Eirik Larsen Følstad

Managing availability in wireless inter domain access

This paper deals with how the availability of wireless/cellular access networks depend on the cooperation between the operators as well as with transmission network operators and professional land lords. The forthcoming 4G network will consist of diverse sets of wireless/cellular networks integrated into IP-based networks. Mobility, QoS and seamless handover between the networks are key features. In the work of Gustafsson and Jonsson (2003), the concept of always best connected is defined as means that the user is connected through the best available device and access technology at all times. Availability of the access is fundamental for QoS and critical services (e.g. emergency services, health services) are more and more dependent of wireless/mobile access. Availability can be increased by utilization of several accesses through seamless handover and/or multihoming. Usually, the availability has been calculated assuming independencies between the access network operators, but in this paper we show that the actual cooperation between the market actors has significant impact on the availability. We propose a solution by usage of the IMH 802.21 framework to build and distribute network topology information with availability estimates allowing to predict the overall availability for the access networks accessible as one of the criteria for a handover decision.

Failures and changes in cellular access networks; A study of field data

The operator diversity of different wireless and cellular networks integrated by IP-based networks does not imply independencies in the respective access networks. We have used incident and change records covering more than 1000 days from a GSM/UMTS network operator. Service failures vs. population density and time periodicity of failures have been studied. Our results indicate higher failure intensity in rural areas than in the urban areas and higher failure intensity during working hours. Leased services and power give major contributions to the failure intensity. This indicates dependencies between network operators. The operator staffs logged common root causes for failures show that the restoration times for the affected BTS/Node B are not identical. The number of changes in the network is significant compared to the number of failures. Our analysis does not indicate correlations between logged network changes and failures.

A Survey on Network Resiliency Methodologies against Weather-based Disruptions

Due to the increasing dependence on network services 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 communication 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.

Maximizing the reliability of dual homed, critical services in wireless/cellular networks

In the modern society the wireless access to any service has become a commodity. However, various services have different dependability requirements. For critical services the reliability, i.e., the probability for an uninterrupted service, is utmost important. In wireless/cellular networks the execution of handover is one of the key mechanisms to provide an uninterrupted service for a mobile user. Dual homing may be utilized to increase the service reliability where disjointed access points are used for the two connections across possible different access technologies and network operators. The novelty of this paper is how a shortest path algorithm is used to efficiently find the (near-)optimal selection of access points along a projected route for a dual homed critical service. This optimization for reliability takes the radio connections, including handovers, and backhaul network into account. Backhaul network may be composed of a web of autonomous sub-networks made up of different technologies and layers, for instance SDH over an optical network layer.

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 users 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.

Determining dependencies in multi technology inter domain wireless access; A case study

For critical services the availability of the wireless access is one of the fundamental QoS requirements. Availability can be used as one of the criteria in handover/multihoming decision. Assuming independency between different access networks will over estimate the availability. Dependencies will be retrieved by a detailed structure function including all equipment used. In this paper we address the feasibility to derive the structure function from the operations support systems (OSSs) for the access networks available at a given location, in a multi technology multi operator wireless access environment. A field trial is performed to derive the detailed structure function in a commercial network.