Buffer Requirements Research Articles

Rethinking FTP

Whole-file transfer is a basic primitive for Internet content dissemination. Content servers are increasingly limited by disk arm movement, given the rapid growth in disk density, disk transfer rates, server network bandwidth, and content size. Individual file transfers are sequential, but the block access sequence on a content server is effectively random when many slow clients access large files concurrently. Although larger blocks can help improve disk throughput, buffering requirements increase linearly with block size. This article explores a novel block reordering technique that can reduce server disk traffic significantly when large content files are shared. The idea is to transfer blocks to each client in any order that is convenient for the server. The server sends blocks to each client opportunistically in order to maximize the advantage from the disk reads it issues to serve other clients accessing the same file. We first illustrate the motivation and potential impact of aggressive block reordering using simple analytical models. Then we describe a file transfer system using a simple block reordering algorithm, called Circus. Experimental results with the Circus prototype show that it can improve server throughput by a factor of two or more in workloads with strong file access locality.

3G Long Term Evolution Baseband Processing with Application-Specific Processors

Data rates in the upcoming 3G long term evolution (LTE) standard will be manifold when compared to the current universal mobile telecommunications system. Implementing receivers conforming with the high-capacity transmission techniques is challenging due to the complexity and computational requirements of algorithms. In this study, the software defined radio (SDR) is targeted and the four essential baseband functions of the 3G LTE receiver, namely, list sphere decoding, fast Fourier transform, QR decomposition, and turbo decoding, are addressed and the functions are implemented as application specific processors (ASPs). As a result, the design space that describes the essential computational challenges of 3G LTE receivers is clarified and estimates of area, power, and interprocessor communication buffer requirements are presented.

Trends in highly scalable crossbar-based packet switch architecture

A combined input and crosspoint queued (CICQ) switch is receiving significant attention to be the next generation high speed packet switch for its scalability; however, a multi-cabinet implementation of a combined input and crosspoint queued (CICQ) switch unavoidably introduces a large round-trip time (RTT) latency between the line cards and switch fabric, resulting a large crosspoint (CP) buffer requirement. In this paper, virtual crosspoint queues (VCQs) that significantly reduces the CP buffer requirement of the CICQ switch is investigated. The VCQs unit resides inside the switch fabric, is dynamically shared among virtual output queues (VOQ) from the same source port, and is operated at the line rate, making the implementation practical. A threshold-based exhaustive round-robin (T-ERR) arbitration is employed to reduce buffer hogging at VCQ. The T-ERR at VCQ and CP arbiters serves packets residing in a longer queue more frequently than packet residing in a shorter queue. Consequently, the T-ERR, drastically increases the throughput of the CICQ switch with small CP buffers. A multi-cabinet implementation of CICQ switch do not support multicasting traffic well since a combination of small CP buffer in the switch fabric and a large RTT latency between the line cards and switch fabric results in non-work conservation of the intra-switch link. Deployment of multicast FIFO buffer between the input buffer and CP buffer shows a promise. With its ability to achieve high throughput independent of RTT and switch port size, the integration of the VCQ architecture and T-ERR scheduler to the CICQ switch is ideal for supporting ever-increasing Internet traffic that requires higher data rate, larger switch size, and efficient multicasting.

A Hybrid Video-on-Demand Data Broadcasting and Receiving Scheme of Harmonic and Staggered Schemes

In providing video-on-demand (VoD) services to a number of clients through networks, the bandwidth requirements of video transmission restrict VoD services. For this reason, many significant broadcasting-based VoD schemes have been proposed to efficiently support services. However, the broadcasting-based VoD schemes approach needs frequency channel hopping, using many channels at the same time and managing many segments of a video. These make it difficult to implement. In this paper, we propose a harmonic staggered broadcasting scheme which has a simple structure and substantially improved VoD efficiency. The proposed scheme substantially reduces the number of segments required and the frequency for switching channels. Also this new scheme performs significantly better than the existing VoD schemes in viewer's waiting time and buffer requirements with simplicity. The numerical results demonstrate that the viewer's waiting time of the harmonic staggered broadcasting scheme is close to the harmonic broadcasting scheme and the buffer requirements of this can be adjusted by a video dividing coefficient <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> .

MPEG-4 Bandwidth Prediction for Broadband Cable Networks

In this paper, we analyze the bandwidth requirements of MPEG-4 and propose and evaluate the accuracy of two new MPEG-4 video traffic models. The first predicts the size of the B-frame while the second predicts the size of the group of pictures (GOP). In a broadband cable network, the B-frame prediction model can be employed by a cable headend to provision video bandwidth efficiently or more importantly, reduce bit rate variability and bandwidth requirements via selective B-frame dropping, thereby minimizing buffering requirements and packet losses at the set top box. It will be shown that the model provides highly accurate prediction for a wide variety of video types, in particular, high action and regular movies encoded in high quality resolution. This is an important benefit since high motion MPEG videos demand the highest bandwidth and generate the widest range of bit rate requirements. Although the B-frame prediction model is very simple to implement, this paper also proposes two methods to simplify its operation further without sacrificing prediction accuracy. We then enhance the B-frame and GOP prediction models using a new scene change detector metric.

Broadcasting scheme with low client buffers and bandwidths for video-on-demand applications

Efficient data broadcasting is independent of request arrivals, and is thus highly promising when transmitting popular videos. A conventionally adopted broadcasting method is periodic broadcasting, which divides a popular video into segments, which are then simultaneously broadcast on different data channels. Once clients want to watch the video, they download the segments from these channels. The skyscraper broadcasting (SkB) scheme supports clients with small bandwidths. An SkB client requires only two-channel bandwidths to receive video segments. This work proposes a reverse SkB (RSkB) scheme, which extends SkB by reducing buffering spaces. The RSkB is mathematically shown to achieve on-time video delivery and two-channel client bandwidths. A formula for determining the maximum number of segments buffered by an RSkB client is presented. Finally, an analysis of RSkB reveals that its client buffer requirements are usually 25---37% lower than SkB. Extensive simulations of RSkB further demonstrate that RSkB yields lower client buffer demand than other proposed systems.

Study on TCP Flow-Competing Congestion and Buffer Requirement of the Congested Links

This paper first presents an analysis model named flow-competing congestion model(FCCM)for this type of congestion.Based on FCCM,the paper derives the distribution of competing flows at the congested link, and analyzes the conditions under which the flow-competing congestion would happen.This paper also explores how much buffers a congested link requires to keep full link utilization when the flow-competing congestion occurs. This paper proves that when sizing buffers for a congested internet link with the aim of keeping full link utilization, the buffer requirement of the flow-competing congestion is not bigger than the minimum buffer requirement of the famous BSCL(buffer sizing for congested internet links)scheme.

Cache-aware timing analysis of streaming applications

Of late, there has been a considerable interest in models, algorithms and methodologies specifically targeted towards designing hardware and software for streaming applications. Such applications process potentially infinite streams of audio/video data or network packets and are found in a wide range of devices, starting from mobile phones to set-top boxes. Given a streaming application and an architecture, the timing analysis problem is to determine the timing properties of the processed data stream, given the timing properties of the input stream. This problem arises while determining many common performance metrics related to streaming applications and the mapping of such applications onto hardware architectures. Such metrics include the maximum delay experienced by any data item of the stream and the maximum backlog or the buffer requirement to store the incoming stream. Most of the previous work related to estimating or optimizing these metrics take a high-level view of the architecture and neglect micro-architectural features such as caches. In this paper, we show that an accurate estimation of these metrics, however, heavily relies on an appropriate modeling of the processor micro-architecture. Towards this, we present a novel framework for cache-aware timing analysis of stream processing applications. Our framework accurately models the evolution of the instruction cache of the underlying processor as a stream is processed, and the fact that the execution time involved in processing any data item depends on all the previous data items occurring in the stream. The main contribution of our method lies in its ability to seamlessly integrate program analysis techniques for micro-architectural modeling with known analytical methods for analyzing streaming applications, which treat the arrival/service of event streams as mathematical functions. This combination is powerful as it allows to model the code/cache-behavior of the streaming application, as well as the manner in which it is triggered by event arrivals. We employ our analysis method to an MPEG-2 encoder application and our experiments indicate that detailed modeling of the cache behavior is efficient, scalable and leads to more accurate timing/buffer size estimates.

Throughput-Buffering Trade-Off Exploration for Cyclo-Static and Synchronous Dataflow Graphs

Multimedia applications usually have throughput constraints. An implementation must meet these constraints, while it minimizes resource usage and energy consumption. The compute intensive kernels of these applications are often specified as cyclo-static or synchronous dataflow graphs. Communication between nodes in these graphs requires storage space which influences throughput. We present an exact technique to chart the Pareto space of throughput and storage trade-offs, which can be used to determine the minimal buffer space needed to execute a graph under a given throughput constraint. The feasibility of the exact technique is demonstrated with experiments on a set of realistic DSP and multimedia applications. To increase scalability of the approach, a fast approximation technique is developed that guarantees both throughput and a, tight, bound on the maximal overestimation of buffer requirements. The approximation technique allows to trade off worst-case overestimation versus run-time.

Design and performance of speculative flow control for high-radix datacenter interconnect switches

High-radix switches are desirable building blocks for large computer interconnection networks, because they are more suitable to convert chip I/O bandwidth into low latency and low cost than low-radix switches [J. Kim, W.J. Dally, B. Towles, A.K. Gupta, Microarchitecture of a high-radix router, in: Proc. ISCA 2005, Madison, WI, 2005]. Unfortunately, most existing switch architectures do not scale well to a large number of ports, for example, the complexity of the buffered crossbar architecture scales quadratically with the number of ports. Compounded with support for long round-trip times and many virtual channels, the overall buffer requirements limit the feasibility of such switches to modest port counts. Compromising on the buffer sizing leads to a drastic increase in latency and reduction in throughput, as long as traditional credit flow control is employed at the link level. We propose a novel link-level flow control protocol that enables high-performance scalable switches that are based on the increasingly popular buffered crossbar architecture, to scale to higher port counts without sacrificing performance. By combining credited and speculative transmission, this scheme achieves reliable delivery, low latency, and high throughput, even with crosspoint buffers that are significantly smaller than the round-trip time. The proposed scheme substantially reduces message latency and improves throughput of partially buffered crossbar switches loaded with synthetic uniform and non-uniform bursty traffic. Moreover, simulations replaying traces of several typical MPI applications demonstrate communication speedup factors of 2 to 10 times.

Advanced generalized conservative staircase method for broadcasting popular movies

The generalized conservative staircase broadcasting method has a better performance in terms of the combination of the subscriber's access latency, buffer requirement and disk I/O transfer rate as compared with the conservative staircase broadcasting method. However, it may cause a film to become discontinuous at a subscriber's site. In this work, we first point out the defect and explain how it causes the film to become discontinuous. Then we present an advanced generalized conservative staircase broadcasting method to ensure continuity. Finally, we analyze that the proposed method keeps the same performance as the conservative staircase broadcasting method .

Studies on the passive-star-coupler architecture for optical-burst-switched networks

Considering the state of the art of wavelength conversion technology, it is likely to dictate a more limited and sparse deployment of wavelength converters in optical burst switching (OBS) networks. Without wavelength conversion capabilities at optical switches, how to avoid burst contention becomes an important issue. This paper proposes an approach to controlling wavelength-division-multiplexing passive optical stars, consisting in queuing arrivals for delayed reception, to be used in OBS networks. This solution brings optical star networks a step closer to all-optical realization. In addition, it allows almost total utilization of the channels, obtainable until now only by time-division multiplexing control. The proposed solution does not suffer performance degradation under heterogeneous traffic conditions and increasing number of nodes. It is thus unique in offering the potential for an all-optical solution and providing at the same time high throughput, low delay, small buffer requirements, and robustness under all traffic conditions.

A Generalized FAST TCP scheme

FAST TCP has been shown to be promising in terms of system stability, throughput and fairness. However, it requires buffering which increases linearly with the number of flows bottlenecked at a link. This paper proposes a new TCP algorithm that extends FAST TCP to achieve ( α , n ) -proportional fairness in steady state, yielding buffer requirements which grow only as the n th power of the number of flows. We call the new algorithm Generalized FAST TCP. We prove stability for the case of a single bottleneck link with homogeneous sources in the absence of feedback delay. Simulation results verify that the new scheme is stable in the presence of feedback delay, and that its buffering requirements can be made to scale significantly better than standard FAST TCP.

Comparison of Shoemaker–McLean–Pratt and Modified Mehlich Buffer Tests for Lime Requirement on Pennsylvania Soils

The Shoemaker–McLean–Pratt (SMP) buffer test is commonly used in Pennsylvania and throughout the United States to determine the lime requirement (LR) of acid soils. The buffer contains potassium chromate, a carcinogen, and all waste must be collected for disposal in a hazardous waste facility. An alternative to the SMP buffer is the Mehlich buffer. Although the Mehlich buffer contains barium chloride (BaCl2), also a hazardous and regulated compound, calcium chloride (CaCl2) has been shown to be an effective substitute. The goal of this study was to compare the SMP buffer and the modified Mehlich buffer (CaCl2 substituted for BaCl2) for estimating LR on PA soils and to determine if the modified Mehlich buffer could provide an effective alternative to the SMP test. Twenty‐two agriculturally important Pennsylvania soils with pH values ranging from 4.5 to 6.4 were collected, and the actual LR of each soil was determined by incubating soils for 3 months with calcium carbonate. The modified Mehlich buffer was a more accurate predictor of the lime required to raise soils to either pH 6.5 (r2=0.92) or 7.0 (r2=0.87) in comparison to the SMP buffer (r2=0.87 and 0.82, respectively). Comparison of calibration equations for Mehlich buffer versus lime requirement derived in this study were similar to those developed on soils from other states and geographic regions.

A Complete Framework to Support Controlled Burst Retransmission in Optical Burst Switching Networks

It is widely accepted that retransmitting bursts in Optical Burst Switching networks improves the throughput at higher layers. Since the data is transported in large bursts and there are burst losses due to contention, indiscriminate retransmission can defeat the purpose of burst-level retransmissions. For many applications, retransmission after a certain time would be of no use and it may not be necessary to retransmit all the lost packets. We propose a framework for retransmission with parameters to control the retransmission rate and thus the increase in the network load. We propose a network model for controlled retransmission and a modified functional architecture of the ingress node. The existing work lacks an accurate analysis to estimate the impact of retransmissions on the network load while studying the improvement in the end-to-end packet recovery. We provide theoretical analysis to evaluate the load at each node due to both fresh and retransmitted bursts. We propose some metrics to quantify the benefit of retransmission and the impact of the retransmission parameters proposed on the network performance. We show that with controlled retransmission, the buffer requirement at the ingress node is proportional to the steady-state rate of retransmitted bursts. We validate the analytical model arid also study the impact of retransmission on the network performance with extensive simulations.

An efficient scheme for broadcasting popular videos at low buffer demand

Data broadcasting is independent of arrivals of requests, and thus it is suitable to transmit popular videos that may interest many viewers at a particular period of time. One broadcasting method (called periodic broadcasting) is to divide a popular video into segments, which are then simultaneously broadcast on different data channels. Once clients want to watch the video, they download the segments from these channels. Specially, the greedy disk-conserving broadcasting (GDB) scheme supports a client with a small bandwidth. In comparison with other similar schemes such as the skyscraper broadcasting (SkB) and the client-centric approach (CCA) schemes, the GDB clients have smaller waiting time. Extending GDB, this work designs a reverse GDB (RGDB) scheme to achieve small buffering spaces as well as low bandwidths at the client. We further mathematically prove that RGDB still guarantees on-time video delivery at small client bandwidths. A formula is derived for the maximum number of segments buffered by an RGDB client. Finally, an analysis shows that RGDB has 33–50% smaller client buffer requirements than GDB in most situations.

Buffer Control to Support a Seamless Stream Handoff in a WLAN that Employs Simulcast Streaming

This paper studies the buffer control issues that are related to supporting a seamless stream handoff in a WLAN environment that employs simulcast streaming. We analyze the impacts of the handoff disruption period and inter-AR synchronization variance. We also derive theoretical results that concern how a seamless stream handoff can be guaranteed in terms of the minimum buffer and backlog requirements. Based on the results, an MH-controlled-AR-pushed buffer control scheme is proposed and its cooperation with FMIPv6 is also discussed. The simulation results confirm the effectiveness of our scheme. In general, the deployment of a few-hundred-millisecond video-clip buffer in ARs and MHs is sufficient to achieve the seamless stream handoff most of the time, subject to fairly relaxed constraints of the inter-AR synchronization variance (ranging plusmn 150 ms) and handoff disruption period (around 50 ms).

Analysis of performance trade-offs for an adaptive channel-aware wireless scheduler

In this paper, we consider the scheduling problem where data packets from K input-flows need to be delivered to K corresponding wireless receivers over a heterogeneous wireless channel. Our objective is to design a wireless scheduler that achieves good throughput and fairness performance while minimizing the buffer requirement at each wireless receiver. This is a challenging problem due to the unique characteristics of the wireless channel. We propose a novel idea of exploiting both the long-term and short-term error behavior of the wireless channel in the scheduler design. In addition to typical first-order Quality of Service (QoS) metrics such as throughput and average delay, our performance analysis of the scheduler permits the evaluation of higher-order metrics, which are needed to evaluate the buffer requirement. We show that variants of the proposed scheduler can achieve high overall throughput or fairness as well as low buffer requirement when compared to other wireless schedulers that either make use only of the instantaneous channel state or are channel-state independent in a heterogenous channel.

Energy-aware disk scheduling for soft real-time I/O requests

In this work, we develop energy-aware disk scheduling algorithm for soft real-time I/O. Energy consumption is one of the major factors which bar the adoption of hard disk in mobile environment. Heat dissipation of large scale storage system also calls for an energy-aware scheduling technique to further increase the storage density. The basic idea in this work is to properly determine the I/O burst size so that device can be in standby mode between consecutive I/O bursts and that it can satisfy the soft real-time requirement. We develop an elaborate model which incorporates the energy consumption characteristics, overhead of mode transition in determining the appropriate I/O burst size and the respective disk operating schedule. Efficacy of energy-aware disk scheduling algorithm greatly relies on not only disk scheduling algorithm itself but also various operating system and device firmware related concerns. It is crucial that the various operating system level and device level features need to be properly addressed within disk scheduling framework. Our energy-aware disk scheduling algorithm successfully addresses a number of outstanding issues. First, we examine the effect of OS and hard disk firmware level prefetch policy and incorporate its effect in our disk scheduling framework. Second, our energy aware scheduling framework can allocate a certain fraction of disk bandwidth to handle sporadically arriving non real-time I/O's. Third, we examine the relationship between lock granularity of the buffer management and energy consumption. We develop a prototype software with energy-aware scheduling algorithm. In our experiment, proposed algorithm can reduce the energy consumption to one fourth if we use energy-aware disk scheduling algorithm. However, energy-aware disk scheduling algorithm increases buffer requirement significantly, e.g., from 4 to 140 KByte. We carefully argue that the buffer overhead is still justifiable given the cost of DRAM chip and importance of energy management in modern mobile devices. The result of our work not only provides the energy efficient scheduling algorithm but also provides an important guideline in capacity planning of future energy efficient mobile devices.

High-Performance Reduction Circuits Using Deeply Pipelined Operators on FPGAs

Field-programmable gate arrays (FPGAs) have become an attractive option for accelerating scientific applications. Many scientific operations such as matrix-vector multiplication and dot product involve the reduction of a sequentially produced stream of values. Unfortunately, because of the pipelining in FPGA-based floating-point units, data hazards may occur during these sequential reduction operations. Improperly designed reduction circuits can adversely impact the performance, impose unrealistic buffer requirements, and consume a significant portion of the FPGA. In this paper, we identify two basic methods for designing serial reduction circuits: the tree-traversal method and the striding method. Using accumulation as an example, we analyze the design trade-offs among the number of adders, buffer size, and latency. We then propose high-performance and area-efficient designs using each method. The proposed designs reduce multiple sets of sequentially delivered floating-point values without stalling the pipeline or imposing unrealistic buffer requirements. Using a Xilinx Virtex-ll Pro FPGA as the target device, we implemented our designs and present performance and area results.