Preferential survival in models of complex ad hoc networks

There has been a rich interplay in recent years between (i) empirical investigations of real world dynamic networks, (ii) analytical modeling of the microscopic mechanisms that drive the emergence of such networks, and (iii) harnessing of these mechanisms to either manipulate existing networks, or engineer new networks for specific tasks. We continue in this vein, and study the deletion phenomenon in the web by following two different sets of web-sites (each comprising more than 150,000 pages) over a one-year period. Empirical data show that there is a significant deletion component in the underlying web networks, but the deletion process is not uniform. This motivates us to introduce a new mechanism of preferential survival (PS), where nodes are removed according to a degree-dependent deletion kernel. We use the mean-field rate equation approach to study a general dynamic model driven by Preferential Attachment (PA), Double PA (DPA), and a tunable PS, where c nodes (c<1) are deleted per node added to the network, and verify our predictions via large-scale simulations. One of our results shows that, unlike in the case of uniform deletion, the PS kernel when coupled with the standard PA mechanism, can lead to heavy-tailed power law networks even in the presence of extreme turnover in the network. Moreover, a weak DPA mechanism, coupled with PS, can help make the network even more heavy-tailed, especially in the limit when deletion and insertion rates are almost equal, and the overall network growth is minimal. The dynamics reported in this work can be used to design and engineer stable ad hoc networks and explain the stability of the power law exponents observed in real-world networks.Comment: 9 pages, 6 figure

Keypeer: A Scalable, Resilient Distributed Public-Key System Using Chord

Current Public Key Infrastructures (PKIs) do not deliver public keys and revocations in a scalable and timely manner so that users can benefit from the availability of the most up-to-date information. Even when the data is current and online, users can often face significant delays when accessing what is essentially a centralized systems architecture. In this paper, we take a different approach and propose Keypeer, a fully distributed system where servers form a Distributed Hashing Table (DHT) (e.g., a Chord ring) on behalf of interested users that holds the public keys as well as the revocation information as it is published by the Certificate Authority (CA). Keypeer algorithm, running on top of this distributed infrastructure, shuffles the addresses before hashing them creating replicas of the same data to be inserted at several nodes. Based on this architectural approach, the Keypeer system provides a high degree of resilience and scalability when compared to most existing approaches, where data is not totally lost even in the case when nodes abruptly disappear from the system. Keypeer also offers protection against fraud caused by nodes that maliciously keep outdated information. As a result, the Keypeer system offers the fast reliable delivery of keys and trust in the received data. In this paper, we present the design, initial implementation, and evaluation of the Keypeer system deployed on the PlanetLab overlay

Wireless Incentive Engineering

The successful operation of emerging public wireless LANs requires flexible network mechanisms that can support differentiated or tiered services for a variety of applications such as bursty transactional web applications as well as reservation demanding voice and video applications. Congestion pricing has been proposed as one promising solution to traffic control because it accurately models the cost that each user&apos;s traffic imposes on network congestion points. The underlying assumption of congestion pricing is that users will respond to a monetary-based price signal to maximize their own utility. We observe, however, that monetary service charge is largely a business concern and not a traffic control concern because operators and users prefer simple, predictable, and stable service charges such as flat-rate or block-rate charging. Therefore, we argue, that traffic control techniques such as congestion pricing should be decoupled from monetary service charges. Under such a new regime, however, a user&apos;s response to a non-monetary price signal would be quite different from utility maximization, and without the appropriate incentives for users to cooperate such a regime would lead to the &quot;tragedy of the commons&quot; phenomenon, undermining any future differentiated service offerings by wireless Internet service providers. To address this problem we propose wireless incentive engineering mechanisms for mobile devices and access points that provide incentives for mobile users to cooperatively use different classes of services without relying on monetary service charging. Wireless incentive engineering possesses a number of beneficial properties including minimizing the algorithmic and protocol overhead on mobile devices and access points, Nash bargaining fairness, and incentiv..

Incentive Engineering in Wireless LAN Based Access Networks

Traffic regulation in public and private wireless LANs face a number of significant challenges, particularly in commercial networks where there is a need for efficient regulation of bursty transactional applications, support for bandwidth reservation services while inhibiting bandwidth hogging by mobile devices, and incentivizing user cooperation. In this paper, we take a new approach to solving these problems by applying incentive engineering techniques to wireless access networks. We design two incentive-based allocation service classes: an instantaneous allocation (IA) class, which provides better throughput, and a stable allocation (SA) class, which provides better allocation stability. Our approach possesses a number of beneficial properties including minimizing the algorithmic and protocol overhead on mobile devices, Nash bargaining fairness for the IA service, and incentive compatibility for mobile users promoting the truthfully selection of service class and bandwidth declaration. We use analysis, simulation and experimental results from a wireless testbed to demonstrate the effectiveness of wireless incentive engineering

PlanetLab and Its Applicability to the ProActive Enterprise

Current Information Technology (IT) models for security, content distribution, network and systems management, and provisioning do not match the level of complexity and flexibility required by today&apos;s enterprise. Private enterprises increasingly need to deal with internal security threats the same way as they deal with external security threats. Increasing mobility and globalization demand that applications be pervasive, i.e., working wherever an enterprise&apos;s employees operate. At the same time, the cost of maintaining applications, including deploying them and provisioning the proper resources, must be minimized, and enterprises need to be able to manage and deploy new services without impacting the existing operational services. In this paper, we suggest that PlanetLab [1], currently a world-wide research platform, is a potential IT delivery vehicle that can solve many of the challenges facing IT organizations, and it has the potential to become a commercially viable platform for enterprise organizations