Suoheng Li

Design QoS-Aware Multi-Path Provisioning Strategies for Efficient Cloud-Assisted SVC Video Streaming to Heterogeneous Clients

We layout a network infrastructure that leverages the storage and computing power of a cloud residing in the core for collecting network status and computing multi-path scalable video coding (SVC) streaming provisioning strategies. Therefore, in addition to its conventional tasks in the application layer, the cloud also gets involved in the network layer for the optimization of routing and forwarding. We call this scheme as cloud-assisted SVC streaming, and use it to further improve the performance of SVC streaming by using close cooperation between cloud and network. Compared to source-routing based provisioning, the cloud-assisted scheme can provide more cost-effective provisioning strategies by utilizing better knowledge of network environment together with more powerful computation power. We then propose several multi-path provisioning algorithms for cloud-assisted SVC streaming in heterogeneous networks. To the best of our knowledge, these are the first proposals to work on the problem of adaptive multi-path SVC streaming under the bandwidth, delay and differential delay constraints. Our design of the provisioning algorithms starts from an approach that is based on Max Flow and an Auxiliary Graph. Several extensions are then made based on this approach to address the situations such as provisioning from multiple sources and provisioning in dynamic network environments with rapid background traffic fluctuations. Simulations in both static and dynamic network environments show that the proposed algorithms can achieve effective performance improvements in terms of request blocking probability, bandwidth utilization, packet delay, packet loss rate, and video playback quality.

Demonstration of online spectrum defragmentation enabled by OpenFlow in software-defined elastic optical networks

We propose and experimentally demonstrate a control-plane framework to realize online spectrum defragmentation (DF) in software-defined elastic optical networks. Experimental results show that the spectrum DF enabled by OpenFlow reduces the blocking probability effectively.

Demonstrations of Efficient Online Spectrum Defragmentation in Software-Defined Elastic Optical Networks

Elastic optical networks (EONs) facilitate agile spectrum management in the optical layer. When coupling with software-defined networking, they function as software-defined EONs (SD-EONs) and provide service providers more freedom to customize their infrastructure dynamically. In this paper, we investigate how to overcome spectrum fragmentation in SD-EONs with OpenFlow-controlled online spectrum defragmentation (DF), and conduct system implementations to facilitate highly-efficient online DF. We first consider sequential DF, i.e., the scenario that involves a sequence of lightpath reconfigurations to progressively consolidate the spectrum utilization. We modify our previous DF algorithm to make sure that the reconfigurations can be performed in batches and the “make-before-break” scheme can be applied to all of them. The modified algorithm is implemented in an OpenFlow (OF) controller, and we design OF extensions to facilitate synchronous batch reconfiguration. Then, we further simplify the DF operations by designing and implementing parallel DF that can accomplish all the DF-related lightpath reconfigurations simultaneously. All these DF implementations are experimentally demonstrated in an SD-EON control plane testbed that consists of 14 stand-alone OF agents and one OF controller, which are all implemented based on high-performance Linux servers. The experimental results indicate that our OF-controlled online DF implementations perform well and can improve network performance in an efficient way.

Alkali metal substitution effects in Mg1-xAxB2 (A = Li and Na)

Abstract We report the alkali metal substitution effects on the structure and superconductivity of Mg 1− x A x B 2 (A=Li and Na) compounds. X-ray diffraction results show that nearly single phase Mg 1− x A x B 2 can be obtained for x ⩽0.15 Li and x ⩽0.2 Na substitution. The lattice parameters a and c decrease with Li substitution. As substituted by Na, both a and c show an increase at low Na concentration, then decrease with substitution at higher Na concentrations. The change of a with Li and Na substitution is explained by two overlapping effects: ion size and an increase of in-plane coupling upon hole doping. The tendency of c -axis contraction in Mg 1− x Li x B 2 is consistent with theoretical prediction. The T c decreases when Li concentration is increased, while the change of T c upon Na substitution is not apparent.

Popularity-driven content caching

This paper presents a novel cache replacement method - Popularity-Driven Content Caching (PopCaching). PopCaching learns the popularity of content and uses it to determine which content it should store and which it should evict from the cache. Popularity is learned in an online fashion, requires no training phase and hence, it is more responsive to continuously changing trends of content popularity. We prove that the learning regret of PopCaching (i.e., the gap between the hit rate achieved by PopCaching and that by the optimal caching policy with hindsight) is sublinear in the number of content requests. Therefore, PopCaching converges fast and asymptotically achieves the optimal cache hit rate. We further demonstrate the effectiveness of PopCaching by applying it to a movie.douban.com dataset that contains over 38 million requests. Our results show significant cache hit rate lift compared to existing algorithms, and the improvements can exceed 40% when the cache capacity is limited. In addition, PopCaching has low complexity.

Demonstration of OpenFlow-Controlled Network Orchestration for Adaptive SVC Video Manycast

Software defined networking (SDN) makes networks programmable and application-aware by decoupling network control and management (NC&M) from data forwarding and leveraging centralized NC&M to facilitate user-customized routing and switching. Inspired by these, this paper investigates how to realize the OpenFlow-controlled (OF-controlled) network orchestration that can facilitate efficient scalable video coding (SVC) streaming to heterogeneous clients. Specifically, we consider real-time SVC streaming and address the situation in which video sources reside in geographically- distributed servers and clients can join and leave the streaming services dynamically. We formulate this as a multi-source multi-destination manycast problem and realize the networking system with an OF-controlled SDN architecture. We first design the OF controller to enable efficient network operations. Then, we focus on solving the multi-source multi-destination SVC video manycast problem and design several algorithms. Initially, an integer linear programming (ILP) model is formulated to obtain the optimal solutions for small-scale problems. Next, we try to make the manycast algorithm suitable for practical implementation, and design two time-efficient heuristics. Simulation results indicate that the heuristics can provide close-to-optimal solutions. Finally, we build an OF network testbed that consists of OF switches, SVC video servers and clients, and perform SVC streaming experiments to demonstrate our design. Experimental results verify that the proposed scheme can allocate bandwidth intelligently and ensure high-quality video streaming. To the best of our knowledge, this is the first work that accomplishes experimental demonstration of OF-controlled network orchestration for adaptive SVC video manycast.

Thermopower and thermal conductivity of superconducting perovskite MgCNi 3

The thermopower and thermal conductivity of superconducting perovskite MgCNi 3 (T c 8 K) have been studied. The thermopower is negative from room temperature to 10 K. Combined with the negative Hall coefficient reported previously, the negative thermopower definitely indicates that the carrier in MgCNi 3 is electron type. The nonlinear temperature dependence of thermopower below 150 K is explained by the electron-phonon interaction renormalization effects. The thermal conductivity is of the order for intermetallics, larger than that of borocarbides, and smaller than MgB 2 . In the normal state, the electronic contribution to the total thermal conductivity is slightly larger than the lattice contribution. The transverse magnetoresistance of MgCNi 3 is also measured. It is found that the classical Kohlers rule is valid above 50 K. An electronic crossover occurs at T * ∼50 K, resulting in the abnormal behavior of resistivity, thermopower, and magnetoresistance below 50 K.

Transport properties of Ru-doped La1.85Sr0.15CuO4 and the effect of carrier concentration compensation

This paper is a study of the structure and transport properties of Ru-doped La1.85Sr0.15CuO4. It is found that Ru substitution for Cu has two effects. (1) Ru doping introduces disorder into the system, which causes a metal–insulator transition with high localization. (2) There is a hole-filling effect due to the valence of the Ru ion being higher than that of the Cu ion. Increase of the strontium content could compensate for the imbalance of valence caused by doping with the high-valence Ru ion. A universal curve for Tc versus the number of holes per Cu site is observed for the La2−ySryCu1−xRuxO4 system, indicating that a rigid-band model holds and Tc correlates with features in the density of states, such as a Van Hove singularity.

Preparation, structure and superconductivity of Ru1222 and Ta-doped Ru1212

Abstract The samples Ru1−xTaxSr2GdCu2Oy (Ru1212) (x=0, 0.05, 0.15) and RuSr2Gd1.4Ce0.6Cu2Oy (Ru1222) were synthesized by solid-state reaction. X-ray diffraction data indicate that all samples are in a single phase. Ta doping apparently suppresses superconductivity for Ru1−xTaxSr2GdCu2Oy system. The effect of the annealing procedure on superconductivity is significant for Ru1212 system. Oxygen content is crucial to superconductivity accompanied by an apparent change of lattice parameters for Ru1222, the increase of oxygen content results in a decrease of lattice parameters and an increase of Tc.

Flexible Traffic Engineering: When OpenFlow Meets Multi-Protocol IP-Forwarding

In this letter, we present flexible traffic engineering (F-TE), a solution to achieve highly efficient traffic engineering in a hybrid network where IPv4 and IPv6 protocols co-exist. By leveraging the programmability of OpenFlow (OF), we design the OF system to facilitate IP forwarding interchanging (i.e., switching the packets between IPv4 and IPv6 at each hop according to the network status). The OF system is implemented in a real network testbed. We conduct experiments with video streaming to verify that the proposed F-TE can improve network throughput effectively with adaptive IP interchanging.