Issues in ATM Support of High-Performance, Geographically Distributed Computing

This report experimentally assesses the effect of the underlying network in a cluster-based computing environment. The assessment is quantified by application-level benchmarking, process-level communication, and network file input/output. Two testbeds were considered, one small cluster of Sun workstations and another large cluster composed of 32 high-end IBM RS/6000 platforms. The clusters had Ethernet, fiber distributed data interface (FDDI), Fibre Channel, and asynchronous transfer mode (ATM) network interface cards installed, providing the same processors and operating system for the entire suite of experiments. The primary goal of this report is to assess the suitability of an ATM-based, local-area network to support interprocess communication and remote file input/output systems for distributed computing

Hepatitis C virus quasispecies and pseudotype analysis from acute infection to chronicity in HIV-1 co-infected individuals

HIV-1 infected patients who acquire HCV infection have higher rates of chronicity and liver disease progression than patients with HCV mono-infection. Understanding early events in this pathogenic process is important. We applied single genome sequencing of the E1 to NS3 regions and viral pseudotype neutralization assays to explore the consequences of viral quasispecies evolution from pre-seroconversion to chronicity in four co-infected individuals (mean follow up 566 days). We observed that one to three founder viruses were transmitted. Relatively low viral sequence diversity, possibly related to an impaired immune response, due to HIV infection was observed in three patients. However, the fourth patient, after an early purifying selection displayed increasing E2 sequence evolution, possibly related to being on suppressive antiretroviral therapy. Viral pseudotypes generated from HCV variants showed relative resistance to neutralization by autologous plasma but not to plasma collected from later time points, confirming ongoing virus escape from antibody neutralization

An Optically Interconnected Distributed Shared Memory System: Architecture and Performance Analysis

This paper introduces an optically interconnected distributed shared memory (OIDSM) system. The distributed shared memory (DSM) approach integrates both shared memory and distributed memory system ideas to extract the strengths of each while balancing their respective weaknesses. The OIDSM system is a DSM system based on a photonic network to support the high communication requirement of DSM. The OIDSM employs wavelength division multiple access on the photonic network, enabling multiple channels to be formed on a single optical fiber. A result of the high communication capacity is the simplification of the global address mapping problem. This simplified uniform address allocation scheme is introduced. The advantages of the proposed approach are examined through a performance analysis based on a closed queueing network which has been validated through extensive simulation. The performance of the OIDSM system is evaluated in terms of transaction time of a memory request and system thro..

A Collisionless Multiple Access Protocol for a Wavelength Division Multiplexed Star-Coupled Configuration: Architecture and Performance Analysis

This paper introduces a collisionless wavelength division multiple access protocol for a passive star-coupled photonic network and shows that it possesses significant performance and flexibility advantages over alternative approaches. A performance modeling technique is introduced, basedon a semi-markov analytic model, that eliminates many of the unrealistic assumptions of past approaches to analytical modeling. The performance of the protocol is analyzed using this analytical model and discrete-event simulation. The proposed protocol is control channel based: one WDM channel is used to reserve access for data packet transmission on the remaining data channels. Control channel access arbitration is achieved through time-division multiplexing, enabling all active nodes the opportunity to transmit once every control cycle. This approach significantly reduces the long synchronization delays typical of time-division multiplexing systems: the control cycle length is proportional to the cont..

Reconfigurable Parallel Computer Architecture Based on Wavelength-Division Multiplexed Optical Interconnection Network

Reconfigurability is a desirable characteristic in parallel computer architecture that supports the structural parallelism inherent to multiple parallel algorithms. This paper presents a novel approach to achieve reconfigurability via a multiple-domain wavelengthdivision multiplexed optical interconnection network. A network structure is defined to host a set of point-to-point guest interconnection topologies. Fast complete reconfiguration takes place by re-labeling node identifiers and re-tuning receiver filters according to a local table at each node. For a network of size N , the connecting fiber complexity is O(N ), the same order of the link complexities of the individual topologies. The proposed network avoids the possible edge dilation, congestion, and cumulative switching latencies associated with previously proposed approaches. Keywords: Parallel computer architecture, reconfigurability, interconnection networks, virtual topology, optical interconnection. 1. Introduction The..

WDM Cluster Ring: A Low-Complexity Partitionable Reconfigurable Processor Interconnection Structure

Wavelength selectivity of light sources and filters enable reconfigurable and partitionable parallel computer interconnection at low space complexity via wavelength-division multiplexing (WDM). Large scale processor networks can be built by mixing wavelength-division and passive space-division. In a multi-domain WDM network clusters of processors can be assigned ordered wavelength channel sets such that interprocessor communication takes place on a conflict-free point-to-point basis. This paper presents a multi-domain WDM processor interconnection structure based on a ring of processor clusters. The cluster ring has a limited space complexity and is easily partitionable into sub-networks, each can be reconfigured to multiple connectivities by appropriately tuning node transceivers. Reconfiguration of arbitrarily-sized sub-networks into grids, binary trees, and multistage connectivities is demonstrated. The objective is supporting multi-user parallel computing with a relaxed application..

Architectures For Distributed Shared Memory . . .

This paper studies the interaction between the access protocol used to provide arbitration for a wavelengthdivision multiple access photonic network and the cache coherence protocol required to support a distributed shared memory environment. The architecture is based on wavelength division multiplexing which enables multiple multi-access channels to be realized on a single optical fiber. Larger blocks are supported to reduce the per bit overhead and increase the exploitation of spatial locality, while false sharing is reduced through a mechanism to provide a finer granularity of invalidation. Two main approaches have been considered to harness the enormous available bandwidth of WDMA optical networks: reservation (control-channel based) or pre-allocation media access protocols. This paper extends the function of a control channel to include broadcast support of cache-level control information, in addition to its primary role of data channel reservation, thereby enabling a snooping ba..

Time-Space-Wavelength Networks for Low-Complexity Processor Interconnection

This paper studies a flexible hierarchic design approach of large processor networks with distributed media access. The cluster-based interconnection combines passive metal buses and passive optical star couplers at two hierarchic levels, independently employing interleaved TDMA for conflict-free interprocessor communication. The system delay analysis highlights the tradeoffs of arbitrarily combining space-division at the local level, wavelengthdivision at the global level, with time-division as a conflictfree access scheme at both levels and in the form of a speedup factor associated with optical transmission. The frame synchronization time that dominates the access delay in TDMA-based protocols is broken down into two additive rather than multiplicative factors. The paper proposes a simple distributed slot synchronization scheme that does not require a centralized system clock. It is shown that this hierarchic approach has the advantages of modularity, expansion flexibility, complexi..

Performance Impact of Switching Latency on WDMA Protocols

This paper investigates the impact of fast wavelength tunable device switching latency on the performance of media access protocols for star-coupled wavelength-division multiplexed photonic networks. The relative impact with a reservation based protocol (TDMA-C) and two pre-allocation based protocols (I-TDMA* and I-SA) are compared. TDMA-C is control channel based, with one WDM channel allocated to reserve access for data packet transmission on the remaining data channels. Control channel access arbitration is achieved through time-division multiplexing, enabling all active nodes the opportunity to transmit once every control cycle. I-SA and I-TDMA* are designed for a network where channels are pre-allocated to the nodes for reception where each node has a home channel it uses for all data packet receptions. The performance of the protocols is evaluated through discrete-event simulation in terms of network throughput and average packet delay. In particular, this paper examines the per..