Performance Management in ATM Networks

ATM is representative of the connection-oriented resource provisioning classof protocols. The ATM network is expected to provide end-to-end QoS guaranteesto connections in the form of bounds on delays, errors and/or losses. Performancemanagement involves measurement of QoS parameters, and application of controlmeasures (if required) to improve the QoS provided to connections, or to improvethe resource utilization at switches. QoS provisioning is very important for realtimeconnections in which losses are irrecoverable and delays cause interruptionsin service. QoS of connections on a node is a direct function of the queueing andscheduling on the switch. Most scheduling architectures provide static allocationof resources (scheduling priority, maximum buffer) at connection setup time. Endto-end bounds are obtainable for some schedulers, however these are precluded forheterogeneously composed networks. The resource allocation does not adapt to theQoS provided on connections in real time. In addition, mechanisms to measurethe QoS of a connection in real-time are scarce.In this thesis, a novel framework for performance management is proposed. Itprovides QoS guarantees to real time connections. It comprises of in-service QoSmonitoring mechanisms, a hierarchical scheduling algorithm based on dynamicpriorities that are adaptive to measurements, and methods to tune the schedulers atindividual nodes based on the end-to-end measurements. Also, a novel scheduler isintroduced for scheduling maximum delay sensitive traffic. The worst case analysisfor the leaky bucket constrained traffic arrivals is presented for this scheduler. Thisscheduler is also implemented on a switch and its practical aspects are analyzed.In order to understand the implementability of complex scheduling mechanisms,a comprehensive survey of the state-of-the-art technology used in the industry isperformed. The thesis also introduces a method of measuring the one-way delayand jitter in a connection using in-service monitoring by special cells

Sigmoid volvulus complicating pregnancy: a case report

Sigmoid volvulus in pregnancy is a rare, but devastating pathology owing to its adverse effects on the mother as well as the foetus. It can lead to maternal mortality in 5-50% cases and foetal mortality in up to 30% cases. A high index of suspicion is necessary and timely surgical intervention is the key to improving feto-maternal outcomes. We present a case of a 32-year-old pregnant woman who presented with sigmoid volvulus at 28 weeks of gestation. The patient was taken up for an emergency laparotomy, where the sigmoid colon was found to be extremely dilated and twisted. Bowel resection and primary anastomosis was done. An anastamotic leak occurred postoperatively, due to which re-exploration and colostomy was done. The patient had a spontaneous abortion after the surgery. She was discharged after five days with a functional stoma and elective colostomy closure was done after six weeks

Performance Monitoring in ATM Networks

ATM networks provide end-to-end QoS guarantees to connections for their lifetime in the form of bounds on delays, errors and losses. Performance management involves accurate measurement of these parameters and taking control measures, if required, to improve performance. This is very important for real time connections in which losses are irrecoverable and delays cause interruptions in service. In this paper an intelligent management architecture and an information flow model for performance management proposed in the literature is reviewed. A brief description of the related ITU-T standard for performance monitoring is given and several schemes for measurement or estimation of QoS parameters are documented. Future work required in the area is also presented in the last section

On QoS Provisioning in ATM Networks

ATM is representative of the connection-oriented resource provisioning class of protocols. An ATM network isexpected to provide end-to-end QoS guarantees to connections in the form of bounds on delays, errors and/or losses.Performance management involves measurement of QoS parameters, and application of control measures (if required)to improve the QoS provided to connections, or to improve the resource utilization at switches. QoS provisioning is veryimportant for real-time connections in which losses are irrecoverable and delays cause interruptions in service. Mostscheduling disciplines provide static allocation of resources at connection setup time. End-to-end bounds are obtainablefor some schedulers, however these are precluded for heterogeneously composed networks. The resource allocation doesnot adapt to the QoS provided to connections in real-time. In addition, mechanisms to measure the QoS of a connectionin real-time are scarce.A novel framework for QoS management is proposed in this paper to provide QoS guarantees to real-time connections.It comprises of in-service QoS monitoring mechanisms, a hierarchical scheduling algorithm based on dynamicpriorities that are adaptive to measurements, and methods to tune the schedulers at individual nodes based on the endto-end measurements

Delay Monitoring in ATM Networks

ATM networks provide end-to-end QoS guarantees to connectionsfor their lifetime, in the form of bounds on delays, errors andlosses. Performance management involves measurement of theseparameters accurately and taking control measures if required, toimprove performance. This is very important for real time connectionsin which losses are irrecoverable and delays cause interruptions inservice. In this paper, we concentrate on delay monitoringmechanisms. After presenting the OAM standard for ATM and a fewsolutions in the literature, problems still remaining are formulatedand directions being pursued to obtain solutions are indicated. This paper was published in the Proceedings of the 3rd Annual Conferenceon Advanced Telecommunications and Information Distribution ResearchProgram (ATIRP), pp. 259-263, February 1-5, 1999, University of Maryland,University College, MD.</I

An End-to-End Measurement-Based Scheduling Architecture for ATM Networks

ATM networks provide end-to-end QoS guarantees to connections for theirlifetime in the form of bounds on delay, error and/or loss. Theguarantees are important for real-time connections in which losses areirrecoverable and delays cause interruptions in service. Performancemanagement involves measurement of QoS parameters and applying controlmeasures, if required, to improve performance or resource utilization. Inthis paper, we propose a new hierarchical scheduling algorithm based ondynamic priorities which are adaptive to end-to-end QoS measurements madeon QoS sensitive (real-time) connections. This architecture can providebounds on average delay and delay variation with varying backgroundnetwork traffic. This paper has been submitted to INFOCOM 2000, Tel Aviv Israel, March 26-30, 2000.</I

Novel Topical Microbicides Through Combinatorial Strategies

Purpose Developing microbicides for topical epithelial applications is extremely challenging, as evidenced by the scarcity of approved products even after decades of research. Chemical enhancers, including surfactants, are known to be effective antimicrobial agents but are typically toxic towards epithelial cells. Here, we report on the discovery of unique surfactant formulations with improved safety and efficacy profile for epithelial applications, via a combination of high throughput screening techniques. Methods Over three-hundred formulations derived from nine surfactants were screened for antibacterial properties against E. coli in vitro. A subset of these formulations showed high antibacterial activity and was screened for cytotoxicity in vitro. Formulations showing high antibacterial activity and reduced cytotoxicity compared to their individual components were tested for efficacy against B. thailendensis, a model for melioidosis-causing B. pseudomallei. Results Lead formulations showed lower toxicity towards epidermal keratinocytes, with LC50 values up to 3.5-fold higher than their component surfactants, while maintaining antibacterial efficacy against B. thailendensis. Conclusions Our results demonstrate that such a combinatorial screening approach can be used for designing safe and potent microbicides for epithelial applications

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data