Josué Kuri

A Pattern Matching Based Filter for Audit Reduction and Fast Detection of Potential Intrusions

We present a pattern matching approach to the problem of misuse detection in a computer system, which is formalized as the problem of multiple approximate pattern matching. This permits very fast searching of potential attacks. We study the probability of matching of the model and its relation to the filtering efficiency of potential attacks within large audit trails. Experimental results show that in a worst case, up to 85 % of an audit trail may be filtered out when searching a set of attacks without probability of false negatives. Moreover, by filtering 98 % of the audit trail, up to 50 % of the attacks may be detected.

Models for the Logical Topology Design Problem

We address the logical topology design problem (LTD) in WDM transport networks under static traffic assumptions. We start with one of the standard MILP formulations of the LTD problem that aims at optimizing the network congestion. We propose an improvement to this model that additionally optimizes the average hop count. We then derive a new MILP model that compels the traffic to be atomically routed. This last model enables fair comparisons of solutions obtained with MILP formulations and with metaheuristic algorithms. The latter allow us to deal with large size networks whereas the former are limited by their computational complexity. In this paper Tabu Search is used to tackle the LTD problem. We compare and discuss the logical topologies computed by the various methods described in the paper.

Routing and grooming of scheduled lightpath demands in a multi-granularity switching network: a mathematical model

Technological improvements allow advanced optical cross-connect architectures to be developed. Multi-granularity switching optical cross-connects (MG-OXCs) are equipments able to switch wavelengths, to aggregate (disaggregate) wavelengths into (from) groups of wavelengths called wavebands and to switch wavebands. In previous studies, we described a new traffic model based on Scheduled Lightpath Demands (SLDs) that make it possible to take into account the time and space distribution of traffic in the planning of all-optical WDM mesh networks. We proposed a mathematical model to optimize the routing of a set of SLDs in a WDM with standard wavelength-switching optical Cross-Connects (WXCs). In order to compare the cost of provisioning a set of SLDs in a network of WXCs against the cost of instantiating the same set in a network of MG-OXCs, it is necessary to extend the model used for the standard case. In this paper, we present a generalization of the model that permits to solve the problem of optimally instantiating SLDs in a network equipped with MG-OXCs.

Topological Design and Lightpath Routing in WDM Mesh Networks: A Combined Approach

Multicommodity flow models are commonly used to formulate the logical topology design (LTD) problem and the lightpath routing (LR) problem as mixed integer linear programming (MILP) problems. In general, MILP formulations are intractable even for relatively small networks due to the combinatorial complexity of the problem. In this paper we propose improvements to these models and a method to solve the LTD and the LR problems in a combined manner. The interest is two fold: firstly, by tackling the two problems with separate models, problem instances of realistic size (up to 14 nodes in this paper) can be dealt with. Furthermore, different combinations of optimization models and objective functions can be investigated in a modular manner. Secondly, the mechanisms proposed to combine the problems allow to keep track of the global design problem when solving each individual step.

Fast multipattern search algorithms for intrusion detection

Presents new search algorithms to detect the occurrences of any pattern from a given pattern set in a text, allowing in the occurrences a limited number of spurious text characters among those of the pattern. This is a common requirement in intrusion detection applications. Our algorithms exploit the ability to represent the search state of one or more patterns in the bits of a single machine word and to update all the search states in a single operation. We show analytically and experimentally that the algorithms are able of rapidly searching large sets of patterns, allowing a large number of spurious characters, yielding about a 75-fold improvement over the classical algorithm.

ATM traffic management in an LMDS wireless access network

We investigate the capacity of LMDS to support ATM services in the local loop. In particular, we evaluate the performance of a MAC protocol for this system when transporting voice and IP traffic using the VBR and GFR service categories of ATM, respectively. Our results show that the MAC protocol is well suited for voice traffic but in general lacks efficient bandwidth management mechanisms to support the more dynamic bandwidth requirements of IP traffic.

A MAC Protocol for IP Differentiated Services in a WDM Metropolitan Area Network

This paper presents a Media Access Control (MAC) protocol for a WDM passive optical star. The protocol supports scalable service differentiation for Internet traffic in the spirit of the IETFs Diffserv architecture. We describe the functional elements of the protocol (signaling, arbitration, service disciplines and buffer management techniques) and the way they interact to support the Diffservs Expedited Forwarding (EF) PHB and Assured Forwarding (AF) PHB group, where PHB stands for Per-Hop-Behavior. Extensive simulation results give quantitative estimations of the performance of the protocol under combined EF/AF traffic.

IP Differentiated Services over a WDM Passive Optical Star

Important recent advances in the field of opto-electronic devices make WDM optical networks a promising solution for the next generation Internet. Such technologies can be considered in the long-haul, metro and access sections of carrier’s infrastructures. The main issue in this paper is the design of a Metropolitan Area Network based on a WDM passive optical star well suited for IP differentiated services. Our proposal focuses on both the MAC protocol and buffer management at the end nodes. Various simulation results outline the capacity of our proposal to satisfy the IP Diffsery [1] QoS requirements, as they are specified by the IETF. For that purpose, both Expedited Forwarding [3] and Assured Forwarding [4] are investigated.

Grooming of Scheduled Demands in Multi-Layer Optical Networks

Introducing multiple switching granularities in transport networks aims in part at reducing their cost by taking advantage of traffic aggregation. As a matter of fact, an appropriate aggregation of low-rate connections into highrate connections and the use for the latter of a switching technology whose cost-per-bit is lower than for the former can result in lower infrastructure costs. The economic gain, when compared to single switching granularity networks, depends on both traffic-related factors such as the time/space distribution of connections and equipment or network architecture factors such as the cost of ports and matrices for each switching granularity, the topology of the network, the provisioning algorithms used for routing and grooming of connections, etc. In other chapters of this book, traffic grooming has been investigated in contexts such as protection/restoration, multicast, and multi-domain networks. In this chapter, we consider the problem of efficiently grooming (a) electrical “subwavelength” demands into lightpaths, and (b) lightpaths into wavebands. Whereas most investigations deal with either permanent or random traffic demands, we focus in this chapter on a particular class of traffic demands referred to as scheduled demands, or SxDs, introduced in [1, 2]. A scheduled traffic demand corresponds to a connection or set of connections for which the network operator knows in advance the set-up and tear-down dates. These connections could be requested, for example, by a company to connect its headquarters to its production centers during office hours, or to interconnect its data centers during the night, when database backups are performed. Since companies tend to have well-established operations and procedures, they can provide relatively accurate information to the network operator

Tabu search algorithm to solve a logical topology design problem in WDM networks considering implementation cost

We propose a Tabu Search (TS) algorithm to solve the problem of designing a logical topology for packet-switched traffic over a WDM mesh network. The cost of mapping such a logical topology over a physical network is taken into account. The algorithm provides approximate solutions of good quality (i.e., close to the optimal ones) to the corresponding optimization problem and allows us to solve problem instances of large size, which is usually impossible with algorithms solving exactly the Integer Linear Programming (ILP) formulations of the problem. The algorithm makes it possible to evaluate the cost-performance tradeoff between designing a logical topology with small congestion and a large number of (possibly expensive) lightpaths and designing a less expensive topology with higher congestion.