the important problems in ATM networks is meeting the quality of service requirements for real-time and non-real-time traffics. The authors propose a priority leaky bucket scheme with queue-length-threshold scheduling policy. The motivation of this proposed leaky bucket scheme is to meet the quality of service for real-time traffic while providing more improved services for non-real-time traffic. Using the embedded Markov chain method, the authors obtain the joint distribution of the queue lengths, the loss probability and the mean waiting time. Numerical results show the effects of the system parameters such as the buffer size and the token pool size on the performance of the proposed scheme.

On the departure process of a leaky bucket system with long-range dependent input traffic

Due to the strong experimental evidence that the traffic to be offered to future broadband networks will display long-range dependence, it is important to study the possible implications that such traffic may have for the design and performance of these networks. In particular, an important question is whether the offered traffic preserves its long-range dependent nature after passing through a policing mechanism at the interface of the network. One of the proposed solutions for flow control in the context of the emerging ATM standard is the so-called leaky bucket scheme. In this paper we consider a leaky bucket system with long-range dependent input traffic. We adopt the following popular model for long-range dependent traffic: Time is discrete. At each unit time a random number of sessions is initiated, having the distribution of a Poisson random variable with mean \lambda. Each of these sessions has a random duration \tau, where the integer random variable \tau has finite mean, infinite variance, and a regularly varying tail, i.e., P(\tau > k) \sim k^{-\alpha}L(k), where 1<\alpha<2 and L(\cdot) is a slowly varying function. Once a session is initiated, it generates one cell at each unit of time until its termination. We examine the departure process of the leaky bucket policing mechanism driven by such an arrival process, and show that it too is long-range dependent for any token buffer size and any – finite or infinite – cell buffer size. Moreover, upper and lower bounds for the covariance sequence of the output process are established. The above results demonstrate that long-range dependence cannot be removed by the kinds of flow control schemes that are currently being envisioned for broadband networks.

Performance analysis of a Leaky Bucket scheme with a threshold in the data buffer

We investigate Leaky Bucket (LB) schemes with a threshold in the data buffer, where the leak rate changes depending on the contents of the data buffer. We use a Markov modulated Poisson process (MMPP) as a bursty input traffic. We obtain the limiting distributions of the system state at an embedded point and at an arbitrary time. As performance measures we obtain cell loss probability and mean cell delay. We present some numerical results to show the effects of the threshold value, the rate of token generation, the size of the token pool and the size of the data buffer on the performances of the LB scheme with a threshold. Numerical examples show that the LB scheme with a threshold improves the system performance in comparison with the LB scheme without a threshold.

The use of hop-delay for policing in ATM networks

The large delay-bandwidth product in wide-area high-speed networks renders conventional control methods, which rely on network feedback in order to react to the network congestion, unusable. This makes preventive control methods, such as policing, essential in maintaining an acceptable quality of services (QoS) offered to user connections. However, existing policing mechanisms which rely purely on source measurements are not effective in policing traffic sources that have large correlations in their output bit rate. In this paper a new approach, which exploits the relative invariability of the cell transfer delay in a long-haul broadband network, is proposed for policing. The idea is to discard from the measurements of the policing function arrival statistics which are no longer related to traffic states inside the network, hence making the policing simpler and more responsive to traffic violations. A new policing mechanism has been developed by applying the new approach in an existing policing scheme—the so-called leaky bucket scheme. Numerical results obtained from the mathematical model developed for the new mechanism show that it has a better cell loss performance than the original leaky bucket. Results from computer simulation substantiate these observations. The results also show that a small increase in the counter size in the new mechanism can yield a large improvement in the cell loss performance, thereby reducing the complexity of policing mechanisms using the new approach. Comparisons in terms of the dynamic characteristics when both mechanisms are policing the effective bandwidth show that the original scheme admits more cells from a violation source before control action takes place. The original scheme is also found to admit more cells from a violation source in the long term.

A flexible traffic shaper for high speed networks: design and comparative study with leaky bucket

Maximizing bandwidth utilization and providing performance guarantees, in the context of multimedia networking, are two incompatible goals. Heterogeneity of the multimedia sources calls for effective traffic control schemes to satisfy their diverse Quality of Service (QoS) requirements. These include admission control at connection set up, traffic control at the source ends and efficient scheduling schemes at the switches. The emphasis in this paper is on traffic control at the source end. Most multimedia sources are bursty in nature. Traffic shapers have been mainly studied hitherto from the point of view of their effectiveness in smoothing the burstiness. The Leaky Bucket (LB) scheme, to cite an example, is a mean rate policer smoothing at the token generation rate. Studies on bursty sources show that burstiness promotes statistical multiplexing at the cost of possible congestion. Smoothing, on the other hand, helps in providing guarantees at the cost of utilization. Thus need for a flexible scheme which can provide a reasonable compromise between utilization and performance is imminent. Recent studies have also questioned the suitability of LB for policing real-time traffic due to the excessive delays. We argue for a policy which is less stringent on short term burstiness than the LB. We propose a new traffic shaper which can adjust the burstiness of the input traffic to obtain reasonable bandwidth utilization while maintaining statistical service guarantees. The performance study is conducted in two parts. In the first part, we study the effect of varying the shaper parameters on the input characteristics. In the second part, we dimension our scheme and a LB equivalently and compare the mean and peak rate policing behavior with delay and loss as the performance parameters. Adopting a less stringent attitude towards short term burstiness is shown to result in considerable advantage while policing real-time traffic. Future research possibilities in this topic are explored.

Discrete-time analysis of the leaky bucket scheme with threshold-based token generation intervals

In the ATM network, the leaky bucket scheme is a promising method that regulates input traffics for preventive congestion control. In order to satisfy the loss probability constraint of more bursty input traffic, it is known that the leaky bucket scheme with static token generation interval requires larger data buffer and token pool size. This causes an increase in the mean waiting time for input traffic to pass the leaky bucket scheme, which would be inappropriate for real time traffics such as voice and video. The authors present the leaky bucket scheme with threshold-based token generation intervals in which the token generation interval changes according to buffer occupancy. The proposed leaky bucket scheme is analysed in the discrete-time case by assuming the arrival process to be a Markov-modulated Bernoulli process (MMBP). The authors show that the quality of service (QoS) of input traffics is satisfied with smaller data buffer and token pool size in the proposed leaky bucket scheme.

Analysis of a rate-based access control mechanism for high-speed networks

The authors present an analysis of a rate-based access control mechanism for high-speed networks that is based on the buffered leaky bucket scheme. The analysis assumes a discrete time environment representative of asynchronous transfer mode (ATM) networks and a batch arrival process that captures cell arrivals generated by segmentation of large user packets or superposition of a number of arrival streams. The solution method is based on matrix analytic techniques, but the particular structure of the system allowed for a number of important improvements. It is shown that the problem can be partitioned and that the matrix G, central to the matrix analytic technique, can be computed using exact recursive procedures instead of the traditional iterative approach. These improvements not only extend the range of systems that can be handled, but also eliminate computational issues such as convergence rate and stopping criterion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>