Nils Agne Nordbotten

A routing methodology for achieving fault tolerance in direct networks

Massively parallel computing systems are being built with thousands of nodes. The interconnection network plays a key role for the performance of such systems. However, the high number of components significantly increases the probability of failure. Additionally, failures in the interconnection network may isolate a large fraction of the machine. It is therefore critical to provide an efficient fault-tolerant mechanism to keep the system running, even in the presence of faults. This paper presents a new fault-tolerant routing methodology that does not degrade performance in the absence of faults and tolerates a reasonably large number of faults without disabling any healthy node. In order to avoid faults, for some source-destination pairs, packets are first sent to an intermediate node and then from this node to the destination node. Fully adaptive routing is used along both subpaths. The methodology assumes a static fault model and the use of a checkpoint/restart mechanism. However, there are scenarios where the faults cannot be avoided solely by using an intermediate node. Thus, we also provide some extensions to the methodology. Specifically, we propose disabling adaptive routing and/or using misrouting on a per-packet basis. We also propose the use of more than one intermediate node for some paths. The proposed fault-tolerant routing methodology is extensively evaluated in terms of fault tolerance, complexity, and performance.

XML and Web Services Security Standards

XML and Web services are widely used in current distributed systems. The security of the XML based communication, and the Web services themselves, is of great importance to the overall security of these systems. Furthermore, in order to facilitate interoperability, the security mechanisms should preferably be based on established standards. In this paper we provide a tutorial on current security standards for XML and Web services. The discussed standards include XML Signature, XML Encryption, the XML Key Management Specification (XKMS), WS-Security, WS-Trust, WS-SecureConversation, Web Services Policy, WS-SecurityPolicy, the eXtensible Access Control Markup Language (XACML), and the Security Assertion Markup Language (SAML).

An Efficient Fault-Tolerant Routing Methodology for Meshes and Tori

In this paper we present a methodology to design fault-tolerant routing algorithms for regular direct interconnection networks. It supports fully adaptive routing, does not degrade performance in the absence of faults, and supports a reasonably large number of faults without significantly degrading performance. The methodology is mainly based on the selection of an intermediate node (if needed) for each source-destination pair. Packets are adaptively routed to the intermediate node and, at this node, without being ejected, they are adaptively forwarded to their destinations. In order to allow deadlock-free minimal adaptive routing, the methodology requires only one additional virtual channel (for a total of three), even for tori. Evaluation results for a 4 x 4 x 4 torus network show that the methodology is 5-fault tolerant. Indeed, for up to 14 link failures, the percentage of fault combinations supported is higher than 99.96%. Additionally, network throughput degrades by less than 10% when injecting three random link faults without disabling any node. In contrast, a mechanism similar to the one proposed in the BlueGene/L, that disables some network planes, would strongly degrade network throughput by 79%.

Methods for service discovery in Bluetooth scatternets

This paper presents methods for service discovery in multi-hop Bluetooth ad hoc networks, so called scatternets. Two service discovery protocols based on filtering of service requests are proposed. Extensive simulation results are presented showing that the protocols significantly reduce network traffic. Reducing the network traffic is important as many Bluetooth devices have limited power sources and, therefore, benefit from keeping links idle in power saving modes. It is also explained how the proposed protocols can interact with reactive routing protocols and effectively assist route discovery. Finally, an implementation providing functionality for both searching and browsing for services is suggested, effectively extending the Bluetooth SDP to the scatternet.

A routing methodology for dynamic fault tolerance in meshes and tori

This paper proposes a fully distributed fault-tolerant routing methodology for tori and meshes. A dynamic fault-model is supported, enabling the network to remain fully operational at all times. Contrary to most previous proposals that support a dynamic fault-model, the methodology is able to tolerate concave fault regions, thereby avoiding disabling healthy nodes in most practical scenarios. The methodology provides high network performance through the use of adaptive routing and provides graceful performance degradation in the presence of faults.

A Fully Adaptive Fault-Tolerant Routing Methodology Based on Intermediate Nodes

Massively parallel computing systems are being built with thousands of nodes. Because of the high number of components, it is critical to keep these systems running even in the presence of failures. Interconnection networks play a key-role in these systems, and this paper proposes a fault-tolerant routing methodology for use in such networks. The methodology supports any minimal routing function (including fully adaptive routing), does not degrade performance in the absence of faults, does not disable any healthy node, and is easy to implement both in meshes and tori. In order to avoid network failures, the methodology uses a simple mechanism: for some source-destination pairs, packets are forwarded to the destination node through a set of intermediate nodes (without being ejected from the network). The methodology is shown to tolerate a large number of faults (e.g., five/nine faults when using two/three intermediate nodes in a 3D torus). Furthermore, the methodology offers a gracious performance degradation: in an 8 × 8 × 8 torus network with 14 faults the throughput is only decreased by 6.49%.

A new adaptive fault-tolerant routing methodology for direct networks

Interconnection networks play a key role in the fault tolerance of massively parallel computers, since faults may isolate a large fraction of the machine containing many healthy nodes. In this paper, we present a methodology to design fully adaptive fault-tolerant routing algorithms for direct interconnection networks that can be applied to different regular topologies. The methodology is mainly based on the selection of an intermediate node (if needed) for each source-destination pair. Packets are adaptively routed to the intermediate node and, from this node, they are adaptively forwarded to their destination. This methodology requires only one additional virtual channel, even for tori. Evaluation results show that the methodology is 7-fault tolerant, and for up to 14 faults, more than 99% of the combinations are tolerated, also without significantly degrading performance in the presence of faults.

An effective fault-tolerant routing methodology for direct networks

Current massively parallel computing systems are being built with thousands of nodes, which significantly affect the probability of failure. M. E. Gomex proposed a methodology to design fault-tolerant routing algorithms for direct interconnection networks. The methodology uses a simple mechanism: for some source-destination pairs, packets are first forwarded to an intermediate node, and later, from this node to the destination node. Minimal adaptive routing is used along both subpaths. For those cases where the methodology cannot find a suitable intermediate node, it combines the use of intermediate nodes with two additional mechanisms: disabling adaptive routing and using misrouting on a per-packet basis. While the combination of these three mechanisms tolerates a large number of faults, each one requires adding some hardware support in the network and also introduces some overhead. In this paper, we perform an in-depth detailed analysis of the impact of these mechanisms on network behaviour. We analyze the impact of the three mechanisms separately and combined. The ultimate goal of this paper is to obtain a suitable combination of mechanisms that is able to meet the trade-off between fault-tolerance degree, routing complexity, and performance.

Automatic security classification by machine learning for cross-domain information exchange

Cross-domain information exchange is necessary to obtain information superiority in the military domain, and should be based on assigning appropriate security labels to the information objects. Most of the data found in a defense network is unlabeled, and usually new unlabeled information is produced every day. Humans find that doing the security labeling of such information is labor-intensive and time consuming. At the same time there is an information explosion observed where more and more unlabeled information is generated year by year. This calls for tools that can do advanced content inspection, and automatically determine the security label of an information object correspondingly. This paper presents a machine learning approach to this problem. To the best of our knowledge, machine learning has hardly been analyzed for this problem, and the analysis on topical classification presented here provides new knowledge and a basis for further work within this area. Presented results are promising and demonstrates that machine learning can become a useful tool to assist humans in determining the appropriate security label of an information object.

Data Loss Prevention Based on Text Classification in Controlled Environments

Loss of sensitive data is a common problem with potentially severe consequences. By categorizing documents according to their sensitivity, security controls can be performed based on this classification. However, errors in the classification process may effectively result in information leakage. While automated classification techniques can be used to mitigate this risk, little work has been done to evaluate the effectiveness of such techniques when sensitive content has been transformed (e.g., a document can be summarized, rewritten, or have paragraphs copy-pasted into a new one). To better handle these more difficult data leaks, this paper proposes the use of controlled environments to detect misclassification. By monitoring the incoming information flow, the documents imported into a controlled environment can be used to better determine the sensitivity of the document(s) created within the same environment. Our evaluation results show that this approach, using techniques from machine learning and information retrieval, provides improved detection of incorrectly classified documents that have been subject to more complex data transformations.