397,316 research outputs found
A Novel Network Coded Parallel Transmission Framework for High-Speed Ethernet
Parallel transmission, as defined in high-speed Ethernet standards, enables
to use less expensive optoelectronics and offers backwards compatibility with
legacy Optical Transport Network (OTN) infrastructure. However, optimal
parallel transmission does not scale to large networks, as it requires
computationally expensive multipath routing algorithms to minimize differential
delay, and thus the required buffer size, optimize traffic splitting ratio, and
ensure frame synchronization. In this paper, we propose a novel framework for
high-speed Ethernet, which we refer to as network coded parallel transmission,
capable of effective buffer management and frame synchronization without the
need for complex multipath algorithms in the OTN layer. We show that using
network coding can reduce the delay caused by packet reordering at the
receiver, thus requiring a smaller overall buffer size, while improving the
network throughput. We design the framework in full compliance with high-speed
Ethernet standards specified in IEEE802.3ba and present solutions for network
encoding, data structure of coded parallel transmission, buffer management and
decoding at the receiver side. The proposed network coded parallel transmission
framework is simple to implement and represents a potential major breakthrough
in the system design of future high-speed Ethernet.Comment: 6 pages, 8 figures, Submitted to Globecom201
Modeling, Analysis and Impact of a Long Transitory Phase in Random Access Protocols
In random access protocols, the service rate depends on the number of
stations with a packet buffered for transmission. We demonstrate via numerical
analysis that this state-dependent rate along with the consideration of Poisson
traffic and infinite (or large enough to be considered infinite) buffer size
may cause a high-throughput and extremely long (in the order of hours)
transitory phase when traffic arrivals are right above the stability limit. We
also perform an experimental evaluation to provide further insight into the
characterisation of this transitory phase of the network by analysing
statistical properties of its duration. The identification of the presence as
well as the characterisation of this behaviour is crucial to avoid
misprediction, which has a significant potential impact on network performance
and optimisation. Furthermore, we discuss practical implications of this
finding and propose a distributed and low-complexity mechanism to keep the
network operating in the high-throughput phase.Comment: 13 pages, 10 figures, Submitted to IEEE/ACM Transactions on
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Versatile Markovian models for networks with asymmetric TCP sources
In this paper we use Stochastic Petri Nets (SPNs) to study the interaction of multiple TCP sources that share one or two buffers, thereby considerably extending earlier work. We first consider two sources sharing a buffer and investigate the consequences of two popular assumptions for the loss process in terms of fairness and link utilization. The results obtained by our model are in agreement with existing analytic models or are closer to results obtained by ns-2 simulations. We then study a network consisting of three sources and two buffers and provide evidence that link sharing is approximately minimum-potential-delay-fair in case of equal round-trip times. \u
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Microfluidic droplet control by photothermal interfacial flow
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Droplet-based microfluidics is an emerging field that can perform a variety of discrete operation of
tiny amount of reagent or individual cell. Noncontact manipulation of droplets in a microfluidic platform can
be achieved by using the Marangoni convection due to a local temperature gradient given by the irradiation
of heating light. This method provides noncontact, selective and flexible manipulation for droplets flowing in
microfluidic network. Although the potential of this selective operation method of droplets was confirmed,
the driving force exerted on droplets has not been quantitatively obtained. In this study, we have developed a
measurement system of the temperature field around droplets during the manipulation by light irradiation
and evaluated the manipulation force. In O/W emulsion system with oleic acid and buffer solution, oleic acid
for droplet and buffer solution for continuous phase, the temperature distribution around the droplets was
measured by laser-induced fluorescence. From the balance of drag force and photo-induced Marangoni force,
the driving force was determined. From the results, we confirmed the applicability of the noncontact droplet
manipulation using the photothermal Marangoni effect
The Social Cost of Air Traffic Delays
The so-called buffer time or buffer delay allows airlines to control for excessive delays by introducing extra time in their schedule in addition to what is technically required. . We study the differences between unregulated markets - where airlines are free to fix their buffer times strategically - and a situation where a social planner would control for time schedules, and in particular the buffer time. To do so, we use a calibrated model of a network of three cities - one of them being a hub - served by a single airline. Welfare losses that follow from delays are relatively small as compared to the potential benefits that would follow from a decrease in ticket prices. The model thus advocates that, at least for the connections that are considered, fares rather than delays should be the focus of institutions aiming at enhancing passengers’ welfare
Congestive Loss in Wireless Ad hoc Network: Network Performance Analysis
Communication in wireless network is quite susceptible to mobility, nodes capacity and power consumption level. These might contributes to the major problem of TCP performance degradation where there are highly potential of packet loss and packet reordering. In this research, we manage to observe the impact of packet behavior once the node’s capacity is limited when passing on-going data. This condition occurs when the node’s buffer starts to be overloaded. A simulation study by using OPNET Modeler 14.5 is conducted to achieve the purpose. A static ad hoc topology with the size of users (2n where n=0, 1, 2, 3 and 4) is used to observe several parameters such as throughput, number of packet dropped, retransmission count and end-to-end TCP delay. The results show that the size of buffer for ad hoc node influence the network performance whenever number of users is changed. In future, we plan to extend this study in a way of deeply understanding the effect of mobility in wireless network
PRODUCTION SEQUENCING AND STABILITY ANALYSIS OF A JUST-IN-TIME SYSTEM WITH SEQUENCE DEPENDENT SETUPS
Just-In-Time (JIT) production systems is a popular area for researchers but real-world issues such as sequence dependent setups are often overlooked. This research investigates an approach for determining stability and an approach for mixed product sequencing in production systems with sequence dependent setups and buffer thresholds which signal replenishment of a given buffer. Production systems in this research operate under JIT pull production principles by producing only when demand exists and idle when no demand exists.
In the first approach, an iterative method is presented to determine stability for a multi-product production system that operates with replenishment signals and may have sequence dependent setups. In this method, a network of nodes representing machine states and arcs representing the buffer inventory levels is used to find a stable trajectory for the production system via an iterative procedure. The method determines suitable buffer levels for the production system that ensure that a trajectory originating from any point within a buffer region will always map to a point contained on another buffer region for all future mappings.
This iterative method for determining the stability of a production system was implemented using an algorithm to calculate the buffer inventory regions for all arcs in a given arc-node network. The algorithm showed favorable results for two and three product systems in which sequence dependent setups may exist.
In the second approach, a product sequencing algorithm determines a product sequence for a production system based on system parameters – setup times, buffer levels, usage rates, production rates, etc. The algorithm selects a product by evaluating the goodness of each product that has reached the replenishment threshold at the current time. The algorithm also incorporates a lookahead function that calculates the goodness for some time interval into the future. The lookahead function considers all branches of the tree of potential sequences to prevent the sequence from travelling down a dead-end branch in which the system will be unable to avoid a depleted buffer. The sequencing algorithm allows the user to weight the five terms of the goodness equations (current and lookahead) to control the behavior of the sequence
Carbon storage of headwater riparian zones in an agricultural landscape
<p>Abstract</p> <p>Background</p> <p>In agricultural regions, streamside forests have been reduced in age and extent, or removed entirely to maximize arable cropland. Restoring and reforesting such riparian zones to mature forest, particularly along headwater streams (which constitute 90% of stream network length) would both increase carbon storage and improve water quality. Age and management-related cover/condition classes of headwater stream networks can be used to rapidly inventory carbon storage and sequestration potential if carbon storage capacity of conditions classes and their relative distribution on the landscape are known.</p> <p>Results</p> <p>Based on the distribution of riparian zone cover/condition classes in sampled headwater reaches, current and potential carbon storage was extrapolated to the remainder of the North Carolina Coastal Plain stream network. Carbon stored in headwater riparian reaches is only about 40% of its potential capacity, based on 242 MgC/ha stored in sampled mature riparian forest (forest > 50 y old). The carbon deficit along 57,700 km headwater Coastal Plain streams is equivalent to about 25TgC in 30-m-wide riparian buffer zones and 50 TgC in 60-m-wide buffer zones.</p> <p>Conclusions</p> <p>Estimating carbon storage in recognizable age-and cover-related condition classes provides a rapid way to better inventory current carbon storage, estimate storage capacity, and calculate the potential for additional storage. In light of the particular importance of buffer zones in headwater reaches in agricultural landscapes in ameliorating nutrient and sediment input to streams, encouraging the restoration of riparian zones to mature forest along headwater reaches worldwide has the potential to not only improve water quality, but also simultaneously reduce atmospheric CO<sub>2</sub>.</p
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