Managed access dependability for critical services in wireless inter domain environment

The Information and Communications Technology (ICT) industry has through the last decades changed and still continues to affect the way people interact with each other and how they access and share information, services and applications in a global market characterized by constant change and evolution. For a networked and highly dynamic society, with consumers and market actors providing infrastructure, networks, services and applications, the mutual dependencies of failure free operations are getting more and more complex. Service Level Agreements (SLAs) between the various actors and users may be used to describe the offerings along with price schemes and promises regarding the delivered quality. However, there is no guarantee for failure free operations whatever efforts and means deployed. A system fails for a number of reasons, but automatic fault handling mechanisms and operational procedures may be used to decrease the probability for service interruptions. The global number of mobile broadband Internet subscriptions surpassed the number of broadband subscriptions over fixed technologies in 2010. The User Equipment (UE) has become a powerful device supporting a number of wireless access technologies and the always best connected opportunities have become a reality. Some services, e.g. health care, smart power grid control, surveillance/monitoring etc. called critical services in this thesis, put high requirements on service dependability. A definition of dependability is the ability to deliver services that can justifiably be trusted. For critical services, the access networks become crucial factors for achieving high dependability. A major challenge in a multi operator, multi technology wireless environment is the mobility of the user that necessitates handovers according to the physical movement. In this thesis it is proposed an approach for how to optimize the dependability for critical services in multi operator, multi technology wireless environment. This approach allows predicting the service availability and continuity at real-time. Predictions of the optimal service availability and continuity are considered crucial for critical services. To increase the dependability for critical services dual homing is proposed where the use of combinations of access points, possibly owned by different operators and using different technologies, are optimized for the specific location and movement of the user. A central part of the thesis is how to ensure the disjointedness of physical and logical resources so important for utilizing the dependability increase potential with dual homing. To address the interdependency issues between physical and logical resources, a study of Operations, Administrations, and Maintenance (OA&M) processes related to the access network of a commercial Global System for Mobile Communications (GSM)/Universal Mobile Telecommunications System (UMTS) operator was performed. The insight obtained by the study provided valuable information of the inter woven dependencies between different actors in the delivery chain of services. Based on the insight gained from the study of OA&M processes a technological neutral information model of physical and logical resources in the access networks is proposed. The model is used for service availability and continuity prediction and to unveil interdependencies between resources for the infrastructure. The model is proposed as an extension of the Media Independent Handover (MIH) framework. A field trial in a commercial network was conducted to verify the feasibility in retrieving the model related information from the operators' Operational Support Systems (OSSs) and to emulate the extension and usage of the MIH framework. In the thesis it is proposed how measurement reports from UE and signaling in networks are used to define virtual cells as part of the proposed extension of the MIH framework. Virtual cells are limited geographical areas where the radio conditions are homogeneous. Virtual cells have radio coverage from a number of access points. A Markovian model is proposed for prediction of the service continuity of a dual homed critical service, where both the infrastructure and radio links are considered. A dependability gain is obtained by choosing a global optimal sequence of access points. Great emphasizes have been on developing computational e cient techniques and near-optimal solutions considered important for being able to predict service continuity at real-time for critical services. The proposed techniques to obtain the global optimal sequence of access points may be used by handover and multi homing mechanisms/protocols for timely handover decisions and access point selections. With the proposed extension of the MIH framework a global optimal sequence of access points providing the highest reliability may be predicted at real-time

The cost for meeting SLA requirements; Implications for customers and providers

A Service Level Agreement (SLA) describes the service, the service-level objectives (SLOs), the price the customer should pay and the compensation if the SLOs are not met. There is a trade-off for the provider between the costs for improving the deployed service quality vs. probability of paying compensation. We propose how to estimate the provider's optimal service deployment. We show that the optimal deployed service quality is dependent on the SLOs, deployment cost, compensation and observation interval. A service deployment based on cost optimization results in targeted dependability objective values that are significantly better than stated in the SLOs. The proposed approach provides valuable insight for an aggregator, who buys services from other providers, to negotiate adequate SLOs, price and compensation from the providers to make a valuable offer for its own customers

Using genetic algorithms to improve the reliability of dual homed wireless critical services

The wireless access to any service in different contexts is nowadays taken for granted. However, the dependability requirements are different for various services and contexts. Critical services put high requirement on the service reliability, i.e., the probability of no service interruption should be close to one. Dual homing may be used to increase the service reliability in a multi technology, multi operator wireless environment, where the user's mobility necessitates access point selections and handovers. To allow the user to assess the risk of the service session, a prediction of the service reliability is necessary. This prediction must fulfil the need for the optimal sequence of access point selections and handovers with regard to service reliability and being computation efficient to accomplish the need for the real-time operation. We demonstrate how genetic algorithms (GA) may be used to predict and to improve the (near) optimal service reliability by fast and simple heuristics, far more computationally efficient than an Integer Linear Programming (ILP) optimization

The cost for meeting SLA requirements; Implications for customers and providers

A Service Level Agreement (SLA) describes the service, the service-level objectives (SLOs), the price the customer should pay and the compensation if the SLOs are not met. There is a trade-off for the provider between the costs for improving the deployed service quality vs. probability of paying compensation. We propose how to estimate the provider's optimal service deployment. We show that the optimal deployed service quality is dependent on the SLOs, deployment cost, compensation and observation interval. A service deployment based on cost optimization results in targeted dependability objective values that are significantly better than stated in the SLOs. The proposed approach provides valuable insight for an aggregator, who buys services from other providers, to negotiate adequate SLOs, price and compensation from the providers to make a valuable offer for its own customers.(c) 2015 Elsevier Ltd. All rights reserved. This is the authors' accepted and refereed manuscript to the article. Locked until 2017-09-21. Author's post-print is released with a Creative Commons Attribution Non-Commercial No Derivatives License

A Survey on Network Resiliency Methodologies against Weather-based Disruptions

Due to the increasing dependence on network ser- vices of our society, research has recently been concentrating on enhancing traditional protection strategies to withstand large- scale failures, as in case of disaster events. The recently-formed EU-funded RECODIS project aims at coordinating and fostering research collaboration in Europe on disaster resiliency in com- munication networks. In particular, the Working Group (WG) 2 of the RECODIS project focuses on developing new network- resiliency strategies to survive weather-based disruptions. As a first step, WG2 members have conducted a comprehensive literature survey on existing studies on this topic. This paper classifies and summarizes the most relevant studies collected by WG2 members in this first phase of the project. While the majority of studies regarding weather-based disruptions deals with wireless network (as wireless channel is directly affected by weather conditions), in this survey we cover also disaster- resiliency approaches designed for wired network if they leverage network reconfiguration based on disaster “alerts”, considering that many weather-based disruptions grant an “alert” thanks to weather forecast