37635676
Efficient Algorithms for Approximate String Matching with Swaps
Most research on the edit distance problem and thek-differences problem considered the set of edit operations consisting of changes, insertions, and deletions. In this paper we include theswapoperation that interchanges two adjacent characters into the set of allowable edit operations, and we present anO(tmin(m,n))-time algorithm for the extended edit distance problem, wheretis the edit distance between the given strings, and anO(kn)-time algorithm for the extendedk-differences problem. That is, we add swaps into the set of edit operations without increasing the time complexities of previous algorithms that consider only changes, insertions, and deletions for the edit distance andk-differences problems.
44748347
A Linear-Time Algorithm for Concave One-Dimensional Dynamic Programming
11301244
On the effectiveness of route-based packet filtering for distributed DoS attack prevention in power-law internets
Denial of service (DoS) attack on the Internet has become a pressing problem. In this paper, we describe and evaluate route-based distributed packet filtering (DPF), a novel approach to distributed DoS (DDoS) attack prevention. We show that DPF achieves proactiveness and scalability, and we show that there is an intimate relationship between the effectiveness of DPF at mitigating DDoS attack and power-law network topology.The salient features of this work are two-fold. First, we show that DPF is able to proactively filter out a significant fraction of spoofed packet flows and prevent attack packets from reaching their targets in the first place. The IP flows that cannot be proactively curtailed are extremely sparse so that their origin can be localized---i.e., IP traceback---to within a small, constant number of candidate sites. We show that the two proactive and reactive performance effects can be achieved by implementing route-based filtering on less than 20% of Internet autonomous system (AS) sites. Second, we show that the two complementary performance measures are dependent on the properties of the underlying AS graph. In particular, we show that the power-law structure of Internet AS topology leads to connectivity properties which are crucial in facilitating the observed performance effects.
17238529
A distributed protocol for multi-class QoS provision in noncooperative many-switch systems
This paper presents an architecture for multi-class quality of service (QoS) provision in wide area networks. Users or applications are assumed to be selfish and end-to-end QoS is determined by the service levels received by an application traffic flow at each router or switch along a path. In previous work, we have given a comprehensive analysis of the noncooperative multi-class QoS provision game for single-switch systems showing when Nash equilibria exist and under what conditions they are Pareto and/or system optimal. In this paper, we propose a specific network architecture for facilitating noncooperative and of provision in many-switch systems such as the Internet with emphasis on realizability. We shield the user from having to choose the service classes on the switches along a route-a hard combinatorial optimization problem even assuming perfect knowledge about network state-while preserving the basic premise of selfishness. This is achieved by employing a set of QoS agents installed at routers which act on behalf of an user's traffic flow. The QoS agent intercepts packets entering a switch implementing generalized processor sharing (GPS) packet scheduling-and using only constant space packet header overhead and zero per-connection state at the routers-determines which service class to assign the packet to to satisfy the user's end-to-end QoS requirement at minimum cost. We present simulation results which show that our architecture is able to provide stable, stratified services to application traffic with diverse QoS requirements.
1974420
Performance evaluation of multiple time scale TCP under self-similar traffic conditions
Measurements of network traffic have shown that self-similarity is a ubiquitous phenomenon spanning across diverse network environments. In previous work, we have explored the feasibility of exploiting long-range correlation structure in self-similar traffic for congestion control. We have advanced the framework of multiple time scale congestion control and shown its effectiveness at enhancing performance for rate-based feedback control. In this article, we extend the multiple time scale control framework to window-based congestion control, in particular, TCP. This is performed by interfacing TCP with a large time scale module that adjusts the aggressiveness of bandwidth consumpton behavior exhibited by TCP as a function of large time scale network state, that is, information that exceeds the time horizon of the feedback loop as determined by RTT. How to effectively utilize such information—due to its probabilistic nature, dispersion over multiple time scales, and realization on top of existing window-based congestion controls—is a nontrivial problem. First, we define a modular extension of TCP (a function call with a simple interface that applies to various flavors of TCP, e.g., Tahoe, Reno, and Vegas) and show that it significantly improves performance. Second, we show that multiple time scale TCP endows the underlying feedback control with proacativity by bridging the uncertainty gap associated with reactive controls which is exacerbated by the high delay-bandwidth product in broadband wide area networks. Third, we investigate the influence of three traffic control dimensions—tracking ability, connection duration, and fairness—on performance. Performance evaluation of multiple time scale TCP is facilitated by a simulation benchmark environment based on physical modeling of self-similar traffic. We explicate our methodology for disc
6656251
A Comparative Study of Genetic Search
We present a comparative study of genetic algorithms and their search properties when treated as a combinatorial optimization technique. This is done in the context of the NP-hard problem MAX-SAT, the comparison being relative to the Metropolis process, and by extension, simulated annealing. Our contribution is twofold. First, we show that for large and diicult MAX-SAT instances, the contribution of cross-over to the search process is marginal. Little is lost if it is dispensed altogether, running mutation and selection as an enlarged Metropolis process. Second, we show that for these problem instances , genetic search consistently performs worse than simulated annealing when subject to similar resource bounds. The correspondence between the two algorithms is made more precise via a decomposition argument, and provides a framework for interpreting our results.
35766217
Efficient Shaping of User-Specified QoS Using Aggregate-Flow Control
Architecting networks capable of providing scalable, efficient, and fair services to users with diverse QoS requirements is a pressing problem. The two principal issues are: design of "good" per-hop behavior and edge control. In previous work [2,3], we studied aggregate-flow QoS control from a noncooperative resource provisioning context. In [20], the framework was generalized by, one, solving an optimal aggregate-flow per-hop behavior problem, and two, showing how it can be used coupled with end-to-end label control to facilitate scalable and fair QoS when driven by selfish users and service providers. In this paper, we focus on optimal aggregate-flow per-hop control and complement analysis by experimental performance evaluation. We show that user-specified, diverse QoS is efficiently facilitated over the optimal per-hop behavior network substrate using adaptive label control end-to-end.