On detection algorithms for spurious retransmissions in TCP

In TCP, a spurious packet retransmission can be caused by either spurious timeout (STO) or spurious fast retransmit (SFR). The "lost" packets are unnecessarily retransmitted and the evoked congestion control process causes network underutilization. In this paper, we focus on spurious retransmission detection. We first present a survey on some important and interesting spurious retransmission detection algorithms. Based on the insights obtained, we propose a novel yet simple detection algorithm called split-and-retransmit (SnR). SnR only requires a minor modification to the TCP sender while leaving the receiver intact. The key idea is to split the retransmitted packet into two smaller ones before retransmitting them. As the packet size is different, the ACK triggered will carry different ACK numbers. This allows the sender to easily distinguish between the original transmission and the retransmission of a packet without relying on, e.g., TCP options. We then compare our SnR with STODER, F-RTO and Newreno under both loss-free and lossy network environments. We show that our SnR is resilient to packet loss and yields good performance under various simulation settings. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of WCNC, 2010, p. 1-

Selectivity and Metaplasticity in a Unified Calcium-Dependent Model

A unified, biophysically motivated Calcium-Dependent Learning model has been shown to account for various rate-based and spike time-dependent paradigms for inducing synaptic plasticity. Here, we investigate the properties of this model for a multi-synapse neuron that receives inputs with different spike-train statistics. In addition, we present a physiological form of metaplasticity, an activity-driven regulation mechanism, that is essential for the robustness of the model. A neuron thus implemented develops stable and selective receptive fields, given various input statistic

Closest playback-point first: A new peer selection algorithm for P2P VoD systems

Peer-to-peer (P2P) based video-on-demand (VoD) streaming service has been gaining popularity recently. Unlike live streaming, a VoD peer always starts its playback from the beginning of a stored video. The playback-points of different peers, as well as the amount of video contents/pieces they cached, depend on when they join the video session, or their viewing ages. As a result, the upload bandwidth of younger peers tends to be underutilized because older peers are not interested in their cached video pieces. The collaborative piece exchange among peers is undermined due to the unbalanced supply and demand. To address this issue, a playback-point based request peer selection algorithm is proposed in this paper. Specifically, when a peer requests a particular video piece, among the set of potential providers, a request is sent to the peer that has the smallest playback-point difference with itself. We call this request peer selection algorithm closest playback-point first (CPF). With CPF, peers with similar available content can be loosely grouped together for a more balanced collaborative piece exchange. Extensive packet-level simulations show that with CPF, the video playback quality is enhanced and the VoD server load is significantly reduced. © 2011 IEEE.published_or_final_versionThe IEEE Global Telecommunications Conference (GLOBECOM 2011), Houston, TX, USA, 5-9 December 201

Minimizing the communication overhead of iterative scheduling algorithms for input-queued switches

Communication overhead should be minimized when designing iterative scheduling algorithms for input-queued packet switches. In general, the overall communication overhead is a function of the number of iterations required per time slot (M) and the data bits exchanged in an input-output pair per iteration (B). In this paper, we aim at maximizing switch throughput while minimizing communication overhead. We first propose a single-iteration scheduling algorithm called Highest Rank First (HRF). In HRF, the highest priority is given to the preferred input-output pair calculated in each local port at a RR (Round Robin) order. Only when the preferred VOQ(i,j) is empty, input i sends a request with a rank number r to each output. The request from a longer VOQ carries a smaller r. Higher scheduling priority is given to the request with a smaller r. To further cut down its communication overhead to 1 bit per request, we design HRF with Request Compression (HRF/RC). The basic idea is that we transmit a single bit code in request phase. Then r can be decoded at output ports from the current and historical codes received. The overall communication overhead for HRF/RC becomes 2 bits only, i.e. 1 bit in request phase and 1 bit in grant phase. We show that HRF/RC renders a much lower hardware cost than multi-iteration algorithms and a single-iteration algorithm π-RGA [11]. Compared with other iterative algorithms with the same communication overhead (i.e. SRR [10] and 1-iteration iSLIP [6]), simulation results show that HRF/RC always produces the best delay-throughput performance. © 2011 IEEE.published_or_final_versionProceedings of the IEEE Global Telecommunications Conference (GLOBECOM 2011), Houston, TX, USA, 5-9 December 201

A new optimization algorithm for network component analysis based on convex programming

Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing, 2009, p. 509-512Paper no. 2203Network component analysis (NCA) has been established as a promising tool for reconstructing gene regulatory networks from microarray data. NCA is a method that can resolve the problem of blind source separation when the mixing matrix instead has a known sparse structure despite the correlation among the source signals. The original NCA algorithm relies on alternating least squares (ALS) and suffers from local convergence as well as slow convergence. In this paper, we develop new and more robust NCA algorithms by incorporating additional signal constraints. In particular, we introduce the biologically sound constraints that all nonzero entries in the connectivity network are positive. Our new approach formulates a convex optimization problem which can be solved efficiently and effectively by fast convex programming algorithms. We verify the effectiveness and robustness of our new approach using simulations and gene regulatory network reconstruction from experimental yeast cell cycle microarray data. ©2009 IEEE.published_or_final_versio

Effects of local and global stressors on the status and future persistence of intertidal canopy-forming algae

Marine canopy-forming seaweeds are among the most important habitat-forming species along temperate and polar rocky coasts. They form diverse, productive and valuable "forest" habitats that play a key role in coastal primary production, nutrient cycling and disturbance regulation, and facilitate abundant algae and animal communities. They are also some of the most heavily impacted coastal habitats, facing increasing pressures from urban sprawl, pollution, overfishing and climatic instabilities. Identifying the type and strength of interactions between multiple anthropogenic and natural stressors can help setting achievable management targets for degraded ecosystems and support ecological resilience through local actions. My research focuses primarily on understanding the effects of multiple local and global stressors on canopy-forming seaweeds of the genus Cystoseira, with and emphasis on field investigation and experimentation. I approached my research integrating different approaches: 1) I investigated which are the factors driving the loss of canopy-forming seaweeds at global level. The results allowed to detect important synergistic interactions between nutrient enrichment, caused mainly by human activities, and different other stressors such as heavy metals, the presence of competitors, low light and increasing temperature. This suggested that local management of nutrient levels would provide the greatest opportunity for preventing the shift from canopy to mat-forming algae; 2) as second step, I analysed the status of the intertidal Cystoseira populations around the Italian coast, and explored which factors are most likely to influence it. The results reported severe depletion of intertidal populations of Cystoseira, and identified urbanization as one of the main factors related to these poor conditions, confirming the need for urgent management actions to reduce human pressures on these valuable habitat forming species; 3) then, I experimentally investigated the effects of extreme events caused by climate change. I focused my attention on the effects of abrupt increases of air temperature caused by heat-wave events on the intertidal C. compressa around the Italian coast. The results indicated that extreme heat-wave negatively affect the photosynthetic activity of C. compressa, and that local biodiversity and thermal history of the alga seem to play a role reducing or increasing respectively the impact of such extreme events. 4) I also explored the possible overlooked role of the epiphytic bacteria growing on C. compressa. Bacteria can interact with seaweeds in symbiotic, pathological and opportunistic ways, modulating the health, performance and resilience of their hosts and could, therefore play a critical role on the responses of Cystoseira spp. to stress factors. I characterised for the first time the epiphytic bacteria associated to the surface of C. compressa using Illumina Miseq sequences of V1-V3 hypervariable regions of 16S rRNA gene, and investigated their seasonal variations and their relationships with the bacterial populations in the surrounding seawater. I found that bacterial populations associated to C. compressa were clearly distinct from those in the surrounding media, and identified a clear successional pattern, interestingly characterized by an increase in abundance of potential microbial pathogens associated to older thalli of C. compressa; 5) the previous quantitative descriptive work represented an important base-knowledge to further explore experimentally whether surface bacteria could influence the responses of their hosting Cystoseira populations to stressors. I analysed experimentally in the field the interacting effects of nutrient enrichment and heat-wave events on C. compressa population, and explored whether any resulting changes in the photosynthetic activity of C. compressa were associated to changes in the epiphytic bacterial communities. The heat wave caused marked declines of the photosynthetic activity of the intertidal C. compressa. These effects persisted for at least 3 hours, while recovery generally occurred after 24 hours. The heat-wave altered the structure of the epiphytic bacteria of C. compressa. Thalli exposed to the heat-wave presented an increase of OTUs previously shown to be associated with the natural degradation of the thalli of C. compressa, or implied in causing disease or damage to macroalgae. As observed for the photosynthetic activity, these differences decreased over time, suggesting that the microbial community has the ability to recover. Differently from previous work, this experiment did not detect significant effects related to nutrient enrichment, suggesting that the effects of nutrients could be context dependent. These results open new questions concerning the mechanisms by which the epibacterial community could influence the responses and future persistence of these important canopy-forming seaweeds

Request-peer selection for load-balancing in P2P live streaming systems

Theme: Services, Applications and BusinessUnlike peer-to-peer (P2P) file sharing, P2P live streaming systems have to meet real-time playback constraints, which makes it very challenging yet crucial to maximize the peer uplink bandwidth utilization so as to deliver content pieces in time. In general, this is achieved by adopting tailor-made piece selection and request-peer selection algorithms. The design philosophy is to regulate the network traffic and to balance the load among peers. In this paper, we propose a new request-peer selection algorithm. In particular, a peer in the network estimates the service response time (SRT) between itself and each neighboring peer. An SRT is measured from when a data piece request is sent until the requested piece arrives. When a peer makes a piece request, the neighbor with smaller SRT and fewer data pieces would be favored among potential providers. This is because smaller SRT implies excess serving capacity and fewer data pieces suggests less piece requests received. We evaluate the performance of our request-peer selection algorithm through extensive packet level simulations. Our simulation results show that the traffic load in the network is better balanced in the sense that the difference of the normalized number of data packets uploaded by each peer is getting smaller and the number of repeated piece requests generated by each peer (due to request failure) is significantly reduced. We also found that the load of streaming server is reduced, and the overall quality of service, measured by playback continuity, startup delay etc, is improved as well. © 2012 IEEE.published_or_final_versio

Developing an interactive game platform to promote learning and teamwork on mobile devices: an experience report

In the past few Years, many new development toolkits such as the Nebula2 and/or mobile technologies including the WiFi or mobileTV have opened up exciting learning opportunities on mobile devices. On top of it, new technologies continue to fuel the rapid growth of newly merged fields of research like the edutainment for educational entertainment. In a recent teaching development project, we have developed an interactive game platform to facilitate learning and more importantly the spirit of teamwork for collaborative problem-solving on desktop and pocket PCs. With the great challenges imposed by globalization, we strongly believe that learning to collaboratively analyze and then apply the "appropriate" knowledge to solve a specific problem is always the key to success. In this paper, we discuss about an on-going work, and share our relevant experience in system development. Furthermore, evaluation strategies will be thoroughly examined. After all, our work shed light on many interesting directions for future exploration. © 2008 IEEE.published_or_final_versio