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Computers, IEEE Transactions on

Issue 5 • Date May 2009

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Displaying Results 1 - 16 of 16
  • [Front cover]

    Page(s): c1
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    Freely Available from IEEE
  • [Inside front cover]

    Page(s): c2
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    Freely Available from IEEE
  • On the Multihop Performance of Synchronization Mechanisms in High Propagation Delay Networks

    Page(s): 577 - 590
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1748 KB) |  | HTML iconHTML  

    We analyze the single and multihop performance of time synchronization mechanisms for challenging environments characterized by high propagation delays, low duty-cycle operation, and imprecise clocks, such as underwater acoustic sensor networks. We find that receiver-receiver-based schemes are unsuitable for such environments, and therefore focus primarily on sender-receiver schemes. According to our analysis, a one-way dissemination approach provides good clock skew estimation but poor offset estimation while a two-way exchange approach provides accurate offset estimation but imprecise clock skew estimation. In average, using one-way scheme can result in significant cumulative propagation error over multiple hops, and using two-way can lead to high variance of propagation error. We develop and analyze a hybrid one-way dissemination/two-way exchange technique, and verify the performance of our hybrid scheme through trace-based experiments. The results suggest that this hybrid approach can provide bounded average error propagation in multihop settings and significantly lower variance of propagation error. View full abstract»

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  • Differentiating Services with Noncongestive Queuing (NCQ)

    Page(s): 591 - 604
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2399 KB) |  | HTML iconHTML  

    We discuss a new packet service paradigm, called "Less Impact Better Servicerdquo (LIBS), which is realized through a novel queuing discipline, called "noncongestive queuingrdquo (NCQ). NCQ prioritizes small packets when conditions permit and utilizes service thresholds to confine the delay impact of prioritization on congestive applications. We show that LIBS and NCQ satisfy more users with diverse demands on delay and throughput. We obtained both analytical and simulation results, which are very promising. Diversity is simulated by using FTP, sensor, and VoIP traffic. View full abstract»

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  • Coordinated En-Route Web Caching in Multiserver Networks

    Page(s): 605 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1823 KB) |  | HTML iconHTML  

    With the emergence of various advanced networks that comprise a group of geographically distributed servers, such as content delivery networks (CDNs) and peer-to-peer (P2P) systems, coordinated en-route Web caching in multiserver networks becomes increasingly attractive but remains of great challenge as solutions for single-server networks become invalid here. In this paper, we first establish mathematical formulation for this problem that takes into account all requests (to any server) that pass through the intermediate nodes on a response path and caches the requested object optimally among these nodes so that system's total gain is maximized. Then, we derive efficient dynamic programming-based methods for finding optimal solutions to the problem for the unconstrained case and two QoS-constrained cases, respectively. For each case, we present a caching scheme to illustrate application of the corresponding method. Finally, we evaluate the proposed schemes on different performance metrics through extensive simulation experiments. The experiment results show that our proposed schemes can yield a steady performance improvement and achieve desired QoS in a multiserver network. To the best of our knowledge, these are the first results for solving the problem of coordinated en-route Web caching in multiserver networks. View full abstract»

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  • Practical Deadlock-Free Fault-Tolerant Routing in Meshes Based on the Planar Network Fault Model

    Page(s): 620 - 633
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4666 KB) |  | HTML iconHTML  

    The number of virtual channels required for deadlock-free routing is important for cost-effective and high-performance system design. The planar adaptive routing scheme is an effective deadlock avoidance technique using only three virtual channels for each physical channel in 3D or higher dimensional mesh networks with a very simple deadlock avoidance scheme. However, there exist one idle virtual channel for all physical channels along the first dimension and two idle virtual channels for channels along the last dimension in a mesh network based on the planar adaptive routing algorithm. A new deadlock avoidance technique is proposed for 3D meshes using only two virtual channels by making full use of the idle channels. The deadlock-free adaptive routing scheme is then modified to a deadlock-free adaptive fault-tolerant routing scheme based on a planar network (PN) fault model. The proposed deadlock-free adaptive routing scheme is also extended to n-dimensional meshes still using two virtual channels. Sufficient simulation results are presented to demonstrate the effectiveness of the proposed algorithm. View full abstract»

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  • A Safe Stochastic Analysis with Relaxed Limitations on the Periodic Task Model

    Page(s): 634 - 647
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3770 KB) |  | HTML iconHTML  

    This paper proposes a safe stochastic analysis for fixed-priority scheduling, which is applicable to a broader spectrum of periodic tasks than the ones analyzable by any of the existing techniques. The proposed analysis can find a safe upper-bound of deadline miss probability for periodic tasks with (1) arbitrary execution time distributions, (2) varying interrelease times with the period as the minimum, and (3) the maximum utilization factor Umax that can be greater than 1. One challenge for this is that the release times of tasks are not known a priori because we are not limiting the interrelease times of each task to a constant, i.e., the period. In such a situation, the relative phases of task instances at run time can be arbitrary. Thus, we need to consider all possible phase combinations among jobs to find the worst case deadline miss probability, which is not tractable. To handle this difficulty, we first derive the worst case phase combination for harmonic task sets. Then, we present a safe way to transform a nonharmonic task set to a harmonic task set such that the deadline miss probabilities obtained with the worst case phase combination for the transformed harmonic task set are guaranteed to be worse than those for the original nonharmonic task set with all possible phase combinations. Therefore, the worst case deadline miss probabilities of the transformed harmonic tasks can be used as safe upper-bounds of deadline miss probabilities of the original nonharmonic tasks. Through experiments, we show that the safe upper-bound computed by the proposed analysis is tight enough for practical uses. View full abstract»

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  • Prediction-Based Micro-Scheduler: Toward Responsive Scheduling of General-Purpose Operating Systems

    Page(s): 648 - 661
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3326 KB) |  | HTML iconHTML  

    In this paper, we propose a novel scheduling technique to improve the responsiveness of a real-time process while maintaining relative execution rates of non-real-time processes, called the prediction-based micro-scheduler. It runs upon an existing macro-scheduler and it conditionally rearranges the scheduling pattern generated by the macro-scheduler based on urgent interval prediction and lock hold time prediction. The rearrangement occurs if one process seeks to enter a long nonpreemptible section and the operation is predicted to significantly disturb the future execution of a real-time process. We implemented the prototype on Linux 2.6.19. Experimental results show that the average OS latency of a real-time process is reduced up to 34 percent of the original one while still maintaining relative execution rates of non-real-time processes. Moreover, the performance degradation caused by the micro-scheduler does not exceed 5 percent. View full abstract»

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  • Provably Secure Steganography

    Page(s): 662 - 676
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (899 KB) |  | HTML iconHTML  

    Steganography is the problem of hiding secret messages in "innocent-lookingrdquo public communication so that the presence of the secret messages cannot be detected. This paper introduces a cryptographic formalization of steganographic security in terms of computational indistinguishability from a channel, an indexed family of probability distributions on cover messages. We use cryptographic and complexity-theoretic proof techniques to show that the existence of one-way functions and the ability to sample from the channel are necessary conditions for secure steganography. We then construct a steganographic protocol, based on rejection sampling from the channel, that is provably secure and has nearly optimal bandwidth under these conditions. This is the first known example of a general provably secure steganographic protocol. We also give the first formalization of "robustrdquo steganography, where an adversary attempts to remove any hidden messages without unduly disrupting the cover channel. We give a necessary condition on the amount of disruption the adversary is allowed in terms of a worst case measure of mutual information. We give a construction that is provably secure and computationally efficient and has nearly optimal bandwidth, assuming repeatable access to the channel distribution. View full abstract»

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  • An Efficient Directed Localization Recursion Protocol for Wireless Sensor Networks

    Page(s): 677 - 691
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3862 KB) |  | HTML iconHTML  

    The establishment of a localization system is an important task in wireless sensor networks. Due to the geographical correlation between sensed data, location information is commonly used to name the gathered data and address nodes and regions in data dissemination protocols. In general, to estimate its location, a node needs the position information of at least three reference points (neighbors that know their positions). In this work, we propose a different scheme in which only two reference points are required in order to estimate a position. To choose between the two possible solutions of an estimate, we use the known direction of the recursion. This approach leads to a recursive localization system that works with low-density networks (increasing by 40 percent the number of nodes with estimates in some cases), reduces the position error by almost 30 percent, requires 37 percent less processor resources to estimate a position, uses fewer beacon nodes, and also indicates the node position error based on its distance to the recursion origin. No GPS-enabled node is required, since the recursion origin can be used as a relative coordinate system. The algorithm's evaluation is performed by comparing it with a similar localization system; also, experiments are made to evaluate the impact of both systems in geographic algorithms. View full abstract»

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  • Modeling Detection Latency with Collaborative Mobile Sensing Architecture

    Page(s): 692 - 705
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1917 KB) |  | HTML iconHTML  

    Detection latency, which is defined as the time from the target arrival to the time of the first detection, is an important metric for the performance of sensor networks carrying out target detection, especially when the target is malicious or hostile. It characterizes the efficiency of detecting the presence of a target in a region of interest. Traditionally, stationary sensor networks are used to perform such sensing tasks. Consequently, nearly all research literature for the target detection problem has focused on stationary sensor networks. This paper addresses the problem of detecting the presence/absence of a target using a mobile sensor network. An analytic method is proposed to model the detection latency based on a collaborative sensing architecture. Detection latency for different node mobility models is presented. The accuracy of the analytic model is verified by simulations. This paper also compares the performance of mobile and stationary sensor networks. The comparison shows that if the target is present at the worst possible location in a given deployment, then detection latency of mobile sensor networks is considerably shorter as compared to that of stationary networks with the same number of nodes. View full abstract»

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  • Enhancing Downlink Performance in Wireless Networks by Simultaneous Multiple Packet Transmission

    Page(s): 706 - 718
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2463 KB) |  | HTML iconHTML  

    In this paper, we consider using simultaneous Multiple Packet Transmission (MPT) to improve the downlink performance of wireless networks. With MPT, the sender can send two compatible packets simultaneously to two distinct receivers and can double the throughput in the ideal case. We formalize the problem of finding a schedule to send out buffered packets in minimum time as finding a maximum matching problem in a graph. Since maximum matching algorithms are relatively complex and may not meet the timing requirements of real-time applications, we give a fast approximation algorithm that is capable of finding a matching at least 3/4 of the size of a maximum matching in O(|E|) time, where |E| is the number of edges in the graph. We also give analytical bounds for maximum allowable arrival rate, which measures the speedup of the downlink after enhanced with MPT, and our results show that the maximum arrival rate increases significantly even with a very small compatibility probability. We also use an approximate analytical model and simulations to study the average packet delay, and our results show that packet delay can be greatly reduced even with a very small compatibility probability. View full abstract»

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  • Call-for-Papers on Computer Arithmetic

    Page(s): 719
    Save to Project icon | Request Permissions | PDF file iconPDF (27 KB)  
    Freely Available from IEEE
  • Build Your Career in Computing [advertisement]

    Page(s): 720
    Save to Project icon | Request Permissions | PDF file iconPDF (83 KB)  
    Freely Available from IEEE
  • TC Information for authors

    Page(s): c3
    Save to Project icon | Request Permissions | PDF file iconPDF (77 KB)  
    Freely Available from IEEE
  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE

Aims & Scope

The IEEE Transactions on Computers is a monthly publication with a wide distribution to researchers, developers, technical managers, and educators in the computer field.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Albert Y. Zomaya
School of Information Technologies
Building J12
The University of Sydney
Sydney, NSW 2006, Australia
http://www.cs.usyd.edu.au/~zomaya
albert.zomaya@sydney.edu.au