Abstract-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.

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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).

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Abstract. 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%.

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