1347401
Decentralized utilization control in distributed real-time systems
Many real-time systems must control their CPU utilizations in order to meet end-to-end deadlines and prevent overload. Utilization control is particularly challenging in distributed real-time systems with highly unpredictable workloads and a large number of end-to-end tasks and processors. This paper presents the decentralized end-to-end utilization control (DEUCON) algorithm that can dynamically enforce desired utilizations on multiple processors in such systems. In contrast to centralized control schemes adopted in earlier work, DEUCON features a novel decentralized control structure that only requires localized coordination among neighbor processors. DEUCON is systematically designed based on recent advances in distributed model predictive control theory. Both control-theoretic analysis and simulations show that DEUCON can provide robust utilization guarantees and maintain global system stability despite severe variations in task execution times. Furthermore, DEUCON can effectively distribute the computation and communication cost to different processors and tolerate considerable communication delay between local controllers. Our results indicate that DEUCON can provide scalable and robust utilization control for large-scale distributed real-time systems executing in unpredictable environments
15273314
Feedback control real-time scheduling in ORB middleware
Existing real-time ORB middleware standards such as RT-CORBA do not adequately address the challenges of 1) providing robust performance guarantees portably across different platforms, and 2) managing unpredictable workload. To overcome this limitation, we have developed software called FCS/nORB that integrates a Feedback Control real-lime Scheduling (FCS) service with the nORB small-footprint real-time ORB designed for networked embedded systems. FCS/nORB features feedback control loops that provide real-time performance guarantees by automatically adjusting the rate of remote method invocations transparently to an application. FCS/nORB thus enables real-time applications to be truly portable in terms of real-time performance as well as functionality, without the need for hand tuning. This paper presents the design, implementation, and evaluation of FCS/nORB. Our extensive experiments on a Linux testbed demonstrate that FCS can provide deadline miss ratio and utilization guarantees in face of changes in the platform and task execution times, while introducing a small amount of overhead.
2802999
Indistinguishability: The Other Aspect of Privacy
Uncertainty and indistinguishability are two independent aspects of privacy. Uncertainty refers to the property that the attacker cannot tell which private value, among a group of values, an individual actually has, and indistinguishability refers to the property that the attacker cannot see the difference among a group of individuals. While uncertainty has been well studied and applied to many scenarios, to date, the only effort in providing indistinguishability has been the well-known notion of k-anonymity. However, k-anonymity only applies to anonymized tables. This paper defines indistinguishability for general situations based on the symmetry among the possible private values associated with individuals. The paper then discusses computational complexities of and provides practical algorithms for checking whether a set of database views provides enough indistinguishability.
18686814
FGS Coding with Adaptive Reference for Low-Delay Applications
This paper presents the design of a fine granularity SNR scalable video coder for low-delay applications. Specifically, temporal prediction is introduced into the FGS layer of closed-loop P-frames. The prediction is formed adaptively from the enhancement layer reference and the base layer reference, utilizing information coded in the base layer. This novel FGS coder can control drift that may occur due to partial decoding of the FGS layer, while at the same time achieving high coding efficiency. Effort is also spent on reducing the complexity of the new solution by using low-complexity motion compensation and by minimizing additional transform operations. With minimal increase in the complexity, the FGS coding performance of closed-loop P-frames can be improved by as much as 4.5 dB for one FGS layer on a base layer coded at QP 42.
826404
On the effectiveness of secure overlay forwarding systems under intelligent distributed DoS attacks
In the framework of a set of clients communicating with a critical server over the Internet, a recent approach to protect communication from distributed denial of service (DDoS) attacks involves the usage of overlay systems. SOS, MAYDAY, and I3 are such systems. The architecture of these systems consists of a set of overlay nodes that serve as intermediate forwarders between the clients and the server, thereby controlling access to the server. Although such systems perform well under random DDoS attacks, it is questionable whether they are resilient to intelligent DDoS attacks which aim to infer architectures of the systems to launch more efficient attacks. In this paper, we define several intelligent DDoS attack models and develop analytical/simulation approaches to study the impacts of architectural design features of such, overlay systems on the system performance in terms of path availability between clients and the server under attacks. Our data clearly demonstrate that the system performance is indeed sensitive to the architectural features and the different features interact with each other to impact overall system performance under intelligent DDoS attacks. Our observations provide important guidelines in the design of such secure overlay forwarding systems
5860034
Achieving undo in bitmap-based collaborative graphics editing systems
Bitmap-based collaborative graphics editing systems are a special class of real-time collaborative editing systems. Undo is an important and difficult problem in these systems. Existing solutions show low efficiency because additional space cost should be added to achieve the function of undo. In this paper, we propose a new solution to resolve the undo problem. The basic idea is to reduce space cost through exploring relations among operations. The algorithm given in the paper can undo any operation at any time, and can greatly reduce the space cost while increasing a few time cost. The issues about undo scope and undo mode are also discussed in the paper.
34312633
Research on Reliable Communication in Real-Time Collaborative Designing Systems
Real-time collaborative designing systems allow users to view and design the same document from geographically distributed sites connected by web. In these systems, each action should be transferred to other sites correctly, timely and orderly. While a lot of researches focus mainly on providing reliable network environment to support collaborative works, we propose a new kind of reliable communication architecture for collaborative group. This architecture is based on UDP protocol for end-to-end transmission, and adopts a new Site-based Reliable Communication Protocol (SRCP) that depends on collaborative site itself to choose reliable communication channel and provide reliable transmission. Each site checks the connection status and chooses reliable path to transfer actions dynamically. Lost actions can be detected and retransferred faster when comparing to other architectures. The protocol and algorithms are given in detail in this paper.