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6. Dynamic Bandwidth-Efficient BCube Topologies for Virtualized Data Center Networks

Author

Asghari, Vahid, Moghaddam, Reza Farrahi, and Cheriet, Mohamed

Subjects
Computer Science - Networking and Internet Architecture, Computer Science - Performance
Abstract

Network virtualization enables computing networks and data center (DC) providers to manage their networking resources in a flexible manner using software running on physical computers. In this paper, we address the existing issues with the classic DC network topologies in virtualized environment, and investigate a set of DC network topologies with the capability of providing dynamic structures according to the service-level required by the active traffic in a virtual DC network. In particular, we propose three main approaches to modify the structure of a classic BCube topology as a topology benchmark, and investigate their associated structural features and maximum achievable interconnected bandwidth for different routing scenarios. Finally, we run an extensive simulation program to check the performance of the proposed modified topologies in a simulation environment which considers failure analysis and also traffic congestion. Our simulation experiments, which are consistent to our design goals, show the efficiency of the proposed modified topologies comparing to the classic BCube in terms of bandwidth availability and failure resiliency., Comment: 16 pages, 4 figures, and 4 tables

Published
2015

9. A Monte-Carlo Approach to Lifespan Failure Performance Analysis of the Network Fabric in Modular Data Centers

Author

Moghaddam, Reza Farrahi, Asghari, Vahid, Moghaddam, Fereydoun Farrahi, Lemieux, Yves, and Cheriet, Mohamed

Subjects
Computer Science - Performance, Computer Science - Distributed, Parallel, and Cluster Computing, Computer Science - Networking and Internet Architecture, 62N05, 68M15, 90B25, B.4.3, C.2.1, B.4.5, C.4, G.3
Abstract

Data centers have been evolved from a passive element of compute infrastructure to become an active, core part of any ICT solution. In particular, modular data centers (MDCs), which are a promising design approach to improve resiliency of data centers, can play a key role in deploying ICT infrastructure in remote and inhospitable environments in order to take advantage of low temperatures and hydro- and wind-electric capabilities. This is because of capability of the modular data centers to survive even in lack of continuous on-site maintenance and support. The most critical part of a data center is its network fabric that could impede the whole system even if all other components are fully functional, assuming that other analyses has been already performed to ensure the reliability of the underlying infrastructure and support systems. In this work, a complete failure analysis of modular data centers using failure models of various components including servers, switches, and links is performed using a proposed Monte-Carlo approach. The proposed Monte-Carlo approach, which is based on the concept of snapshots, allows us to effectively calculate the performance of a design along its lifespan even up to the terminal stages. To show the capabilities of the proposed approach, various network topologies, such as FatTree, BCube, MDCube, and their modifications are considered. The performance and also the lifespan of each topology design in presence of failures of their components are studied against the topology parameters., Comment: 29 Pages, 14 figures

Published
2014
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18. Approaches for Adaptive Resource Allocation in Cognitive Radio Networks.

Author

Asghari, Vahid Reza and Asghari, Vahid Reza

Abstract

Proposing efficient spectrum utilization techniques to alleviate spectrum congestion is one of the most important challenges in wireless communication technologies operating at specific spectrum bands. In fact, the growth of wireless application demands has caused the frequency allocation table for wireless services to become over congested. On the other hand, recent measurement studies have shown that the radio frequency spectrum in its current shape is inefficiently utilized. Hence, for the purpose of alleviating the long-standing problem of spectrum congestion, the federal communication commission (FCC) is actively revising the traditional spectrum allocation policies and moving towards the adoption of opportunistic spectrum-sharing techniques using cognitive radio. Cognitive radio (CR) is a technology that has the ability of sensing the environment in which it operates and adapting to its changes. For instance, through sensing, CR detects the portions of the spectrum that are un-occupied (also referred to as spectrum holes) at a specific location or time. One of the most efficient ways to identify spectrum holes is to sense the activity of the primary users operating within the secondary users' (cognitive user) range of communication. In this dissertation, we study different approaches for adaptive resource allocation in spectrum-sharing CR networks. In this context, we propose utilizing spectrum sensing information about the primary users' activity and secondary channel knowledge to adaptively adjust the secondary transmission parameters such as time, power and rate while adhering to the generated interference at the primary receivers. In this case, a proper resource management is needed so as to maximize the throughput performance of the secondary users and avoid performance degradation for the primary users. The existence and specification of such resource allocation are necessary issues and will be investigated in this dissertation for different operating sc

Published
2011

23. End-to-End Performance of Cooperative Relaying in Spectrum-Sharing Systems With Quality of Service Requirements.

Author

Asghari, Vahid and Aissa, Sonia

Subjects
*RADIO frequency, *RELAY control systems, *SPECTRUM allocation, *BANDWIDTHS, *QUALITY of service, *ORDER statistics, *NONPARAMETRIC statistics
Abstract

We propose adopting a cooperative relaying technique in spectrum-sharing cognitive radio (CR) systems to more effectively and efficiently utilize available transmission resources, such as power, rate, and bandwidth, while adhering to the quality of service (QoS) requirements of the licensed (primary) users of the shared spectrum band. In particular, we first consider that the cognitive (secondary) user's communication is assisted by an intermediate relay that implements the decode-and-forward (DF) technique onto the secondary user's relayed signal to help with communication between the corresponding source and the destination nodes. In this context, we obtain first-order statistics pertaining to the first- and second-hop transmission channels, and then, we investigate the end-to-end performance of the proposed spectrum-sharing cooperative relaying system under resource constraints defined to assure that the primary QoS is unaffected. Specifically, we investigate the overall average bit error rate (BER), ergodic capacity, and outage probability of the secondary's communication subject to appropriate constraints on the interference power at the primary receivers. We then consider a general scenario where a cluster of relays is available between the secondary source and destination nodes. In this case, making use of the partial relay selection method, we generalize our results for the single-relay scheme and obtain the end-to-end performance of the cooperative spectrum-sharing system with a cluster of L available relays. Finally, we examine our theoretical results through simulations and comparisons, illustrating the overall performance of the proposed spectrum-sharing cooperative system and quantify its advantages for different operating scenarios and conditions. [ABSTRACT FROM PUBLISHER]

Published
2011
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24. Symbol Error Probability of Rectangular QAM in MRC Systems With Correlated η - μ Fading Channels.

Author

Asghari, Vahid, da Costa, Daniel Benevides, and Aïssa, Sonia

Subjects
*PROBABILITY measures, *RADIO transmitter fading, *ERROR analysis in mathematics, *AMPLITUDE modulation, *SIGNAL-to-noise ratio, *HYPERGEOMETRIC functions, *MONTE Carlo method, *MULTIVARIATE analysis, *SIMULATION methods & models
Abstract

In the context of η-μ generalized fading scenarios, this paper provides a general closed-form expression for the average symbol error probability (SEP) of arbitrary M-ary quadrature amplitude modulation (QAM) constellations in maximal-ratio combining (MRC) schemes over non-identical correlated channels. For such a scenario, the moment-generating function (MGF) of the signal-to-noise ratio (SNR) at the combiner output is obtained by rearranging the Gaussian components used to model the correlation between the diversity branches. The average SEP is then derived in terms of Lauricella multivariate hypergeometric functions, which can be implemented in most popular numerical softwares, such as Mathematica. The proposed analytical expressions are validated through Monte Carlo simulations, and insightful discussions are provided from the numerical results. [ABSTRACT FROM AUTHOR]

Published
2010
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