With the large increase in the adoption of blockchain technologies, their underlying peer-to-peer networks must also scale with the demand. In this context, previous works highlighted the importance of ensuring efficient and resilient communication for the underlying consensus and replication mechanisms. However, they were mainly focused on mainstream, Proof-of-Work-based Distributed Ledger Technologies like Bitcoin or Ethereum.In this paper, the problem is investigated in the context of consensus-validation based blockchains, like the XRP Ledger. The latter relies on a Federated Byzantine Agreement (FBA) consensus mechanism which is proven to have a good scalability in regards to transaction throughput. However, it is known that significant increases in the size of the XRP Ledger network would be challenging to achieve. The main reason is the flooding mechanism used to disseminate the messages related to the consensus protocol, which creates many duplicates in the network. Squelching is a recent solution proposed for limiting this duplication, however, it was never evaluated quantitatively in real-life scenarios involving the XRPL production network. In this paper, our aim is to assess this mechanism using a real-life controllable testbed and the XRPL production network, to assess its benefit and compare it to alternative solutions relying on Named Data Networking and on a gossip-based approach.

Metarouting allows for the modeling of routing protocols using an algebraic structure called routing algebra. Routing protocols requiring design or validation can easily be modeled using this approach. To date, however, existing research on routing algebras has mainly focused on applying this approach to routing protocols that are generally used in networks which have a single addressing and forwarding protocol. The basic algebraic structures used in such contexts are semirings, Sobrinho’s algebras and algebras of endomorphisms. In this paper, we propose the modification of these existing routing algebras to deal with networks that contain multiple forwarding protocols where tunnels are omnipresent. To achieve this, we define new algebraic structures derived from the three aforementioned ones, in order to model the generalized routing problem with automatic tunneling entitled valid paths algebra. All of our routing algebras are defined as semi-direct products of two structures, the well-known shortest paths algebra and the proposed valid paths algebra. These new algebras are isotonic and non-monotonic with a partial order. We propose a fixed point for those new algebras and we prove the iterative convergence to the optimal solution of the valid shortest paths problem.

Most current routing protocols are based on path computation algorithms in graphs (e.g., Dijkstra, Bellman-Ford, etc.). These algorithms have been studied for a long time and are very well understood, both in a centralized and distributed context, as long as they are applied to a network having a single communication protocol. The problem becomes more complex in the multi-protocol case, where there is a possibility of encapsulation of some network protocols into others, therefore inducing nested tunnels. The classic algorithms cited above no longer work in this case because they cannot manage the protocol encapsulations and the corresponding protocol stacks. In this work, we propose a highly parallelizable algorithm that takes into account protocol encapsulations as well as protocol conversions in order to compute shortest paths in a multi-protocol network. To achieve this computation efficiently, we study the transitive closure between subpaths (i.e., the concatenation of two subpaths to obtain a longer one) in the case where each subpath induces a protocol stack, and thus tunnels. Leveraging on Software-Defined Networks with a controller having a highly parallel architecture enables us to compute the routing tables of all nodes in a very efficient way. Experimentation results on both random and realistic topologies show that our algorithm outperforms the previous solutions proposed in the literature.

Federated Byzantine Agreement protocols applied in the XRP Ledger and Stellar use voting to reach a consensus. Participants of these protocols select whom to trust in the network and effectively communicate with the trustees to reach an agreement on transactions. Most trustees, for example 80% in the XRP Ledger, must agree on the same transactions for them to appear in the blockchain. However, disruptions to the communication between the trustees can prevent the trustees from reaching an agreement. Thus, halting the blockchain. In this paper, we propose a novel robustness metric to measure the Federated Byzantine Agreement protocol tolerance to node failures. We show that the XRP Ledger Consensus Protocol is vulnerable to targeted attacks. An attacker has to disconnect only 9% of the highest-degree nodes to halt the blockchain. We propose a mitigation strategy which maintains critical XRP Ledger network topology properties whilst increasing the robustness up to 45%.

The XRP Ledger relies on a trusted set of validator nodes to advance the ledger history. Nodes use flood-based broad-casting to disseminate messages. Flooding offers strong message delivery guarantees at the cost of high network utilisation caused by duplicate messages. In this paper, we present pemcast, an application layer algorithm for efficient one-to-many message routing. The algorithm leverages limited topology awareness and application layer multi-casting to deliver messages in the network. The evaluation shows that compared to flooding and gossiping algorithms, pemcast can maintain similar reliability whilst generating significantly less redundant traffic.

Metarouting models routing protocols in the form of an algebraic structure called routing algebra. It aims to help designing or validating routing protocols. Most research work on routing algebras have been applied to routing protocols used in networks having a single addressing and forwarding protocol. In this context, some of the basic algebraic structures used are semirings. In this paper, we define a new algebraic structure for dealing with networks containing multiple forwarding protocols, which may induce many (and possibly nested) tunnels. We widely generalize the semiring structure for modeling the routing problem with automatic tunneling. We define a new model of routing algebra with tunneling. It is defined as a semi-direct product of two structures, the well-know shortest paths algebra and a new proposed valid paths algebra. We show that it has a fixed point and we prove the iterative convergence to the optimal solution of the valid shortest paths problem.

Big Data technologies and tools have being used for the past decade to solve several scientific and industry problems, with Hadoop/YARN becoming the “de facto” standard for these applications, although other technologies run on top of it. As any other distributed application, those big data technologies rely heavily on the network infrastructure to read and move data from hundreds or thousands of cluster nodes. Although these technologies are based on reliable and efficient distributed algorithms, there are scenarios and conditions that can generate bottlenecks and inefficiencies, i.e., when a high number of concurrent users creates data access contention. In this paper, we propose a novel network topology called Multi-Layer-Mesh and a path switching algorithm based on SDN, that can increase the performance of a big data cluster while reducing the amount of utilized resources (network equipment), in turn reducing the energy and cooling consumption. A thorough simulation-based evaluation of our algorithms shows an average improvement in performance of 31.77% and an average decrease in resource utilization of 36.03% compared to a traditional Spine-Leaf topology, in the selected test scenarios.

Real-time interactive communications, such as videoconferencing, have strong QoS requirements. Adapting such communications to network dynamics needs network management capabilities that traditional networks cannot provide. Recently, SDN has shown to be a potential solution for solving these network adaptation challenges. In a companion paper written by our team, we have proposed a videoconferencing system using SVC multicast trees built over an SDN network. This system minimizes the overall bandwidth consumption and provides the highest possible QoS to the users although it is not adaptable to network dynamics happening over the lifetime of the communication. In this paper, we complement our system, by providing efficient algorithms able to modify the connections between the participants during a videoconference in order to timely react to network changes. The simulation results confirm the efficiency of our solution in terms of time processing and bandwidth savings.

Videoconferencing applications have strong latency requirements and consume large portions of a network's bandwidth. Current videoconferencing solutions are not efficiently implemented as they often rely on a central server and do not leverage network layering services. In this paper, we investigate the impact of using Scalable Video Coding and Software Defined Networking techniques on videoconferencing. Specifically we propose an algorithm capable of reducing the bandwidth consumed by videoconferencing using Software Defined Networking to compute and deploy multicast trees, as well as taking advantage of the Scalable Video Coding layering feature that allows to sacrifice video quality for usability purposes. We show that by smartly dropping video layers at specific locations in the network, the overall bandwidth usage by videoconferencing decreases, and in a separate capacity study we show that our solution allows networks to support more videoconferencing calls as compared to existing solutions.

Summary The identification of performance issues and the diagnosis of their root causes are time‐consuming and complex tasks, especially in clustered environments. To simplify these tasks, researchers have been developing tools with built‐in expertise for practitioners. However, various limitations exist in these tools that prevent their efficient usage in the performance testing of clusters (e.g. the need of manually analysing huge volumes of distributed results). In a previous work, we introduced a policy‐based adaptive framework (PHOEBE) that automates the usage of diagnosis tools in the performance testing of clustered systems, in order to improve a tester's productivity, by decreasing the effort and expertise needed to effectively use such tools. This paper extends that work by broadening the set of policies available in PHOEBE, as well as by performing a comprehensive assessment of PHOEBE in terms of its benefits, costs and generality (with respect to the used diagnosis tool). The performed evaluation involved a set of experiments in assessing the different trade‐offs commonly experienced by a tester when using a performance diagnosis tool, as well as the time savings that PHOEBE can bring to the performance testing and analysis processes. Our results have shown that PHOEBE can drastically reduce the effort required by a tester to do performance testing and analysis in a cluster. PHOEBE also exhibited consistent behaviour (i.e. similar time‐savings and resource utilisations), when applied to a set of commonly used diagnosis tools, demonstrating its generality. Finally, PHOEBE proved to be capable of simplifying the configuration of a diagnosis tool. This was achieved by addressing the identified trade‐offs without the need for manual intervention from the tester. Copyright © 2017 John Wiley & Sons, Ltd.

Achieving high-quality voice conference calls over the Internet is a difficult task. Heterogeneous mobile devices and network dynamics must be properly managed by multiparty VoIP systems to ensure a good quality of experience. In this paper, we propose a multiparty VoIP system based on SDN technology that uses both multicast distribution and dynamic stream adaptation to optimize the conference call quality for each participant. We define a tree construction algorithm that includes two modes: a minimum spanning tree mode and a shortest path tree mode. We have simulated conference calls with various parameters and results show that a trade-off can be achieved between path latency and bandwidth consumption when using multicasted streams with adaptive bitrates. Compared to a typical multiparty VoIP system, up to two-third bandwidth consumption reduction is possible with only a small increase of the average path latency. Our solution could be leveraged by other types of real-time applications such as online gaming.

Summary Nowadays, clustered environments are commonly used in high‐performance computing and enterprise‐level applications to achieve faster response time and higher throughput than single machine environments. Nevertheless, how to effectively manage the workloads in these clusters has become a new challenge. As a load balancer is typically used to distribute the workload among the cluster's nodes, multiple research efforts have concentrated on enhancing the capabilities of load balancers. Our previous work presented a novel adaptive load balancing strategy (TRINI) that improves the performance of a clustered Java system by avoiding the performance impacts of major garbage collection, which is an important cause of performance degradation in Java. The aim of this paper is to strengthen the validation of TRINI by extending its experimental evaluation in terms of generality, scalability and reliability. Our results have shown that TRINI can achieve significant performance improvements, as well as a consistent behaviour, when it is applied to a set of commonly used load balancing algorithms, demonstrating its generality. TRINI also proved to be scalable across different cluster sizes, as its performance improvements did not noticeably degrade when increasing the cluster size. Finally, TRINI exhibited reliable behaviour over extended time periods, introducing only a small overhead to the cluster in such conditions. These results offer practitioners a valuable reference regarding the benefits that a load balancing strategy, based on garbage collection, can bring to a clustered Java system. Copyright © 2016 John Wiley & Sons, Ltd.

In this work, we propose an efficient health-care monitoring system for the daily home activity of persons. We intend to combine a good optimization of the resources (e.g. network and energy) and an automatic evaluation of the person's dependency while ensuring a high accuracy for detecting unusual behaviors. The proposed system considers the person's context and predicts the health condition based on the usual behavior and energy consumption for each daily activity. The proposed system requires a minimum set of sensed data with short training periods for predicting the person's behavior changes.

This work focuses on the evaluation of the need and help required by elderly and dependent persons. We study the most widely used evaluation models in the health domain. We propose a new algorithm to assess and compare the performance of these models and the possibility to use them in future eHealth systems and platforms. The objective is to shed some light on the weakness of existing models and to gain a better knowledge about the context of persons in order to provide them with eHealth services that match their context and meet their needs.

In this paper, we present an experimental evaluation of the recently standardized Opus codec used in a VoIP context. Opus operates in both narrow and wideband modes, similar to Adaptive Multi-Rate (AMR). Through the use of the Wideband Perceptual Evaluation of Speech Quality (WB-PESQ) metric, we have conducted an extensive set of experiments using multiple audio samples encoded at different bit-rates, to investigate the impact of packet loss on resulting speech quality. Using these results, fitting functions for each bit-rate were computed to provide a straightforward manner of evaluating speech quality when given a specified packet loss rate. Using ns-2, a simulation analysis was conducted to evaluate the effect of background traffic on transmitted Opus streams. We observed that, when using different levels of background traffic, the observed packet loss rates varied heavily depending on the stream bit-rate. By correlating this information with the fitting functions derived previously, we were able to define switching thresholds. These are points where the speech quality of a lower bit-rate stream is greater than that of a higher bit-rate stream for the same levels of link bandwidth saturation.

Modern computer applications, especially at enterprise-level, are commonly deployed with a big number of clustered instances to achieve a higher system performance, in which case single machine based solutions are less cost-effective. However, how to effectively manage these clustered applications has become a new challenge. A common approach is to deploy a front-end load balancer to optimise the workload distribution between each clustered application. Since then, many research efforts have been carried out to study effective load balancing algorithms which can control the workload based on various resource usages such as CPU and memory. The aim of this paper is to propose a new load balancing approach to improve the overall distributed system performance by avoiding potential performance impacts caused by Major Java Garbage Collection. The experimental results have shown that the proposed load balancing algorithm can achieve a significant higher throughput and lower response time compared to the round-robin approach. In addition, the proposed solution only has a small overhead introduced to the distributed system, where unused resources are available to enable other load balancing algorithms together to achieve a better system performance.

Local knowledge routing schemes based on virtual coordinates taken from the hyperbolic plane have attracted considerable interest in recent years. In this paper, we propose a new approach for seizing the power of the hyperbolic geometry. We aim at building a scalable and reliable system for creating and managing overlay networks over the Internet. The system is implemented as a peer-to-peer infrastructure based on the transport layer connections between the peers. Through analysis, we show the limitations of the Poincaré disk model for providing virtual coordinates. Through simulations, we assess the practicability of our proposal. Results show that peer-to-peer overlays based on hyperbolic geometry have acceptable performances while introducing scalability and flexibility in dynamic peer-to-peer overlay networks.

Television transmitted over IP (IPTV) presents numerous opportunities for users as well as service providers, and has attracted significant interest from business and research communities in recent years. Among the emerging IPTV delivery architectures, the peer-to-peer based delivery mechanism is considered attractive due to the relative ease of service deployment. However, the question of how well P2PTV applications would support a growing number of users has not been fully investigated so far. In this paper, we try to address this question by studying scalability and efficiency factors in a typical P2P based live streaming network. Through the use of the data provided by a production P2PTV system, we carry out simulations whose results show that there are still hurdles to overcome before P2P based live streaming could become widely used.

A P2PTV system allows users to watch live video streams redistributed by other users via a peer-to-peer (P2P) network. In an ideal world, each peer in a P2P network would be able to redistribute more bytes than it receives. A P2PTV system built from such peers can support a virtually unlimited number of peers; with only a single copy of content stream injected into the network, it can redistribute the content to all peers. Two factors in the development of the Internet prevented the realization of this scenario: the deployment of asymmetric access networks and the adoption of NAT boxes. For real-time live streaming, such peer asymmetry and incompatibility is a limiting factor on the P2P network scalability. We first develop a basic formal analysis of the effect of bandwidth asymmetry on P2P network scalability. Then we present several characteristics of peer asymmetry as measured on the Zattoo P2PTV network. Our simulation results, driven by the measured peer characteristics, confirm that we cannot rely on P2P network alone to distribute live streaming content on today's Internet.

In the context of mobile ad hoc networks (MANETs) routing, we propose a clustering algorithm called Connectivity, Energy and Mobility driven Clustering Algorithm (CEMCA). The aim of CEMCA consists in appropriately choosing the cluster head to reduce routing overhead. In order to reduce traffic and energy consumption, the control messages are sent only when needed, according to the speed of the node. Each node has a quality that indicates its suitability as a cluster head. This quality takes into account the node connectivity, battery energy and mobility. These parameters are very important for the stability of the cluster. Simulation experiments are carried out to validate our algorithm in terms of stability of the clusters and their members and the quality of the connectivity. The results are compared to a previous approach called Weight Clustering Algorithm (WCA) and they show that CEMCA is performing better.

A growing number of applications create overlays on top of the Internet. Several unsolved issues at the network layer can explain this trend to implement network services such as multicast, mobility and security at the application layer. However overlays require some form of internal addressing, routing and naming. Therefore their topologies are usually kept simple but this limits their flexibility and scalability. Our aim is to design an efficient and robust addressing, routing and naming framework for complex overlays. Our only assumption is that they are constrained by the Internet topology. Applications using our framework will be relieved from managing their own overlay topologies. This paper presents our framework in detail as well as some performance results concerning its routing efficiency, its reliability to network dynamics and its naming scalability.

IPv6 is intended to be the next network layer protocol of the Internet and it is designed to overcome the limitations of the current IPv4 protocol. However, the lack of resources in routers is still the issue in the deployment of state storing protocols in the IPv6 network. In particular, multicast protocols have taken the resources up to their limits for maintaining multicast tree information. The aim of this paper is to study the possible benefit of distributing the multicast tree states on the IPv6 topology in order to optimize the IPv6 network resource usage. To be able to carry out this study, we first had to map the topology of the current IPv6 network. We have used our network cartographer software in order to build an accurate map of the IPv6 network. We then studied the distribution of multicast states by using a simple repartition function. We have found that the use of this function can heavily decrease the number of states stored by the most loaded nodes at the cost of a small overall increase of the total number of states on the topology.

The lack of resources in routers becomes a crucial issue with the deployment of state storing protocols such as QoS or multicast ones. In particular, single or any source multicast protocols most probably take over resources up to their limits for maintaining multicast tree information. The aim of this paper is to study the possibility and benefit of using multiple shortest paths in order for a new member to reach a multicast tree. Such a mechanism would not reduce the overall amount of state information in the network but it would distribute this amount more evenly among all routers. The idea is to use an alternate shortest path provided by the underlying unicast routing protocol to avoid a saturated router, that is a router that can not or does not want to store any more multicast state information. As the simulation results are very sensitive to the topology used, we have used as input topology a real public Internet map. We have then simulated our multipath-aware join mechanism upon samples of this map. We have found that depending on the tree size, the use of our mechanism can increase successful join attempts by up to 55% when the network is half saturated

Recent advances in scale-free networks have claimed that their topologies are very weak against attacks. The inhomogeneous connectivity distribution of large-scale current communication networks, such as the Internet, could be exploited by evil hackers in order to damage these systems. However, there have not been many studies on the approaches and consequences of such targeted attacks. In this paper, we propose an in-depth study of the Internet topology robustness to attacks at the network layer. Several attacking techniques are presented, as well as their effects on the connectivity of the Internet. We show that although the removal of a small fraction of nodes (less than 10%) can damage the Internet connectivity, such a node removal attack would still require a large amount of work to be carried out. To achieve this, we study in detail the interactions between the intradomain and interdomain levels of the Internet through the use of an overlay.

Many protocols and applications need a discovery mechanism to enable a given client node to locate one or several specific nodes involved in the same communication. However, there is no protocol ready to fulfill this service at the network layer. Every protocol usually implements its own solution. In particular, multicast protocols often use a search technique called expanding ring search. This method searches for those specific nodes in all directions and thus uses much bandwidth. However, a typical search can usually restrict its scan in a specific direction. To answer this problem, we propose a network layer search service in replacement of the expanding ring search whenever it is appropriate. This service is based on an oriented multicasting protocol in order to ensure an efficiency higher than the expanding ring search. The oriented multicasting principle is to channel the multicasting of search packets towards a special node, involved in the communication, in order to scan only a limited area. We describe both the network layer search service and the oriented multicasting and we provide comparative simulation results between our service and the expanding ring search.

Creating a network topology is the first step in building a scenario for a network protocol simulation. The simulation results usually depend on the topology layout, especially for routing and multicasting protocols. Therefore the topology used should be generated with the highest possible accuracy. In particular, protocols designed for the Internet should be simulated over Internet-like topologies. Many topology generators currently exist but the discovery of power laws in the Internet has brought new constraints upon the generated topologies. We introduce a flexible novel way to create Internet-like topologies. It is based on an algorithm that performs a sampling on a measured Internet map. The created topologies accurately comply with the newly found power laws as well as other more common topology properties such as the average path length.

An increasing number of Internet applications and services will require the use of multicast in the near future. However, only a few techniques are currently used in network-layer multicast routing protocols, such as flooding, pruning or reverse path construction methods. We propose an algorithm to define a new way of multicasting. The base principle is to perform a limited multicast channeled around the unicast path joining the sender to a specific destination, hence the name "oriented". This algorithm is close to reverse path multicast algorithms but the flooding is much more controlled. A protocol based on our algorithm could have many applications such as performing network node searches in a specific area. The algorithm is tailored as to be scalable to enable its use in an inter-domain environment.