Buffer Requirements Research Articles

A Design Framework for Multi-Resolution Video Servers

Video can be encoded into multiple-resolution format in nature. A multi-resolution or scalable video stream is a video sequence encoded such that subsets of the full resolution video bit stream can be decoded to recreate lower resolution video streams. Employing scalable video enables a video server to provide multiple resolution services for a variety of clients with different decoding capabilities and network bandwidths connected to the server. The inherent advantages of the multi-resolution video server include: heterogeneous client support, storage efficiency, adaptable service, and interactive operations support. For designing a video server, several issues should be dealt with under a unified framework including data placement/retrieval, buffer management, and admission control schemes for deterministic service guarantee. In this paper, we present a general framework for designing a large-scale multi-resolution video server. First, we propose a general multi-resolution video stream model which can be implemented by various scalable compression techniques. Second, given the proposed stream model, we devise a hybrid data placement scheme to store scalable video data across disks in the server. The scheme exploits both concurrency and parallelism offered by striping data across the disks and achieves the disk load balancing during any resolution video service. Next, the retrieval of multi-resolution video is described. The deterministic access property of the placement scheme permits the retrieval scheduling to be performed on each disk independently and to support interactive operations (e.g. pause, resume, slow playback, fastforward and rewind) simply by reconstructing the input parameters to the scheduler. We also present an efficient admission control algorithm which precisely estimates the actual disk workload for the given resolution services and hence permits the buffer requirement to be much smaller. The proposed schemes are verified through detailed simulation and implementation.

Queue Length Analysis of Non-Preemptive DiffServ Networks

Abstract Considering that differential services (DiffServ) networking technologies are under development to support diverse quality-of-service (QoS) requirements, this letter provides the upper and lower bounds of the expected queue length for each priority class in a non-preemptive priority queueing system. The results illustrate the possible performance gain in terms of buffer requirement and/or waiting time that Diffserv networks can provide compared to those that do not support service differentiation.

First segment partition for video-on-demand broadcasting protocols

Broadcasting is an efficient transmission scheme to provide on-demand service for very popular movies in a multicast environment. In this paper, a comparative study is first performed to evaluate various broadcasting protocols in terms of maximum waiting time, client buffer requirement and receiver bandwidth. It is found that some existing broadcasting schemes are not practical to provide a small delay video-on-demand (VoD) service if the client buffer size is not large enough. It is shown that the staggered [1] and skyscraper [3] protocols are the only feasible solutions to support an insensitive delay VoD system with limited client buffer and receiver bandwidth. Two first segment partition schemes are then proposed to further reduce the maximum waiting time of these two broadcasting schemes. The results show that if 15 min of video data can be stored in the buffer, Skyscraper with our proposed schemes can serve the customers within 10 s using 16 video channels. For Staggered broadcasting with our schemes, the maximum waiting time can also be reduced from 7.5 min to less than 1 min.

Reducing bandwidth requirement for delivering video over wide area networks with proxy server

Due to the high bandwidth requirement and rate variability of compressed video, delivering video across wide area networks (WANs) is a challenging issue. Proxy servers have been used to reduce network congestion and improve client access time on the Internet by caching passing data. We investigate ways to store or stage partial video in proxy servers to reduce the network bandwidth requirement over WAN. A client needs to access a portion of the video from a proxy server over a local area network (LAN) and the rest from a central server across a WAN. Therefore, client buffer requirement and video synchronization are to be considered. We study the tradeoffs between client buffer, storage requirement on the proxy server, and bandwidth requirement over WAN. Given a video delivery rate for the WAN, we propose several frame staging selection algorithms to determine the video frames to be stored in the proxy server. A scheme called chunk algorithm, which partitions a video into different segments (chunks of frames) with alternating chunks stored in the proxy server, is shown to offer the best tradeoff. We also investigate an efficient way to utilize client buffer when the combination of video streams from WAN and LAN is considered.

Design and Simulation of a New Queuing Architecture for Large-Scale ATM Switches

The authors study the different buffering techniques used in the literature to solve the contention problem in asynchronous transfer mode (ATM) switching architectures. The objective of this study is to determine the buffer requirements needed to achieve a given quality of service (e.g., a given cell loss probability). On the basis of this study, the authors propose a combined central and output queuing (CCOQ) technique to be used in designing large-scale ATM switches. Also, a general design technique for an N× N large-scale ATM switch is proposed with a suitable CCOQ buffer size to reduce both the cell loss probability and the complexity of the memory modules. The switch has to be designed such that it can be implemented using the smallest number of VLSI chips possible. It should be also reliable for commercial use. The switch should support multicast and priority control functions.

An effective feedback control mechanism for DiffServ architecture

As a scalable QoS (Quality of Service) architecture, DiffServ (Differentiated Service) mainly consists of two components: traffic conditioning at the edge of the DiffServ domain and simple packet forwarding inside the DiffServ domain. DiffServ has many advantages such as flexibility, scalability and simplicity. But when providing AF (Assured Forwarding) services, DiffServ has some problems such as unfairness among aggregated flows or among micro-flows belonging to an aggregated flow. In this paper, a feedback mechanism for AF aggregated flows is proposed to solve this problem. Simulation results show that this mechanism does improve the performance of DiffServ. First, it can improve the fairness among aggregated flows and make DiffServ more friendly toward TCP (Transmission Control Protocol) flows. Second, it can decrease the buffer requirements at the congested router and thus obtain lower delay and packet loss rate. Third, it also keeps almost the same link utility as in normal DiffServ. Finally, it is simple and easy to be implemented.

Automatic recovery from disk failure in continuous-media servers

Continuous-media (CM) servers have been around for some years. Apart from server capacity, another important issue in the deployment of CM servers is reliability. This study investigates rebuild algorithms for automatically rebuilding data stored in a failed disk into a spare disk. Specifically, a block-based rebuild algorithm is studied with the rebuild time and buffer requirement modeled. A buffer-sharing scheme is then proposed to eliminate the additional buffers needed by the rebuild process. To further improve rebuild performance, a track-based rebuild algorithm that rebuilds lost data in tracks is proposed and analyzed. Results show that track-based rebuild, while it substantially outperforms block-based rebuild, requires significantly more buffers (17-135 percent more) even with buffer sharing. To tackle this problem, a novel pipelined rebuild algorithm is proposed to take advantage of the sequential property of track retrievals to pipeline the reading and writing processes. This pipelined rebuild algorithm achieves the same rebuild performance as track-based rebuild, but reduces the extra buffer requirement to insignificant levels (0.7-1.9 percent). Numerical results computed using models of five commercial disk drives demonstrate that automatic rebuild of a failed disk can be done in a reasonable amount of time, even at relatively high server utilization (e.g., less than 1.5 hours at 90 percent utilization).

Strip based coding for large images using wavelets

Thanks to advances in sensor technology, today we have many applications (space-borne imaging, medical imaging, etc.) where images of large sizes are generated. Straightforward application of wavelet techniques for above images involves certain difficulties. Embedded coders such as EZW and SPIHT require that the wavelet transform of the full image be buffered for coding. Since the transform coefficients also require storing in high precision, buffering requirements for large images become prohibitively high. In this paper, we first devise a technique for embedded coding of large images using zero trees with reduced memory requirements. A 'strip buffer' capable of holding few lines of wavelet coefficients from all the subbands belonging to the same spatial location is employed. A pipeline architecure for a line implementation of above technique is then proposed. Further, an efficient algorithm to extract an encoded bitstream corresponding to a region of interest in the image has also been developed. Finally, the paper describes a strip based non-embedded coding which uses a single pass algorithm. This is to handle high-input data rates. (C) 2002 Elsevier Science B.V. All rights reserved.

IDMP-based fast handoffs and paging in IP-based 4G mobile networks

We consider the use of our previously proposed Intra-Domain Mobility Management Protocol (IDMP) in fourth-generation mobile networks. On evaluating the heterogeneous access technologies, cellular layouts, and application characteristics of 4G environments, we realize a need to reduce both handoff latency and the frequency of mobility-related signaling. We first present IDMP's fast intradomain handoff mechanism that uses a duration-limited proactive packet multicasting solution. We quantify the expected buffering requirements of our proposed multicasting scheme for typical 4G network characteristics and compare it with alternative IP-based fast handoff solutions. We also present a paging scheme under IDMP that replicates the current cellular paging structure. Our paging mechanism supports generic paging strategies and can significantly reduce the mobility-related IP signaling load.

Minimizing Buffer Requirements under Rate-Optimal Schedule in Regular Dataflow Networks

Large-grain synchronous dataflow graphs or multi-rate graphs have the distinct feature that the nodes of the dataflow graph fire at different rates. Such multi-rate large-grain dataflow graphs have been widely regarded as a powerful programming model for DSP applications. In this paper we propose a method to minimize buffer storage requirement in constructing rate-optimal compile-time (MBRO) schedules for multi-rate dataflow graphs. We demonstrate that the constraints to minimize buffer storage while executing at the optimal computation rate (i.e. the maximum possible computation rate without storage constraints) can be formulated as a unified linear programming problem in our framework. A novel feature of our method is that in constructing the rate-optimal schedule, it directly minimizes the memory requirement by choosing the schedule time of nodes appropriately. Lastly, a new circular-arc interval graph coloring algorithm has been proposed to further reduce the memory requirement by allowing buffer sharing among the arcs of the multi-rate dataflow graph. We have constructed an experimental testbed which implements our MBRO scheduling algorithm as well as (i) the widely used periodic admissible parallel schedules (also known as block schedules) proposed by Lee and Messerschmitt (IEEE Transactions on Computers, vol. 36, no. 1, 1987, pp. 24---35), (ii) the optimal scheduling buffer allocation (OSBA) algorithm of Ning and Gao (Conference Record of the Twentieth Annual ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages, Charleston, SC, Jan. 10---13, 1993, pp. 29---42), and (iii) the multi-rate software pipelining (MRSP) algorithm (Govindarajan and Gao, in Proceedings of the 1993 International Conference on Application Specific Array Processors, Venice, Italy, Oct. 25---27, 1993, pp. 77---88). Schedules generated for a number of random dataflow graphs and for a set of DSP application programs using the different scheduling methods are compared. The experimental results have demonstrated a significant improvement (10---20%) in buffer requirements for the MBRO schedules compared to the schedules generated by the other three methods, without sacrificing the computation rate. The MBRO method also gives a 20% average improvement in computation rate compared to Lee's Block scheduling method.

Exploitation of DWDM for optical packet switching with quality of service guarantees

This paper addresses the problem of building optical packet switches that are able to effectively cope with variable length packet traffic and quality of service management, therefore able to support IP traffic. The paper aims at showing that the availability of dense wavelength division multiplexing is crucial. By suitably exploiting the wavelength dimension a multistage fiber delay line buffer can be implemented, with fine granularity and long delay with an architecture of limited complexity. This is necessary to fulfill the buffering requirements of variable length packets. Furthermore, the wavelength domain is proved to be more effective than the time domain to manage different levels of quality of service. Algorithms are presented that are peculiarly designed for this environment showing that they can effectively differentiate the packet loss probability between three priority classes.

Phosphate Is Required to Maintain the Outer Membrane Integrity and Membrane Potential of Respiring Yeast Mitochondria

The buffer requirements to maintain mitochondrial intactness and membrane potential in in vitro studies were investigated, using gradient purified yeast mitochondria. It was found that the presence of phosphate is crucial for generation of a stable membrane potential and for preserving the intactness of the outer membrane, as assessed by probing the accessibility of Tom40p to trypsin and the leakage of cytochrome b2 from the intermembrane space. Upon addition of respiratory substrate in the absence of phosphate, mitochondria generate a membrane potential that collapses within 1 min. Under the same conditions, the mitochondrial outer membrane is disrupted. The presence of phosphate prevents both phenomena. The ΔpH component of the proton motive force appears to be responsible for the compromised outer membrane integrity. The collapse of the membrane potential is reversible to a limited extent. Only when phosphate is added soon enough after the addition of exogenous respiratory substrate can a stable membrane potential be obtained again. Within a few minutes, this capacity is lost. The presence of Mg2+ prevents rupture of the outer membrane, but does not prevent rapid dissipation of the membrane potential. Similar results were obtained for mitochondria isolated and stored in the presence of dextran or bovine serum albumin.

The Analysis and Performance of Multi-Rate Service in Distributed Video-on-Demand Systems

In this paper, we develop an end-to-end analysis of a distributed Video-on-Demand (VoD) system that includes an integrated model of the server and the network subsystems with analysis of its impact on client operations. The VoD system provides service to a heterogeneous client base at multiple playback rates. A class-based service model is developed where an incoming video request can specify a playback rate at which the data is consumed on the client. Using an analytical model, admission control conditions at the server and the network are derived for multi-rate service. We also develop client buffer requirements in presence of network delay bounds and delay jitter bounds using the same integrated framework of server and network subsystems. Results from an extensive simulation show that request handling policies based on limited redirection of blocked requests to other resources perform better than load sharing policies. The results also show that downgrading the service for blocked requests to a lower bitrate improves VoD system performance considerably. Combining the downgrade option with restrictions on access to high bitrate request classes is a powerful tool for manipulating an incoming request mix into a workload that the VoD system can handle.

MCoRe: an adaptive scheme for rerouting multicast connections in mobile ATM networks

In this paper we propose multicast connection rerouting (MCoRe), a novel scheme for efficient multicasting in mobile asynchronous transfer mode (ATM) networks. We investigate and evaluate McoRe's performance in mobile ATM networks in the presence of mobile source fand/or receivers. In the past, multicasting from and to mobile hosts in mobile ATM networks has not received much attention from researchers. MCoRe is based on active network (AN) technologies, where the computation required for rerouting connections is performed at switches. Due to intra-network processing, MCoRe is efficient, requires minimal buffer requirements, has low handoff latency and high reuse, and incurs low signaling overheads. Apart from that, MCoRe preserves cell ordering, prevents cell duplication and minimizes cell loss during source or receiver migration. We show how shortest path tree adapts to source migration without incurring high signaling overheads. With MCoRe, source migration is transparent to the multicast group members and does not entail reconstruction of existing multicast tree. We also show how receiver migration is achieved and how cell ordering is preserved, when the receiver rejoins the multicast session.

Phased RGSS: An improved disk array scheduling for continuous media retrieval

This paper proposed a disk array scheduling algorithm called Phased RGSS which improves the initial service latency over RGSS presented by Kang and Park [IEICE Trans. Inform. Systems E81-D (8) (1998)] without increasing the buffer requirement for jitter-free service for continuous media retrieval. A specific data layout should be provided in order for Phased RGSS to be applied. The data layout makes disk arm movement more effective. The characteristics of Phased RGSS are proved by analysis of buffer requirement as well as initial startup delay.

WINTRAC: a TCP window adjustment scheme for bandwidth management

In TCP, congestion control as well as error recovery are implemented by a sliding window. The dynamics of TCP specifically, a mismatch between the TCP window and the bandwidth-delay product of the network can sometimes cause the network switches or routers to accumulate large queues, resulting in buffer overflows, reduced throughput, unfairness and underutilization. It is generally accepted that there is a limit to how much control can be accomplished from the congestion control mechanisms in the end systems. Some mechanisms are needed in the intermediate network elements to complement the endpoint congestion avoidance mechanisms. We describe in this paper, a new TCP rate control scheme based on a simple recursive algorithm. The idea behind the algorithm is to match the offered network load to the available resources by modifying at an intermediate network element, the receiver’s advertised window in TCP acknowledgments returning to the source. We show through simulations that the scheme can efficiently control TCP traffic to limit queue buildups and buffer requirements at the network nodes, resulting in significant improvements in delay, packet loss rates, fairness in the distribution of the maximum achievable window size, and link utilization.

Dynamic planning based protocols for real-time communication in LAN and switched LAN environments

The problem of real-time communication over a multiple access network has been well studied in the recent past. However, there are very few protocols that can bound the worst case channel access time to ensure predictability of message transmission for the LAN environment. In addition, there has been no prior work addressing real-time communication over a switched (extended) local area network (SLAN), where several LAN segments are connected through a switch. In this paper, we propose real-time protocols for the LAN and the SLAN. The proposed protocols are based on CSMA/CD with deterministic collision resolution and belong to the dynamic planning based category, where an admission test is performed for guaranteeing message transmission. The admission test used in the proposed protocols is based on the worst case channel access time that can elapse before a particular node can start transmitting its message. We also compute the worst case buffer requirement at the switch for the proposed SLAN protocols. We study the effectiveness of the proposed protocols through extensive simulation studies.

Managing Latency and Buffer Requirements in Processing Graph Chains

Real-time signal-processing applications for high assurance systems are commonly designed using a processing-graph software architecture. Here we demonstrate the management of latency and buffer requirements in such an architecture—the US Navy’s processing graph method (PGM). By applying recent results in real-time scheduling theory to the subset of PGM employed by the US DARPA rapid prototyping of application-specific signal processors (RASSP) synthetic aperture radar (SAR) benchmark application, we identify inherent real-time properties of nodes in a PGM graph, and demonstrate how these properties can be exploited to perform useful and important system-level analyses such as schedulability analysis, end-to-end latency analysis, and memory requirements analysis. More importantly, we develop relationships between properties such as latency and buffer bounds and show how one may be traded off for the other.

Quality-of-service dependent curve characterization for multimedia networks

Unlike conventional deterministic bounding curve characterization, quality-of-service (QoS) dependent (e.g., the portion of buffer-overflow time intervals) curve characterization allows bound-violation for a certain portion of time and results in flexible, pointwisely smaller constraint functions to utilize valuable network resources. Our derivations show that the portion of bound-violation for an L/sup P/-sense (1/spl les/p/spl les//spl infin/) constraint function has a normalized tail bound decaying with x/sup -p/, and L/sup p/-sense constraint functions reduce to deterministic ones when p=/spl infin/. Therefore, our QoS-dependent constraint functions are obvious generalizations of conventional deterministic constraint functions. We further apply L/sup P/-sense constraint functions to reduce buffer requirements for multi-hop connections according to the required bound on the portion of time prone to buffer overflows.

Buffer Requirements and Server Ordering in a Tandem Queue with Correlated Service Times

We analyze the intermediate buffer requirements in a tandem queue where service times of each customer are deterministically correlated between the servers and arbitrarily distributed between customers. The major issue at hand is the determination of intermediate buffer sizes assuring no blocking when the arrivals pattern is arbitrary and unpredictable. The analysis shows that the worst arrival process is the Just-in-Time (JIT) process. Further, it shows that ordering of the servers with respect to service rates may be detrimental, and that the most vulnerable architectural design is that in which the servers have almost the same service rates. It is shown that the total buffer requirement in the system may be quite sensitive to the server ordering: A proper ordering requires just O(M) (where M is the number of queues) buffer size, while an improper ordering may require O(M2).