Browsing by Author "DuHung-Chang, David"
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Item A Network-Aware Approach for Video and Metadata Streaming(2007-04-30) Raghuveer, Aravindan; Kusmierek, Ewa; DuHung-Chang, DavidProviding 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, DART(Dynamic Scheduling Algorithm for Reduced Trace delivery), 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.Item Adaptive Proportional Routing: A Localized QoS Routing Approach(2002-07-18) Nelakuditi, Srihari; Zhang, Zhi-Li; Tsang, Rose P.; DuHung-Chang, DavidMost of the QoS routing schemes proposed so far require periodic exchange of QoS state information among routers, imposing both communication overhead on the network and processing overhead on core routers. Furthermore, stale QoS state information causes theperformance of these QoS routing schemes to degrade drastically. In order to circumvent these problems, we focus on localized QoS routing schemes where the edge routers make routing decisions using only ``local'' information and thus reducing the overhead at core routers. We first describe virtual capacity based routing (vcr), a theoretical scheme based on the notion of virtual capacity of a route. We then propose proportional sticky routing (psr), an easily realizable approximation of vcr and analyze its performance. We demonstrate through extensive simulations that adaptive proportional routing is indeed a viable alternative to the global QoS routing approach.Item An Architecture for Proxy-Assisted Periodic Broadcast for Large Scale Video Streaming(2003-09-17) Kusmierek, Ewa; DuHung-Chang, David; Dong, YingfeiMany multimedia applications rely on video streaming techniques. However, large scale video delivery is still very challenging since it requires a large amount of resources such as storage space, network bandwidth and I/Obandwidth. In this paper we propose a proxy-assisted periodic broadcast architecture for video delivery to a large number of clients over the Internet. Our video delivery technique is based on a combination of periodic broadcast by central server and proxy server caching. A proxy server caches either part or the whole video based on the video popularity. We assume that each proxy server may have different capability and that the video popularity in each community can be different and dynamically changing. A video stored in the central server is partitioned into two parts, a server prefix and a server suffix, based onthe aggregated demand for the video from all communities. In principle, the server prefix is delivered by unicast and the server suffix is delivered by periodic broadcast. Such an approach allows to significantly reduce the required I/O bandwidth at a server. The combination of proxy prefix and server prefix defines a wide spectrum of different videodelivery modes. The transmission of a video can be either partially unicast or partially period broadcast depending on the relationship between proxy prefix and server prefix. We further define and solve the optimization problems for proxy prefix selection and server prefixselection in order to minimize the total resource requirements. Performance of our system is evaluated through a number of tests.Item An Efficient Client Collaboration Framework for Large-Scale Streaming(2005-08-08) Kusmierek, Ewa; Dong, Yingfei; DuHung-Chang, DavidIn this paper, we propose a loopback approach in a two-level streaming architecture to exploit collaborative client/proxy buffers for improving the quality and efficiency of large-scale streaming applications. At the upper level we use a Content Delivery Network (CDN) to deliver video from a central server to proxy servers. At the lower level a proxy server delivers video with the help of collaborative client caches. In particular, a proxy server and its clients in a local domain cache different portions of a video and form delivery loops. In each loop, a single video stream originates at the proxy, passes through a number of clients, and finally is passed back to the proxy. As a result, with limited bandwidth and storage space contributed by collaborative clients, we are able to significantly reduce the required network bandwidth, I/O bandwidth, and cache space of a proxy. Furthermore, we develop a local repair scheme to address the client failure issue for enhancing service quality and eliminating most required repairing load at the central server. For popular videos, our local repair scheme is able to handle most of single-client failures without service disruption and retransmissions from the central server. Our analysis and simulations have shown the effectiveness of the proposed Loopback Scheme.Item APL: Autonomous Passive Localization for Wireless Sensors Deployed in Road Networks(2007-07-02) Jeong, Jaehoon; Guo, Shuo; He, Tian; DuHung-Chang, DavidIn road networks, sensor nodes are deployed sparsely (hundreds of meters apart) to save costs. This makes the existing localization solutions based on the ranging ineffective. To address this issue, this paper introduces an autonomous passive localization scheme, called APL. Our work is inspired by the fact that vehicles move along routes with a known map. Using vehicle-detection timestamps, 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 road map, in order to identify where sensors are located in roadways. We evaluate our design outdoor in local roadways and show that our distance estimate method works well despite of traffic noises. In addition, we show that our localization scheme is effective in a road network with eighteen intersections, where we found no location matching error, even with a maximum sensor time synchronization error of 0.3[sec] and the vehicle speed deviation of 10[km/h].Item CFTL: A Convertible Flash Translation Layer with Consideration of Data Access Patterns(2009-09-14) Park, Dongchul; Debnath, Biplob; DuHung-Chang, DavidNAND flash memory-based storage devices are increasingly adopted as one of the main alternatives for magnetic disk drives. The flash translation layer (FTL) is a software/hardware interface inside NAND flash memory, which allows existing disk-based applications to use it without any significant modifications. Since FTL has a critical impact on the performance of NAND flash-based devices, a variety of FTL schemes have been proposed to improve their performance. However, existing FTLs perform well for either a read intensive workload or a write intensive workload, not for both of them due to their static address mapping schemes. To overcome this limitation, in this paper, we propose a novel FTL addressing scheme named Convertible Flash Translation Layer (CFTL, for short). CFTL is adaptive to data access patterns so that it can dynamically switch the mapping of a data block to either read-optimized or write-optimized mapping scheme in order to fully exploit the benefits of both schemes. By judiciously taking advantage of both schemes, CFTL resolves the intrinsic problems of the existing FTLs. In addition to this convertible scheme, we propose an efficient caching strategy so as to considerably improve the CFTL performance further with only a simple hint. Consequently, both of the convertible feature and caching strategy empower CFTL to achieve good read performance as well as good write performance. Our experimental evaluation with a variety of realistic workloads demonstrates that the proposed CFTL scheme outperforms other FTL schemes.Item DECOR: Distributed and Energy Efficient Collection of Raw Data in Sensor Networks(2010-02-23) Sharafkandi, Sarah; DuHung-Chang, David; Razavi, AlirezaIn wireless sensor networks, collection of raw sensor data at a base station provides the flexibility to perform offline detailed analysis on the data which may not be possible with in-network data aggregation. However, lossless data collection consumes considerable amount of energy for communication while sensors usually have limited energy. In this paper, we propose a Distributed and Energy Efficient algorithm for collection of Raw data in sensor networks called DECOR. DECOR exploits spatial correlation to reduce the communication energy in sensor networks with highly correlated data. In our approach, at each neighborhood, one sensor shares its raw data as a reference with the rest of sensors without any suppression or compression. Other sensors use this reference data to compress their observations by representing them in the forms of mutual differences. In a highly correlated network, transmission of reference data consumes significantly more energy than transmission of compressed data. Thus, we first attempt to minimize the number of reference transmissions. Then, we try to minimize the size of mutual differences. We derive analytical lower bounds for both these phases and based on our theoretical results, we propose a two-step distributed data collection algorithm which reduces the communication energy significantly compared to existing methods. In addition, we modify our algorithm for lossy communication channels and we evaluate its performance through simulation.Item Energy-Aware Scheduling with Quality of Surveillance Guarantee in Wireless Sensor Networks(2006-06-21) Jeong, Jaehoon; Sharafkandi, Sarah; DuHung-Chang, DavidWe propose and evaluate an energy-efficient scheduling algorithm for detection of mobile targets in wireless sensor networks. We consider a setting where the sensors are deployed for both road surveillance and mobile target tracking. A typical example would be where some sensors are deployed along the entrance roads of a city to detect the vehicles entering the city and other sensors can wake up and track the vehicles after detection. We show that there exists a tradeoff between overall energy consumed by the sensors and the average detection time of a target, both of which are very critical aspects in our problem. To this end, we define the quality of surveillance (QoSv) as the reciprocal value of the average detection time for vehicles. We propose an optimal scheduling algorithm that guarantees the detection of every target with specified QoSv and at the same time minimizes the overall energy consumed by the sensor nodes. By minimizing the energy consumed, we maximize the lifetime of the sensor network and by the quality of surveillance guarantee we ensure that no target goes undetected. We theoretically derive the upper bound on the lifetime of the sensor network for a given QoSv guarantee and prove that our method can always achieve this upper bound. Our simulation results validate the claims made on the algorithm optimality and QoSv guarantee.Item Experimental Analysis of VI Architecture(2000-03-29) Jacobson, Irene; MacDonald, Jim; DuHung-Chang, DavidSince the TCP/IP protocol is slow, the Virtual Interface Architecture (VIA) was designed to increase the speed of the connection between machines in a cluster. VIA allows the application program to communicate directly with the Network Interface Card (NIC). It bypasses the TCP/IP protocol stack, therefore decreasing latency and increasing data throughput. VIA was developed to work in a System Area Network (SAN) consisting of a cluster of high volume file servers. This report describes the testing that was done on the Giganet cLAN, the test results, and some comparisons with TCP/IP. The testing that was done with VIA over Giganet cLAN determined the latency for small packet sizes and throughput for large packet sizes. The lowest latency was 14.2 microseconds with a packet size of 288 bytes. The highest throughput was 87.7 MB/second. The report also compares the latency and throughput results with TCP/IP over Giganet cLAN and overGigabit Ethernet using the Intel PRO/1000 Gigabit Server Adapter. An echo program was used to find the latency and throughput of Giganet cLAN and Gigabit Ethernet on the same machines. The average test results of both mediums were close. The lowest latency for TCP/IP over GiganetcLAN was 84 microseconds and the highest throughput was 37.6 MB/sec. The lowest latency forTCP/IP over Gigabit Ethernet was 68 microseconds and the highest throughput was 39.85 MB/sec. For packet sizes over 350 Kbytes, the throughput started to decrease for both Giganet cLAN and Gigabit Ethernet over TCP/IP. Since the throughput decreased with both mediums, the probable cause is the TCP/IP implementation in Windows NT Server 4.0. The average time it takes to make a VI connection was measured at 1.152 microseconds. So in VIA applications, the number of VI connections made should be minimized.Item Full-Sharing Optimal Scheduling for VOD Service on Broadband Cable Networks(2002-06-27) Dong, Yingfei; Zhang, Zhi-Li; DuHung-Chang, DavidCable Access Networks (CANs) have become one of the most important forms of broadband services, which significantly improve the bandwidth to home and spur many multimedia applications to real life. %into reality. However, providing efficient Video-On-Demand (VOD) service on CANs isstill a challenging issue due to the lack of effective approaches to exploit the unique characteristics of CANs. Previous streaming approaches were intended for general network settings and do not consider these unique characteristics. In this study, we address the schedulingissue in the VOD service over CANs by fully utilizing the characteristics of CANs, such as subchannel sharing and potential large buffer space at CAN clients. We propose an optimal full-sharing scheduling approach that minimizes the bandwidth consumption of streaming sessions. Through analysis and simulation, we have shown that our approach has remarkable advantages in minimizing the bandwidth consumption of VOD service on CANs, compared with the previous approaches. As a result, our approach can satisfy more simultaneous VOD sessions on a fixed-capacity channel.Furthermore, we design two adaptation algorithms which not only keep bandwidth consumption minimal but also significantly reduce the mean service delay to 30% or less of the mean service delay without adaptation.Item Highly Adaptive Lookup Systems for Peer-to-Peer Computing(2004-02-20) Kusmierek, Ewa; DuHung-Chang, David; Beyer, James C.The performance of file sharing peer-to-peer systems depends to a large degree on the speed of lookup operation. A number of proposed solutions rely on distributed hashing techniques. Traditionally nodes are assigned fixed length identifiers which does not allow the table to expand or shrink with the increase or decrease in the node count. With the fixed length identifiers, the performance deteriorates when the number of nodes reaches a high value. On the other hand, the overhead of maintaining per-node state (i.e., information of all adjacent nodes) can be unnecessarily large if the number of nodes is small. The focus of our study is to propose a way to combine the distributed and dynamic nature of the system in a way that allows large and unpredictable changes in both the number and the distribution of nodes while providing scalability and good performance. Our approach is based on dynamic distributed hashing techniques; node identifier length varies with the number of nodes in the system. Hence, the system can adapt to the changing conditions and maintain good performance. In this paper, we describe the operations of the proposed adaptive system and verify its performance through simulations.Item Hot Data Identification for Flash Memory Using Multiple Bloom Filters(2010-10-05) Park, Dongchul; DuHung-Chang, DavidHot data identification can be applied to a variety of fields. Particularly in flash memory, it has a critical impact on its performance (due to garbage collection) as well as its lifespan (due to wear leveling). Although this is an issue of paramount importance in flash memory, it is the least investigated one. Moreover, all existing schemes focus only or mainly on a frequency viewpoint. However, recency factor also must be considered as much importantly as the frequency for hot data identification. In this paper, we propose a novel hot data identification scheme adopting multiple bloom filters to efficiently capture finer-grained recency as well as frequency. In addition to this scheme, we propose a window-based direct address counting (named WDAC) algorithm to approximate an ideal hot data identification as our baseline. Unlike the existing baseline algorithm that cannot appropriately capture recency information due to its exponential batch decay, our WDAC algorithm using a sliding window concept can capture very fine-grained recency information. Our experimental evaluation with diverse realistic workloads including real SSD traces demonstrates that our proposed scheme outperforms the state-of-the-art hot data identification scheme. In particular, our scheme not only consumes less memory (50% less) and requires less computational overhead up to 58%, but also improves its performance up to 65%.Item HotDataTrap: A Sampling-based Hot Data Identification Scheme for Flash Memory(2011-04-20) Park, Dongchul; Debnath, Biplob; NamJin, Young; DuHung-Chang, David; Kim, Youngkyun; Kim, YoungchulHot data identification is an issue of paramount importance in flash-based storage devices since it has a great impact on their overall performance as well as retains a big potential to be applicable to many other fields. However, it has been least investigated. In this paper, we propose a novel on-line hot data identification scheme named HotDataTrap. The main idea is to maintain a working set of potential hot data items in a cache based on a sampling approach. This sampling scheme enables HotDataTrap to early discard some of the cold items so that it can reduce runtime overheads and a waste of memory spaces. Moreover, our two-level hierarchical hash indexing scheme helps HotDataTrap directly look up a requested item in the cache and save a memory space further by exploiting spatial localities. Both our sampling approach and hierarchical hash indexing scheme empower HotDataTrap to precisely and efficiently identify hot data even with a very limited memory space. Our extensive experiments with various realistic workloads demonstrate that our HotDataTrap outperforms the state-of-the-art scheme by an average of 335% and our two-level hash indexing scheme considerably improves further HotDataTrap performance up to 50.8%.Item MCTA: Target Tracking Algorithm based on Minimal Contour in Wireless SensorNetworks(2007-01-26) Jeong, Jaehoon; Hwang, TaeHyun; He, Tian; DuHung-Chang, DavidThis paper proposes a minimal contour tracking algorithm (MCTA) that reduces energy consumption for tracking mobile targets in wireless sensor networks in terms of sensing and communication energy consumption. MCTA conserves energy by letting only a minimum number of sensor nodes participate in communication and perform sensing for target tracking. MCTA uses the minimal tracking area based on the vehicular kinematics. The modeling of target's kinematics allows for pruning out part of the tracking area that cannot be mechanically visited by the mobile target within scheduled time. So, MCTA sends the tracking area information to only the sensor nodes within minimal tracking area and wakes them up. Compared to the legacy scheme which uses circle-based tracking area, our proposed scheme uses less number of sensors for tracking in both communication and sensing without target missing. Through simulation, we show that MCTA outperforms the circle-based scheme with about 60% energy saving under certain ideal situations.Item Proxy-Assisted Periodic Broadcast for Video Streaming with Multiple Servers(2003-09-17) Kusmierek, Ewa; DuHung-Chang, DavidLarge scale video streaming over Internet requires a large amount of resources such as server I/O bandwidth, network bandwidth. A number of video delivery techniques can be used to lower these requirements. Periodic broadcast by a central server combined with proxy caching offers a significant reduction of the aggregate network and server I/O bandwidth usage. However, the resources available to a single server are still limited. In this paper we propose a system with multiple geographically distributed servers. Multiple servers beside offering increased resources and service availability, allow a further reduction ofnetwork bandwidth usage. The challenge is how to use multiple servers efficiently. We first analyze the dependence of the resource requirements on the number and locations of the servers in a proxy-assisted periodicbroadcast video delivery system. Based on the character of the function describing such a dependence, we formulate and solve the problem of video location and delivery in a way that minimizes resource usage. We explore the trade-offs between network and I/O bandwidth requirements. We evaluate our proposed solutions through a number of tests.Item TMA: Trajectory-based Multi-Anycast for Multicast Data Delivery in Vehicular Networks(2011-07-26) Jeong, Jaehoon; He, Tian; DuHung-Chang, DavidThis paper describes Trajectory-based Multi-Anycast (TMA) Forwarding, tailored and optimized for the multicast data delivery in vehicular networks. To our knowledge, this is the first attempt to investigate the efficient multicast data delivery in vehicle networks based on the trajectories of vehicles in the multicast group. Due to the privacy concern, we assume only a central server knows the trajectory of each vehicle and the estimated current location of the vehicle. Therefore, after receiving a request of multicast data delivery from a source vehicle, the central server has to figure out how the data has to be delivered to the vehicles in the multicast group. For a given target vehicle in the multicast group, multiple packet-andvehicle rendezvous points are computed as a set of relay nodes to temporarily hold the data along the vehicle's trajectory. This set of rendezvous points can be considered an Anycast set for the target vehicle. We have formulated the multicast data delivery as the data delivery to the anycast sets of the multicast group vehicles. Through theoretical analysis and extensive simulation, it is shown that our design provides an efficient multicast for moving vehicles under a variety of vehicular traffic conditions.Item VISA: Virtual Scanning Algorithm for Dynamic Protection of Road Networks(2008-08-22) Jeong, Jaehoon; Gu, Yu; He, Tian; DuHung-Chang, DavidThis paper proposes a Virtual Scanning Algorithm (VISA), tailored and optimized for road network surveillance. Our design uniquely leverages upon the facts that (i) the movement of targets (e.g., vehicles) is confined within roadways and (ii) 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 ten times longer than legacy duty cycling algorithms.