Dynamics on Games: Simulation-Based Techniques and Applications to Routing

We consider multi-player games played on graphs, in which the players aim at fulfilling their own (not necessarily antagonistic) objectives. In the spirit of evolutionary game theory, we suppose that the players have the right to repeatedly update their respective strategies (for instance, to improve the outcome w.r.t. the current strategy profile). This generates a dynamics in the game which may eventually stabilise to an equilibrium. The objective of the present paper is twofold. First, we aim at drawing a general framework to reason about the termination of such dynamics. In particular, we identify preorders on games (inspired from the classical notion of simulation between transitions systems, and from the notion of graph minor) which preserve termination of dynamics. Second, we show the applicability of the previously developed framework to interdomain routing problems

Predictable MAC-level Performance in Low-power Wireless Under Interference

Predictable performance is key for many WSN applications. Recent efforts use models of the environment, the employed hardware and protocols to predict network performance. Towards this end, we present an intentionally simple model of ContikiMAC, Contikiâ\u80\u99s default MAC layer, targeting worst-case bounds for packet delivery rate and latency. Our experiments reveal problems in the performance of ContikiMAC which makes the protocol perform much worse than predicted and hence prohibits predictable performance with the current ContikiMAC implementation. We show that the reason for this performance degradation is that ContikiMAC looses phase-lock. To solve this problem, we add fine-grained timing information into the acknowledgment. We show that this mechanism solves these problems and enables predictable performance with ContikiMAC even under high external interference

Scheduling UWB Ranging and Backbone Communications in a Pure Wireless Indoor Positioning System

International audienceIn this paper, we present and evaluate an ultra-wideband (UWB) indoor processing architecture that allows the performing of simultaneous localizations of mobile tags. This architecture relies on a network of low-power fixed anchors that provide forward-ranging measurements to a localization engine responsible for performing trilateration. The communications within this network are orchestrated by UWB-TSCH, an adaptation to the ultra-wideband (UWB) wireless technology of the time-slotted channel-hopping (TSCH) mode of IEEE 802.15.4. As a result of global synchronization, the architecture allows deterministic channel access and low power consumption. Moreover, it makes it possible to communicate concurrently over multiple frequency channels or using orthogonal preamble codes. To schedule communications in such a network, we designed a dedicated centralized scheduler inspired from the traffic aware scheduling algorithm (TASA). By organizing the anchors in multiple cells, the scheduler is able to perform simultaneous localizations and transmissions as long as the corresponding anchors are sufficiently far away to not interfere with each other. In our indoor positioning system (IPS), this is combined with dynamic registration of mobile tags to anchors, easing mobility, as no rescheduling is required. This approach makes our ultra-wideband (UWB) indoor positioning system (IPS) more scalable and reduces deployment costs since it does not require separate networks to perform ranging measurements and to forward them to the localization engine. We further improved our scheduling algorithm with support for multiple sinks and in-network data aggregation. We show, through simulations over large networks containing hundreds of cells, that high positioning rates can be achieved. Notably, we were able to fully schedule a 400-cell/400-tag network in less than 11 s in the worst case, and to create compact schedules which were up to 11 times shorter than otherwise with the use of aggregation, while also bounding queue sizes on anchors to support realistic use situations

Phase Changes in the Evolution of the IPv4 and IPv6 AS-Level Internet Topologies

In this paper we investigate the evolution of the IPv4 and IPv6 Internet topologies at the autonomous system (AS) level over a long period of time.We provide abundant empirical evidence that there is a phase transition in the growth trend of the two networks. For the IPv4 network, the phase change occurred in 2001. Before then the network's size grew exponentially, and thereafter it followed a linear growth. Changes are also observed around the same time for the maximum node degree, the average node degree and the average shortest path length. For the IPv6 network, the phase change occurred in late 2006. It is notable that the observed phase transitions in the two networks are different, for example the size of IPv6 network initially grew linearly and then shifted to an exponential growth. Our results show that following decades of rapid expansion up to the beginning of this century, the IPv4 network has now evolved into a mature, steady stage characterised by a relatively slow growth with a stable network structure; whereas the IPv6 network, after a slow startup process, has just taken off to a full speed growth. We also provide insight into the possible impact of IPv6-over-IPv4 tunneling deployment scheme on the evolution of the IPv6 network. The Internet topology generators so far are based on an inexplicit assumption that the evolution of Internet follows non-changing dynamic mechanisms. This assumption, however, is invalidated by our results.Our work reveals insights into the Internet evolution and provides inputs to future AS-Level Internet models.Comment: 12 pages, 21 figures; G. Zhang et al.,Phase changes in the evolution of the IPv4 and IPv6 AS-Level Internet topologies, Comput. Commun. (2010

On low-latency-capable topologies, and their impact on the design of intra-domain routing

An ISP's customers increasingly demand delivery of their traffic without congestion and with low latency. The ISP's topology, routing, and traffic engineering, often over multiple paths, together determine congestion and latency within its backbone. We first consider how to measure a topology's capacity to route traffic without congestion and with low latency. We introduce low-latency path diversity (LLPD), a metric that captures a topology's flexibility to accommodate traffic on alternative low-latency paths. We explore to what extent 116 real backbone topologies can, regardless of routing system, keep latency low when demand exceeds the shortest path's capacity. We find, perhaps surprisingly, that topologies with good LLPD are precisely those where routing schemes struggle to achieve low latency without congestion. We examine why these schemes perform poorly, and offer an existence proof that a practical routing scheme can achieve a topology's potential for congestion-free, low-delay routing. Finally we examine implications for the design of backbone topologies amenable to achieving high capacity and low delay

Topology Generation Based on Network Design Heuristics

INTRODUCTION Building increasingly precise and realistic network topologies is an important issue for the purpose of evaluating networking applications. Still, the generation of router-level topologies has not been widely covered. Though, the properties of the router-level topologies have a significant impact on simulation results. For instance, the evaluation of applications such as Voice/Video over IP, P2P, routing protocols and traffic engineering methods critically depends on the properties captured by the topology model. We believe that today's network topologies are the fruits of a careful design taking into account practical constraints. We argue that it is possible to generate realistic network topologies by reproducing and automating the work of a human network designer. Due to the computational complexity of network design, heuristics are often used to build networks. The networking literature contains lots of network design methods which are currently seldom used by resea

BGP-based interdomain traffic engineering

In a few years, the Internet has quickly evolved from a research network connecting a handful of users to the largest distributed system ever built. The Internet connects more than 20,000 Autonomous Systems (ASs) which are administratively independent networks. While the initial Internet was designed to provide a best-effort connectivity among these ASs, there is nowadays a growing trend to deploy new services such as Voice/Video over IP or VPNs. To support these emergent services, ASs need to better engineer their Internet traffic. Traffic Engineering encompasses several goals such as better spreading the traffic load inside a network and obtaining better end-to-end performance (lower latency or higher bandwidth). Engineering the traffic inside a single AS is feasible and pretty well understood. To the opposite, interdomain traffic engineering is still a difficult problem. The main issue comes from the current Internet routing architecture, articulated around the Border Gateway Protocol (BGP). BGP propagates a subset of the Internet topology for scalability and stability reasons and does not optimize a single global objective. This limits the control each AS has on its routing and has dramatic implications for interdomain traffic engineering. In this thesis, we evaluate the primitive BGP-based routing control mechanisms. For this purpose, we designed and implemented a new approach for modeling BGP on large Internet-scale network topologies. Finally, to overcome the limitations of BGP in terms of routing control, we propose Virtual Peerings, a new mechanism based on a combination of BGP and IP tunneling. We apply Virtual Peerings to solve various interdomain traffic engineering problems such as balancing the load of Internet traffic received by an AS or decreasing the end-to-end latency of Internet paths.(FSA 3)--UCL, 200