Publications

Designing energy-efficient clusters has recently become an important concern to make these systems economically attractive for many applications. Since the cluster interconnect is a major part of the system, the focus of this paper is to characterize and optimize the energy consumption in the entire interconnect. Using a cycle-accurate simulator of an InfiniBand Architecture (IBA) compliant interconnect fabric and actual designs of its components, we investigate the energy behavior on regular and irregular interconnects. The energy profile of the three major components (switches, network interface cards (NICs), and links) reveals that the links and switch buffers consume the major portion of the power budget. Hence, we focus on energy optimization of these two components. To minimize power in the links, first we investigate the dynamic voltage scaling (DVS) algorithm and then propose a novel dynamic link shutdown (DLS) technique. The DLS technique makes use of an appropriate adaptive routing algorithm to shut down the links intelligently. We also present an optimized buffer design for reducing leakage energy in 70nm technology. Our analysis on different networks reveals that, while DVS is an effective energy conservation technique, it incurs significant performance penalty at low to medium workload. Moreover, energy saving with DVS reduces as the buffer leakage current becomes significant with 70nm design. On the other hand, the proposed DLS technique can provide optimized performance-energy behavior (up to 40 percent energy savings with less than 5 percent performance degradation in the best case) for the cluster interconnects.

InfiniBand Architecture (IBA) is envisioned to be the default communication fabric for future system area networks (SANs) or clusters. However, IBA design is currently in its infancy since the released specification outlines only higher level functionalities, leaving it open for exploring various design alternatives. In this paper, we investigate four corelated techniques for providing high and predictable performance in IBA. These are: 1) using the Shortest Path First (SPF) algorithm for deterministic packet routing, 2) developing a multipath routing mechanism for minimizing congestion, 3) developing a selective packet dropping scheme to handle deadlock and congestion, and 4) providing multicasting support for customized applications. These designs are implemented in a pipelined, IBA-style switch architecture, and are evaluated using an integrated workload consisting of MPEG-2 video streams, besteffort traffic, and control traffic on a versatile IBA simulation testbed. Simulation results with 15-node and 30-node irregular networks indicate that the SPF routing, multipath routing, packet dropping, and multicasting schemes are quite effective in delivering high and assured performance in clusters.

The popularity of multimedia streaming services via wireless networks presents major challenges in the management of network bandwidth. One challenge is to quickly and precisely estimate the available bandwidth for the decision of streaming rates of layered and scalable multimedia services. Previous studies based on wired networks are too burdensome to be applied to multimedia applications in wireless networks. In this paper, a new method, IdleGap, is suggested to estimate the available bandwidth of a wireless LAN based on the information from a low layer in the protocol stack. We use a network simulation tool, NS-2, to evaluate our new method with various ranges of cross-traffic and observation times. Our simulation results show that IdleGap accurately estimates the available bandwidth for all ranges of cross-traffic (100 Kbps ∼ 1 Mbps) with a very short observation time of 10 seconds.

The InfiniBand Architecture (IBA) is a promising communication standard for building clusters and system area networks. However, the IBA specification has left out security aspects, resulting in potential security vulnerabilities, which could be exploited with moderate effort. In this paper, we view these vulnerabilities from three classical security aspects—confidentiality, authentication, and availability—and investigate the following security issues. First, as groundwork for secure services in IBA, we present partition-level and queue-pair-level key management schemes, both of which can be easily integrated into IBA. Second, for confidentiality and authentication, we present a method to incorporate a scalable encryption and authentication algorithm into IBA, with little performance overhead. Third, for better availability, we propose a stateful ingress filtering mechanism to block denial-of-service (DoS) attacks. Finally, to further improve the availability, we provide a scalable packet marking method tracing back DoS attacks. Simulation results of an IBA network show that the security performance overhead due to encryption/authentication on network latency ranges from 0.7 percent to 12.4 percent. Since the stateful ingress filtering is enabled only when a DoS attack is active, there is no performance overhead in a normal situation.

In this paper, we propose a Randomly Ordered Activation and Layering (ROAL) protocol. Each node under the ROAL protocol can decide its eligibility regarding a given coverage degree K at randomly generated activation time using only the coverage status informed from its neighbor nodes located within its sensing region. A new concept of layer coverage also provides a simple and effective reconfiguration method for energy balancing. Using the layer concept, we also propose a circulation scheme to reconfigure the set of working nodes in an autonomous way, where the reconfiguration can be performed with a small and almost constant energy consumption. We also provide the model of the expected coverage and connectivity for the layer coverage and show a proper range in which only one node can be activated with regard to a node density and the sensing radius of a node. The simulation results show that the ROAL protocol can guarantee K-coverage with more than 95% coverage ratio, which almost closes to the coverage ratio that is achieved using the geographic coordinate. A significantly extended network lifetime is also observed against the original topology of a given network. Meanwhile, the experimental results on the circulation scheme show that the fraction of total reconfiguration energy becomes less than 1% of the energy consumed for the reconfiguration. Also, we obtain a greatly reduced packet latency, which corresponds to only 5% of the delay that occurred in the ROAL protocol

Stage-level reconfigurable chip multiprocessor (CMP) aims to achieve highly reliable and fault tolerant computing by using interwoven pipeline stages and on-chip interconnect for communicating with each other. The existing crossbar-switch based stage-level reconfigurable CMPs offer high reliability at the cost of significant area/power overheads. These overheads make realizing large CMPs prohibitive due to the area and power consumed by heavy interconnection networks. On other hand, area/ power-efficient architectures offer less reliability and inefficient stage-level resource utilization. In this paper, I propose a hierarchical multiplexing interconnection structure in lieu of crossbar interconnect to design area/power-efficient stage-level reconfigurable CMP. The proposed approach is able to keep the reliability offered by the crossbar-switch while reducing the area and power overheads. Experimental results show that the proposed approach reduces area by up to 21% and power by up to 32% when compared with the crossbar-switch based interconnection network.