A survey on network resiliency methodologies against weather-based disruptions
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paper_title: Telecommunications Power Plant Damage Assessment for Hurricane Katrina– Site Survey and Follow-Up Results

paper_content:

This paper extends knowledge of disaster impact on the telecommunications power infrastructure by discussing the effects of Hurricane Katrina based on an on-site survey conducted in October 2005 and on public sources. It includes observations about power infrastructure damage in wire-line and wireless networks. In general, the impact on centralized network elements was more severe than on the distributed portion of the grids. The main cause of outage was lack of power due to fuel supply disruptions, flooding and security issues. This work also describes the means used to restore telecommunications services and proposes ways to improve logistics, such as coordinating portable generator set deployment among different network operators and reducing genset fuel consumption by installing permanent photovoltaic systems at sites where long electric outages are likely. One long term solution is to use of distributed generation. It also discusses the consequences on telecom power technology and practices since the storm.
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paper_title: Effects of Temperature and Humidity on Radio Signal Strength in Outdoor Wireless Sensor Networks

paper_content:

Many wireless sensor networks operating outdoors are exposed to changing weather conditions, which may cause severe degradation in system performance. Therefore, it is essential to explore the factors affecting radio link quality in order to mitigate their impact and to adapt to varying conditions. In this paper, we study the effects of temperature and humidity on radio signal strength in outdoor wireless sensor networks. Experimental measurements were performed using Atmel ZigBit 2.4GHz wireless modules, both in summer and wintertime. We employed all the radio channels specified by IEEE 802.15.4 for 2.4GHz ISM frequency band with two transmit power levels. The results show that changes in weather conditions affect received signal strength. Of the studied weather variables, variation in signal strength can be best explained by the variation in temperature. We also show that frequency diversity can reduce the effects of channel-specific variation, and the difference between the transmit power levels.
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paper_title: Network survivability modeling

paper_content:

Critical services in a telecommunication network should be continuously provided even when undesirable events like sabotage, natural disasters, or network failures happen. It is essential to provide virtual connections between peering nodes with certain performance guarantees such as minimum throughput, maximum delay or loss. The design, construction and management of virtual connections, network infrastructures and service platforms aim at meeting such requirements. In this paper we consider the network's ability to survive major and minor failures in network infrastructure and service platforms that are caused by undesired events that might be external or internal. Survive means that the services provided comply with the requirement also in presence of failures. The network survivability is quantified as defined by the ANSI T1A1.2 committee which is the transient performance from the instant an undesirable event occurs until steady state with an acceptable performance level is attained. The assessment of the survivability of a network with virtual connections exposed to link or node failures is addressed in this paper. We have developed both simulation and analytic models to cross-validate our assumptions. In order to avoid state space explosion while addressing large networks we decompose our models first in space by studying the nodes independently and then in time by decoupling our analytic performance and recovery models which gives us a closed form solution. The modeling approaches are applied to both small and real-sized network examples. Three different scenarios have been defined, including single link failure, hurricane disaster, and instabilities in a large block of the system (transient common failure). The results show very good correspondence between the transient loss and delay performance in our simulations and in the analytic approximations.
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paper_title: Telecommunications Power Plant Damage Assessment for Hurricane Katrina– Site Survey and Follow-Up Results

paper_content:

This paper extends knowledge of disaster impact on the telecommunications power infrastructure by discussing the effects of Hurricane Katrina based on an on-site survey conducted in October 2005 and on public sources. It includes observations about power infrastructure damage in wire-line and wireless networks. In general, the impact on centralized network elements was more severe than on the distributed portion of the grids. The main cause of outage was lack of power due to fuel supply disruptions, flooding and security issues. This work also describes the means used to restore telecommunications services and proposes ways to improve logistics, such as coordinating portable generator set deployment among different network operators and reducing genset fuel consumption by installing permanent photovoltaic systems at sites where long electric outages are likely. One long term solution is to use of distributed generation. It also discusses the consequences on telecom power technology and practices since the storm.
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paper_title: The restoration of telecom power damages by the Great East Japan Earthquake

paper_content:

This digest introduces the unprecedented damages of NTT's telecommunications buildings caused by the Great East Japan Earthquake, and the restoration measures. We also explain NTT's current disaster countermeasures against power system issues by blackouts, earthquakes, water damages such as tsunami and tidal wave, and issues to be solved in the future.
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paper_title: Spatiotemporal risk-averse routing

paper_content:

A cyber-physical system is often designed as a network in which critical information is transmitted. However, network links may fail, possibly as the result of a disaster. Disasters tend to display spatiotemporal characteristics, and consequently link availabilities may vary in time. Yet, the requested connection availability of traffic must be satisfied at all times, even under disasters. In this paper, we argue that often the spatiotemporal impact of disasters can be predicted, such that suitable actions can be taken, before the disaster manifests, to ensure the availability of connections. Our main contributions are three-fold: (1) we propose a generic grid-based model to represent the risk profile of a network area and relate the risk profile to the availability of links and connections, (2) we propose a polynomial-time algorithm to identify connections that are vulnerable to an emerging disaster risk, and (3) we consider the predicted spatiotemporal disaster impact, and propose a polynomial-time algorithm based on an auxiliary graph to find the most risk-averse path under a time constraint.
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paper_title: Large-Scale Network-Service Disruption: Dependencies and External Factors

paper_content:

Large-scale service disruptions in communication have been observed in the past but are not well-understood. The goal of this work is to gain a better understanding of disruptions in communication services in response to large-scale external disturbances such as hurricanes. In particular, Hurricane Ike is drawn as a case study, and heterogeneous data is obtained from networks, storm, and system administrators. Using the data, we first study network-wide disruptions and dependences among different unreachable subnets. Our findings show that 120 out of 230 subnets in our data set were unreachable, among which 88 subnets became unreachable dependently at a time scale of seconds or less than three minutes. We then study dependencies between communication service-disruptions and external factors such as weather and power. Unreachable subnets are found to be weakly correlated with the storm. Power outages and lack of spare power are reported to be certain causes of communication disruptions. New research issues emerge for information acquisition across communication and power infrastructures as well as weather, and information sharing among organizations.
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paper_title: The Effects of Tropical Weather on Radio-Wave Propagation Over Foliage Channel

paper_content:

This paper investigates the dynamic property of a tropical forested channel due to the weather effect on very high frequency (VHF) and ultrahigh frequency (UHF) radio-wave propagation. In this paper, continuous-wave (CW) envelope fading waveforms are recorded over a period of 50 s with static antennas. This paper focuses on the analysis of the combined effect of wind and rain, which is often encountered in a tropical forest. The induced temporal effects are discussed and compared with theoretical models. It is found that the distribution of temporal fading components resembles a Rician distribution function. Its Rician K factor gradually decreases as the strength of either wind or rain increases due to the movement of the forest components.
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paper_title: Performance analysis of MISO multi-hop FSO links over log-normal channels with fog and beam divergence attenuations

paper_content:

The performance analysis of a multi-hop decode and forward relaying free-space optical (FSO) communication system is presented in this paper. The considered FSO system uses intensity modulation and direct detection as means of transmission and reception. Atmospheric turbulence impacts are modeled as a log-normal channel, and different weather attenuation effects and geometric losses are taken into account. It is shown that multi-hop is an efficient technique to mitigate such effects in FSO communication systems. A comparison with direct link and multiple-input single-output (MISO) systems considering correlation effects at the transmitter is provided. Results show that MISO multi-hop FSO systems are superior than their counterparts over links exhibiting high attenuation. Monte Carlo simulation results are provided to validate the bit error rate (BER) analyses and conclusions.
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paper_title: Effects of Temperature and Humidity on Radio Signal Strength in Outdoor Wireless Sensor Networks

paper_content:

Many wireless sensor networks operating outdoors are exposed to changing weather conditions, which may cause severe degradation in system performance. Therefore, it is essential to explore the factors affecting radio link quality in order to mitigate their impact and to adapt to varying conditions. In this paper, we study the effects of temperature and humidity on radio signal strength in outdoor wireless sensor networks. Experimental measurements were performed using Atmel ZigBit 2.4GHz wireless modules, both in summer and wintertime. We employed all the radio channels specified by IEEE 802.15.4 for 2.4GHz ISM frequency band with two transmit power levels. The results show that changes in weather conditions affect received signal strength. Of the studied weather variables, variation in signal strength can be best explained by the variation in temperature. We also show that frequency diversity can reduce the effects of channel-specific variation, and the difference between the transmit power levels.
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paper_title: Comparing the Life Time of Terrestrial Wireless Sensor Networks by Employing Hybrid FSO/RF and Only RF Access Networks

paper_content:

The increased interest in long lasting wireless sensor networks motivates to use Free Space Optics (FSO) link along with radio frequency (RF) link for communication. Earlier results show that RF/FSO wireless sensor networks has life time twice as long as RF only wireless sensor networks. However, for terrestrial applications, the effect of weather such as rain or snow on optical wireless communication link is major concern, that should be taken into account in the performance analysis. In this paper, life time performance of hybrid wireless sensor networks is compared to wireless sensor networks using RF only for terrestrial applications and weather effects of rain and snow.
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paper_title: Gust buffeting and aeroelastic behaviour of poles and monotubular towers

paper_content:

Abstract The evolution in the constructional field and the realization of ever more slender and light structures have emphasized the increasing difficulty of properly evaluating the actions and effects of wind on poles and monotubular towers. Faced with this situation the Italian constructors, united in a consortium coordinated by ACS ACAI Servizi, entrusted the Department of Structural and Geotechnical Engineering of Genova University with the task of formulating an ad hoc calculation procedure for this type of structure. This gave rise to a wide-ranging research project in which theoretical models, experimental evaluations and engineering methods were developed in parallel through an effective and quite a unique co-operation between researchers, designers and builders. This paper illustrates the physical aspects, the general principles and the basic formulation of the method proposed, with special emphasis on gust buffeting and aeroelastic phenomena. Preliminary results of full-scale measurements of the structural damping are also presented. The conclusions highlight the scientific and technical perspectives of this research.
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paper_title: Dynamic monitoring and numerical modelling of communication towers with FBG based accelerometers

paper_content:

Abstract This study presents the dynamic monitoring of two telecommunication tall slender steel towers with an optical FBG accelerometer. Numerical simulation for both towers was used recurring to finite elements modelling in order to demonstrate the feasibility of using optical technology in this type of structural monitoring. The results show a good agreement between experimental and simulated data, demonstrating that the optical accelerometer can be a very useful tool in the monitoring of tall slender structures.
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paper_title: The past 20 years of telecommunication structures in Portugal

paper_content:

Abstract This paper reviews the analysis and design of telecommunication structures and presents the main problems observed for various types of structures. The nation of Portugal is selected for a case study, and more specifically, the evolution of Portuguese structural design standards for telecommunications systems is summarised using comparative analyses that cover a subset of the most relevant topics for design, including wind profiles, drag coefficients, dynamic effects and reliability classes. These analyses focus on characterisation of the effects of wind action, which plays a fundamental role in the behaviour and design of these structures. Following the comparative analyses of standards, the more common problems observed over the past 20 years in guyed masts and towers located in Portugal are presented and discussed.
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paper_title: WiMAX: The Innovative Broadband Wireless Access Technology

paper_content:

The telecommunication industry has been through disruptive times, but data networking service revenue has continued to rise. The telecom industry is expected to continue to grow as demand increases for cable and high-speed Internet in previously unserviced locations and as local telephone companies upgrade their lines in response to increasing competition. This paper presents an extended overview of the Worldwide Interoperability for Microwave Access (WiMAX) and its applications in higher generation wireless networks as a cost effective solution to answering the challenges posed by the digital divide. It looks at the technology behind WiMAX and networks design and deployment factors that impact WiMAX coverage. A cell site coverage simulation at different frequency bands using Wireless simulation tool is presented. Also the paper makes a comparison of WiMAX with two enhanced third generation (3G) technologies that are potential competitors to WiMAX. It then goes on describe the business models in WiMAX and states some of the benefits and drawbacks of a mobile WiMAX network.
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paper_title: Design of weather disruption-tolerant wireless mesh networks

paper_content:

Owing to high costs of deployment and maintenance of fiber optic infrastructure, wireless mesh networks (WMNs) with transmission rates of 1–10 Gb/s per a millimeter-wave link (utilizing the 71–86 GHz band), seem to be a promising alternative to wired backbone Metropolitan Area Networks. However, due to the nature of high-frequency wireless communications, such links are very susceptible to weather disruptions, and especially to rain storms resulting in remarkable signal attenuation.
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paper_title: Protection Strategies and Fault Avoidance in Free Space Optical Mesh Networks

paper_content:

Although fiber technology has been advanced to produce a wide range of fiber types to meet specific needs, new fiber deployment requires long-term planning and installation until full service is established. There are many applications that demand high-data rate connectivity urgently, be it Internet, voice, video or all three. Such applications are due to a natural emergency, a large short term event, or enterprise that needs immediate and private service; free space optical or wireless optical is an optical communication method that meets such needs. Additionally, it is apparent that FSO full-duplex point-to-point links have limited service availability. In addition to natural and man- made link failures, atmospheric conditions may also cause failures because the optical beam is highly attenuated by fog and other airborne particles. As a consequence, only mesh FSO provides enhanced service availability if proper fault detection and protection strategies are incorporated on the node and network level. In this paper, we review the FSO technology, we discuss the mesh FSO topology, and we describe fault detection, fault avoidance and protection strategies of the FSO mesh when one or more of its links fail. We also discuss engineering and traffic management and security issues.
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paper_title: Adaptive Wireless Mesh Networks: Surviving Weather without Sensing It

paper_content:

Large-scale wireless mesh networks, like the ones used as cellular back-haul, operate under circumstances, where individual links are affected by weather conditions. Reliability requirements in wireless mesh networks necessitate the ability to reconfigure the network in the face of changing environmental conditions. In this paper, we present a predictive routing protocol for wireless mesh networks, which operate at millimeter-wave bands with directional links, that uses in-network parameter prediction to make the network adaptive, as opposed to using meteorological weather information from external sources, such as weather radars. We validate our approach through simulations based on real-world weather events, observed through a network of weather radars, and comparisons with approaches that do not make use of predictions but may use the link quality as a parameter in routing decision making. Our results show that our link quality-based predictive approach can achieve throughput performance that is almost 8% better than a link quality-based routing algorithm that does not use prediction for the real weather scenario we use for our simulations.
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paper_title: Field measurement of an implemented solar powered BS-based wireless mesh network

paper_content:

Developing effective communications infrastructure, that is, a BS-based communication system, in “off-grid” locations without electricity (rural areas without power grid, areas affected by disasters, etc.) is a challenging research area in the information and communication technology sector. Since users in such areas usually exhibit demands for stable communication (e.g., mail service with constant delivery delay, voice call service with consistent quality), the BSs need to operate utilizing available resources under an energy-constricted environment. With the absence of power grid in rural regions and the occurrence of power outage in disaster-stricken areas, ambient energy sources such as solar and wind energy have become viable alternatives to power BSs. These energy harvesting BSs, however, have to confront the variable behavior of the ambient energy sources, which lead to variable amounts and rates of energy available over time. In this article, we present our considered wireless mesh network exploiting solar energy harvesting BSs, and conduct a study based on field experiments to estimate the factors that influence their energy harvesting capability. Particularly, the results of our conducted experiments demonstrate that the ON/OFF states of the radio links have a direct impact on the power consumption of the BSs. Also, the manner in which the amount of solar radiation during different weather conditions over different days affects the array voltage in an energy harvesting BS is investigated.
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paper_title: Reliable routing and resource allocation scheme for hybrid RF/FSO networks

paper_content:

Significant success of wireless networks in the last decade has changed the paradigms of communication networks design. In particular, the growing interest in wireless mesh networks (WMNs) is observed. WMNs offer an attractive alternative to conventional cable infrastructures, especially in urban areas, where the cost of new installations is almost prohibitive. Unfortunately, the performance of WMNs is often limited by the cluttered RF spectrum and channel interference. Free space optical (FSO) technology is a possible solution for IP traffic connectivity, but weather-based disruptions, e.g., clouds, fog, and snow, highly affect the service availability in the network. However, FSO links can provide much higher data rates than RF links and do not interfere with RF links. In this paper, we first outline the important aspects that should be taken into account when determining allocation of network resources (link capacities) for the purpose of serving the demands. The latter part of the paper is to introduce the respective ILP model as well as heuristic algorithm to determine routing in hybrid RF/FSO networks with special focus on resistance of FSO links to weather-based disruptions.
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paper_title: Survivable millimeter-wave mesh networks

paper_content:

Millimeter-wave mesh networks have the potential to provide cost-effective high-bandwidth solutions to many current bandwidth-constrained networks including cellular backhaul. However, the availability of such networks is severely limited due to their susceptibility to weather, such as precipitation and humidity. In this paper, we present a rigorous approach to survivable millimeter-wave mesh networks based on experimentation, modeling, and simulation. Individual link performance is characterised using frame error-rate measurements from millimeter-wave transmissions on test links over a period of one year. A geometric model based on radar-reflectivity data is used to characterise rain storms and determine their impact on spatially correlated links of a mesh network. To mitigate the impact of link impairments on network services, we present two cross-layered routing protocols to route around the failures: P-WARP (predictive weather-assisted routing protocol) and XL-OSPF (cross-layered open shortest-path first). We conduct a performance analysis of the proposed mesh network under the presence of actual weather events as recorded by the US National Weather Service. Results show that the proposed approach yields the highest dependability when compared against existing routing methods.
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paper_title: Design of weather disruption-tolerant wireless mesh networks

paper_content:

Owing to high costs of deployment and maintenance of fiber optic infrastructure, wireless mesh networks (WMNs) with transmission rates of 1–10 Gb/s per a millimeter-wave link (utilizing the 71–86 GHz band), seem to be a promising alternative to wired backbone Metropolitan Area Networks. However, due to the nature of high-frequency wireless communications, such links are very susceptible to weather disruptions, and especially to rain storms resulting in remarkable signal attenuation.
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paper_title: Performance Comparison of Weather Disruption-Tolerant Cross-Layer Routing Algorithms

paper_content:

With growing demand for high-speed access to mobile handheld devices, there is a significant cost benefit in deploying fixed wireless-mesh networks for backhaul access. However, enabling reliable broadband access over high-frequency radios (such as millimeter-wave networks) posses a fundamental challenge due to weather disruptions in general and rain attenuation in particular. In this paper, we present an analysis of the impact of precipitation on millimeter-wave mesh networks based on radar measurements of real storms in the Midwest US. Furthermore, we compare two novel algorithms that use physical-layer information to optimize routing at the network layer: P-WARP (Predictive Weather-Assisted Routing Protocol) and XL-OSPF (Cross-Layered Open Shortest Path First). Finally, we present simulation studies to compare the performance of the proposed protocols and evaluate the dependability of the end-user service during weather disruptions.
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paper_title: Protection Strategies and Fault Avoidance in Free Space Optical Mesh Networks

paper_content:

Although fiber technology has been advanced to produce a wide range of fiber types to meet specific needs, new fiber deployment requires long-term planning and installation until full service is established. There are many applications that demand high-data rate connectivity urgently, be it Internet, voice, video or all three. Such applications are due to a natural emergency, a large short term event, or enterprise that needs immediate and private service; free space optical or wireless optical is an optical communication method that meets such needs. Additionally, it is apparent that FSO full-duplex point-to-point links have limited service availability. In addition to natural and man- made link failures, atmospheric conditions may also cause failures because the optical beam is highly attenuated by fog and other airborne particles. As a consequence, only mesh FSO provides enhanced service availability if proper fault detection and protection strategies are incorporated on the node and network level. In this paper, we review the FSO technology, we discuss the mesh FSO topology, and we describe fault detection, fault avoidance and protection strategies of the FSO mesh when one or more of its links fail. We also discuss engineering and traffic management and security issues.
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paper_title: High reliable optical wireless links for the last mile access

paper_content:

In the last couple of years the need for higher data rates and more bandwidth has arisen. This development will continue in the next couple of decades and allegorizes a challenge for the future next generation networks. Taking this into account the end-user will need higher data rates, getting theoretical access to the full available bandwidth of the backbone delivered to the home. Free space optics (FSO) is an excellent supplement to conventional radio links and fiber optics, capable of handling point-to-point and point-to-multipoint connections. On the one hand-side FSO is a broadband wireless solution for the "last mile" connectivity in metropolitan networks, on the other hand-side FSO can be used to interlink locations within one local area network. In the last years different types of cost-effective systems were developed and realized at the Institute of Broadband Communication of Graz University of Technology (TU Graz). The first type was based on a modular concept using available standard components allowing demonstrations at a data rate of 2 times 10 Mbit/s for short distances up to 300 m at a specific power margin of 25 dB/km. Later the units were improved to allow a data rate of 100 Mbit/s, higher data rates are currently under development. The reliability and availability of a FSO-link is mainly determined by the local atmospheric conditions, in free space the transmitted light is reflected, refracted or absorbed by objects, rain, fog, wind or sun. All these parameters directly influence the quality of a FSO-link and indirectly affect the quality of an access network. Many FSO-installations (permanent and nomadic use) have been set-up in the area of Styria by TU Graz and cooperation partners. In this contribution we will show some practical installations for different events, including the latest permanent installation, which was started in the summer of 2007 together with the municipality of Dobl, a small suburb of Graz, and the ML11 GmbH, an IT-company. Within this cooperation the elementary school of Dobl was connected to the Internet via FSO. The FSO-units were successfully installed and the setup is now used to explore the influence of weather on the FSO-link in the area of Graz.
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paper_title: Network survivability modeling

paper_content:

Critical services in a telecommunication network should be continuously provided even when undesirable events like sabotage, natural disasters, or network failures happen. It is essential to provide virtual connections between peering nodes with certain performance guarantees such as minimum throughput, maximum delay or loss. The design, construction and management of virtual connections, network infrastructures and service platforms aim at meeting such requirements. In this paper we consider the network's ability to survive major and minor failures in network infrastructure and service platforms that are caused by undesired events that might be external or internal. Survive means that the services provided comply with the requirement also in presence of failures. The network survivability is quantified as defined by the ANSI T1A1.2 committee which is the transient performance from the instant an undesirable event occurs until steady state with an acceptable performance level is attained. The assessment of the survivability of a network with virtual connections exposed to link or node failures is addressed in this paper. We have developed both simulation and analytic models to cross-validate our assumptions. In order to avoid state space explosion while addressing large networks we decompose our models first in space by studying the nodes independently and then in time by decoupling our analytic performance and recovery models which gives us a closed form solution. The modeling approaches are applied to both small and real-sized network examples. Three different scenarios have been defined, including single link failure, hurricane disaster, and instabilities in a large block of the system (transient common failure). The results show very good correspondence between the transient loss and delay performance in our simulations and in the analytic approximations.
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paper_title: On Protected Traffic Routing in Wireless Networks with Partial Multiple Link Failures

paper_content:

In this paper we study an optimization problem relevant for wireless networks. In such networks links are subject to capacity disruptions caused by changing weather/channel condition that force to adapt the modulation and coding schemes to the observed condition. To cope with this issue in network optimization, we propose a new strategy called the Flow Thinning Strategy. For traffic protection we assume (possibly) over-dimensioned normal path-flows (i.e., path-flows defined for the availability state with all links fully available, the so called normal state) that are thinned in a failure state-dependent way to adapt to fluctuating reduced capacity. What is important, the normal flows cannot be increased or restored in any way. Moreover, we assume that the demand volumes to be realized in states can be reduced as compared to the normal demands. To solve a link cost minimization problem corresponding to the above assumptions, we develop an original non-compact linear programming model together with its solution algorithm based on path generation. We also present a numerical study that compares the performance of the assumed flow-thinning routing with other routing strategies studied before. In the presented version, our model is applicable to wireless networks with non-interfering point-to-point links such as free space optical links or microwave links.
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paper_title: Network Reliability With Geographically Correlated Failures

paper_content:

Fiber-optic networks are vulnerable to natural disasters, such as tornadoes or earthquakes, as well as to physical failures, such as an anchor cutting underwater fiber cables. Such real-world events occur in specific geographical locations and disrupt specific parts of the network. Therefore, the geography of the network determines the effect of physical events on the network's connectivity and capacity. In this paper, we develop tools to analyze network failures after a `random' geographic disaster. The random location of the disaster allows us to model situations where the physical failures are not targeted attacks. In particular, we consider disasters that take the form of a `random' line in a plane. Using results from geometric probability, we are able to calculate some network performance metrics to such a disaster in polynomial time. In particular, we can evaluate average two-terminal reliability in polynomial time under `random' line-cuts. This is in contrast to the case of independent link failures for which there exists no known polynomial time algorithm to calculate this reliability metric. We also present some numerical results to show the significance of geometry on the survivability of the network and discuss network design in the context of random line-cuts. Our novel approach provides a promising new direction for modeling and designing networks to lessen the effects of geographical disasters or attacks.
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paper_title: Network adaptability from disaster disruptions and cascading failures

paper_content:

Disasters can cause severe service disruptions due to large-scale correlated cascading failures in telecom networks. Major network disruptions due to disasters — both natural (e.g., Hurricane Sandy, 2011 Japan Tsunami) and human-made (e.g., 9/11 terrorist attack) — deprive the affected population of essential network services for weeks and severely hamper rescue operations. Many techniques exist to provide fast network protection, but they are optimized for limited faults without addressing the extent of disaster failures. Thus, there is a pressing need for novel robust survivability methods to mitigate the effects of disasters on telecom networks. While researchers in climatology, geology, and environmental science have been studying how to predict disasters and assess disaster risks for certain regions, networking research can exploit this information to develop novel methods to prepare networks to handle disasters with the knowledge of risky regions and to better prepare them for a predicted disaster. The events during the aftermath of a disaster should also be considered. For instance, methods to re-arrange network resources and services on a partially damaged network, which is the property of a self-organizing network, should be developed, and new algorithms to manage the post-disaster traffic deluge and to relieve the rescue operations after a disaster, with the knowledge of the post-disaster failures, should be investigated. Since cloud services today are an integral part of our society and massive amounts of content/services have been created and shared over the cloud, loss/disruption of critical content/ services caused by disasters can significantly affect the security and economic well being of our society. As the network is becoming increasingly an end-to-content (vs. end-toend) connection provider, we have to ensure reachability of content from any point of a network, which we call content connectivity (in contrast to network connectivity) after disaster failures. This article presents the nature of possible disruptions in telecom networks caused by disaster events, and sheds light on how to prepare the network and cloud services against disasters, and adapt them for disaster disruptions and cascading failures.
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paper_title: Live migration of an entire network (and its hosts)

paper_content:

Live virtual machine (VM) migration can move applications from one location to another without a disruption in service. However, applications often consist of multiple VMs and rely on the state of the underlying network for basic reachability, access control, and QoS functionality. Rather than migrating an individual VM, we show how to migrate an ensemble---the VMs, the network, and the management system---to a different set of physical resources. Our LIME (LIve Migration of Ensembles) design leverages recent advances in Software Defined Networking (SDN) for a clear separation between the controller and the data-plane state in the switches. Transparent to the application running on the controller, LIME clones the data-plane state to a new set of switches, and then incrementally migrates the traffic sources (e.g., the VMs). During this transition, both networks deliver traffic and LIME maintains synchronized state. Experiments with our initial prototype, built on the Floodlight OpenFlow controller, suggest that network migration does not have to be a disruptive, middle-of-the-night maintenance event, but can become an integral network management mechanism completely transparent to applications.
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paper_title: Bandwidth-aware allocation of resilient Virtual Software Defined Networks

paper_content:

Currently, it is hard to imagine our lives without the Internet, where services are accessed and shared by billions of users every day. However, even after many years, the Internet cannot guarantee Quality of Service (QoS) for the main services to current and future clients. To deal with this problem, clients establish Service Level Agreements (SLAs) with their Internet Service Providers (ISPs), including resilience parameters. The Internet is recognized to be resilient enough for many services, but it is still sensitive to failure events that affect the performance of these services. Software Defined Networks (SDNs) together with Virtual Network (VNs) approaches aim to enhance the management, planning and resource usage of networks. When both approaches are mixed together, we have Virtual Software Defined Network (VSDN). However, the allocation of VSDNs considering resilience issues is still an open issue. Within this context, this paper presents an algorithm for VSDN allocation, called Bw-Risk-Ratio, that considers resilience factors, as well as it deploys the VSDN according to QoS parameters defined in the SLA. Experiments using a real network topology show the effectiveness of the algorithm to deploy the VSDN resilient to failure events when compared to existing solutions.
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paper_title: Optimal Model for Failure Foresight Capacitated Controller Placement in Software-Defined Networks

paper_content:

Controller placement is an important problem in software-defined networks. If a controller fails, there may be no controller with enough spare capacity to serve switches of the failed controller, which leads to switches being disconnected from the controller. Even if there are controllers with enough spare capacity, reassigning switches of the failed controller may drastically increase the worst case latency. In this letter, we propose a mathematical model for the capacitated controller placement that plans ahead for the failures to avoid a drastic increase in the worst case latency and disconnections. The objective of our model is to minimize the worst case latency between the switches and their $K{\mathrm{ th}}$ reference controllers. We also introduce a variant of the proposed model that minimizes the worst case latencies with and without failures together. Our simulation results show that the controller placements that plan ahead for the failures result in much lower latency compared with the placement without planning ahead.
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paper_title: Network adaptability to disaster disruptions by exploiting degraded-service tolerance

paper_content:

The rapid increase in network traffic with new bandwidth-hungry applications such as cloud computing and telemedicine makes disaster survivability a crucial concern as the data (and revenue) loss caused by large-scale correlated cascading failures can be very high. To alleviate their impact, new measures should be taken since the nature of the network changes dramatically as available resources decrease during disasters. We develop a metric, called degraded-service tolerance, which can reduce protection cost and network disruption, and support maximal carried traffic in case of disasters. Degraded-service-tolerant connections can be admitted and recovered with reduced bandwidth under resource crunch. Our scheme re-assigns resources among connections by leveraging their degraded-service tolerance. A case study shows how our proposal can be applied to boost network performance during the resource crunch following a disaster.
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paper_title: Disaster-resilient control plane design and mapping in software-defined networks

paper_content:

Communication networks, such as core optical networks, heavily depend on their physical infrastructure, and hence they are vulnerable to man-made disasters, such as Electromagnetic Pulse (EMP) or Weapons of Mass Destruction (WMD) attacks, as well as to natural disasters. Large-scale disasters may cause huge data loss and connectivity disruption in these networks. As our dependence on network services increases, the need for novel survivability methods to mitigate the effects of disasters on communication networks becomes a major concern. Software-Defined Networking (SDN), by centralizing control logic and separating it from physical equipment, facilitates network programmability and opens up new ways to design disaster-resilient networks. On the other hand, to fully exploit the potential of SDN, along with data-plane survivability, we also need to design the control plane to be resilient enough to survive network failures caused by disasters. Several distributed SDN controller architectures have been proposed to mitigate the risks of overload and failure, but they are optimized for limited faults without addressing the extent of large-scale disaster failures. For disaster resiliency of the control plane, we propose to design it as a virtual network, which can be solved using Virtual Network Mapping techniques. We select appropriate mapping of the controllers over the physical network such that the connectivity among the controllers (controller-to-controller) and between the switches to the controllers (switch-to-controllers) is not compromised by physical infrastructure failures caused by disasters. We formally model this disaster-aware control-plane design and mapping problem, and demonstrate a significant reduction in the disruption of controller-to-controller and switch-to-controller communication channels using our approach.
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paper_title: Network Function Virtualization: Challenges and Directions for Reliability Assurance

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Network Function Virtualization (NFV) is an emerging solution that aims at improving the flexibility, the efficiency and the manageability of networks, by leveraging virtualization and cloud computing technologies to run network appliances in software. Nevertheless, the "notarization" of network functions imposes software reliability concerns on future networks, which will be exposed to software issues arising from virtualization technologies. In this paper, we discuss the challenges for reliability in NFVIs, and present an industrial research project on their reliability assurance, which aims at developing novel fault injection technologies and systematic guidelines for this purpose.
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paper_title: Reliable routing and resource allocation scheme for hybrid RF/FSO networks

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Significant success of wireless networks in the last decade has changed the paradigms of communication networks design. In particular, the growing interest in wireless mesh networks (WMNs) is observed. WMNs offer an attractive alternative to conventional cable infrastructures, especially in urban areas, where the cost of new installations is almost prohibitive. Unfortunately, the performance of WMNs is often limited by the cluttered RF spectrum and channel interference. Free space optical (FSO) technology is a possible solution for IP traffic connectivity, but weather-based disruptions, e.g., clouds, fog, and snow, highly affect the service availability in the network. However, FSO links can provide much higher data rates than RF links and do not interfere with RF links. In this paper, we first outline the important aspects that should be taken into account when determining allocation of network resources (link capacities) for the purpose of serving the demands. The latter part of the paper is to introduce the respective ILP model as well as heuristic algorithm to determine routing in hybrid RF/FSO networks with special focus on resistance of FSO links to weather-based disruptions.
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paper_title: Network design requirements for disaster resilience in IaaS clouds

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Many corporations rely on disaster recovery schemes to keep their computing and network services running after unexpected situations, such as natural disasters and attacks. As corporations migrate their infrastructure to the cloud using the infrastructure as a service model, cloud providers need to offer disaster-resilient services. This article provides guidelines to design a data center network infrastructure to support a disaster-resilient infrastructure as a service cloud. These guidelines describe design requirements, such as the time to recover from disasters, and allow the identification of important domains that deserve further research efforts, such as the choice of data center site locations and disaster-resilient virtual machine placement.
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paper_title: Restoration in optical cloud networks with relocation and services differentiation

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Optical cloud networks allow for the integrated management of both optical and IT resources. In this paradigm, cloud services can be provisioned in an anycast fashion; i.e., only the source node asking for a service is specified, while it is up to the cloud control/management system to select the most suitable destination data center (DC) node. During the cloud service provisioning process, resiliency is crucial in order to guarantee continuous network operations also in the presence of failures. On the one hand, a survivability strategy needs to be able to meet the availability requirements of each specific cloud service, while on the other hand it must be efficient in using backup resources. This paper proposes a restoration-based survivability strategy, which combines the benefits of both cloud service relocation and service differentiation concepts. The former is used to enhance the restorability performance (i.e., the percentage of successfully restored cloud services) offered by restoration, while the latter ensures that critical services are given the proper consideration while backup resources are assigned. The paper proposes both an integer linear programming (ILP) formulation, which guarantees optimal results, and a heuristic, which trades the optimality of the solution achieved by the ILP for faster processing times. Simulation results show that the average service availability and restorability performance obtained by both the ILP and the heuristic are very close to that achievable using a protection-based strategy, but with the inherent benefit, in terms of efficient use of resources, offered by a restoration-based approach.
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paper_title: Progressive recovery for network virtualization after large-scale disasters

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Network virtualization allows users to build cusomized interconnected storage/computing configurations for their business needs. Today this capability is being widely used to improve the scalability and reliability of cloud-based services, including virtual infrastructures services. However, as more and more business-critical applications migrate to the cloud, disaster recovery is now a major concern. Although some studies have looked at network virtualization design under such scenarios, most have only studied pre-fault protection provisioning. Indeed, there is a pressing need to address post-fault recovery, since physical infrastructure repairs will likely occur in a staged progressive manner due to constraints on available resources. Hence this paper studies progressive recovery design for network virtualization and evaluates several heuristic strategies.
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paper_title: Probabilistic region failure-aware data center network and content placement

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Data center network (DCN) and content placement with the consideration of potential large-scale region failure is critical to minimize the DCN loss and disruptions under such catastrophic scenario. This paper considers the optimal placement of DCN and content for DCN failure probability minimization against a region failure. Given a network for DCN placement, a general probabilistic region failure model is adopted to capture the key features of a region failure and to determine the failure probability of a node/link in the network under the region failure. We then propose a general grid partition-based scheme to flexibly define the global nonuniform distribution of potential region failure in terms of its occurring probability and intensity. Such grid partition scheme also helps us to evaluate the vulnerability of a given network under a region failure and thus to create a "vulnerability map" for DCN and content placement in the network. With the help of the "vulnerability map", we further develop an integer linear program (ILP)-based theoretical framework to identify the optimal placement of DCN and content, which leads to the minimum DCN failure probability against a region failure. A heuristic is also suggested to make the overall placement problem more scalable for large-scale networks. Finally, an example and extensive numerical results are provided to illustrate the proposed DCN and content placement.
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paper_title: Disaster-aware datacenter placement and dynamic content management in cloud networks

paper_content:

Recent targeted attacks and natural disasters have made disaster-resilient cloud network design an important issue. Network operators are investigating proactive and reactive measures to prevent huge data loss and service disruptions in case of a disaster. We present novel techniques for disaster-aware datacenter placement and content management in cloud networks that can mitigate such loss by avoiding placement in given disaster-vulnerable locations. We first solve a static disaster-aware datacenter and content placement problem by adopting an integer linear program with the objective to minimize risk, defined as expected loss of content. It is a measure of how much, in terms of cost or penalty, a network operator may lose probabilistically due to possible disasters in a cloud network. We also show how a service provider's budget constraint can affect disaster-aware placement design. Since disaster scenarios, content popularity, and/or importance are always changing in time, content placement should rapidly adapt to these changes. We propose a disaster-aware dynamic content-management algorithm that can adjust the existing placement based on dynamic settings. Besides reducing the overall risk and making the network disaster-aware, reducing network resource usage and satisfying quality-of-service requirements can also be achieved in this approach. We also provide a cost analysis of employing a dynamic disaster-aware placement design in the network based on real-world cloud pricing.
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paper_title: Rapid data evacuation for large-scale disasters in optical cloud networks

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In case of large-scale disasters, cloud networks may be vulnerable to data loss. We propose a rapid data-evacuation strategy to move maximum amount of data from disaster regions using survived resources under strict time constraints.
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paper_title: A Survey of Delay- and Disruption-Tolerant Networking Applications

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Delay- and Disruption-Tolerant Networking (DTN) is a new communication paradigm that can span across multiple networks and cope with harsh conditions not envisioned in the Internet model. After more than ten years of active research in the field, numerous implementations and applications have emerged with a wide variety of performance and application domains. In this survey, we summarize recent developments in the field and highlight those areas with high potential for future development.
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paper_title: On Service Resilience in Cloud-Native 5G Mobile Systems

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To cope with the tremendous growth in mobile data traffic on one hand, and the modest average revenue per user on the other hand, mobile operators have been exploring network virtualization and cloud computing technologies to build cost-efficient and elastic mobile networks and to have them offered as a cloud service. In such cloud-based mobile networks, ensuring service resilience is an important challenge to tackle. Indeed, high availability and service reliability are important requirements of carrier grade, but not necessarily intrinsic features of cloud computing. Building a system that requires the five nines reliability on a platform that may not always grant it is, therefore, a hurdle. Effectively, in carrier cloud, service resilience can be heavily impacted by a failure of any network function (NF) running on a virtual machine (VM). In this paper, we introduce a framework, along with efficient and proactive restoration mechanisms, to ensure service resilience in carrier cloud. As restoration of a NF failure impacts a potential number of users, adequate network overload control mechanisms are also proposed. A mathematical model is developed to evaluate the performance of the proposed mechanisms. The obtained results are encouraging and demonstrate that the proposed mechanisms efficiently achieve their design goals.
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paper_title: Applications in Delay-Tolerant and Opportunistic Networks

paper_content:

This chapter contains sections titled: Application Scenarios Challenges for Applications Over DTN Critical Mechanisms for DTN Applications DTN Applications (Case Studies) Conclusion: Rethinking Applications for DTNs References
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paper_title: Optimal assignment of cells in C-RAN deployments with multiple BBU pools

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Cloud Radio Access Network (C-RAN) is receiving increasing attention not only within the research community but also from operators and standardization bodies. However, even a good technology will be deployed only if it is economically viable. In our previous work, for larger scale deployment we recommend to divide the area into multiple BBU Pools. In this paper we show how to optimally assign cells to different BBU Pools in such a scenario. By using Integer Linear Programming (ILP) method we derive engineering guidelines for minimizing the CAPital EXpenditure (CAPEX) of C-RAN deployment.
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paper_title: Networking named content

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Current network use is dominated by content distribution and retrieval yet current networking protocols are designed for conversations between hosts. Accessing content and services requires mapping from the what that users care about to the network's where. We present Content-Centric Networking (CCN) which uses content chunks as a primitive---decoupling location from identity, security and access, and retrieving chunks of content by name. Using new approaches to routing named content, derived from IP, CCN simultaneously achieves scalability, security, and performance. We describe our implementation of the architecture's basic features and demonstrate its performance and resilience with secure file downloads and VoIP calls.
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paper_title: Software-Defined and Virtualized Future Mobile and Wireless Networks: A Survey

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With the proliferation of mobile demands and increasingly multifarious services and applications, mobile Internet has been an irreversible trend. Unfortunately, the current mobile and wireless network (MWN) faces a series of pressing challenges caused by the inherent design. In this paper, we extend two latest and promising innovations of Internet, software-defined networking and network virtualization, to mobile and wireless scenarios. We first describe the challenges and expectations of MWN, and analyze the opportunities provided by the software-defined wireless network (SDWN) and wireless network virtualization (WNV). Then, this paper focuses on SDWN and WNV by presenting the main ideas, advantages, ongoing researches and key technologies, and open issues respectively. Moreover, we interpret that these two technologies highly complement each other, and further investigate efficient joint design between them. This paper confirms that SDWN and WNV may efficiently address the crucial challenges of MWN and significantly benefit the future mobile and wireless network.
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paper_title: Named data networking

paper_content:

Named Data Networking (NDN) is one of five projects funded by the U.S. National Science Foundation under its Future Internet Architecture Program. NDN has its roots in an earlier project, Content-Centric Networking (CCN), which Van Jacobson first publicly presented in 2006. The NDN project investigates Jacobson's proposed evolution from today's host-centric network architecture (IP) to a data-centric network architecture (NDN). This conceptually simple shift has far-reaching implications for how we design, develop, deploy, and use networks and applications. We describe the motivation and vision of this new architecture, and its basic components and operations. We also provide a snapshot of its current design, development status, and research challenges. More information about the project, including prototype implementations, publications, and annual reports, is available on named-data.net.
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paper_title: SDN and Virtualization-Based LTE Mobile Network Architectures: A Comprehensive Survey

paper_content:

Software-defined networking (SDN) features the decoupling of the control plane and data plane, a programmable network and virtualization, which enables network infrastructure sharing and the "softwarization" of the network functions. Recently, many research works have tried to redesign the traditional mobile network using two of these concepts in order to deal with the challenges faced by mobile operators, such as the rapid growth of mobile traffic and new services. In this paper, we first provide an overview of SDN, network virtualization, and network function virtualization, and then describe the current LTE mobile network architecture as well as its challenges and issues. By analyzing and categorizing a wide range of the latest research works on SDN and virtualization in LTE mobile networks, we present a general architecture for SDN and virtualization in mobile networks (called SDVMN) and then propose a hierarchical taxonomy based on the different levels of the carrier network. We also present an in-depth analysis about changes related to protocol operation and architecture when adopting SDN and virtualization in mobile networks. In addition, we list specific use cases and applications that benefit from SDVMN. Last but not least, we discuss the open issues and future research directions of SDVMN.
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paper_title: Wireless network cloud: architecture and system requirements

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With the growth of the mobile communication network, from second-generation to third-generation or fourth-generation networks, technologists in the mobile industry continue to consider advanced wireless network architectures that have the potential to reduce networking costs and provide increased flexibility with respect to network features. In this paper, we propose the wireless network cloud (WNC), a wireless system architecture for a wireless access network. This system makes use of emerging cloud-computing technology and various technologies involved with wireless infrastructure, such as software radio technology and remote radio head technology. Based on open information technology architecture, the WNC provides all the necessary transmission and processing resources for a wireless access network operating in a cloud mode. Note that it is useful to separate the hardware and software for different wireless standards and various services and business models, as well as to meet the new system requirements for emerging wireless technologies, such as collaborative processing at different scales of network use. We analyze several important system challenges involving computational requirements of virtual base stations, I/O throughput, and timing networks for synchronization. Based on current information technologies, we make several suggestions with respect to future system design.
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paper_title: Survivability Analysis of Next-Generation Passive Optical Networks and Fiber-Wireless Access Networks

paper_content:

Passive optical networks (PONs) are currently evolving into next-generation PONs (NG-PONs) which aim at achieving higher data rates, wavelength channel counts, number of optical network units (ONUs), and extended coverage compared to their conventional counterparts. Due to the increased number of stages and ONUs, NG-PONs face significant challenges to provide the same level of survivability like conventional PONs without exceeding the budget constraints of cost-sensitive access networks. Toward this end, partial optical protection, in combination with interconnecting a subset of ONUs through a wireless mesh network (WMN) front-end, are promising solutions to render NG-PONs survivable in a cost-effective manner. In this paper, we present a probabilistic analysis of the survivability of NG-PONs and hybrid fiber-wireless (FiWi) access networks, taking both optical and wireless protection into account. In addition, we propose different selection schemes to wirelessly upgrade a subset of ONUs, and investigate their performance for a wide range of fiber link failure scenarios and different NG-PON topologies.
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paper_title: Cloud technologies for flexible 5G radio access networks

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The evolution toward 5G mobile networks will be characterized by an increasing number of wireless devices, increasing device and service complexity, and the requirement to access mobile services ubiquitously. Two key enablers will allow the realization of the vision of 5G: very dense deployments and centralized processing. This article discusses the challenges and requirements in the design of 5G mobile networks based on these two key enablers. It discusses how cloud technologies and flexible functionality assignment in radio access networks enable network densification and centralized operation of the radio access network over heterogeneous backhaul networks. The article describes the fundamental concepts, shows how to evolve the 3GPP LTE a
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paper_title: Proposal of Information Acquisition Method Utilizing CCN in a Time of Large Scale Natural Disaster

paper_content:

We focused on Content Centric Networking (CCN) of the next generation network. CCN is the technology for which data is reused over the whole network by storing cache of data in each router. In this paper, we propose the information acquisition method utilizing CCN in a time of large scale natural disaster. We attempted a comparison between IP network and CCN over the network simulator. In this comparative verification, we established the cache hit ratio, the number of hops, and data acquisition time as the evaluation item. On comparative verification, we could confirm the utility of the CCN. CCN technology has a great potential that various information can be provided to victims in poor network conditions of a time of large scale natural disaster.
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Title: A Survey on Network Resiliency Methodologies Against Weather-Based Disruptions

Section 1: INTRODUCTION
Description 1: Introduce the purpose of the paper, the significance of network resiliency against weather-based disruptions, and an overview of existing studies.

Section 2: Modeling Infrastructure Disruption
Description 2: Discuss the modeling of disaster impacts on infrastructure, providing examples from significant events and analysis methodologies.

Section 3: Effect on Wireless Channel Quality
Description 3: Explore the impact of weather conditions on wireless channel quality and present different modeling studies capturing these effects.

Section 4: Ensuring Wireless Channel Quality by Structural Design
Description 4: Discuss considerations in structural design aimed at maintaining wireless channel quality under adverse weather conditions, including relevant standards and empirical challenges.

Section 5: RESILIENCY AGAINST WEATHER-BASED DISRUPTIONS IN WIRELESS NETWORKS
Description 5: Provide a survey of the main challenges and strategies for ensuring resiliency in wireless networks, specifically focusing on different wireless technologies.

Section 6: Alert-based Reconfiguration Against Weather-Based Disruptions in Wired Networks
Description 6: Discuss alert-based reconfiguration techniques for wired networks to maintain connectivity during large-scale weather disruptions.

Section 7: Alert-based Reconfiguration in Cloud Networks
Description 7: Examine strategies for dynamic content management and service relocation in cloud networks using alert-based reconfiguration to mitigate weather-based disruptions.

Section 8: Resiliency Against Weather-Based Disruptions in Converged Networks
Description 8: Explore ongoing research and proposed solutions to ensure resiliency in converged networks, considering the deployment of various access technologies.

Section 9: Advanced Technology for Resiliency Against Weather-Based Disruptions
Description 9: Review advanced and experimental networking technologies that provide new solutions for network resiliency against weather-based disruptions, such as Delay Tolerant Networking and Information Centric Networking.

Section 10: CONCLUSIONS
Description 10: Summarize the key findings of the survey, emphasize the importance of the discussed methodologies, and suggest future research directions.