AQM Stability in Multiple Bottleneck Networks

In this paper, we highlight that multiple bottlenecks can affect the performance of active queue management controllers, which are usually configured on a single bottleneck basis, as if each controller were the only element regulating the TCP traffic along its path. To see this, we consider a network scenario where RED is configured at each router, according to previously developed control theoretic techniques. These configuration rules assure stability in a single bottleneck scenario. Yet, we show that instability may arise when two link become congested. We justify this result through a multiple bottleneck model and give guidelines for new cooperative AQM controllers.

Achieving Fair Bandwidth Distribution in WiFi Networks: A Game Theoretical Approach

International audience; Achieving fair bandwidth distribution among uplink and downlink ows in IEEE 802.11 infrastructure networks is a complex issue, due to the well-known features of the Distributed Coordination Function (DCF) which regulates the access to the shared medium. Indeed, the dynamic adaptation of the contention windows causes phenomena of short-term unfairness, while the use of homogeneous contention parameters among the contending nodes makes the aggregated downlink bandwidth equal to the uplink bandwidth of a single node. We propose a dynamic tuning of the contention parameters used by the nodes, based on simple network monitoring functionalities and rational strategies. Spe…

Embedding Evolution in Epidemic-Style Forwarding

International audience; In this work, we introduce a framework to let forwarding schemes evolve in order to adapt to changing and a priori unknown environments. The framework is inspired by genetic algorithms: at each node a genotype describes the forwarding scheme used, a selection process fosters the diffusion of the fittest genotypes in the system and new genotypes are created by combining existing ones or applying random changes. A case study implementation is presented and its performance evaluated via numerical simulations.

Availability in BitTorrent Systems

In this paper, we investigate the problem of highly available, massive-scale file distribution in the Internet. To this end, we conduct a large-scale measurement study of BitTorrent, a popular class of systems that use swarms of actively downloading peers to assist each other in file distribution. The first generation of BitTorrent systems used a central tracker to enable coordination among peers, resulting in low availability due to the tracker's single point of failure. Our study analyzes the prevalence and impact of two recent trends to improve BitTorrent availability: (i) use of multiple trackers, and (ii) use of Distributed Hash Tables (DHTs), both of which also help to balance load be…

Evolutionary Epidemic Routing

About the Stability of Active Queue Management Mechanism

In this paper, we discuss the influence of multiple bottlenecks on the stability of Active Queue Management (AQM) controllers, usually configured on a single bottleneck basis. To see this, we consider a network scenario where RED is configured at each router according to previously developed control theoretic techniques. These configuration rules assure stability in a single bottleneck scenario. Yet, we show that instability may arise when two links become congested. We justify this result through a multiple bottleneck model.

An analytical model of a new packet marking algorithm for TCP flows: Preliminary insights

In differentiated services networks, packet marking schemes can be devised to differentiate packets belonging to a same TCP flow, with the goal of improving the experienced performance. This paper presents an analytical model for an adaptive packet marking scheme proposed in our previous work. The model combines three specific sub-models aimed at describing i) the TCP sources aggregate ii) the marker, and iii) the network status. Some preliminary simulative results seem to validate the model.

Modeling Energy Demand Aggregators for Residential Consumers

International audience; Energy demand aggregators are new actors in the energy scenario: they gather a group of energy consumers and implement a demand- response paradigm. When the energy provider needs to reduce the current energy demand on the grid, it can pay the energy demand aggregator to reduce the load by turning off some of its consumers loads or postponing their activation. Currently this operation involves only greedy energy consumers like industrial plants. In this paper we want to study the potential of aggregating a large number of small energy consumers like home users as it may happen in smart grids. In particular we want to address the feasibility of such approach by conside…

AQM Generalized Nyquist stability in multiple bottlenecks networks

The influence of multiple bottlenecks on the stability of Active Queue Management (AQM) controllers, usually configured on a single bottleneck basis is discussed. We consider a network scenario where RED is configured at each router according to previously developed control theoretic techniques. These configuration rules assure stability in a single bottleneck scenario. We show that instability may arise when two links become congested. We justify this result through a multiple bottleneck model using the Generalized Nyquist stability criterion.

The Effect of Heterogeneous Link Capacities in BitTorrent-like File Sharing System

AQM generalized nyquist stability in multiple bottleneck networks

Abstract The influence of multiple bottlenecks on the stability of Active Queue Management (AQM) controllers, usually configured on a single bottleneck basis is discussed. We consider a network scenario where RED is configured at each router according to previously developed control theoretic techniques. These configuration rules assure stability in a single bottleneck scenario. We show that instability may arise when two links become congested. We justify this result through a multiple bottleneck model using the Generalized Nyquist stability criterion.

Is Admission-Controlled Traffic Self-Similar?

It is widely recognized that the maximum number of heavy-tailed flows that can be admitted to a network link, while meeting QoS targets, can be much lower than in the case of markovian flows. In fact, the superposition of heavy-tailed flows shows long range dependence (self-similarity), which has a detrimental impact on network performance. In this paper, we show that long range dependence is significantly reduced when traffic is controlled by a Measurement-Based Admission Control (MBAC) algorithm. Our results appear to suggest that MBAC is a value added tool to improve performance in the presence of self-similar traffic, rather than a mere approximation for traditional (parameter-based) ad…

The role of the Access Point in Wi-Fi networks with selfish nodes

In Wi-Fi networks, mobile nodes compete for accessing the shared channel by means of a random access protocol called Distributed Coordination Function (DCF), which is long term fair. But recent drivers allow users to configure protocol parameters differently from their standard values in order to break the protocol fairness and obtain a larger share of the available bandwidth at the expense of other users. This motivates a game theoretical analysis of DCF. Previous studies have already modeled access to a shared wireless channel in terms of non-cooperative games among the nodes, but they have mainly considered ad hoc mode operation. In this paper we consider the role of the Access Point (AP…

Performance evaluation of Peer-to-Peer file sharing systems: analytical models and simulation tools

Performance Evaluation of a new Adaptive Packet Marking Scheme for TCP over DiffServ Networks

In differentiated services (DiffServ) networks, packets may receive a different treatment according to their differentiated services code point (DSCP) label. As a consequence, packet marking schemes can be devised to differentiate packets belonging to the same TCP flow, with the goal of improving the experienced performance. The paper presents an extensive performance evaluation of a new adaptive packet marking scheme, applied to a traffic scenario composed of TCP flows with different lengths. The proposed marking scheme is most efficient when applied to a scenario composed of all long-lived flows. In a realistic mixed traffic scenario, composed of both long-lived and short-lived TCP flows,…

Evaluating activator-inhibitor mechanisms for sensors coordination

The possibility to employ reaction-diffusion models to build spatial patterns in sensor networks has been advocated in other works. Nevertheless it has not been investigated how the biologically-inspired solutions perform in comparison to more traditional ones taking into account specificities of sensor networks like severe energy constraints. In this paper we present some preliminary results on the comparison between a biologically inspired coordination mechanism based on activator-inhibitor interaction and a simple mechanism, where nodes do not communicate but activate their sensing circuitry according to some probability.

Smart plugs: A low cost solution for programmable control of domestic loads

International audience; Balancing energy demand and production is becoming a more and more challenging task for energy utilities. This is due to a number of different reasons among which the larger penetration of renewable energies which are more difficult to predict and the meagre availability of financial resources to upgrade the existing power grid. While the traditional solution is to dynamically adapt energy production to follow the time-varying demand, a new trend is to drive the demand itself by means of Direct Load Control (DLC). In this paper we consider a scenario where DLC functionalities are deployed at a large set of small deferrable energy loads, like appliances of residential…

About the stability of active queue management mechanisms

In this paper, we discuss the influence of multiple bottlenecks on the stability of active queue management (AQM) controllers, usually configured on a single bottleneck basis. To see this, we consider a network scenario where RED is configured at each router according to previously developed control theoretic techniques. These configuration rules assure stability in a single bottleneck scenario. Yet, we show that instability may arise when two links become congested. We justify this result through a multiple bottleneck model.

A game theoretic approach to MAC design for infrastructure networks

Wireless network operation intrinsically assumes different forms of cooperation among the network nodes, such as sharing a common wireless medium without interfering, relaying frames belonging to other nodes, controlling the transmission power for optimizing spectrum reuse, coding cooperatively multiple frames for improving information redundancy, and so on. For this reason, Game Theory has been extensively employed to model wireless networks. In particular, we propose a game-theoretic approach for defining a generalized medium access protocol for slotted contention-based channels. Contention-based channels are largely adopted in data networks, e.g. in WiFi and WiMax networks and in some em…

Performance modeling of epidemic routing

In this paper, we develop a rigorous, unified framework based on ordinary differential equations (ODEs) to study epidemic routing and its variations. These ODEs can be derived as limits of Markovian models under a natural scaling as the number of nodes increases. While an analytical study of Markovian models is quite complex and numerical solution impractical for large networks, the corresponding ODE models yield closed-form expressions for several performance metrics of interest, and a numerical solution complexity that does not increase with the number of nodes. Using this ODE approach, we investigate how resources such as buffer space and the number of copies made for a packet can be tra…

MAC Design for WiFi Infrastructure Networks: A Game-Theoretic Approach

In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios because of non-standard configurations of the nodes. Due to the proliferation of open source drivers and programmable cards, enabling an easy customization of the channel access policies, we propose a game-theoretic analysis of random access schemes. Assuming that each node is rational and implements a best response strategy, we show that…

Active queue management stability in multiple bottleneck networks

In this paper, we show that the active queue management (AQM) controllers, usually configured on a single bottleneck basis, may not prevent instability in the presence of multiple bottlenecks. We justify this result through a multiple bottleneck model.

Performance analysis of selfish access strategies on WiFi infrastructure networks

In this paper we propose a game-theoretic approach for characterizing WiFi network performance in presence of intelligent nodes employing cognitive functionalities. We assume that a cognitive WiFi node is aware of its application requirements and is able to dynamically estimate the network status, in order to dynamically change its access strategy by tuning the contention window settings. We prove that, for infrastructure networks with bidirectional traffic and homogeneous application requirements, selfish access strategies are able to reach equilibrium conditions, which are also Pareto optimal. Indeed, we show that the station strategies converge toward values which maximize a per-node uti…

A new Three Color Marker for TCP flows

In Differentiated Services networks, packets may receive a different treatment according to their Differentiated Services Code Point (DSCP) label. As a consequence, packet marking schemes can be devised to differentiate packets belonging to a same TCP flow, with the goal of improving the experienced performance. This paper presents an extensive performance evaluation of a new adaptive packet marking scheme, which relies on three different service classes, provided by the DiffServ network. The scheme provides protection of vulnerable packets in the TCP flows and adaptivity through "probes" packets. The performance have been evaluted in a traffic scenario composed of TCP flows with different …

On the Benefits of Random Linear Coding for Unicast Applications in Disruption Tolerant Networks

In this paper, we investigate the benefits of using a form of network coding known as Random Linear Coding (RLC) for unicast communications in a mobile Disruption Tolerant Network (DTN) under epidemic routing. Under RLC, DTN nodes store and then forward random linear combinations of packets as they encounter other DTN nodes. We first consider the case where there is a single block of packets propagating in the network and then consider the case where blocks of K packets arrive according to a Poisson arrival process. Our performance metric of interest is the delay until the last packet in a block is delivered. We show that for the single block case, when bandwidth is constrained, applying RL…

Large Scale Control of Deferrable Domestic Loads in Smart Grids

International audience; In this paper, we investigate a realistic and low-cost deployment of large scale direct control of inelastic home appliances whose energy demand cannot be shaped, but simply deferred. The idea is to exploit 1) some simple actuators to be placed on the electric plugs for connecting or disconnecting appliances with heterogeneous control interfaces, including non-smart appliances, and 2) the Internet connections of customers for transporting the activation requests from the actuators to a centralized controller. Our solution requires no interaction with home users: in particular, it does not require them to express their energy demand in advance. A queuing theory model …

Resource sharing optimality in WiFi infrastructure networks

In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios. Assuming that a contending node can dynamically change its strategy, by tuning its contention parameters to non-standard values on the basis of channel observations, we prove that, for infrastructure networks with bidirectional traffic and homogeneous application requirements, selfish access strategies are able to reach equilibrium condi…

Unidirectional probabilistic direct control for deferrable loads

International audience; The idea of harnessing the inherent flexibility in demand of many types of electric loads has been largely discussed in the last years for coping with the need to maintain the energy demand-supply balance. In particular, the fine tuning of the operation conditions of different thermostatic loads (such as air-conditioning, refrigerators, etc.) has appeared as the most natural solution for load control with minimal user discomfort. In this paper we focus on an alternative approach: deploying simple open-loop control strategies for deferrable loads with minimal communication overhead. The idea is to send a multicast control message to a group of users, on the basis of t…

Unidirectional Direct Load Control through Smart Plugs

International audience; Balancing energy demand and production is be-coming a more and more challenging task for energy utilities also because of the larger penetration of renewable energies which are more difficult to predict and control. While the traditional solution is to dynamically adapt energy production to follow time-varying demand, a new trend is to drive demand itself. Most of the ongoing actions in this direction involve greedy energy consumers, like industrial plants, supermarkets or large buildings. Pervasive communication technologies may allow in the near future to push further the granularity of such approach, by having the energy utility interacting with residen-tial appli…

Scalable and Privacy-Preserving Admission Control for Smart Grids

International audience; Energy demand and production need to be constantly matched in the power grid. The traditional paradigm to continuously adapt the production to the demand is challenged by the increasing penetration of more variable and less predictable energy sources, like solar photovoltaics and wind power. An alternative approach is the so called direct control of some inherently flexible electric loads to shape the demand. Direct control of deferrable loads presents analogies with flow admission control in telecommunication networks: a request for network resources (bandwidth or energy) can be delayed on the basis of the current network status in order to guarantee some performanc…

On Unstructured File Sharing Networks

We study the interaction among users of unstructured file sharing applications, who compete for available network resources (link bandwidth or capacity) by opening multiple connections on multiple paths so as to accelerate data transfer. We model this interaction with an unstructured file sharing game. Users are players and their strategies are the numbers of sessions on available paths. We consider a general bandwidth sharing framework proposed by Kelly [1] and Mo and Walrand [2], with TCP as a special case. Furthermore, we incorporate the Tit-for-Tat strategy (adopted by BitTorrent [3] networks) into the unstructured file sharing game to model the competition in which a connection can be …

An analytical model of a new packet marking algorithm for TCP flows

In Differentiated Services networks, packets may receive a different treatment according to their Differentiateo Services Code Point (DSCP) label. As a consequence, packet marking schemes can also be devised to differentiate packets belonging to a same TCP flow, with the goal of improving the performance experienced. This paper presents an analytical model for an adaptive packet marking scheme proposed in our previous work. The model combines three specific sub-models aimed at describing (i) the TCP sources aggregate, (ii) the marker, and (iii) the network status. Preliminary simulation results show quite accurate predictions for throughput and average queue occupancy. Besides, the research…

Optimal Delay-Power Tradeoff in Sparse Delay Tolerant Networks: a preliminary study

In this paper we present a first attempt to study analytically the tradeoff between delivery delay and resource consumption for epidemic routing in Delay Tolerant Networks. We assume that the nodes cooperate in order to minimize a common cost equal to a weighted sum of the packet delivery delay and the total number of copies, which is strongly related to the power consumption. In this framework we determine the best policy each node should deploy in a very simple scenario where all the nodes have perfect knowledge of the system status. The result is used as an ideal reference to evaluate the performance of some heuristics proposed, investigating potential performance improvements and config…

Adaptive Low Priority Packet Marking for Better TCP Performance

This paper proposes a packet marking scheme for TCP traffic. Unlike previous literature work, in our scheme the majority of TCP packets are transmitted as high priority. The role of a low priority packet appears that of a probe, whose goal is to early discover network congestion conditions. Low priority packets are marked according to an adaptive marking algorithm. Numerical results show that our scheme provides improved throughput/delay performance.

Teletraffic Engineering for Direct Load Control in Smart Grids

International audience; The traditional paradigm for power grid operation is to continuously adapt energy production to demand. This paradigm is challenged by the increasing penetration of renewable sources, that are more variable and less predictable. An alternative approach is the direct load control of some inherently flexible electric loads to shape the demand. Direct control of deferrable loads presents analogies with flow admission control in telecommunication networks: a request for network resources (bandwidth or energy) can be delayed on the basis of the current network status in order to guarantee some performance metrics. In this paper we go beyond such an analogy, showing that u…

A Network Formation Game Approach to Study BitTorrent Tit-for-Tat

The Tit-for-Tat strategy implemented in BitTorrent (BT) clients is generally considered robust to selfish behaviours. The authors of [1] support this belief studying how Tit-for-Tat can affect selfish peers who are able to set their upload bandwidth. They show that there is a "good" Nash Equilibrium at which each peer uploads at the maximum rate. In this paper we consider a different game where BT clients can change the number of connections to open in order to improve their performance. We study this game using the analytical framework of network formation games [2]. In particular we characterize the set of pairwise stable networks the peers can form and how the peers can dynamically reach…

Medium access in WiFi networks: strategies of selfish nodes [Applications Corner]

This article provides a game theoretical analysis of the WiFi MAC protocol to understand the risks or the advantages offered by possible modifications of MAC functionalities implemented at the driver level.