Relaxed multiple routing configurations: IP fast reroute for single and correlated failures

Multi-topology routing is an increasingly popular IP network management concept that allows transport of different traffic types over disjoint network paths. The concept is of particular interest for implementation of IP fast reroute (IP FRR). The authors have previously proposed an IP FRR scheme based on multi-topology routing called Multiple Routing Configurations (MRC). MRC supports guaranteed, instantaneous recovery from any single link or node failure in biconnected networks as well as from many combined failures, provided sufficient bandwidth on the surviving links. Furthermore, in MRC different failures result in routing over different network topologies, which gives a good control of the traffic distribution in the networks after a failure     

Attitude Research for Intercultural Communication and Interaction

The attitude data available on foreign groups are generally not enough for reconstructing their perception of a theme or problem. Attitude data show, for instance, whether a foreign group is for or against socialism, but they will not reveal whether the members of the group use the word socialism to refer to democracy or to communism, nor whether they identify it with Sweden or Red China, etc. The Associative Group Analysis technique (AGA)-which relies on the comparative analysis of free verbal associations produced by samples of people from the investigator's own and his target culture-offers attitude data as well as data on denotative, referential meanings. An associationbased attitude index has shown as a group measure high positive correlation with the criterion measures of the Semantic Differential evaluation scales and an attitude questionnaire. A second method of analysis focusing on the denotative, referential meaning was applied to universally approved value concepts: freedom, equality, etc. U.S. and Korean groups (N = 50) were tested, and the analysis has shown a variety of different culturally specific denotative components. The findings support Sapir's observation about the deceptive nature of certain universally approved “labels” to which various people attach different interpretations.     

Verifying a distributed list system: A case history

The background for this paper is twofold: One is the definition of a caching protocol for shared memory parallel computers called SCI, and the other is the usage of rewriting techniques in program verification. The paper concentrates on a linked list system, which is a central aspect of the caching protocol. We first describe an informal proof of this system, including a rather large invariant. Thereafter we show how the list system and the invariant can both be described in the formalism of rewriting logic, and we use this to carry through a significant part of the verification mechanically, using the OBJ3 interpreter.     

On Verification of Parallel Message-Passing Processes

One way to reason about parallel processes is to assume that the execution of each process is subdivided into ‘small enough’ steps, and that these are executed in an interleaved fashion, thus obtaining a sequential program. The steps should be so small that for any parallel execution there will, in a suitable sense, exist a corresponding interleaved execution ending in the same state. The usual way to ensure this is to require that each step should contain at most one global access. However, if the global entities are communication channels, then larger steps may in some cases be allowed, and this may make reasoning about the programs easier. This paper explores these cases, and discusses consequences or verification and deadlock avoidance. Received December 2000 / Accepted in revised form September 2001     

Dielectric logging with downhole invasion effects

The transfer impedance between conducting coils is evaluated to estimate the downhole dielectric properties that can contribute to more effective exploration and production of gas/oil reservoirs. The earth formation with a borehole-mud filtrate invasion is simulated by concentric zones of variable dielectric properties to account for rocks saturated by different fluids. We have imposed analytical restrictions to allow only magnetic-dipole coupling between logging coils and to limit logging source frequencies from 10 to 30 MHz for typical coil spacings. Depending on the depth of invasion front, guided waves may exist in the invaded formation. When guided waves do not exist, rapidly converging branchcut integrations are used to evaluate the transfer impedance. When the invasion front begins to support guided waves the numerical convergence becomes somewhat slower using spatial-band-limited integrations. Both types of integration are used to produce inversion charts from which dielectric properties and invasion-front radii can be estimated from downhole-measurable transfer impedances. Ambiguity in parameter inversion is also demonstrated to provide insight for developing a future inverse process based on array processing of adequately sampled data.     

A methodology for developing deadlock-free dynamic network reconfiguration processes. Part II

For pt.I see ibid., vol.16, no.5, p.412-427 (2005). Dynamic network reconfiguration is defined as the process of changing from one routing function to another while the network remains up and running. The main challenge is in avoiding deadlock anomalies while keeping restrictions on packet injection and forwarding minimal. Current approaches either require virtual channels in the network or they work only for a limited set of routing algorithms and/or fault patterns. In this paper, we present a methodology for devising deadlock free and dynamic transitions between old and new routing functions that is consistent with newly proposed theory [J. Duato et al., (2005)]. The methodology is independent of topology, can be applied to any deadlock-free routing function, and puts no restrictions on the routing function changes that can be supported. Furthermore, it does not require any virtual channels to guarantee deadlock freedom. This research is motivated by current trends toward using increasingly larger Internet and transaction processing servers based on clusters of PCs that have very high availability and dependability requirements, as well as other local, system, and storage area network-based computing systems.     

Interconnection Networks: Architectural Challenges for Utility Computing Data Centers

Advancing research will enable an interconnection network to support the same seamless virtualization found in other parts of hardware, such as CPUs. Such a network thus poses particular challenges as well as opportunities for a utility computing data center.     

Multiple Routing Configurations for Fast IP Network Recovery

As the Internet takes an increasingly central role in our communications infrastructure, the slow convergence of routing protocols after a network failure becomes a growing problem. To assure fast recovery from link and node failures in IP networks, we present a new recovery scheme called Multiple Routing Configurations (MRC). Our proposed scheme guarantees recovery in all single failure scenarios, using a single mechanism to handle both link and node failures, and without knowing the root cause of the failure. MRC is strictly connectionless, and assumes only destination based hop-by-hop forwarding. MRC is based on keeping additional routing information in the routers, and allows packet forwarding to continue on an alternative output link immediately after the detection of a failure. It can be implemented with only minor changes to existing solutions. In this paper we present MRC, and analyze its performance with respect to scalability, backup path lengths, and load distribution after a failure. We also show how an estimate of the traffic demands in the network can be used to improve the distribution of the recovered traffic, and thus reduce the chances of congestion when MRC is used.     

Layered routing in irregular networks

Freedom from deadlock is a key issue in cut-through, wormhole, and store and forward networks, and such freedom is usually obtained through careful design of the routing algorithm. Most existing deadlock-free routing methods for irregular topologies do, however, impose severe limitations on the available routing paths. We present a method called layered routing, which gives rise to a series of routing algorithms, some of which perform considerably better than previous ones. Our method groups virtual channels into network layers and to each layer it assigns a limited set of source/destination address pairs. This separation of traffic yields a significant increase in routing efficiency. We show how the method can be used to improve the performance of irregular networks, both through load balancing and by guaranteeing shortest-path routing. The method is simple to implement, and its application does not require any features in the switches other than the existence of a modest number of virtual channels. The performance of the approach is evaluated through extensive experiments within three classes of technologies. These experiments reveal a need for virtual channels as well as an improvement in throughput for each technology class.     

A new proposal to deal with congestion in InfiniBand-based fat-trees

The overall performance of High-Performance Computing applications may depend largely on the performance achieved by the network interconnecting the end-nodes; thus high-speed interconnect technologies like InfiniBand are used to provide high throughput and low latency. Nevertheless, network performance may be degraded due to congestion; thus using techniques to deal with the problems derived from congestion has become practically mandatory. In this paper we propose a straightforward congestion-management method suitable for fat-tree topologies built from InfiniBand components. Our proposal is based on a traffic-flow-to-service-level mapping that prevents, as much as possible with the resources available in current InfiniBand components (basically Virtual Lanes), the negative impact of the two most common problems derived from congestion: head-of-line blocking and buffer-hogging. We also provide a mathematical approach to analyze the efficiency of our proposal and several ones, by means of a set of analytical metrics. In certain traffic scenarios, we observe up to a 68% of the ideal performance gain that could be achieved in HoL-blocking and buffer-hogging prevention.