Youngmi Jin

Equilibria of a noncooperative game for heterogeneous users of an ALOHA network

A noncooperative group of users sharing a channel via ALOHA is considered. Depending on their quality-of-service requirements and willingness to pay, the users will select a desired throughput. The users then participate in a noncooperative game wherein they adjust their transmission-probability parameters in an attempt to attain their desired throughputs. The possible equilibrium points reached by such a community of users are studied.

Dynamics of competition between incumbent and emerging network technologies

The Internet is by all accounts an incredible success, but in spite or maybe because of this success, its deficiencies have come under increasing scrutiny and triggered calls for new architectures to succeed it. Those architectures will, however, face a formidable incumbent in the Internet, and their ability to ultimately replace it is likely to depend equally on technical superiority as on economic factors. The goal of this paper is to start developing models that can help provide a quantitative understanding of a competition between the Internet and a new system, and show what factors affect it most strongly. A model for the adoption of competing network technologies by individual users is formulated and solved. It accounts for both the intrinsic value of each technology and the positive externalities derived from their respective numbers of adopters. Using this model, different configurations are explored and possible outcomes characterized. More importantly, configurations are identified where small differences in the attributes of either technology can lead to vastly different results. The paper provides initial results that can help identify parameters that significantly affect the likelihood of success of new network technologies.

Distributed Contention Window Control for Selfish Users in IEEE 802.11 Wireless LANs

In this paper, we study non-cooperative user behavior in random-access wireless networks in which users have freedom to choose their back-off contention window size according to networks congestion status. We formulate a non- cooperative game and show the existence and uniqueness of its equilibrium point. We also propose an iterative method leading to the equilibrium point of the game. A discussion of alternative game formulations in the same problem context is also given.

Dynamics of usage-priced communication networks: the case of a single bottleneck resource

In this paper, we study end-user dynamics of communication networks employing usage-based pricing. We propose a generic network access mechanism in which users modify their access control parameter based on the quality of service they receive in order to maximize their net benefit. For the examples of users sharing access to a bandwidth resource via a single trunk with Erlang loss dynamics and for a differentiated services (diffserv) network, we study the equilibrium/fixed points and give analytical results on convergence assuming the network prices are fixed.

Nash equilibria of a generic networking game with applications to circuit-switched networks

A generic mechanism for end-user transmission rate control into a differentiated services Internet is formulated and basic results of corresponding Nash equilibria are proved. We consider specific examples of the mechanism including additive increase and multiplicative decrease inspired by present day TCP congestion control. For the example of users sharing access to a bandwidth resource via resizable provisioned label-switched paths (MPLS), we study the equilibria and the performance of the generic mechanism and give analytical results on convergence to equilibria. The fairness of the resulting equilibria when user demands exceed available network resources is also studied.

A Channel Aware MAC Protocol in an ALOHA Network with Selfish Users

We consider a game theoretic model incorporating channel state information into slotted ALOHA in a fading environment. Each user sets a threshold for her channel gain and sends a packet only when the channel gain is higher than the threshold at a given slot. This threshold is decided to maximize the net benefit of a user, utility minus power consumption. The asymptotic behaviors of the total throughput at a symmetric Nash equilibrium point are studied for fading and non-fading environments in a homogeneous system. It is shown that the total throughput in a fading environment increases as the number of users increases, while the total throughput in the simple classical slotted ALOHA decreases when users are sensitive enough to power consumption. Convergence to the symmetric Nash equilibrium is also studied.

Stable Nash equilibria of ALOHA medium access games under symmetric, socially altruistic behavior

We consider the effects of altruistic behavior on random medium access control (slotted ALOHA) for local area communication networks. For an idealized, synchronously iterative, two-player game with asymmetric player demands, we find a Lyapunov function governing the “better-response” Jacobi dynamics under purely altruistic behavior. Though the positions of the interior Nash equilibrium points do not change in the presence of altruistic behavior, the nature of their local asymptotic stability does. There is a region of partially altruistic behavior for which both interior Nash equilibrium points are locally asymptotically stable. Variations of these altruistic game frameworks are discussed considering power (instead of throughput) based costs and linear utility functions.

A model of the spread of randomly scanning Internet worms that saturate access links

We present a simple, deterministic mathematical model for the spread of randomly scanning and bandwidth-saturating Internet worms. Such worms include Slammer and Witty, both of which spread extremely rapidly. Our model, consisting of coupled Kermack-McKendrick (a.k.a. stratified susceptibles-infectives (SI)) equations, captures both the measured scanning activity of the worm and the network limitation of its spread, that is, the effective scan-rate per worm/infective. The Internet is modeled as an ideal core network to which each peripheral (e.g., enterprise) network is connected via a single access link. It is further assumed in this note that as soon as a single end-system in the peripheral network is infected by the worm, the subsequent scanning of the rest of the Internet saturates the access link, that is, there is “instant” saturation. We fit our model to available data for the Slammer worm and demonstrate the models ability to accurately represent Slammers total scan-rate to the core.

Charge sensitive and incentive compatible end-to-end window-based control for selfish users

This paper considers the problem of finding a tamper-resistant and charge-sensitive end-to-end window flow-control mechanism for greedy users. Using a mathematical model of resource distribution, we propose a distributed window flow-control mechanism leading to a flow-rate vector which achieves maximum total utility. Desirable features of the proposed window control algorithm and properties of the equilibrium points are explored. We also prove the convergence of the proposed window control algorithm.

On Maximizing Diffusion Speed Over Social Networks With Strategic Users

A variety of models have been proposed and analyzed to understand how a new innovation (e.g., a technology, a product, or even a behavior) diffuses over a social network, broadly classified into either of epidemic-based or game-based ones. In this paper, we consider a game-based model, where each individual makes a selfish, rational choice in terms of its payoff in adopting the new innovation, but with some noise. We address the following two questions on the diffusion speed of a new innovation under the game-based model: (1) what is a good subset of individuals to seed for reducing the diffusion time significantly, i.e., convincing them to preadopt a new innovation and (2) how much diffusion time can be reduced by such a good seeding. For (1), we design near-optimal polynomial-time seeding algorithms for three representative classes of social network models, Erdös-Rényi, planted partition and geometrically structured graphs, and provide their performance guarantees in terms of approximation and complexity. For (2), we asymptotically quantify the diffusion time for these graph topologies; further derive the seed budget threshold above which the diffusion time is dramatically reduced, i.e., phase transition of diffusion time. Furthermore, based on our theoretical findings, we propose a practical seeding algorithm, called Practical Partitioning and Seeding (PrPaS) and demonstrate that PrPaS outperforms other baseline algorithms in terms of the diffusion speed over a real social network topology. We believe that our results provide new insights on how to seed over a social network depending on its connectivity structure, where individuals rationally adopt a new innovation.