Christina Thorpe

A Survey of Adaptive Carrier Sensing Mechanisms for IEEE 802.11 Wireless Networks

This survey provides a comprehensive review of existing physical carrier sensing enhancements for IEEE 802.11 wireless networks. The original physical carrier sensing mechanism, used by wireless stations to gain access to the medium, is limited. Consequently, IEEE 802.11 networks are vulnerable to the presence of hidden and exposed nodes. Such nodes can significantly decrease system performance by increasing the collision rate and decreasing the channel spatial reuse. The value of the physical carrier sensing threshold is a key factor influencing the presence of hidden and exposed nodes in a wireless network. Several enhancements have been proposed in the literature, which attempt to mitigate the loss in performance caused by the limited carrier sensing. Firstly, the notion of an optimum carrier sensing threshold has been studied, and results indicate that it can be tuned to an optimum value. Building on the positive early results, further work was performed to develop mechanisms that dynamically adjust the threshold according to varying network conditions. This article presents an in-depth survey of the existing literature in the area, detailing the various approaches and their efficacy in addressing the problem of hidden and exposed nodes (and consequently increasing performance). It offers a comparison of the techniques, by evaluating the models, limitations, assumptions, and performance gains.

Enabling IPTV Service Assurance Using OpenFlow

One difficulty facing Internet Protocol Television (IPTV) service providers is the issue of monitoring and managing their service delivery network. An in-depth monitoring regime is required, which performs measurements within different networking devices. When network conditions deteriorate to the point where they could disrupt IPTV services, Network Operators (NOs) can use the measurements as a basis to reconfigure the network with minimal delay. OpenFlow (OF) presents a potential solution to this problem as it provides vendor-neutral access to the packet forwarding interface of the different hardware device types. This work investigates how OF can leverage video packet inspection measurements taken from within the IPTV service delivery network and combine these with OF statistics to make decisions regarding routing in order to assure service quality.

Integration of QoS Metrics, Rules and Semantic Uplift for Advanced IPTV Monitoring

Abstract Increasing and variable traffic demands due to triple play services pose significant Internet Protocol Television (IPTV) resource management challenges for service providers. Managing subscriber expectations via consolidated IPTV quality reporting will play a crucial role in guaranteeing return-on-investment for players in the increasingly competitive IPTV delivery ecosystem. We propose a fault diagnosis and problem isolation solution that addresses the IPTV monitoring challenge and recommends problem-specific remedial action. IPTV delivery-specific metrics are collected at various points in the delivery topology, the residential gateway and the Digital Subscriber Line Access Multiplexer through to the video Head-End. They are then pre-processed using new metric rules. A semantic uplift engine takes these raw metric logs; it then transforms them into World Wide Web Consortium’s standard Resource Description Framework for knowledge representation and annotates them with expert knowledge from the IPTV domain. This system is then integrated with a monitoring visualization framework that displays monitoring events, alarms, and recommends solutions. A suite of IPTV fault scenarios is presented and used to evaluate the feasibility of the solution. We demonstrate that professional service providers can provide timely reports on the quality of IPTV service delivery using this system.

Experience of developing an openflow SDN prototype for managing IPTV networks

IPTV is a method of delivering TV content to endusers that is growing in popularity. It is a paid service, hence the implications of poor video quality may ultimately be a loss of revenue for the provider. Consequently, it is vital to provide service monitoring and reconfiguration mechanisms to ensure quality requirements set out in service level agreements are upheld. This paper describes our experience of building an IPTV Software Defined Network testbed that can be used to develop and validate new approaches for service assurance in IPTV networks. The testbed is modular and many of the concepts detailed in this tutorial may be applied to the management of other end-to-end services.

COCOA: A Synthetic Data Generator for Testing Anonymization Techniques

Conducting extensive testing of anonymization techniques is critical to assess their robustness and identify the scenarios where they are most suitable. However, the access to real microdata is highly restricted and the one that is publicly-available is usually anonymized or aggregated; hence, reducing its value for testing purposes. In this paper, we present a framework (COCOA) for the generation of realistic synthetic microdata that allows to define multi-attribute relationships in order to preserve the functional dependencies of the data. We prove how COCOA is useful to strengthen the testing of anonymization techniques by broadening the number and diversity of the test scenarios. Results also show how COCOA is practical to generate large datasets.

iMOS: Enabling VoIP QoS Monitoring at Intermediate Nodes in an OpenFlow SDN

The growing popularity of outsourced enterprise VoIP services poses a significant quality assurance issue for service providers. VoIP traffic is very sensitive to network impairments and maintaining high QoS across multiple domains can be challenging. We propose to use SDN and our implementation of intermediate VoIP call quality measurement to provide an advanced VoIP monitoring service. Our solution can automatically detect and locate quality issues for VoIP traffic.

A DSL for Deployment and Testing in the Cloud

Cloud computing is becoming increasingly prevalent, more and more software providers are offering their applications as Software-as-a-Service solutions rather than traditional on-premises installations. In order to ensure the efficacy of the testing phase, it is critical to create a test environment that sufficiently emulates the production environment. Thus, Cloud applications should be tested in the Cloud. Cloud providers offer command-line tools for interacting with their platforms. However, writing custom low-level scripts using the providers tool can become very complex to maintain and manage when variability (in terms of providers and platforms) is introduced. The contributions in this paper include: the development of a high level Domain Specific Language for the abstract definition of the application deployment process, and resource requirements, and a generation process that transforms these definitions to automatically produce deployment and instantiation scripts for a variety of providers and platforms. These contributions significantly simplify and accelerate the testing process for Cloud applications.

IEEE802.11k enabled adaptive carrier sense management mechanism (KAPCS2)

The existence of hidden and exposed nodes can have a significant negative impact on the performance of IEEE802.11 networks. Such nodes can increase the probability of collisions and limit the spatial reuse on the channel. The value of the Physical Carrier Sensing Threshold (PCST) is instrumental in the presence of such nodes in a system. This paper presents a new adaptive physical carrier sensing management algorithm for wireless networks. Our KAPCS2 management system maximizes the aggregate system throughput by identifying and addressing problem nodes. It incorporates 802.11k Radio Resource Measurements (RRM) on each node to enable on-line tuning of the PCST.

IEEE802.11k enabled adaptive physical carrier sense mechanism for wireless networks (K-APCS)

The existence of hidden and exposed nodes can have a significantly negative impact on the performance of IEEE802.11 networks. Such nodes can increase the probability of collisions and limit the spatial reuse on the channel. The value of the Physical Carrier Sensing Threshold (PCST) is instrumental to the trade-off between the number of hidden and exposed nodes in a system. This paper presents a new adaptive physical carrier sensing mechanism for wireless networks. The K-APCS algorithm maximizes the aggregate system throughput by optimizing the balance between the spatial reuse and the collision rate of a system. It incorporates 802.11k radio resource measurements and a frame loss bound on each node to enable the on-line tuning of the PCST. Simulations were performed on five variants of carrier sensing mechanisms; results show that K-APCS achieves the maximum spatial reuse with a throughput gain of 28% and the minimum collision rate with a decrease of 0.01%.

Testing a cloud application: IBM SmartCloud inotes: methodologies and tools

IBM SmartCloud is a branded collection of Cloud products and solutions from IBM. It includes Infrastructure as a Service (IaaS), Software as a Service (SaaS), and Platform as a Service (PaaS) offered through public, private and hybrid cloud delivery models. This paper focuses on the software testing process employed for the SmartCloud iNotes SaaS application, providing details of the methodologies and tools developed to streamline testing. The new tools have enabled the testing team to meet the pace of the highly agile development team, enabling a more efficient software development lifecycle. Results indicate that the methodologies and tools used have increased the performance of the testing team: there was a decrease in the number of bugs present in the code (prior to release), and an overall increase in customer satisfaction.