Showing papers by "Peter Key published in 2006"

Performance Analysis of Contention Based Medium Access Control Protocols

Abstract: This paper studies the performance of contention based medium access control (MAC) protocols. In particular, a simple and accurate technique for estimating the throughput of the IEEE 802.11 DCF protocol is developed. The technique is based on a rigorous analysis of the Markov chain that corresponds to the time evolution of the back-off processes at the contending nodes. An extension of the technique is presented to handle the case where service differentiation is provided with the use of heterogeneous protocol parameters, as, for example, in IEEE 802.11e EDCA protocol. Our results provide new insights into the operation of such protocols. The techniques developed in the paper are applicable to a wide variety of contention based MAC protocols. Index Terms—Carrier sense multiple-access protocol with colli- sion avoidance (CSMA/CA), diffusion approximation, fixed point analysis,fluidlimit,IEEE80211,IEEE80211e,performanceevalu- ation, performance of the medium access control (MAC) protocols, wireless local-area networks (WLANs).

Combining Multipath Routing and Congestion Control for Robustness

Abstract: Flexible routing schemes mitigate some of the problems associated with uncertain traffic patterns and workloads by making the exact location of capacity less important: if there is available capacity the routing scheme will find it. In this paper we propose a combined multipath routing and congestion control architecture that can provide performance improvements to the end user and simplifies network dimensioning for operators. We describe a flow-level model, able to handle streaming and file transfer traffic, with stochastic arrivals, and look at a fluid limit. We describe a congestion controller and path selection algorithm that automatically balances traffic across the lowest cost paths, and we suggest ways in which just two paths may be used, with a random selection policy. A notable feature of a multipath congestion controller is that it cannot be tuned to a single RTT, hence it differs from standard TCP with respect to RTT bias. We show that under certain conditions the allocation of flows to paths is optimal and independent of the flow control algorithm used. Scalability of the architecture results from implementing the algorithms at end-systems. We illustrate by examples how such an approach can halve response times and double the load that a network can carry.

Fluid models of integrated traffic and multipath routing

Abstract: In this paper we consider a stochastic model describing the varying number of flows in a network. This model features flows of two types, namely file transfers (with fixed volume) and streaming traffic (with fixed duration), and extends the model of Key, Massoulie, Bain and Kelly [27] by allowing more general bandwidth allocation criteria. We analyse the dynamics of the system under a fluid scaling, and show Lyapunov stability of the fluid limits under a natural stability condition. We provide natural interpretations of the fixed points of these fluid limits. We then compare the fluid dynamics of file transfers under (i) balanced multipath routing and (ii) parallel, uncoordinated routing. We show that for identical traffic demands, parallel uncoordinated routing can be unstable while balanced multipath routing is stable. Finally, we identify multi-dimensional Ornstein-Uhlenbeck processes as second-order approximations to the first-order fluid limit dynamics.

Congestion avoidance within aggregate channels

Abstract: Network congestion avoidance within aggregated channels is disclosed. In one embodiment, a method first transmits a packet associated with a first channel of a plurality of related channels from a source protocol layer (e.g., a source IP layer) of a source through a network (e.g., the Internet). Next, the method triggers an ECN event by the packet at the network. Finally, at least one channel is determined to have decreased packets transmitted therethrough, in response to the triggering of the ECN event (e.g., based on a congestion pricing criteria).

Congestion notification and probing mechanisms for endpoint admission control

Abstract: There has been much interest in admission control schemes that place the burden of admission control decisions on the end users. In these schemes, referred to as Endpoint Admission Control, the decision to join the network is taken by the user, based on the probing of the network using probe packets. Depending on the level of congestion, routers mark the probe packets and thus inform the user of the state of the network. In this paper, we analyze three mechanisms for providing Endpoint Admission Control: virtual-queue marking, random-early marking and tail drop. For each scheme, we analyze the probing duration necessary to guarantee the required QoS and achieve high link utilization. Our main conclusion is that very few probe packets have to be sent when early marking is used, whereas tail drop requires a large number of probe packets.

Efficient Quarantining of Scanning Worms: Optimal Detection and Coordination

Abstract: Current generation worms have caused considerable damage, despite their use of unsophisticated scanning strategies for detecting vulnerable hosts. A number of adaptive techniques have been proposed for quarantining hosts whose behaviour is deemed suspicious. Such techniques have been proven to be effective against fast scanning worms. However, worms could evade detection by being less aggressive. In this paper we consider the interplay between worm strategies and detection techniques, which can be described in game-theoretic terms. We use epidemiological modelling to characterise the outcome of the game (the pay-off function), as a function of the strategies of the worm and the detector. We design detection rules that are optimal against scanning worms with known characteristics. We then identify specific detection rules that are close to optimal, in some mathematically precise sense, against any scanning worm. Finally, we design methods for coordinating information among a set of end-hosts, using Bayesian decision theory. We evaluate the proposed rules using simulations driven by traces from a corporate environment of 600 hosts, and assess the benefits of coordination.

Competitive and considerate congestion control

Abstract: An end-to-end congestion control is provided that emulates a different service differentiation than the common low-normal priority. This protocol is referred to as 4CP (Competitive, Considerate Congestion Control). The target service differentiation enables provisioning of per-flow average bandwidth guarantees to “normal” traffic, but not at the expense of potentially starving the “low” priority traffic (4CP). It thus features incentive compatibility to file-transfer applications that are throughput-greedy but want to be considerate to other traffic. 4CP is implemented and configured as a sender-only adaptation of standard TCP, and requires no special network feedback. Configuration of the bandwidth guarantee is either statically configured or automatically adjusted by 4CP. The automatic mode aims to be TCP-friendly over appropriately large timescale.

Schedulable regions and equilibrium cost for multipath flow control: the benefits of coordination

Abstract: In this paper we consider deterministic differential equation models for the varying number of flows in a network. These arise naturally as limits of stochastic models under joint scaling of flow arrival rates and network capacities. We compare these dynamics under (i) coordinated multipath routing and (ii) parallel, uncoordinated routing. We show that for identical traffic demands, parallel uncoordinated routing can be unstable while balanced multipath routing is stable. In other words, coordination can strictly increase the schedulable region, that is the set of demand vectors for which the system is stable. We also show that, even when uncoordinated multipath routing stabilises the system, coordination can bring further benefits, as it naturally minimises network costs at equilibrium.

Proceedings of the joint international conference on Measurement and modeling of computer systems

Abstract: Welcome to SIGMETRICS/PERFORMANCE 2006 and to Saint-Malo! The ACM SIGMETRICS conference and the Performance conference sponsored by IFIP Working Group 7.3 join every three years, and this is the tenth joint conference. The theme is Measurement and Modeling of Computer Systems, and this year's program reflects the breadth and depth of the subject area. This year's topics cover storage systems, wired, wireless and P2P networks, scheduling and fairness, queuing systems, Markov chains, architecture and security, while the range of methodologies cover measurements, analysis and simulation.As in previous years, the selection process was highly competitive. 219 submissions were received, of which 30 were selected as full papers, and 16 papers were accepted as posters. All papers were reviewed through a double-blind review process. Each paper was reviewed by at least three Program Committee (PC) members not connected with the authors. In some cases additional reviews were sought from specialists outside the PC. The PC itself comprised 51 experts from 15 countries, and the final paper selection was made at the PC meeting held at Columbia University in January 27-28, 2006, which was attended by 35 of the PC members, the two program co-chairs, and the general chair. The quality of submissions was extremely high as reflected in the final program, which we hope that you will find stimulating. It is a special pleasure to have the main conference completed by our keynote speaker Daniel Reed who will give a talk on performance and reliability.After the PC meeting a subcommittee selected the best paper award winners. The Best Paper was awarded to "Maximizing Throughput in Wireless Networks via Gossiping'' by Eytan Modiano, Devavrat Shah, and Gil Zussman (MIT, US). The Kenneth C. Sevcik Outstanding Student Paper was awarded to "GPS Scheduling: Selection of Optimal Weights and Comparison with Strict Priorities'' by Pascal Lieshout, Michel R.H. Mandjes, and Sem Borst (CWI, NL). We congratulate the authors of these papers.