Push-out Scheme Research Articles

Space and Time Priority Queues with Randomized Push-Out Scheme

Space and Time Priority Queues with Randomized Push-Out Scheme

Evaluation of the Waiting Time in a Finite Capacity Queue with Bursty Input and a Generalized Push-Out Strategy

In this paper, we study a finite capacity queue where the arrival process is a special case of the discrete time Markov modulated Poisson process, the service times are generally distributed, and the server takes repeated vacations when the system is empty. The buffer acceptance strategy is based on a generalized push-out scheme: when the buffer is full, an arriving customer pushes out the Nth customer in the queue, where N takes values between 2 and the capacity of the system, and the arriving customer joins the end of the queue. Such a strategy is important when, as well as short waiting times for served customers, the time a pushed-out customer occupies a buffer space is also an important performance measure. The Laplace transform of the waiting time of a served customer is determined. Numerical examples show the influence of the bustiness of the input process and also the trade-off between the average waiting time of served customers and the occupancy of the buffer space of pushed-out customers.

Dynamic Detection and Expulsion Buffer Management Scheme for High-Speed Networks

In this letter, we propose a simple but effective buffer management scheme to achieve fair bandwidth sharing with a FIFO scheduling algorithm, that is, Dynamic Detection and Expulsion (DDE). The DDE scheme dynamically detects buffer occupancy and then precisely expels resided packets on demand through simple comparisons. Simulation results under various traffic conditions show that DDE can arrive at more robust and better fairness, and lower implementation complexity than that of a well-known Pushout (PO) scheme.

Delay Analysis of anM/G/1/KPriority Queueing System with Push-out Scheme

This paper considers anM/G/1/Kqueueing system with push-out scheme which is one of the loss priority controls at a multiplexer in communication networks. The loss probability for the model with push-out scheme has been analyzed, but the waiting times are not available for the model. Using a set of recursive equations, this paper derives the Laplace-Stieltjes transforms (LSTs) of the waiting time and the push-out time of low-priority messages. These results are then utilized to derive the loss probability of each traffic type and the mean waiting time of high-priority messages. Finally, some numerical examples are provided.

A Load-Balancing and Push-Out Scheme for Supporting QoS in MANETs

Currently, mobile ad hoc networks (MANETs) lack load-balancing capabilities, and thus, they fail to provide good performance especially in the case of a large volume of traffic. Ad hoc networks lack also service differentiation. However, in these wireless environments, where channel conditions are variable and bandwidth is scarce, the differentiated services developed for the Internet are suboptimal without lower layers' support. The IEEE 802.11 standard for Wireless LANs is the most widely used WLAN standard today. It has a mode of operation that can be used to provide service differentiation, but it has been shown to perform badly.In this paper, we present a simple but very effective method for support Quality of Service, by the use of load-balancing and push-out scheme. This approach offers to the mobile node: the ability to alleviate congestion by traffic distribution of excessive load, and to support priority of packets in the single MAC buffer. We evaluate the performance of our algorithm and compare it with the original IEEE 802.11b protocol. Simulation results show that this new approach reduces packet loss rate and increases throughput as well as provides service differentiation in the MAC layer.

Priority queueing with finite buffer size and randomized push-out mechanism

The non-preemptive priority queueing with a finite buffer is considered. We introduce a randomized push-out buffer management mechanism which allows to control very efficiently the loss probability of priority packets. The packet loss probabilities for priority and non-priority traffic are calculated using the generating function approach. In the particular case of the standard non-randomized push-out scheme we obtain explicit analytic expressions. The theoretical results are illustrated by numerical examples. The randomized push-out scheme is compared with the threshold based push-out scheme. It turns out that the former is much easier to tune than the latter. The proposed scheme can be applied to the Differentiated Services of the Internet.

Threshold-based selective drop for shared buffer packet switches

We propose a novel buffer management scheme called threshold-based selective drop (TSD) to improve the overall loss performance and fairness by regulating the buffer sharing in a packet switch. A transient analysis of TSD is derived to prove the fairness of buffer allocation. Computer simulation shows that the overall loss performance of TSD approaches to the pushout (PO) scheme, which is considered as an optimal solution with implementation difficulties in high-speed Internet. However, unlike the PO, the TSD will block the unwanted packets before they enter the queue, and does not need to pre-empty the queue for accepting new packets.

Pushout with virtual thresholds buffer management scheme in a shared buffer ATM switch

AbstractIn this paper we investigate the performance metrics of buffer management schemes. In general, the selective pushout (SP) scheme can support very low loss probability of the high‐priority cells, but it may cause unfairness of buffer allocation among different output queues and high overall cell loss probability. In order to fit the dynamic required performance metrics of ATM switches, a novel buffer management scheme called pushout with virtual thresholds (PVT) is proposed. In the PVT scheme, each output queue is guaranteed to increase in length until its virtual threshold (VT). Simulation results show the PVT can dynamically achieve the fairness and low overall cell loss probability or very low loss probability of the high priority cells by adequately adjusting the VT. Specially, when the VT = 0, the PVT control can be viewed as the SP control. Copyright © 2003 John Wiley & Sons, Ltd.

Queueing system with multiple delay and loss priorities for ATM networks

Abstract The asynchronous transfer mode (ATM) has been widely accepted as an effective technique to transport various traffics such as voice, data and video in broadband integrated services digital networks (B-ISDN). To utilize the network resources efficiently and to provide the required quality of service (QoS) of each traffic, a proper priority control is necessary. This paper investigates a priority queueing model with four types of traffics, classified according to the delay and loss sensitivity. A head-of-line (HOL) scheme for cell delay control and a push-out scheme for cell loss control are adopted. Some computational procedures for loss probabilities and waiting times are developed. Several numerical examples are also given.

A fuzzy logic based approach to multipriority control in ATM networks

The priority control function in ATM networks allows users to generate traffic flows with different priorities by using the Cell Loss Priority (CLP) bit. The implementation of this function, however, represents a hard task as the network has to guarantee the Quality of Service (QoS) of the higher priority traffic regardless of the presence of low-priority traffic and, at the same time, to reach an efficient use of network resources. The conventional schemes proposed so far suffer from some limitations either in performance (threshold mechanisms) or in feasible implementation (push-out scheme). We propose a queue management strategy based on fuzzy logic, which combines high performance, guaranteeing the QoS requirements and increasing the throughput, with a low implementation cost. In the paper, we assess the fuzzy mechanism by considering several traffic scenarios ranging from bursty traffic to MPEG video traffic. The presented results show that our mechanism is robust and outperforms conventional mechanisms.

A guaranteed-no-cells-dropped buffer management scheme with selective blocking for cell-switching networks

A guaranteed-no-cells-dropped buffer management scheme with selective blocking for cell-switching networks

Performance evaluation of triggered threshold buffer schemes for ATM networks

To achieve the quality of service for each class of traffic in ATM networks, we propose and analyze two triggered threshold buffer schemes to improve the cell loss rate in ATM networks. In the proposed schemes, there are two thresholds to control the behavior of cell discarding in the ATM switch. When the system is in the heavy traffic situation, we use one threshold to reduce the cell loss rate of the high priority class, and when the system is in the light traffic situation, we use another threshold to improve the cell loss rate of the low priority class. Performance of both the triggered threshold buffer schemes is analyzed and compared. According to the analyzed results, the performance of the proposed priority schemes can be better than that of the partial buffer sharing scheme. Besides, the buffer management complexity in the proposed priority scheme is simpler than that of the push-out scheme.

Sharing memory in banyan-based ATM switches

We study a multistage ATM switch in which shared-memory switching elements are arranged in a banyan topology. By "shared-memory," we mean that each switching element uses output queueing and shares its local cell buffer memory among all its output ports. We apply a buffer management technique called delayed pushout that was originally designed for multistage ATM switches with hierarchical topologies. Delayed pushout combines a pushout mechanism, for sharing memory efficiently among queues within the same switching element, and a backpressure mechanism, for sharing memory across switch stages. The backpressure component has a threshold to restrict the amount of sharing between stages. A synergy emerges when pushout, backpressure, and this threshold are all employed together. Using a computer simulation of the switch under bursty traffic, we study delayed pushout as well as several simpler pushout and backpressure schemes under a variety of traffic conditions. Of the five schemes we simulate, delayed pushout is the only one that performs well under all load conditions.

Design of a generalized priority queue manager for ATM switches

Meeting quality of service (QoS) requirements for various services in ATM networks has been very challenging to network designers. Various control techniques at either the call or cell level have been proposed. In this paper, we deal with cell transmission scheduling and discarding at the output buffers of an ATM switch. We propose a generalized priority queue manager (GPQM) that uses per-virtual-connection queueing to support multiple QoS requirements and achieve fairness in both cell transmission and discarding. It achieves the ultimate goal of guaranteeing the QoS requirement for each connection. The GPQM adopts the earliest due date (EDD) and self-clocked fair queueing (SCFQ) schemes for scheduling cell transmission and a new self-calibrating pushout (SCP) scheme for discarding cells. The GPQM's performance in cell loss rate and delay is presented. An implementation architecture for the GPQM is also proposed, which is facilitated by a new VLSI chip called the priority content-addressable memory (PCAM) chip.

Performance analysis of backpressure congestion control: Preliminary case

In ATM networks, preventive control is widely recognized as a way to avoid congestion efficiently, and it is implemented by a conjunction of call admission control (CAC) and usage parameter control (UPC). However, since congestion may still happen because of unpredictable statistical fluctuations of traffic injected into networks, it would be effective to relieve congestion using reactive control together with preventive control. In this paper, we investigate the performance of backpressure control which is a reactive control scheme with an analytical approach. Moreover, we propose backpressure control with cell pushout scheme to overcome some weaknesses of backpressure control. Numerical results show that the control with push-out scheme improves cell loss performance, without increasing delay too much.

Performance analysis of space-priority mechanisms in an input and output queueing ATM switch

In future high-speed integrated networks asynchronous transfer mode (ATM) switches should be able to accommodate diverse types of applications with different quality of services (QOS) and traffic requirements. Thus some types of priority control schemes are needed in ATM switches to increase the utilisation of switches and satisfy the QOS of each traffic type. The authors consider a nonblocking input and output queueing ATM switch with capacity m in which two classes of traffic are admitted. Each input queue adopts one of two space-priority mechanisms, partial push-out and partial buffer sharing, which assign priorities for buffer access to each traffic type according to its loss probability constraints. The distribution of input queue length and loss probabilities of each traffic class are obtained using the matrix-geometric solution method and their performance compared. Numerical analysis and simulation indicate that the switch utilisation with space-priority mechanisms satisfying the QOS of each traffic class is much higher than that of the switch without control and the required buffer size is reduced while satisfying the same QOS. The partial push-out scheme has a somewhat higher throughput than the partial buffer sharing scheme but the latter is preferred to the former owing to its lower implementation complexity.

A new buffer management scheme for hierarchical shared memory switches

We study a multistage hierarchical asynchronous transfer mode (ATM) switch in which each switching element has its own local cell buffer memory that is shared among all its output ports. We propose a novel buffer management technique called delayed pushout that combines a pushout mechanism (for sharing memory efficiently among queues within the same switching element) and a backpressure mechanism (for sharing memory across switch stages). The backpressure component has a threshold to restrict the amount of sharing between stages. A synergy emerges when pushout, backpressure, and this threshold are all employed together. Using a computer simulation of the switch under symmetric but bursty traffic, we study delayed pushout as well as several simpler pushout and backpressure schemes under a wide range of loads. At every load level, we find that the delayed pushout scheme has a lower cell loss rate than its competitors. Finally, we show how delayed pushout can be extended to share buffer space between traffic classes with different space priorities.

Analysis of a finite buffer queue with different scheduling and push-out schemes

A queueing system M 1, M 2/ G 1, G 2/1/ N with different scheduling and push-out scheme is analyzed in this paper. This work is motivated by the study of the performance of an output link of ATM switches with traffic of two classes with different priorities. However, the queueing model developed in this paper is more general than that of the output link of ATM switches with two-class priority traffic. General service time distributions are allowed for classes 1 and 2 and a general service discipline function, α 1( i, j), is introduced where α 1( i, j) is the probability that a class 1 packet will be served, given that there are i class 1 and j class 2 packets waiting for service. An exact solution is obtained for the loss probabilities for classes 1 and 2, the queue length distribution and the mean waiting time for class 1. The queue length distribution and the mean waiting time for class 2 are calculated approximately. It is shown that the approximation is an upper bound and the error due to the approximation is very small when the loss probability of class 2 is small (e.g., less than 0.01).

A Simulation Study of Space Priorities in a Shared Memory ATM Switch

We study an ATM switch architecture in which the queues for all the switch output ports share space flexibly in a common buffer. Using a computer simulation of this switch under bursty traffic, we investigate various ways to manage space priorities in the shared memory. Our findings support one particular strategy which we call “Selective Pushout.” In this scheme, an arriving cell that finds the shared memory full overwrites a cell with priority less than or equal to itself from the longest output queue in the buffer (even if the arriving cell will be joining a different output queue). We simulated Selective Pushout as well as several simpler pushout and threshold schemes under a variety of load conditions. For each load pattern we studied, the Selective Pushout scheme performed at least as well and usually much better than its competitors. Selective Pushout offered a low overall cell loss rate, with very low losses for the high priority cells.