Multifractal Internet Traffic Model and Active Queue Management

We propose a multilevel (hierarchical) ON/OFF model to simultaneously capture the mono/multifractal behavior of Internet traffic. Parameter estimation methods are developed and applied to estimate the model parameters from real traces. Wavelet analysis and simulation results show that the synthetic traffic (using this new model with estimated parameters) and real traffic share the same statistical properties and queuing behaviors. Based on this model and its statistical properties, as described by the Logscale diagram of traces, we propose an efficient method to predict the queuing behavior of FIFO and RED queues. In order to satisfy a given delay and jitter requirement for real time connections, and to provide high goodput and low packet loss for non-real time connections, we also propose a parallel virtual queue control structure to offer differential quality of services. This new queue control structure is modeled and analyzed as a regular nonlinear dynamic system. The conditions for system stability and optimization are found (under certain simplifying assumptions) and discussed. The theoretical stationary distribution of queue length is validated by simulation

Jitter Analysis of CBR Streams in Multimedia Networks

The performance of real time applications such as video andvoice streams relies on packet delay jitter. Large delay jittercauses buffer overflow or underflow at the receiver end and theuser encounters interrupts. The delay jitter is mainly due to theperturbation of background traffic in the bottleneck router.Fulton and Li provide an analytical approximationfor the first-order and second-order statistics of delay jitter.However, their analysis is based on a Markovian model of thebackground traffic, which is not quite suitable for Internettraffic and requires lots of computational effort. We propose anefficient method to predict the jitter variance of a CBR(constant-bit rate) connection based on the wavelet model of thebackground traffic. The wavelet analysis extracts the statisticalproperties of background traffic and the analysis result can beused to predict an upper bound for the jitter variance of the CBRconnection

A Multilevel ON/OFF Model for Multifractal Internet Traffic

In this paper, an open-loop multilevel ON/OFF modelis proposed to capture the multifractal behavior of the HTTPtraffic on the Internet. It is assumed that the life time of aTCP session and the active time of a burst within a TCP session have a heavy-tail type distribution. The aggregatetraffic of this model is shown to be multifractal. We analyze itssecond and higher order statistics by the wavelet analysis anddevelop a simple method to estimate the model parameters from areal Internet trace. We show that real and synthesized trafficproduce the same Logscale Diagram with accuracy, for properselection of the model parameter. Finally, we compare using theNS-2 simulator the queueing behavior of FIFO queues fed by realand synthetic traffic demands

A Parallel Virtual Queue Structure for Active Queue Management

The Adaptive RED proposed by Feng is shown to have small packetdelay and queue length variation for long-life TCP traffic suchas FTP connection with a large file size. However, a greatportion of Internet traffic is short-life web and UDP traffic.Most web traffic has a small file size and its TCP session ismainly operated in the slow start phase with a small congestionwindow size. Since the file size is small, dropping short-lifeTCP (and UDP) packets is not very effective in alleviatingcongestion level at a bottleneck router. From the viewpoint ofTCP, one or several packet losses in its slow start phase lead toextra delay for retransmission and even cause TCP timeout. Thisdelay severely degrades the performance of delivering shortmessages such as web pages and web browsers experience a longwaiting time even with a high speed network. We first show that the Adaptive RED is vulnerable tothese short-life TCP traffic and propose a virtual parallel queuestructure as a new active queue management scheme (AQM). The ideais to separate the long-life and short-life (including UDP)traffic into two different virtual queues. The first queue is torun the drop-tail policy and work for the short-life TCP and UDPpackets. In order to have a small mean delay, the service rate ofthis drop-tail queue is dynamically determined by its virtualqueue length. The remaining long-life traffic is directed to anAdaptive RED virtual queue. Even the available bandwidth isshared with the drop-tail queue, the simulation results show thatthe queue length variation of the RED queue is still located in adesired region. Note that both virtual queues share the samephysical buffer memory. Those packets in the drop-tail queue willnot be dropped unless the shared buffer is overflowed. Thisparallel virtual queue structure not only keeps the benefits ofRED such as high utilization and small delay, but also greatlyreduces the packet loss rate at the router

A Parallel Virtual Queue Structure for Active Queue Management

The performance of the Adaptive RED scheme is susceptible to bursty web traffic. In this paper a parallel virtual queue structure is proposed for active queue management at the bottleneck router. Real time connections such as web and UDP, and non-real time connections such as FTP are served in two different virtual queues with drop-tail and Adaptive RED policies, respectively. Both queues share the same physical buffer memory. Simulation shows that file delivery for the web traffic is greatly improved due to shorter packet delay and lower packet loss rate, and that the queue length variation for the FTP traffic is small. To improve the goodput of the non-real time connections, a modified Adaptive RED scheme with dynamic queue length thresholds is also proposed. This scheme is able to keep the packet dropping probability within a desired small region. Stability of the queue length under this scheme is studied through analysis and numerical computation

Characteristics of pncA mutations in multidrug-resistant tuberculosis in Taiwan

<p>Abstract</p> <p>Background</p> <p>Pyrazinamide (PZA) is an important first-line drug in multidrug-resistant tuberculosis (MDRTB) treatment. However, the unreliable results obtained from traditional susceptibility testing limits its usefulness in clinical settings. The detection of <it>pncA </it>gene mutations is a potential surrogate of PZA susceptibility testing, especially in MDRTB isolates. The impact of genotypes of <it>M. tuberculosis </it>in <it>pncA </it>gene mutations also remains to be clarified.</p> <p>Methods</p> <p>MDRTB isolates were collected from six hospitals in Taiwan from January 2007 to December 2009. <it>pncA </it>gene sequencing, pyrazinamidase activity testing, and spoligotyping were performed on all of the isolates. PZA susceptibility was determined by the BACTEC MGIT 960 PZA method. The sensitivity and specificity of <it>pncA </it>gene analysis were estimated based on the results of PZA susceptibility testing.</p> <p>Results</p> <p>A total of 66 MDRTB isolates, including 37 Beijing and 29 non-Beijing strains, were included for analysis. Among these isolates, 36 (54.5%) were PZA-resistant and 30 (45.5%) were PZA-susceptible. The PZA-resistant isolates were more likely to have concomitant resistance to ethambutol and streptomycin. Thirty-seven mutation types out of 30 isolates were identified in the <it>pncA </it>gene, and most of them were point mutations. The sensitivities of <it>pncA </it>gene sequencing for PZA susceptibility in overall isolates, Beijing and non-Beijing strains were 80.6%, 76.2%, and 86.7% respectively, and the specificities were 96.7%, 93.8%, and 100% respectively.</p> <p>Conclusions</p> <p>More than half of the MDRTB isolates in this study are PZA-resistant. Analysis of <it>pncA </it>gene mutations helped to identify PZA-susceptible MDRTB isolates, especially in non-Beijing strains.</p