Jacek Rak

LLA: A New Anypath Routing Scheme Providing Long Path Lifetime in VANETs

Vehicular ad-hoc networks (VANETs) are a promising solution to improve the road traffic safety, reduce the environmental pollution, or simply provide the on-board infotainment services. However, these actions are often not possible due to high mobility of vehicles causing frequent failures of VANET links. In this paper, we focus on anypath routing to improve the reliability of multihop VANET communications. In particular, the paper is the first one to address the link stability \hbox{issues and to propose} a method called Long Lifetime Anypaths (LLA) providing stable communication paths. Advantages of our \hbox{approach}, presented in comparison to the reference Shortest Anypath First (SAF) scheme, are confirmed throughout simulations.

κ-Penalty: a novel approach to find κ-Disjoint paths with differentiated path costs

In this paper we investigate the issue of preplanned end-to-end protection against multiple failures. In recent communications networks, such protection is provided by finding a set of k-disjoint paths for each demand. In particular, we analyze here the problem of calculating the set of k-disjoint paths of a demand in multi-cost networks, where each network arc an may be assigned k different costs ¿_h ⁽¹⁾, ¿_h ⁽²⁾, ...., ¿_h ^(k). A novel algorithm, called k-Penalty, is next introduced, in which the relation between values ¿_h ⁽ⁱ⁾ for each arc ¿_h may be arbitrary.

Reliable anycast and unicast routing: protection against attacks

Recent communication networks are commonly protected against random failures, i.e. being the results of forces of nature, human errors, or hardware faults. In simulation experiments, network topologies are often assumed to be more or less regular. Known mechanisms typically refer to the case of unicast traffic protection. However, owing to the observed convergence of technologies/services, the importance of other transmission techniques (e.g. anycast, or multicast) has been increasing. Moreover, it turns out that neither failures of network elements are only the results of random faults, nor topologies of real networks are purely regular.In this paper we introduce a novel technique, called RA (the abbreviation for “resistant-to-attacks”) of protecting the anycast and unicast flows against attacks on irregular networks. In particular, we propose a new metric of link costs to be used in working path computations with the objective to avoid traversing the nodes of high degree (i.e. vulnerable to attacks). The extent of losses after attacks is further decreased by locating the anycast replica servers at low-degree nodes.The ILP model for joint optimization of anycast and unicast flows has been formulated and followed by the time-efficient heuristic algorithm. Path protection scheme for the case of protection against a single node failure is assumed. For each anycast demand, working and backup replica servers are located at different network nodes (disjoint replica model).Simulation results confirm that our approach provides a remarkable decrease (up to 7.47 times) in terms of the total number of connections broken due to attacks, compared to the results for the common case of locating the replica servers at high-degree nodes, and utilizing the metric of distance to find both working and backup paths.

Providing Differentiated Levels of Service Availability in VANET Communications

Inter-vehicle communications seems to be a promising remedy not only for a number of road-safety issues, but also to improve the efficiency of road traffic, as well as to support the on-board infotainment applications. However, it often encounters disruptions due to high mobility of vehicles causing frequent failures of communication links. In this paper, we utilize the idea of multipath vehicle-to-vehicle routing to provide protection against link failures. Three original contributions, presented for the general case of differentiated velocities and directions of vehicles include: 1) probability analysis of end-to-end multipath transmission availability; 2) the concept of differentiated levels of service availability and its application to an example AODV routing scheme; 3) a metric of link costs to increase the lifetime of communication paths.

Region protection/restoration scheme in survivable networks

In this paper we propose the novel concept of a region protection/ restoration, where one backup path protects a certain region of an active path. We show that using the region protection/restoration we can keep both restoration times and network resource utilization ratio at the reasonable level. Since the optimization problem of finding working and backup paths is NP-complete, we developed the heuristic algorithm. We show that in the worst case our algorithm gave network resource utilization ratio only about 3.9 percent higher compared to the optimal one returned by the CPLEX program. Results of the U.S. Long-Distance Network modeling show that region protection gives a good compromise between path and link protection.

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.

Fast Service Recovery Under Shared Protection in WDM Networks

In this paper, we investigate the problem of survivable routing of static demands in connection-oriented WDM networks with shared protection. We first discuss conditions and characteristics of a typical backup path sharing approach with respect to the average length of backup paths, and the values of connection restoration time. Next we propose a new method of sharing the backup paths, called SPGC, which is the first one that does not increase the length of backup paths (thus providing fast restoration of broken connections). The respective ILP model has been introduced. Owing to the complexity of the SPGC problem, an efficient heuristic algorithm designed for the general case of limited wavelength conversion capability has been also proposed. Extensive numerical experiments have shown that the proposed backup path sharing approach provides values of service recovery time which are up to 50% shorter on average, compared to the typical sharing technique. These results were achieved together with a significant reduction of the total link capacity utilization ratio of up to 40%.

Shared Backup Path Protection for Anycast and Unicast Flows Using the Node-Link Notation

In this paper we address the problem of shared backup path protection (SBPP) against random failures of single links in connection-oriented communication networks. Most of recent works has been concentrated on protecting the unicast traffic. Our paper is also focused on shared protection of anycast (i.e. one-to-one-out-of-many) flows. Anycasting is frequently met in practice (e.g. in Content Delivery Networks, peer-to-peer systems, or DNS service). A new ILP model for joint optimization of dedicated working and shared backup paths of anycast and unicast demands is introduced and is followed by extensive simulation research. The model is the first one that provides the optimal solutions to the problem of anycast traffic shared protection by using the Node-Link notation. The results show that our approach reduces the network cost and capacity utilization ratio by 36% and 42% accordingly, compared to the case when capacity sharing is not used.

Simultaneous optimization of unicast and anycast flows and replica location in survivable optical networks

Most of previous works related to survivable networks have been focused on unicast communications. In this paper, we address the problem of network survivability in the context of anycast communications, which has not attracted much attention recently. Anycast transmission is defined as one-to-one-of-many. To assure the network survivability, we use the single backup path approach, i.e., each demand has two node-disjoint paths to provide protection against a single link failure. We formulate new ILP models to find the optimal paths for anycast and unicast connections, as well as to find the optimal location of replica servers. To test the proposed approach, we run extensive numerical experiments using CPLEX solver on four example network topologies with different scenarios of replica server count and the proportion between unicast and anycast traffic. Results prove the efficiency of our solution in terms of various parameters including cost, path length, resource utilization, and time of computation.

RECODIS: Resilient Communication Services Protecting End-user Applications from Disaster-based Failures

Disaster-based failures can seriously disrupt any communication network, making its services unavailable. Such disruptions may be caused by natural disasters, technology-related failures, or malicious attacks, and they are observably increasing in number, intensity and scale. When network services that are a part of critical infrastructure become unavailable, commercial and/or societal problems are inevitable. The issue of limiting the impact of disaster-based failures needs to be urgently addressed due to the lack of suitable mechanisms deployed in the current networks. The COST CA15127 (RECODIS) Action will fill this gap by developing appropriate solutions to provide cost-efficient resilient communications in the presence of disaster-based disruptions considering both existing and emerging communication network architectures. It will be driven by researchers from academia and industry in strong cooperation with governmental bodies. In this paper, we highlight the objectives of RECODIS, its structure, as well as planned outcomes.