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Providing quality of service (QoS) for Internet-based video streaming applications requires the server and/or client to be network-aware and adaptive. We present a dynamic rate and quality adaptation algorithm where the server varies its sending rate (without varying the quality level) to adapt to the network and client conditions and only as a last resort, does quality adaptation. We place the adaptation logic at the client since it has better knowledge about both the demand (buffer conditions, variable bit-rate requirements) and supply (network conditions). Our approach is unique because the server's sending rate is calculated based on the client's varying demand (consumption rate) and the network status. Also, we do not model the network as a black-box but instead augment endpoint observations with a feedback from the network to represent its status more precisely. To make an informed adaptation decision, the client requires sizes of all frames in the variable bit rate video. But the overhead involved in sending this metadata is significant. So we propose a lossy compression technique to reduce the amount of control information and consequently the overhead. We also present a scheduling algorithm, Dynamic Scheduling Algorithm for Reduced Trace delivery (DART), to deliver the compressed control information to the client. This algorithm can be used to deliver any form of metadata (like subtitles, alerts, etc.), especially in applications like IP-TV. Simulations show that the proposed techniques can significantly improve user perceived QoS when compared to other popular adaptation methods. Index Terms--IP-TV, metadata delivery, rate adaptation, QoS, trace compression, underflow curve.

Interlaced Magnetic Recording (IMR) is a promising technology which achieves higher data density and lower write amplification (WA) than Shingled Magnetic Recording (SMR). In IMR, top tracks and bottom tracks are interlaced so each bottom track is partially overlapped with two adjacent top tracks. Top tracks can be updated without any WA, but bottom track updates require reading and rewriting of affected valid data on the two neighboring top tracks. There are few published studies discussing WA in IMR drives. We propose TrackLace to reduce WA for IMR. TrackLace consists of three techniques: Z-Alloc allocates user data to the tracks in alternating directions and spreads unallocated tracks among allocated tracks; Top-Buffer opportunistically utilizes unallocated top tracks to buffer bottom track updates; and Block-Swap progressively swaps bottom track hot data with top track cold data during high space utilization. To further optimize TrackLace performance, we propose a virtual frame design that can keep the relocated block (due to Top-Buffer or Block-Swap) close to its original location and an adaptive buffering mechanism that can avoid unnecessary redirections depending on the write locality. Evaluations show that TrackLace can reduce WA by 45 percent and lower average latency by 31percent compared with baseline schemes. [ABSTRACT FROM AUTHOR]

Shingled Magnetic Recording (SMR) drives can benefit large-scale storage systems by reducing the Total Cost of Ownership (TCO) of dealing with explosive data growth. Among all existing SMR models, Host Aware SMR (HA-SMR) looks the most promising for its backward compatibility with legacy I/O stacks and its ability to use new SMR-specific APIs to support host I/O stack optimization. Building storage systems using HA-SMR drives calls for a deep understanding of the drive’s performance characteristics. To accomplish this, we conduct in-depth performance evaluations on HA-SMR drives with a special emphasis on the performance implications of the SMR-specific APIs and how these drives can be deployed in large storage systems. We discover both favorable and adverse effects of using HA-SMR drives under various workloads. We also investigate the drive’s performance under legacy production environments using real-world enterprise traces. Finally, we propose a novel host-controlled buffer that can help to reduce the severity of the decline in HA-SMR performance under our discovered unfavorable I/O access patterns. Without a detailed comprehensive design, we show the potential of the host-controlled buffer by a case study. [ABSTRACT FROM PUBLISHER]

This paper proposes a deMOtion-based, fLash-awARe hybrid storage cache model, named MOLAR, to effectively integrate Flash-based Solid-State Disks (SSDs) into traditional dynamic random access memory (DRAM)-based memory storage systems where SSDs serve as the Tier-2 cache, while DRAM is considered as the Tier-1 cache. We found that conventional cache algorithms designed for DRAM perform poorly in SSDs due to the limited write cycles and asymmetric read/write performance of Flash memory. InMOLAR, a Flash-aware I/O path structure is designed to adapt the asymmetric read and write performance of SSDs and, moreover, to reduce useless write operations. A new control metric, demotion count, is validated to wisely select the evicted blocks from DRAM to reside in the SSD. Besides, for SSD can improve internal data placement from data access hints, the Logical Block Addresses in the SSD are grouped into the long-lived region and the short-lived region self-adaptively via a heuristic control algorithm based on the change of the block demotion count. Through trace-driven simulations, the overall hit ratio in MOLAR outperforms two traditional policies by 1.44-5.34%. The average access latency in SSDs is reduced by 3.5 x to 4.5x. Moreover, write amplification is effectively reduced by ~36% in two typical Flash address-mapping policies. [ABSTRACT FROM AUTHOR]

With the development of wireless communications, Vehicular Ad Hoc Network (VANET) has received considerable attention on information sharing and data delivery services. In order to collect and control traffic conditions, Intelligent Transportations Systems (ITS) has deployed a number of Road Side Units (RSUs) along the roads to collect and deliver traffic information to the Traffic Control Center (TCC) for analyzing traffic data. Although some VANET architectures have been proposed based on the predictable routes and schedules of buses, none of them considered taking advantage of such traffic infrastructures which already been supplied by ITS and combine them with scheduled buses. In this paper, we propose a two-tier BUSVANET that is fully integrated with RSUs and TCC as traffic infrastructures. In this new architecture, the communications of vehicles, not only benefit from the existence of buses, but also consider the effects of using RSUs and TCC. RSUs are used to ensure service coverage while TCC is helpful for locating the destination vehicle quickly. We also investigate how much benefits can be obtained by taking advantage of this type of traffic infrastructure. [ABSTRACT FROM PUBLISHER]

High-bandwidth and real-time constraints for supporting concurrent video accesses make generic software architecture design for high-performance on-demand video servers challenging. This challenging task can be even more complicated when we consider that a generic software architecture should be applied to different hardware platforms. In this paper, we introduce the design, implementation, and evaluation of a generic software architecture for on-demand video servers. We describe different key components on controlling the storage and network devices within the server. The interactive collaborations between these software components are also illustrated. The experimental results indicate a very promising direction on exploring the right combinations of these software components. The server is, thus, able to increase the number of concurrent video accesses with the same hardware configuration. For instance, with the right combinations, the system achieved about 80 percent of the storage system bandwidth of four disks, about 70 percent of the storage system bandwidth of six disks, and generally reached the maximal achieved SCSI bandwidth when eight disks are used over two SCSI buses (i.e., four disks on each SCSI bus). Our research and experimental results are based on video servers currently under construction across a variety of hardware platforms, including SMP, DMP, and clusters of PC or workstations. The most-advanced prototype server is based on an SGI shared-memory multiprocessor with a mass storage system consisting of RAID-3 disk arrays. With all the enabling/management schemes, we were able to further investigate interesting research issues by considering the user's access profiles for taking advantage of popular video titles. The results were significant, with a range of 60 percent improvement given a 512 Kbyte block size. In addition to the experimental results, theoretical performance models were also developed that closely match to our collected experimental results. Index Terms - Experimental systems, system integration and management, distributed multimedia systems.

Abstract: Much research has been conducted on energy efficient cache buffer management for disk based storage systems. Some of them use greedy prefetching technique to artificially increase disk idle intervals if there is a large number of known future requests. However, this might result in sub-optimal solution by not exploiting the relationship between I/O access pattern (sequential/random) and application pattern (cpu time required for computing). In a cpu-bound application, by explicitly taking into account the required CPU time it may reduce energy conservation by up to 50% and increase power cycle number by 100% compared to an existing efficient prefetching scheme without this consideration. In this paper, we consider the tradeoff between disk power consumption, performance guarantee and disk reliability all together by proposing a Disk characteristic based Power-Optimal Prefetching (DiscPOP) scheme. Specifically, we make three contributions: (i) A theoretical model is proposed to analyze energy-efficient cache buffer management in disk I/O system and it was formulated as an optimization problem. We have shown it can be solved via an Integer Linear Programming (ILP) technique, we further conduct the following research. (ii) For offline cases, we proposed a Greedy Partition algorithm (GP) to divide the problem into several small ones and solve them separately via the proposed ILP algorithm. (iii) For online cases, we proposed two heuristic algorithms based on Lazy Start Power-Optimal Prefetching (LSPOP) technique. Both of them use simple threshold controlled algorithms to select a prefetching start judiciously and cautiously. We use a trace-driven simulation to evaluate our proposed schemes. The results show GP outperforms the traditional aggressive prefetching by up to 26.9% more disk energy conservation and 17.8% power cycle reduction. The online heuristic algorithms can also improve disk energy saving by up to 20.5% and reduce power cycle by 14.3%. [Copyright &y& Elsevier]

This paper proposes Trajectory-based Statistical Forwarding (TSF) scheme, tailored for the multihop data delivery from infrastructure nodes (e.g., Internet access points) to moving vehicles in vehicular ad hoc networks. To our knowledge, this paper presents the first attempt to investigate how to effectively utilize the packet destination vehicle's trajectory for such an infrastructure-to-vehicle data delivery. This data delivery is performed through the computation of a target point based on the destination vehicle's trajectory that is an optimal rendezvous point of the packet and the destination vehicle. TSF forwards packets over multihop to a selected target point where the vehicle is expected to pass by. Such a target point is selected optimally to minimize the packet delivery delay while satisfying the required packet delivery probability. The optimality is achieved analytically by utilizing the packet's delivery delay distribution and the destination vehicle's travel delay distribution. Through theoretical analysis and extensive simulation, it is shown that our design provides an efficient data forwarding under a variety of vehicular traffic conditions. [ABSTRACT FROM PUBLISHER]

Evaluates the performance of iSCI-based storage subsystems which is used as an end-to-end protocol for transporting storage input-output block data over internet protocol networks. Description of the testbed environment and the measurement methods and performance metrics; Applications in storage area networks; Measurement and analysis of block-level input-output access performance and file-level performance study.

Studies localized quality-of-service routing schemes where the edge routers make routing decisions using only local information and thus reduce the overhead at core routers. Description of virtual capacity based routing; Proposed use of proportional sticky routing; Implications on studies of computer networks.

Introduces a series of articles about designing and implementing computer systems capable of processing and distributing large continuous media files to Internet users. INSET: Interactive Video: Thirty Years and Counting, by Richard H....

Road networks are one of important surveillance areas in military scenarios. In these road networks, sensors will be sparsely deployed (hundreds of meters apart) for the cost-effective deployment. This makes the existing localization solutions based on the ranging ineffective. To address this issue, this paper introduces a novel approach based on the passive vehicular traffic measurement, called Autonomous Passive Localization (APL). Our work is inspired by the fact that vehicles move along routes with a known map. Using binary vehicle-detection time stamps, we can obtain distance estimates between any pair of sensors on roadways to construct a virtual graph composed of sensor identifications (i.e., vertices) and distance estimates (i.e., edges). The virtual graph is then matched with the topology of the road map, in order to identify where sensors are located on roadways. We evaluate our design outdoors on Minnesota roadways and show that our distance estimate method works well despite traffic noises. In addition, we show that our localization scheme is effective in a road network with 18 intersections, where we found no location matching error, even with a maximum sensor time synchronization error of 0.07 sec and a vehicle speed deviation of 10 km/h. [ABSTRACT FROM AUTHOR]

This paper proposes a Trajectory-Based Data (TBD) Forwarding scheme, tailored for the data forwarding for roadside reports in light-traffic vehicular ad hoc networks. State-of-the-art schemes have demonstrated the effectiveness of their data forwarding strategies by exploiting known vehicular traffic statistics (e.g., densities and speeds). These results are encouraging, however, further improvements can be made by taking advantage of the growing popularity of GPS-based navigation systems. This paper presents the first attempt to effectively utilize vehicles' trajectory information in a privacy-preserving manner. In our design, such trajectory information is combined with the vehicular traffic statistics for a better performance. In a distributed way, each individual vehicle computes its end-to-end expected delivery delay to the Internet access points based on its position on its vehicle trajectory and exchanges this delay with neighboring vehicles to determine the best next-hop vehicle. For the accurate end-to-end delay computation, this paper also proposes a link delay model to estimate the packet forwarding delay on a road segment. Through theoretical analysis and extensive simulation, it is shown that our link delay model provides the accurate link delay estimation and our forwarding design outperforms the existing scheme in terms of both the data delivery delay and packet delivery ratio. [ABSTRACT FROM AUTHOR]

This paper proposes a VIrtual Scanning Algorithm (VISA), tailored and optimized for road network surveillance. Our design uniquely leverages upon the facts that 1) the movement of targets (e.g., vehicles) is confined within roadways and 2) the road network maps are normally known. We guarantee the detection of moving targets before they reach designated protection points (such as temporary base camps), while maximizing the lifetime of the sensor network. The main idea of this work is virtual scan—waves of sensing activities scheduled for road network protection. We provide design-space analysis on the performance of virtual scan in terms of lifetime and average detection delay. Importantly, to our knowledge, this is the first work to study how to guarantee target detection while sensor network deteriorates, using a novel hole handling technique. Through theoretical analysis and extensive simulation, it is shown that a surveillance system, using our design, sustains orders-of-magnitude longer lifetime than full coverage algorithms, and as much as 10 times longer than legacy duty cycling algorithms. [ABSTRACT FROM PUBLISHER]