Researcher specializd in network science, game theory applied to networks, stochastic processes and their control. Other activity: composer, painter, video producer
2002 IEEE International Conference on Communications. Conference Proceedings. ICC 2002 (Cat. No.02CH37333)
We consider in this paper packets which arrive according to a Poisson process into a finite queue... more We consider in this paper packets which arrive according to a Poisson process into a finite queue. A group of consecutive packets forms a frame (or a message) and one then considers not only the quality of service of a single packet but also that of the whole message. In order to improve required quality of service, either on the frame loss probabilities or on the delay, discarding mechanisms have to be used. We analyze in this paper the performance of the Early Message Discard (EMD) policy at the buffer, which consists of (1) rejecting an entire message if upon the arrival of the first packet of the message, the buffer occupancy exceeds a threshold ¤ , and (2) if a packet is lost, then all subsequent arrivals that belong to the same message are discarded.
2009 International Conference on Game Theory for Networks, 2009
Non-cooperative game theory has gained much interest as a paradigm for decentralized control in c... more Non-cooperative game theory has gained much interest as a paradigm for decentralized control in communication networks. It allows to get rid of the need for a centralized controller. Decentralizing the decision making may result in situations where agents (decision makers) do not have the same view of the network: the information available to agents vary from one agent to another. The global view of the network state cannot be available to an agent as fast as the information on its local state. Incorporating into the decentralized control paradigm this information asymmetry renders it applicable to a much wider class of situations. In this paper we model the above information asymmetry using the one-step delay sharing information pattern from team theory and generalize it to the context of non-cooperative games. We study its properties and apply it to distributed power control problem.
Global Telecommunications Conference, . GLOBECOM . IEEE, 1999
Many works have studied the performance of TCP by modeling the network as a single bottleneck nod... more Many works have studied the performance of TCP by modeling the network as a single bottleneck node. We present a more general model taking into account all the nodes on the path not only the main bottleneck. We show that, in addition to the main bottleneck, the other nodes can seriously affect the performance of TCP. They may cause an
Proceedings of the 4th International ICST Conference on Performance Evaluation Methodologies and Tools, 2009
In the present work we deal with the concept of jamming with incomplete information about the jam... more In the present work we deal with the concept of jamming with incomplete information about the jammer. We consider two scenarios. In the first one a jammer could be either present in the environment bringing extra background noise or absent. The user has only statistical knowledge about either presence or absence of the jammer. Namely, the user knows that in the environment only a natural background noise could be with probability γ meanwhile with probability 1 − γ a jammer could come into the action distributing an extra noise of the total powerJ among the channels. In the second scenario the user does not know exactly the total jamming power. Namely, the user knows that with probability γ it could beJ 1 and with probability 1 − γ it could beJ 2. All the problems are modelled as non-zero sum games. The equilibrium strategies are found in closed form.
2009 3rd IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2009
We present a Bayesian game-theoretic approach for the distributed resource allocation problem in ... more We present a Bayesian game-theoretic approach for the distributed resource allocation problem in the context of K-user fading multiple access channels (MAC). We assume that users have incomplete information about the channel state information (CSI), i.e., each user knows his own channel state, but does not know the states of other users. All users (transmitters) are considered to be rational, selfish, and each one carries the objective of maximizing its own achievable data rate. In such a game-theoretic study, the central question is whether a Bayesian equilibrium (BE) exists. Based on the assumption of two channel states, we prove that there exists exactly one BE in this game.
We study in this paper two competing TCP connections that share a common bottlerreck link. When c... more We study in this paper two competing TCP connections that share a common bottlerreck link. When congestion occurs, one (or both) connections will suffer a loss that will cause its throughput to decrease by a multiplicative factor. The identity of the connection that will suffer a loss is determined by a randomized "loss strategy" that may depend on the throughputs of the connections at the congestion instant. We analyze several such loss strategies. After deriving some results for the general asymmetric case, we focus in particular on the symmetric case and study the infiuence of the strategy on the average throughput and average utilization of the link. As the intuition says, a strategy that assigns a loss to a connection with a higher throughput is expected to give worse performance since the total instantaneous throughput after a loss is expected to be lower with such a strategy. We show that, surprisingly, the average throughput and average link utilizations are invariant: they are the same under any possible strategy; the link utilization is 6/ 7 of the link capacity. We show, in contrast, that the second moment of the throughput does depend on the strategy.
Social scientists have observed that human behavior in society can often be modeled as correspond... more Social scientists have observed that human behavior in society can often be modeled as corresponding to a threshold type policy. A new behavior would propagate by a procedure in which an individual adopts the new behavior if the fraction of his neighbors or friends having adopted the new behavior exceeds some threshold. In this paper we study the question of whether the emergence of threshold policies may be modeled as a result of some rational process which would describe the behavior of non-cooperative rational members of some social network. We focus on situations in which individuals take the decision whether to access or not some content, based on the number of views that the content has. Our analysis aims at understanding not only the behavior of individuals, but also the way in which information about the quality of a given content can be deduced from view counts when only part of the viewers that access the content are informed about its quality. In this paper we present a game formulation for the behavior of individuals using a meanfield model: the number of individuals is approximated by a continuum of atomless players and for which the Wardrop equilibrium is the solution concept. We derive conditions on the problem's parameters that result indeed in the emergence of threshold equilibria policies. But we also identify some parameters in which other structures are obtained for the equilibrium behavior of individuals. Index Terms-User-generated content, Complex Systems, Video popularity, Game theory, Wardrop equilibria I. INTRODUCTION Online media constitute currently the largest share of Internet traffic. A large part of such traffic is generated by platforms that deliver user-generated content (UGC). This includes, among the other ones, YouTube and Vimeo for videos, Flickr and Instagram for images and all social networking platforms. Among such services, a prominent role is played by YouTube. Founded in 2005 by Chad Hurley, Steve Chen and Jawed Karim and acquired in 2006 by Google, YouTube scored in 2011 more than 1 trillion views (or, alternatively, an average of 140 video views for every person on Earth), with more than 3 billion hours of video watched every month and 72 hours of video uploaded every minute by YouTube's users 1. Of course, not all videos posted on YouTube are equal. The key aspect is their "popularity", broadly defined as the number of views they score (also referred to as viewcount).
Mobile ad hoc networks are characterized by a lack of a fixed infrastructure and by node mobility... more Mobile ad hoc networks are characterized by a lack of a fixed infrastructure and by node mobility. In these networks data transfer can be improved by using mobile nodes as relay nodes. As a result, transmission power and the movement pattern of the nodes have a key impact on the performance. In this work we focus on the impact of node mobility through the analysis of a simple one-dimensional ad hoc network topology. Nodes move in adjacent segments with reflecting boundaries according to Brownian motions. Communications (or relays) between nodes can occur only when they are within transmission range of each other. We determine the expected time to relay a message and compute the probability density function of relaying locations. We also provide an approximation formula for the expected relay time between any pair of mobiles.
The problem of jamming plays an important role in ensuring the quality and security of wireless c... more The problem of jamming plays an important role in ensuring the quality and security of wireless communications, especially at this moment when wireless networks are quickly becoming ubiquitous. Since jamming can be considered as a game in which jammer is playing against the user (transmitter) who would like to transmit signal with good quality and at the same time with a reasonable amount of energy, game theory is an appropriate tool for dealing with jamming. Here we investigate the effect of partially available information and correlation among sub-carriers on the user behavior. Specifically, to do so we deal with the scenario when the user does not know how jamming efforts are distributed among sub-carriers and the user does not know the fading channels' gains with certainty. As an object function for the user we consider SINR. We consider zerosum games, so all of them can also be viewed as a minimax problem for the user playing against the nature. We study independent fading channel gains scenario as well as dependent fading channel gains scenario, both in discrete and continuous versions. We show that in all the scenarii the jammers equalize the quality of the best sub-carriers for the transmitter on as low level as their power constraints allow. Meanwhile the transmitter distributes his power among these jamming sub-carriers. We find the equilibrium strategies in closed form and specify the range of sub-carriers where the transmitter can expect the jamming attack. Also, we show for independent plot these strategies depend only on the expected value of the transmitters channel gains meanwhile for the dependent plot they depend on the whole spectra of these gains. Thus, for independent plot the behaviour of the jammer is less fine tuned under environment since it works with the expected gains. The user for both scenarios has to take the whole spectra of the jamming gains but, of course, for the independent scenario he is less specific because of the jammer.
In this paper we investigate the properties of multimodular functions. In doing so we give elemen... more In this paper we investigate the properties of multimodular functions. In doing so we give elementary proofs for properties already established by Hajek and we generalize some of his results. In particular, we extend the relation between convexity and multimodularity to some convex subsets of ℤm. We also obtain general optimization results for average costs related to a sequence of multimodular functions rather than to a single function. Under this general context, we show that the expected average cost problem is optimized by using regular sequences. We finally illustrate the usefulness of this theory in admission control into a D/D/1 queue with fixed batch arrivals, with no state information. We show that the regular policy minimizes the average queue length for the case of an infinite queue, but not for the case of a finite queue. When further adding a constraint on the losses, it is shown that a regular policy is also optimal for the finite queue case.
In this paper we consider a singularly perturbed Markov decision process with ®nitely many states... more In this paper we consider a singularly perturbed Markov decision process with ®nitely many states and actions and the limiting expected average reward criterion. We make no assumptions about the underlying ergodic structure. We present algorithms for the computation of a uniformly optimal deterministic control, that is, a control which is optimal for all values of the perturbation parameter that are su½ciently small. Our algorithms are based on Jeroslow's Asymptotic Linear Programming.
International Journal of Satellite Communications and Networking, 2003
Acknowledgement (ACK) filtering has been proposed as a technique to alleviate the congestion at t... more Acknowledgement (ACK) filtering has been proposed as a technique to alleviate the congestion at the input of a slow channel located on the reverse path of a TCP connection. Old ACKs waiting at the input of the slow channel are erased when new ACKs are to be queued. In the literature the case of one‐ACK per connection at a time has been studied. In this paper we show that this is too aggressive for short transfers where ACKs arrive in bursts due to the slow start phase, and where the TCP source needs to receive the maximum number of ACKs to increase fast its window. We study first static filtering where a certain ACK queue length is allowed. We show analytically how this length needs to be chosen. We present then some algorithms that adapt the filtering of ACKs as a function of the slow channel utilization rather than the ACK queue length. These algorithms provide a good compromise between reducing the ACK queueing delay and passing a large number of ACKs that guarantee a fast window...
2002 IEEE International Conference on Communications. Conference Proceedings. ICC 2002 (Cat. No.02CH37333)
We consider in this paper packets which arrive according to a Poisson process into a finite queue... more We consider in this paper packets which arrive according to a Poisson process into a finite queue. A group of consecutive packets forms a frame (or a message) and one then considers not only the quality of service of a single packet but also that of the whole message. In order to improve required quality of service, either on the frame loss probabilities or on the delay, discarding mechanisms have to be used. We analyze in this paper the performance of the Early Message Discard (EMD) policy at the buffer, which consists of (1) rejecting an entire message if upon the arrival of the first packet of the message, the buffer occupancy exceeds a threshold ¤ , and (2) if a packet is lost, then all subsequent arrivals that belong to the same message are discarded.
2009 International Conference on Game Theory for Networks, 2009
Non-cooperative game theory has gained much interest as a paradigm for decentralized control in c... more Non-cooperative game theory has gained much interest as a paradigm for decentralized control in communication networks. It allows to get rid of the need for a centralized controller. Decentralizing the decision making may result in situations where agents (decision makers) do not have the same view of the network: the information available to agents vary from one agent to another. The global view of the network state cannot be available to an agent as fast as the information on its local state. Incorporating into the decentralized control paradigm this information asymmetry renders it applicable to a much wider class of situations. In this paper we model the above information asymmetry using the one-step delay sharing information pattern from team theory and generalize it to the context of non-cooperative games. We study its properties and apply it to distributed power control problem.
Global Telecommunications Conference, . GLOBECOM . IEEE, 1999
Many works have studied the performance of TCP by modeling the network as a single bottleneck nod... more Many works have studied the performance of TCP by modeling the network as a single bottleneck node. We present a more general model taking into account all the nodes on the path not only the main bottleneck. We show that, in addition to the main bottleneck, the other nodes can seriously affect the performance of TCP. They may cause an
Proceedings of the 4th International ICST Conference on Performance Evaluation Methodologies and Tools, 2009
In the present work we deal with the concept of jamming with incomplete information about the jam... more In the present work we deal with the concept of jamming with incomplete information about the jammer. We consider two scenarios. In the first one a jammer could be either present in the environment bringing extra background noise or absent. The user has only statistical knowledge about either presence or absence of the jammer. Namely, the user knows that in the environment only a natural background noise could be with probability γ meanwhile with probability 1 − γ a jammer could come into the action distributing an extra noise of the total powerJ among the channels. In the second scenario the user does not know exactly the total jamming power. Namely, the user knows that with probability γ it could beJ 1 and with probability 1 − γ it could beJ 2. All the problems are modelled as non-zero sum games. The equilibrium strategies are found in closed form.
2009 3rd IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2009
We present a Bayesian game-theoretic approach for the distributed resource allocation problem in ... more We present a Bayesian game-theoretic approach for the distributed resource allocation problem in the context of K-user fading multiple access channels (MAC). We assume that users have incomplete information about the channel state information (CSI), i.e., each user knows his own channel state, but does not know the states of other users. All users (transmitters) are considered to be rational, selfish, and each one carries the objective of maximizing its own achievable data rate. In such a game-theoretic study, the central question is whether a Bayesian equilibrium (BE) exists. Based on the assumption of two channel states, we prove that there exists exactly one BE in this game.
We study in this paper two competing TCP connections that share a common bottlerreck link. When c... more We study in this paper two competing TCP connections that share a common bottlerreck link. When congestion occurs, one (or both) connections will suffer a loss that will cause its throughput to decrease by a multiplicative factor. The identity of the connection that will suffer a loss is determined by a randomized "loss strategy" that may depend on the throughputs of the connections at the congestion instant. We analyze several such loss strategies. After deriving some results for the general asymmetric case, we focus in particular on the symmetric case and study the infiuence of the strategy on the average throughput and average utilization of the link. As the intuition says, a strategy that assigns a loss to a connection with a higher throughput is expected to give worse performance since the total instantaneous throughput after a loss is expected to be lower with such a strategy. We show that, surprisingly, the average throughput and average link utilizations are invariant: they are the same under any possible strategy; the link utilization is 6/ 7 of the link capacity. We show, in contrast, that the second moment of the throughput does depend on the strategy.
Social scientists have observed that human behavior in society can often be modeled as correspond... more Social scientists have observed that human behavior in society can often be modeled as corresponding to a threshold type policy. A new behavior would propagate by a procedure in which an individual adopts the new behavior if the fraction of his neighbors or friends having adopted the new behavior exceeds some threshold. In this paper we study the question of whether the emergence of threshold policies may be modeled as a result of some rational process which would describe the behavior of non-cooperative rational members of some social network. We focus on situations in which individuals take the decision whether to access or not some content, based on the number of views that the content has. Our analysis aims at understanding not only the behavior of individuals, but also the way in which information about the quality of a given content can be deduced from view counts when only part of the viewers that access the content are informed about its quality. In this paper we present a game formulation for the behavior of individuals using a meanfield model: the number of individuals is approximated by a continuum of atomless players and for which the Wardrop equilibrium is the solution concept. We derive conditions on the problem's parameters that result indeed in the emergence of threshold equilibria policies. But we also identify some parameters in which other structures are obtained for the equilibrium behavior of individuals. Index Terms-User-generated content, Complex Systems, Video popularity, Game theory, Wardrop equilibria I. INTRODUCTION Online media constitute currently the largest share of Internet traffic. A large part of such traffic is generated by platforms that deliver user-generated content (UGC). This includes, among the other ones, YouTube and Vimeo for videos, Flickr and Instagram for images and all social networking platforms. Among such services, a prominent role is played by YouTube. Founded in 2005 by Chad Hurley, Steve Chen and Jawed Karim and acquired in 2006 by Google, YouTube scored in 2011 more than 1 trillion views (or, alternatively, an average of 140 video views for every person on Earth), with more than 3 billion hours of video watched every month and 72 hours of video uploaded every minute by YouTube's users 1. Of course, not all videos posted on YouTube are equal. The key aspect is their "popularity", broadly defined as the number of views they score (also referred to as viewcount).
Mobile ad hoc networks are characterized by a lack of a fixed infrastructure and by node mobility... more Mobile ad hoc networks are characterized by a lack of a fixed infrastructure and by node mobility. In these networks data transfer can be improved by using mobile nodes as relay nodes. As a result, transmission power and the movement pattern of the nodes have a key impact on the performance. In this work we focus on the impact of node mobility through the analysis of a simple one-dimensional ad hoc network topology. Nodes move in adjacent segments with reflecting boundaries according to Brownian motions. Communications (or relays) between nodes can occur only when they are within transmission range of each other. We determine the expected time to relay a message and compute the probability density function of relaying locations. We also provide an approximation formula for the expected relay time between any pair of mobiles.
The problem of jamming plays an important role in ensuring the quality and security of wireless c... more The problem of jamming plays an important role in ensuring the quality and security of wireless communications, especially at this moment when wireless networks are quickly becoming ubiquitous. Since jamming can be considered as a game in which jammer is playing against the user (transmitter) who would like to transmit signal with good quality and at the same time with a reasonable amount of energy, game theory is an appropriate tool for dealing with jamming. Here we investigate the effect of partially available information and correlation among sub-carriers on the user behavior. Specifically, to do so we deal with the scenario when the user does not know how jamming efforts are distributed among sub-carriers and the user does not know the fading channels' gains with certainty. As an object function for the user we consider SINR. We consider zerosum games, so all of them can also be viewed as a minimax problem for the user playing against the nature. We study independent fading channel gains scenario as well as dependent fading channel gains scenario, both in discrete and continuous versions. We show that in all the scenarii the jammers equalize the quality of the best sub-carriers for the transmitter on as low level as their power constraints allow. Meanwhile the transmitter distributes his power among these jamming sub-carriers. We find the equilibrium strategies in closed form and specify the range of sub-carriers where the transmitter can expect the jamming attack. Also, we show for independent plot these strategies depend only on the expected value of the transmitters channel gains meanwhile for the dependent plot they depend on the whole spectra of these gains. Thus, for independent plot the behaviour of the jammer is less fine tuned under environment since it works with the expected gains. The user for both scenarios has to take the whole spectra of the jamming gains but, of course, for the independent scenario he is less specific because of the jammer.
In this paper we investigate the properties of multimodular functions. In doing so we give elemen... more In this paper we investigate the properties of multimodular functions. In doing so we give elementary proofs for properties already established by Hajek and we generalize some of his results. In particular, we extend the relation between convexity and multimodularity to some convex subsets of ℤm. We also obtain general optimization results for average costs related to a sequence of multimodular functions rather than to a single function. Under this general context, we show that the expected average cost problem is optimized by using regular sequences. We finally illustrate the usefulness of this theory in admission control into a D/D/1 queue with fixed batch arrivals, with no state information. We show that the regular policy minimizes the average queue length for the case of an infinite queue, but not for the case of a finite queue. When further adding a constraint on the losses, it is shown that a regular policy is also optimal for the finite queue case.
In this paper we consider a singularly perturbed Markov decision process with ®nitely many states... more In this paper we consider a singularly perturbed Markov decision process with ®nitely many states and actions and the limiting expected average reward criterion. We make no assumptions about the underlying ergodic structure. We present algorithms for the computation of a uniformly optimal deterministic control, that is, a control which is optimal for all values of the perturbation parameter that are su½ciently small. Our algorithms are based on Jeroslow's Asymptotic Linear Programming.
International Journal of Satellite Communications and Networking, 2003
Acknowledgement (ACK) filtering has been proposed as a technique to alleviate the congestion at t... more Acknowledgement (ACK) filtering has been proposed as a technique to alleviate the congestion at the input of a slow channel located on the reverse path of a TCP connection. Old ACKs waiting at the input of the slow channel are erased when new ACKs are to be queued. In the literature the case of one‐ACK per connection at a time has been studied. In this paper we show that this is too aggressive for short transfers where ACKs arrive in bursts due to the slow start phase, and where the TCP source needs to receive the maximum number of ACKs to increase fast its window. We study first static filtering where a certain ACK queue length is allowed. We show analytically how this length needs to be chosen. We present then some algorithms that adapt the filtering of ACKs as a function of the slow channel utilization rather than the ACK queue length. These algorithms provide a good compromise between reducing the ACK queueing delay and passing a large number of ACKs that guarantee a fast window...
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