34587947
Guaranteed Mutually Consistent Checkpointing in Distributed Computations
In this paper, we emplore the isomorphism between vector time and causality to characterize consistency of a set of checkpoints in a distributed computing. A necessary and sufficient condition, to determine if a set of checkpoints can form a consistent global checkpoint, is presented and proved using the isomorphic power of vector time and causality. To the best of our knowledge, this is the first attempt to use the isomorphism for this purpose. This condition leads to a simple and straightforward algorithm for a guaranteed mutually consistent global checkpointing. In our approach, a process can take a checkpoint whenever and wherever it wants while other related process may be asked to take an additional checkpoint for ensuring the mutual consistency. We also show how this condition and the resulting algorithm can be used to obtain a maximum and minimum global checkpoints, another important paradigm for distributed applications.
39342835
Guaranteed Mutually Consistent Checkpointing in Distributed Computations
In this paper, we explore the isomorphism between vector time and causality to characterize consistency of a set of checkpoints in a distributed computing. A necessary and sufficient condition, to determine if a set of local checkpoints can form a consistent global checkpoint, is presented and proved using the isomorphic power of vector time and causality. To the best of our knowledge, this is the first attempt to use the isomorphism for this purpose. This condition leads to a simple and straightforward algorithm for a guaranteed mutually consistent global checkpointing. In our approach, a process can take a checkpoint whenever and wherever it wants while other related process may be asked to take an additional checkpoint for ensuring the mutual consistency. We also show how this condition and the resulting algorithm can be used to obtain a maximum and minimum global checkpoints, another important paradigm for distributed applications.
2702750
A new look at multimedia synchronization in distributed environments
A multimedia system requires to handle automatically and uniformly the generation, manipulation, presentation, storage, and communication of independent discrete and continuous media data. The synchronization between various kinds of media data is a key issue in an integrated multimedia system, and has drawn a considerable attention. In this paper we investigate the synchronization problem in distributed multimedia environments and propose a new approach. Based on a globally synchronized clock, we present an isochronous clock-driven protocol for multimedia synchronization in a distributed environment. We show that the isochronous approach is simple, easy to understand, and more importantly, can guarantee the temporal ordering (including causal order and /spl Delta/-causal order). We believe that with the new developments in the improved NTP over Internet and very high accuracy of synchronized clocks over ATM and LANs, the clock-based distributed synchronization would provide a promising, yet simple and intuitive, alternative to the existing approaches.
12472387
CLID: A general approach to validate security policies in a dynamic network
Many researchers have considered security policy management, including how to configure policies manually and even how to automatically generate security policies based on security requirements. Both can be error prone, especially when properties of the network topology change, because security requirements are usually not bound to any particular route path. Our DETER lab emulation results show that conflicts could be caused by these factors. Therefore, a systematic way to validate the correctness of the security policies is essential. This paper presents an approach, CLID (conflict and looping identification and detection), to verify whether a set of security policies (e.g. IPSec/VPN tunnels) satisfy the given security requirements, without causing any conflicts. This approach utilizes the definition of a security policy lo include network routing data as well as traffic selector information, thus it works for general network topologies. We also analyze and justify the correctness of the approach. The paper concludes with our simulation results and addresses future work.
58339956
IPsec/VPN security policy correctness and assurance
With IPsec/VPN policies being widely deployed, how to correctly specify and configure them is critical in enforcing security requirements, especially among different administrative domains across the Internet. Under current practice, IPsec/VPN policies are specified individually by system administrators from different organizations without any formal coordination. This practice implies unintentional errors due to inconsistent IPsec/VPN policies. Furthermore, Internet routing dynamics may possibly interfere with IPsec/VPN policies such that unexpected conflicts occur due to a mismatch between the routing and IPsec/VPN layers. To deal with these problems, we formally define IPsec security requirements, policies, and their correctness criteria. Based on these definitions, we present an inter-domain architecture to automatically generate correct and efficient security policies. Our approach works when we are given a set of security requirements for a single end-to-end traffic flow. We can also deal with changes when new security requirements are added. Finally, we present simulation results which evaluate the performance of our solutions.
26798727
BANDS: An Inter-domain Internet Security Policy Management System for IPSec/VPN
IPSec/VPN is widely deployed for users to remotely access their corporate data. IPSec policies must be correctly set up for VPN to provide anticipated protection. Manual policy setup is unscalable, inefficient and error-prone. Automated policy generation to comply with and enforce high-level security policies is desired but difficult, especially in an inter-domain environment when a VPN traverses multiple domains. This paper presents a distributed framework and protocol, BANDS, for inter-domain policy negotiation and generation. The BANDS architecture consists of two phases: AS (autonomous system) route path discovery and an inter-domain collaborative protocol for policy negotiation among the autonomous systems discovered in the first phase. Each AS conceptually has one security requirement server responsible for the task of inter-domain policy negotiation. Following this two-step process in BANDS, a set of distributed security policies (for the implementation of policy enforcement) is automatically negotiated/generated based on decentralized and predefined security requirements.
271644
RUMR: robust scheduling for divisible workloads
Divisible workload applications arise in many fields of science and engineering. They can be parallelized in master-worker fashion and relevant scheduling strategies have been proposed to reduce application markspan. Our goal is to developed a practical divisible workload scheduling strategy. This requires that previous work be revisited as several usual assumptions about the computing platform do not hold in practice. We have partially addressed this concern in a previous paper via an algorithm that achieves high performance with realistic resource latency models. In this paper we extend our approach to account for performance prediction errors, which are expected for most real-world performance and applications. In essence, we combine ideas from multiround divisible workload scheduling, for performance, and from factoring-based scheduling, for robustness. We present simulation results to quantify the benefits of our approach compared to our original algorithm and to other previously proposed algorithms.
14988023
Modeling the Effect of Transmit Power and Physical Carrier Sense in Multi-Hop Wireless Networks
In this paper, we extend both Bianchi's and Kumar's models and characterize the channel activities governed by IEEE 802.11 DCF in multi-hop wireless networks from the perspective of an individual sender. In particular, we incorporate the effect of PHY/MAC attributes (such as transmit power and physical carrier sense) that need not be considered in WLANs but become extraordinarily important in multi-hop wireless networks, and derive the throughput attained by each sender. With the use of the analytical model derived, we investigate the impact of transmit power and carrier sense threshold on network capacity, and identify a simple operating condition under which the network may attain throughput that is close to its optimal value.
2952964
Non-Disjoint Discretization for Naive-Bayes Classifiers
Previous discretization techniques have discretized numeric attributes into disjoint intervals. We argue that this is neither necessary nor appropriate for naive-Bayes classifiers. The analysis leads to a new discretization method, Non-Disjoint Discretization (NDD). NDD forms overlapping intervals for a numeric attribute, always locating a value toward the middle of an interval to obtain more reliable probability estimation. It also adjusts the number and size of discretized intervals to the number of training instances, seeking an appropriate trade-off between bias and variance of probability estimation. We justify NDD in theory and test it on a wide cross-section of datasets. Our experimental results suggest that for naiveBayes classifiers, NDD works better than alternative discretization approaches.
6183487
Practical routing and torus assignment for RDT
The connection topology of interconnection networks and the routing algorithm often dominate system performance in MPCs. RDT has already been proved to be one of the best interconnection networks used in such systems. It supports a smaller diameter and degree than most at the size of one thousand to tens of thousands nodes. The floating vector routing algorithm is very effective for transferring messages, which also shows good performance. In this paper, a descending vector routing algorithm is proposed. We also proposed a practical torus assignment named RDT(2,2,1)/a and the deadlock-free routing algorithm. RDT(2,2,1)/a mainly focuses on the MPC that has about one thousand nodes. With a simplified simulation and comparison, the results show that RDT(2,2,1)/a has a better performance at the size of one thousand nodes.
3428244
An Organisational Perspective on Collaborative Business Processes
Business collaboration is about coordinating the flow of information among organisations and linking their business processes. It brings great challenge to keep participating organisations as autonomous entities in integrating business processes of these organisations seamlessly. To address this issue, we develop a new perspective on business collaborations with a novel concept called relative workflow, which defines what a participating organisation can perceive in collaboration. By incorporating a visibility control mechanism, relative workflows allow each organisation to define its own collaboration structure and behaviours. In this paper, we present a formal definition of relative workflows and related algorithms for generating relative workflows, along with a discussion on how to perform tracking over relative workflows.