Joanna Domańska

The drop-from-front strategy in AQM

The article investigates the influence of the way packets are chosen to be dropped (end of the tail, head of the tail) on the performance, i.e. response time for in case of RED and DSRED queues - two representative active queue management mechanisms used in IP routers. In particular, the self-similar traffic is considered. The quantitative analysis is based on simulation and Markov chain models solved numerically.

Necrotising Enterocolitis in Preterm Infants: Epidemiology and Antibiotic Consumption in the Polish Neonatology Network Neonatal Intensive Care Units in 2009

The aim of this study was to describe the epidemiology of necrotising enterocolitis (NEC), antibiotic consumption and the usefulness of microbiological tests in very low birth weight (VLBW) Polish newborns. Methods Prospective surveillance was performed in the year 2009 by local infection control teams. The study covered 910 infants hospitalized in six Polish neonatal intensive care units. Two kinds of indicators were used for the description of antibiotic usage: the duration of treatment (days of treatment, DOTs) and the defined daily dose (DDD). Results NEC incidence was 8.7% and fatality rate was 19%. Chorioamnionitis, late gestational age and low birth weight were identified as risk factors for NEC. Catheterization, mechanical ventilation and other selected procedures were used considerably longer in newborns with NEC than in the remaining neonates. Total usage of antibiotics reached 2.9 DDDs or 1.437 days; the average use of drugs per case of NEC amounted to 0.47 DDD or 23.2 DOTs. The level of antibiotic usage was analysed with correlation to microbiological tests performed and it was non-significantly greater in the group of children with NEC in whom the tests were performed. Conclusions A high risk of developing NEC is closely associated with VLBW and with inflammation of the amnion during labour. We observed no relationship between the consumption of antibiotics in neonates with NEC and positive results of microbiological testing indicating sepsis accompanying NEC or gut colonization with pathogens.

A Choice of Optimal Packet Dropping Function for Active Queue Management

Algorithms of queue management in IP routers determine which packet should be deleted when necessary. The article investigates the influence of packet rejection probability function on the performance, i.e. response time for in case NLRED queues. For standard NLRED the linear packet dropping function is replaced by a quadratic function. Solution presented in this article based on orthogonal polynomials. Depending on a particular criterion of optimization a proper non-linear function may be chosen, but using averaged criterion leads up to choose the linear one as an optimal one.

Late-onset bloodstream infections of Very-Low-Birth-Weight infants: data from the Polish Neonatology Surveillance Network in 2009–2011

BackgroundLate-Onset Bloodstream Infections (LO-BSI) continue to be one of the most important complications associated with hospitalization of infants born with very low birth weight (VLBW). The aims of this study were to assess the epidemiology of LO-BSI together with the risk factors and the distribution of causative pathogens at six Polish neonatal intensive care units that participated in the Polish Neonatology Surveillance Network from January 1, 2009 to December 31, 2011.MethodsThe surveillance covered 1,695 infants whose birth weights were <1501 grams (VLBW) in whom LO-BSI was diagnosed >72 hours after delivery. Case LO-BSI patients were defined according to NeoKISS.ResultsFour hundred twenty seven episodes of LO-BSI were diagnosed with a frequency of 25.3% and an incidence density of 6.7/1000 patient-days (pds). Results of our multivariate analysis demonstrated that surgical procedures and lower gestational age were significantly associated with the risk of LO-BSI. Intravascular catheters were used in infants with LO-BSI significantly more frequently and/or for longer duration: Central venous cathters (CVC) (OR 1.29) and Peripheral venous catheters (PVC) (OR 2.8), as well as, the total duration of total parenteral nutrition (13 vs. 29 days; OR 1.81). Occurrence of LO-BSI was significantly associated with increased the length of mechanical ventilation (MV) (OR 2.65) or the continuous positive airway pressure (CPAP) (OR 2.51), as well as, the duration of antibiotic use (OR 2.98). The occurrence of more than one infection was observed frequently (OR 9.2) with VLBW with LO-BSI. Microorganisms isolated in infants with LO-BSI were dominated by Gram-positive cocci, and predominantly by coagulase-negative staphylococci (62.5%).ConclusionsIndependent risk factor for LO-BSI in VLBV infants are: low gestational age and requirement for surgery. The incidence rates of LO-BSI especially CVC-BSI were higher in the Polish NICUs surveillance than those of other national networks, similar to the central- and peripheral utilization ratio.

Early-onset infections of very-low-birth-weight infants in Polish neonatal intensive care units.

Aim: The objective of this study was to investigate the incidence, causes, the risk factors, etiologic agents and the outcomes of early-onset infections (EOIs) in very-low-birth-weight newborns in Polish neonatal intensive care units. Methods: Continuous prospective infection surveillance conducted during 2009 at 6 Polish neonatal intensive care units and included 910 newborns whose birth weight was lower than 1500 g. Infections were defined according to the Gastmeier’s criteria. EOIs were diagnosed <3 days after delivery. Results: The frequency of early-onset septicemia (EOS) was 7.0% and of early-onset pneumonia (EO-pneumonia) 8.6%. The factors significantly increasing the risk of EOS were low gestational age, small birth weight, low score in the Clinical Risk Index for Babies and Apgar score as well as maternal chorioamnionitis. The perinatal prophylaxis did not have an influence on the occurrence of EOS. The factors considerably increasing the risk of EO-pneumonia were low scores in the Clinical Risk Index for Babies and Apgar scores, a low gestational age and bacterial vaginosis in the child’s mother during pregnancy. The most important etiologic organisms were Gram-positive cocci (39.7% of all the infections, 47.8% in EOS), Streptococcus agalactiae (20% of the EOS), Gram-negative bacilli (33.3% isolates), yeast-like fungi (isolated in 7.9% of cases) and atypical bacteria (22% of the cases of EO-pneumonia). Conclusions: The observed frequency of EOS did not differ from the one described in the literature, whereas the frequency of EO-pneumonia was higher. The bacterial etiologies suggest the vertical transmission of the pathogens and a close relationship between the observed EOIs with maternal environment. The applied perinatal antibiotic prophylaxis was ineffective.

Internet traffic source based on hidden Markov model

This article shows how to use Hidden Markov Models to generate self-similar traffic. The well-known Bellcore traces are used as a training sequence to learn HMM model parameters. Performance of trained model are tested on the remaining portions of the sequences. Then we can use the HMM trained with the Bellcore data as the traffic source model.

The Impact of Self-similarity on Traffic Shaping in Wireless LAN

IEEE 802.11 MAC protocol ist the de facto standard for wireless local area networks (WLANs). In todays Internet, the emerging widespread use of real-time voice, audio, and video applications makes QoS (Quality of Service) a key problem. At the MAC layer, 802.11e defines extensions to enhance the QoS performance of 802.11 WLAN. This MAC layer solution leaves such issues of QoS as QoS guarantee and admission control to the traffic control systems at the higher layers. This article tries to show that implementation of some mechanisms of traffic shaping causes some improvement of the level of QoS in WLANs. First we analyse the influence of the traffic shaping in WLANs stations by the mechanism of token bucket filter. Next the analysis of the behaviour of Access Point with AQM mechanism was carried out. The conducted research has shown that it is possible to achieve certain level of QoS thanks to the implementation of traffic shaping mechanisms. We make our experiments comparatively for the traffic sources with self-similarity and without it. Our results confirm the necessity of taking into account the self-similar character of wireless traffic.

A Few Investigations of Long-Range Dependence in Network Traffic

The paper presents measurements and analysis of a LAN long-range dependence traffic collected in IITiS PAN (The Institute of Theoretical and Applied Informatics of the Polish Academy of Sciences). Several methods of Hurst parameter estimation were used, the results obtained by the methods differ substantially. The analysis was made for the whole traffic and traffics generated by particular types of protocols. We seek for a dependence of Hurst parameter on a protocol type. Then, a MMPP (Markov-Modulated Poisson Process) model was applied to mimic the traces. It allows us to consider Markovian queueing models with long-range dependent and self-similar traffic, an important factor as we dispose an efficient software tool to solve numerically very large continuous-time Markov chains.

Modeling Packet Traffic with the Use of Superpositions of Two-State MMPPs

The aim of this paper is to use the superposition of two-state Markov Modulated Poisson Processes to replicate the statistical nature of internet traffic over several time scales. This paper characterizes of network traffic using Bellcore data and LAN traces collected in IITiS PAN. The fitting procedure for matching second-order self-similar properties of real data traces to that of two-state MMPP’s has also been described.

Enterobacteriaceae infections of very low birth weight infants in Polish neonatal intensive care units: resistance and cross-transmission.

Background: The aims of our study were analysis of the occurrence of infections by members of the Enterobacteriaceae family in 6 Polish neonatal intensive care units in 2009, their drug resistance, the epidemiology of extended-spectrum &bgr;-lactamase (ESBL)-producing strains and the possibility of using modern tools of microbiology diagnosis in infection control, especially for the reduction of antimicrobial resistance. Methods: A prospective surveillance covered 910 newborns. Case patients were defined as neonates with very low birth weight who had clinical signs of septicemia, pneumonia or necrotizing enterocolitis. Early-onset infection was defined as infection diagnosed within 3 days after delivery. Results: The incidence of Enterobacteriaceae infections was 2.6/1000 patient-days. The risk of Enterobacteriaceae pneumonia increased with the length of hospitalization (P = 0.0356). The most common pathogen was Escherichia coli (12.4% of all strains, in early-onset infection 18.5%) and Klebsiella spp. (9.1% of all). The ESBL phenotype was found in 37% of isolates, of which 89.3% were producing CTX-M-type, 70.2% TEM-type and 8.5% SHV-type. Epidemic clones were detected in the 2 studied neonatal intensive care units: 6 of the 9 ESBL-positive Enterobacter cloacae and 16 of the 18 ESBL-positive Klebsiella pneumoniae strains were classified into 1 epidemic clone, which showed resistance to penicillin without inhibitors, amoxycillin/clavulanic acid, cephalosporins, aztreoname, aminoglycosides and trimethoprim/sulfamethoxazole. Conclusions: Enterobacteriaceae bacilli are a significant problem in neonatal intensive care units, especially in early-onset infection and for long hospitalized very low birth weight infants. The observed high drug resistance was in large part related to the dominance of epidemic strains as a result of horizontal transmission. The best way to reduce drug resistance would be adequate procedures of isolation and hand hygiene.