Discard Strategy Research Articles

Supporting User Needs in a Network: A New Queue Management Technique

Traditional network-level Quality of Service (QoS) techniques are efficient from a network perspective, but they have not provided end-to-end QoS that is satisfactory to users. In this letter, a Coordinated Packet Discard scheme for the distribution of end-to-end QoS requirements into local loss constraints, as well as provision of local loss assurance is proposed. Experiments demonstrate its advantages on increasing QoS-satisfied user ratio and improving network efficiency.

On-demand packet discard scheme for TCP over ATM-UBR service

The performance of the TCP over ATM networks is investigated. A TCP packet is segmented into multiple ATM cells at the sending node and reassembled at the receiving node. When congestion occurs, the ATM switch may drop some of the cells. If one or more cells of a TCP packet are dropped, the TCP packet is said to be corrupted. A corrupted packet will be discarded at the receiving node. Transmitting the cells of a corrupted packet will only waste network resources and lower the effective throughput. A major objective of a selective packet discard scheme is to minimise the packet fragmentation problem. Previous approaches such as the early packet discard (EPD) scheme and its variants may drop incoming cells when congestion is anticipated. As a result, the buffer is under-utilised most of the time. Packets may be dropped unnecessarily, and the fragmentation problem cannot be avoided. A new packet discard scheme, called the on-demand packet discard (ODPD) scheme, is presented by the author. The ODPD scheme can fully utilise the available buffer space and effectively avoid the fragmentation problem. The performance of ODPD is found to be better than EPD and its variants under all traffic conditions.

A study of a new selective cell discard scheme with two threshold control on ATM networks

AbstractWhen UBR (Unspecified Bit Rate) service is used on an ATM network, cells are discarded in congestion and imperfect packets are generated that consume network resources in a wasteful manner. As a remedy, the EPD (Early Packet Discard) control is proposed, in which the cells are discarded on a packet basis in congestion by providing a threshold to the input buffer. However, with EDP control, there is a possibility that the EOP (End Of Packet) cell in AAL5 may be discarded. Thus, two successive packets become invalid. For this reason, the TT‐EPD (Two Threshold‐EPD) that prevents discarding of the EOP cell has been proposed. This scheme sets two threshold values (TH1 and TH2) and the fixed TH1 works similarly to EPD control. TH2 carries out dynamic control and secures the input region for the EOP cell in the buffer. In this scheme, the amount of buffer between TH1 and TH2 decreases and there is an increase in the number of acceptance failures in which the cells composing a packet initially accepted are discarded by TH2. In this paper, a method that keeps the amount of buffer between TH1 and TH2 constant to reduce the acceptance missing packets is proposed. The effectiveness of the proposed scheme is demonstrated by simulation. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(8): 50– 57, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10039

A Multi-Agent Architecture for QoS Management in Multimedia Networks

Increasing interest in the transmission of audiovisual applications over best-effort networks (i.e., IP and ATM ABR, and UBR services) and efficient video-aware congestion control techniques have to be designed in order to improve the video quality in the presence of cell loss. This paper presents a new slice-based discard scheme to be used with Guaranteed Frame Rate service (formerly UBR+). The scheme adaptively and selectively adjusts discard levels to the switch's buffer occupancy, video cell payload types, and Forward Error Correction Drop Tolerance. To improve its performance, we introduce a distributed multiagent system that provides a self-regulating network control management by means of automatic adjustment of congestion control parameters. The control agents are distributed in the network and operate on a local scope referred to as a “domain” consisting of two adjacent ATM switches. The aim of the overall Intelligent Quality-of-Service (QoS) control framework is twofold. First, to ensure graceful picture quality degradation by minimizing the cell loss probability for critical video data while guaranteeing a bounded cell transfer delay. Second, to optimize the network effective throughput by reducing the transmission of “nonuseful” data. Performance evaluations show significant improvement over traditional approaches.

Performance Analysis of Generalized Selective Packet Discarding Schemes

Selective packet discarding schemes have been mostly developed and analyzed in the context of ATM networks. However, similar schemes could be applied to non-ATM or more general networks. The analysis of selective packet discarding schemes in a general packet switching environment has been limited to the basic dropping schemes, i.e., Partial Packet Discard (PPD) and Early Packet Discard (EPD), and for only the single traffic source case. In this paper, we extend the mathematical analysis of PPD and EPD for multiple sources and include simulation results to verify the analytical results. Finally, to place the performance of the generalized EPD and PPD in the context of other packet dropping schemes, we also provide simulation results of the Drop from Front (DfF), and preemptive Partial Packet Discard (pPPD) schemes.

Weighted fair discard scheme for buffer management in the presence of network congestion

Data discarding is widely used in networks as a mechanism for buffer management. It enables networks to satisfy various QoS requirements. In this paper, we propose a general weighted fair discard algorithm (WFD) for buffer management in the presence of network congestion and buffer overflow. WFD comprises two parts, discard weight and discard mechanism. Whenever there is a situation of buffer overflow, WFD removes some data from the buffer. The amount of data removed from individual connections is controlled by WFD and is proportional to connections' discard weights. Since discard weights can be flexibly assigned and dynamically adjusted, WFD can thus optimize the performance of various applications more efficiently, as compared with other discard disciplines, such as ‘drop tail’. In addition, certain interesting attributes of WFD are also analyzed in this paper, and results show that we can estimate possible data losses in advance and control them in realtime, as they are extremely useful for multi-streaming or adaptive applications.

A performance model of partial packet discard and early packet discard schemes in ATM switches

In this paper, we develop a concise performance model of partial packet discard (PPD) and early packet discard (EPD) schemes in ATM switches. We study the performance of PPD and EPD with heterogeneous traffic sources. The sources included Poisson, and ON–OFF with long-tailed sojourn time distribution, which is approximated by a hyperexponential distribution. The fairness of EPD is investigated. We automatically generate and numerically solve the underlying Markov chain using a high-level graphical paradigm known as the stochastic reward net. Our numerical results reveal that: (1) the benefit of PPD and EPD is not significant when the queuing system is underloaded with Poisson sources; (2) PPD and EPD can increase the goodput when the system is overloaded or loaded with ON–OFF sources; (3) in All Poisson case, PPD and EPD provide nearly fair service to the sources; (4) the ON–OFF source gets higher goodput than the Poisson source. Because the burstiness of a source will be alleviated by the statistical multiplexing of ATM switches, the ON–OFF source may be viewed as the source that just enters the network, and the Poisson source may be viewed as the source being far away from the network node we are considering and has been regulated and smoothed by the switches it traversed. Therefore, the queuing system with EPD algorithm gives a higher goodput to the sources near it. And the sources far away from the system will have lower goodput. One of our principal conclusions is that per-VC-based scheme is not needed at the core of large ATM networks because the traffic is less bursty at the core of the networks and PPD and EPD are fair under this kind of environment. A per-VC-based scheme may be used at the edge of the ATM cloud. Such a configuration can make the core of the ATM network work at high speed.

An Integrated Framework for Efficient Transport of Real-Time MPEG Video over ATM Best Effort Service

This paper describes a framework for the transport of real-time multimedia traffic generated by MPEG-2 applications over ATM networks using an enhanced UBR best effort service (UBR+). Based on the factors affecting the picture quality during transmission, we propose an efficient and cost-effective ATM best effort delivery service. The proposed framework integrates three major components: 1) a dynamic frame-level priority assignment mechanism based on MPEG data structure and feedback from the network (DexPAS), 2) a novel audio-visual AAL5 SSCS with FEC (AV-SSCS), and 3) an intelligent packet video discard scheme named FEC-PSD, which adaptively and selectively adjusts cell drop levels to switch buffer occupancy, video cell payload type and forward error correction capability of the destination. The overall best-effort video delivery framework is evaluated using ATM network simulation and MPEG2 video traces. The ultimate goal of this framework is twofold: First, minimizing loss of critical video data with bounded end-to-end delay for arriving cells and second, reducing the bad throughput crossing the network during congestion. Compared to previous approaches, performance evaluation shows a good protection of Predictive coded (P-) and Bi-directional Predictive coded (B-) frames at the MPEG video slice layer.

A RED discard strategy for ATM networks and its performance evaluation with TCP/IP traffic

In ATM UBR networks supporting TCP traffic, optimal efficiency can only be envisaged if switches adopt a discard mechanism that operates at the packet level rather than the cell level. In this paper, we define a variant of the RED discard strategy suitable for ATM switches. An interesting feature of this ATM-RED is that it has a similar per-VC implementation complexity as the Early Packet Discard (EPD) algorithm. To study the efficiency of the ATM-RED discard strategy, we compare its performance with plain the UBR, EPD and Fair Buffer Acceptance (FBA) discard strategies by means of simulation with TCP/IP traffic. We give comparative results with respect to different performance criteria such as goodput and fairness in various environments, such as end-to-end ATM networks and IP-based networks with an ATM backbone, in both single-bottlenecked and GFC topologies.

Using selective discard to improve real-time video quality on an ethernet local area network

To support real-time MPEG video on Ethernet, a selective discard scheme can be implemented to trade-off the loss of more important MPEG “I” frames for less important “B” frames. Such a scheme results in better video quality. Copyright © 1999 John Wiley & Sons, Ltd.

Using selective discard to improve real-time video quality on an ethernet local area network

To support real-time MPEG video on Ethernet, a selective discard scheme can be implemented to trade-off the loss of more important MPEG “I” frames for less important “B” frames. Such a scheme results in better video quality. Copyright © 1999 John Wiley & Sons, Ltd.

A detailed experimental performance evaluation on TCP over UBR

The ATM service category UBR is intended for non-real-time applications that do not require guaranteed QoS commitments. With additional, relatively inexpensive control functions such as packet discard schemes, UBR could become a cost-effective alternative for the transmission of data traffic; offering a straightforward and flexible solution as opposed to nrt-VBR and GFR that applies stricter traffic specifications as well as ABR with its sophisticated and complex rate-control protocol. This paper presents the results obtained from a comprehensive set of experiments with TCP over UBR, comprising of measurements taken on different protocol layers. The goal is to experimentally investigate the performance of UBR to carry TCP traffic, to evaluate the performance gain achievable by packet discard schemes and TCP parameter tuning, to study the influence of the TCP implementation, and in a final step, to relate the measurements to simulation results.

Performance analysis of cell discarding techniques for best effort video communications over ATM networks

With increasing interest in the transmission of audio–visual applications over ATM best effort services, efficient video-oriented control mechanisms for improving the video quality in the presence of loss have to be designed. In this paper, we propose and evaluate two new slice-based discard schemes for use with available bit rate and guaranteed frame rate services (e.g. formerly UBR+). The schemes adaptively and selectively adjust the discard level to switch buffer occupancy and video cell payload types. To improve their performance, we also introduce a dynamic frame-level priority data partition technique based on MPEG data structure and feedback from the network. To support these mechanisms, enhancements to the ATM adaptation layer 5 and a new MPEG-2 encapsulation strategy are also proposed. The presented quality of picture (QoP) control framework is evaluated using simulation and actual MPEG video data. The overall aim of the framework is double. First, ensuring a graceful picture quality degradation by minimizing cell loss probability for critical video data, and second optimizing the network effective throughput by reducing transmission of non useful data. In comparison to previous approaches, the performance evaluation have shown a significant reduction of the bad throughput and minimization of losses of intra- and predictive-coded frames at both cell and slice layers.

Packet loss performance of selective cell discard schemes in ATM switches

In transport-layer protocols such as TCP over ATM networks, a packet is discarded when one or more cells of that packet are lost, and the destination node then requires its source to retransmit the corrupted packet. Therefore, once one of the cells constituting a packet is lost, its subsequent cells of the corrupted packet waste network resources. Thus, discarding those cells will enable us to efficiently utilize network resources, and will improve the packet loss probability. We focus on tail dropping (TD) and early packet discard (EPD) as selective cell discard schemes which enforce the switches to discard some of the arriving cells instead of relaying them. We exactly analyze the packet loss probability in a system applying these schemes. Their advantages and limits are then discussed based on numerical results derived through the analysis.

Teletraffic engineering in a broad-band era

This paper gives an overview of the methods and models used for the performance evaluation of asynchronous transfer mode (ATM)-based broad-band integrated services digital networks (B-ISDNs). Because these methods rely heavily upon stochastic processes theory, the relevant concepts from this field are succinctly recalled. The first main topic is traffic modeling. Because of the large impact upon the performance of B-ISDN systems, the concept of traffic burstiness is discussed and various definitions are given and compared. The most common stochastic traffic models are then discussed: on-off, Markov modulated sources, and Markovian process. The field of self-similar traffic is also reviewed. Another approach to source characterization is reviewed as well: bounded traffic models, which instead of a precise statistical description give a set of bounds on the cell generation process. The second main topic is the use of advanced queueing models for the performance evaluation of the ATM statistical multiplexer, the basic B-ISDN modeling concept underlying the design of switching elements, output buffers, rate adapters, etc. The three main solution methods for the statistical multiplexer are reviewed: matrix methods, generating function approach, and fluid flow approximation. This paper concludes with an overview of current topics in B-ISDN teletraffic research: connection admission control, buffer dimensioning, multiquality of service, cell discard schemes, rate-based flow control, per-virtual-connection queueing, and weighted fair queueing.

On TCP performance in ATM networks with per-VC early packet discard mechanisms

Both available bit rate (ABR) service and unspecified bit rate (UBR) service with early packet discard (EPD) schemes have been considered for supporting data applications in ATM networks. Since the transmission control protocol (TCP) is perhaps the most widely used transport layer protocol in existing data networks, the performance of TCP over ATM using ABR and UBR services with EPD schemes is of great interest to ATM equipment vendors and service providers. With regard to this interesting issue, we demonstrate in earlier work [1] some simulation results, which show that (1) with UBR service and EPD schemes, TCP suffers significant performance degradation in terms of fairness and requires a relatively large switch buffer even with a small number of active virtual connections over a LAN configuration, and (2) for the same set of network configurations and with ABR service, TCP achieves good performance in terms of fairness and link utilization, and requires relatively small switch buffer. In this paper, we extend our work [1] by studying the performance of TCP over UBR service where EPD schemes are improved by using per-VC accounting and per-VC queueing techniques. In particular, our simulation results show that in a LAN environment, per-VC based EPD schemes can significantly improve the performance of TCP over UBR service in terms of fairness.

An ATM queue manager handling multiple delay and loss priorities

The asynchronous transfer mode (ATM) technique has been widely accepted as a flexible and effective scheme to transport various traffic over the future broadband network. To fully utilize network resources while still providing satisfactory quality of service (QOS) to all network users, prioritizing the user's traffic according to their service requirements becomes necessary. During call setup or service provisioning, each service can be assigned a service class determined by a delay priority and a loss priority. A queue manager in ATM network nodes will schedule ATM cells departing and discarding sequence based on their delay and loss priorities. Most queue management schemes proposed so far only consider either one of these two priority types. The queue manager handles multiple delay and loss priorities simultaneously. Moreover, a cell discarding strategy, called push-out, that allows the buffer to be completely shared by all service classes, has been adopted in the queue manager. We propose a practical architecture to implement the queue manager by using available VLSI sequencer chips.

Analysis of the effects of SS7 message discard schemes on call completion rates during overload

The author considers the performance of a Signaling System Number 7 network when the routing processors, as opposed to transmission facilities, of signaling transfer points are overloaded. The choice of overload controls in such a situation is implementation-dependent, with an option of simply discarding messages in excess of the signaling transfer point (STP) processing capability. It is this option that is studied. Call completion performance, rather than message throughput is considered as being the primary performance measure of interest since it most accurately reflects the service provided to customers. To determine realistic call completion estimates. the authors explicitly incorporate into their analysis the effects of application-level recovery procedures and customer reattempts, both of which significantly impact the service levels achieved. In so doing, they demonstrate that message throughput can be a very misleading measure of the network's ability to provide service. The need for some form of feedback mechanism to the traffic sources that will allow them to appropriately control traffic entering the network is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lowering the Odds for “Even Up”

Luck or skill? In general, as the above example shows, you may have several courses of action available to you for a given layout. How should you choose your moves in order to discard all of the cards? Or does your choice of moves matter at all? In other words, is the outcome of the game already determined by the deal, regardless of your discarding strategy? To help answer this, first notice that adding the values of adjacent cards is unnecessary. The sum will be even exactly when the two cards share the same parity -either both odd or both even. So you could just as well replace all the aces, threes, fives, sevens, and nines with cards marked a and all the rest with cards marked b. You would then play by removing pairs of adjacent cards that are marked with the same letter. Again, if you get to discard all of the cards, you win; otherwise, at the end of play you will have a pattern of alternating a's and b's.

Mass Rearing and Harvesting Based on an Age-Stage, Two-Sex Life Table: A Potato Tuberworm (Lepidoptera: Gelechiidae) Case Study

Traditional age-specific life table analysis does not take variable development rates into account and deals only with the female population. In this paper, rearing and harvesting of specific life stages are analyzed in the context of a general age-stage, two-sex life table. The question of selecting optimal harvest and discard strategies for the design of insect mass rearing facilities is discussed. The method is demonstrated using data collected from a culture of the potato tuberworm, Phtharimaea aperculella (Zeller).