Alija Pasic

A survey of strategies for communication networks to protect against large-scale natural disasters

Recent natural disasters have revealed that emergency networks presently cannot disseminate the necessary disaster information, making it difficult to deploy and coordinate relief operations. These disasters have reinforced the knowledge that telecommunication networks constitute a critical infrastructure of our society, and the urgency in establishing protection mechanisms against disaster-based disruptions. Hence, it is important to have emergency networks able to maintain sustainable communication in disaster areas. Moreover, the network architecture should be designed so that network connectivity is maintained among nodes outside of the impacted area, while ensuring that services for costumers not in the affected area suffer minimal impact. As a first step towards achieving disaster resilience, the RECODIS project was formed, and its Working Group 1 members conducted a comprehensive literature survey on “strategies for communication networks to protect against large-scale natural disasters,” which is summarized in this article.

Instantaneous recovery of unicast connections in transport networks

The importance of reducing recovery time and latency, e.g., by adding redundancy to the connection is increasing in todays communication networks. Thus, in this paper we investigate dedicated protection approaches which completely avoid control plane signaling and switching matrix reconfiguration when a network failure occurs, i.e., provide quasi instantaneous recovery from failures. As these approaches may require a huge amount of redundancy, we introduce a dynamic routing framework, called General Dedicated Protection (GDP) which provides optimal resilient capacity allocation against multiple link failures, both for routing and network coding. The computational complexity and a theoretical lower bound for GDP will be presented, too. We show the efficiency of the GDP framework through thorough simulations. Finally, we demonstrate that the necessary modules for GDP can be easily adopted in Software Defined Networks (SDNs) with the help of the OpenFlow protocol. In our proof-of-concept implementation we are following the Network Function Virtualization (NFV) approach, which allows the practical deployment of GDP in transport networks.

Survivable routing meets diversity coding

Survivable routing methods have been thoroughly investigated in the past decades in transport networks. However, the proposed approaches suffered either from slow recovery time, poor bandwidth utilization, high computational or operational complexity, and could not really provide an alternative to the widely deployed single edge failure resilient dedicated 1 + 1 protection approach. Diversity coding is a candidate to overcome these difficulties with a relatively simple technique: dividing the connection data into two parts, and adding some redundancy at the source node. However, a missing link to make diversity coding a real alternative to 1+1 in transport networks is finding its minimum cost survivable routing, even in sparse topologies, where previous approaches may fail. In this paper we propose a polynomial-time algorithm with O(|V||E| log |V|) complexity for this routing problem. On the other hand, we show that the same routing problem turns to be NP-hard as soon as we limit the forwarding capabilities of some nodes and the capacities of some links of the network.

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.

Diversity Coding-Based Survivable Routing with QoS and Differential Delay Bounds

Abstract Survivable routing with instantaneous recovery gained much attention in the last decade, as in optical backbone networks even the shortest disruption of a connection may cause tremendous loss of data. Recently, strict delay requirements emerge with the growing volume of multimedia and video streaming applications, which have to be ensured both before and after a failure. Diversity coding provides a nice trade-off between the simplicity of dedicated protection and bandwidth-efficiency of network coding to ensure instantaneous recovery for the connections. Hence, in this paper we thoroughly investigate the optimal structure of diversity coding-based survivable routing, which has a well-defined acyclic structure of subsequent paths and disjoint path-pairs between the communication end-points. We define the delay of these directed acyclic graphs, and investigate the effect of Quality-of-Service and differential delay bounds on the solution cost. Complexity analysis and integer linear programs are provided to solve these delay aware survivable routing problems. We discuss their approximability and provide some heuristic algorithms, too. Thorough experiments are conducted to demonstrate the benefits of diversity coding on randomly generated and real-world optical topologies.

Delay aware survivable routing with network coding in Software Defined Networks

It was demonstrated in transport networks that network (diversity) coding can provide sufficient redundancy to ensure instantaneous single link failure recovery, while near-optimal bandwidth efficiency can be reached. However, in the resulting multi-path routing problem the end-to-end delays were not considered. On the other hand, even in a European-scale network the delay difference of the paths has severe effect on the Quality-of-Service of application scenarios, such as video streaming. Thus, in this paper we thoroughly investigate survivable routing in Software Defined Networks (SDNs) with several additional delay bounds to the bandwidth cost minimization problem. We build on the fact that, if the user data is split into at most two parts, then the minimum cost coding solution has a well-defined acyclic structure of subsequent paths and disjoint path-pairs between the communication end-points. Complexity analysis and integer linear programs are provided to solve these delay aware survivable routing problems in SDNs.

Unambiguous switching link group failure localization in all-optical networks

In this article, we investigate the Advanced Global Neighborhood Failure Localization (AG-NFL) monitoring trail (m-trail) approach, which provides ultra-fast all-optical restoration for any shared protection scheme. In contrast with its previous counterparts, AG-NFL separates the management tasks of protection switching and link maintenance, and focuses on the identification of the proper switching actions in a timely manner rather than unambiguously localizing link failures. We form switching link groups at each node, that is, links whose failures do not have to be distinguished from each other, for example, because their corresponding switching actions can be performed at the same time. Forbidden link-pairs are introduced to identify the minimal set of conflicting switching actions, which minimizes the number of switching link groups. Furthermore, in order to minimize the number of m-trail reconfigurations upon dynamic traffic, we analyze the AG-NFL performance in four different m-trail design scenarios with decreasing dependency on the data plane. We prove that AG-NFL is NP-complete, and we propose an efficient heuristic to solve it. We demonstrate through simulations that unambiguous localization of switching link groups instead of single link failures leads to a significantly improved m-trail performance both in wavelength resources and the number of required transponders, while signaling-free restoration is still provided.

Switching link group Failure Localization via monitoring trails in all-optical networks.

In this paper we investigate a novel monitoring trail (m-trail) approach, called Advanced Global Neighborhood Failure Localization (AG-NFL), which provides ultra-fast all-optical restoration for any shared protection scheme. In contrast with its previous counterparts, AG-NFL aims to identify and perform the proper switching action upon any single link failure rather than unambiguously localizing link failures. We identify switching link groups at each node, i.e., links whose failures do not have to be distinguished from each other, e.g., because the same switching action belongs to them. We prove that AG-NFL is NP-complete, and we propose a yet efficient heuristic to solve it. We demonstrate through simulations that localizing switching link groups instead of single link failures leads to a significantly improved m-trail performance both in wavelength resources and the number of required transponders, while signaling-free restoration is still provided.