Emilio Carlos Gomes Wille

Algorithms for IP network design with end-to-end QoS constraints

The new generation of packet-switching networks is expected to support a wide range of communication-intensive real time multimedia applications. A key issue in the area is how to devise reasonable packet-switching network design methodologies that allow the choice of the most adequate set of network resources for the delivery of a given mix of services with the desired level of end-to-end Quality of Service (e2e QoS) and, at the same time, consider the traffic dynam ics of todays packet-switching networks. In this paper, we focus on problems that arise when dealing with this subject namely Buffer Assignment (BA), Capacity Assignment (CA), Flow and Capacity Assignment (FCA), Topology, Flow and Capacity Assignment (TCFA) problems. Our proposed approach maps the end-users performance constraints into transport-layer performance constraints first, and then into network-layer performance constraints. This mapping is then considered together with a refined TCP/IP traffic modeling technique, that is both simple and capable of producing accu rate performance estimates, for general-topology packet-switching design networks subject to realistic traffic patterns. Sub problems are derived from a general design problem and a collection of heuristic algorithms are introduced for compute approximate solutions. We illustrate examples of network planning/dimensioning considering Virtual Private Networks (VPNs).

Topological design of survivable IP networks using metaheuristic approaches

The topological design of distributed packet switched networks consists of finding a topology that minimizes the communication costs by taking into account a certain number of constraints such as the end-to-end quality of service (e2e QoS) and the reliability. Our approach is based on the exploration of the solution space using metaheuristic algorithms (GA and TS), where candidate solutions are evaluated by solving CFA problems. We propose a new CFA algorithm, called GWFD, that is capable of assign flow and capacities under e2e QoS constraints. Our proposed approach maps the end-user performance constrains into transport-layer performance constraints first, and then into network-layer performance constraints. A realistic representation of traffic patterns at the network layer is considered as well to design the IP network. Examples of application of the proposed design methodology show the effectiveness of our approach.

A new approach to the information set decoding algorithm

An efficient suboptimal soft-decision decoding algorithm for block codes, called the modified information set algorithm with real time information set generation, is presented. In this algorithm the information provided by soft decisions are used to generate, in real time, the information sets used in the decoding. Moreover, a new high performance stop rule, called the sum rule, is used to reduce the number of information sets generated. The algorithms performance is also evaluated by computer simulation.

Discrete Capacity Assignment in IP networks using Particle Swarm Optimization

This paper presents a design methodology for IP networks under end-to-end Quality-of-Service (QoS) constraints. Particularly, we consider a more realistic problem formulation in which the link capacities of a general-topology packet network are discrete variables. This Discrete Capacity Assignment (DCA) problem can be classified as a constrained combinatorial optimization problem. A refined TCP/IP traffic modeling technique is also considered in order to estimate performance metrics for networks loaded by realistic traffic patterns. We propose a discrete variable Particle Swarm Optimization (PSO) procedure to find solutions for the problem. A simple approach called Bottleneck Link Heuristic (BLH) is also proposed to obtain admissible solutions in a fast way. The PSO performance, compared to that one of an exhaustive search (ES) procedure, suggests that the PSO algorithm provides a quite efficient approach to obtain (near) optimal solutions with small computational effort.

Considering end-to-end QoS in IP network design

Traditional approaches to optimal design and planning of packet networks focus on the network-layer infrastructure. We propose a new packet network design and planning approach that is based on user-layer QoS parameters. Our proposed approach maps the end-user performance constrains into transport-layer performance constraints first, and then into network-layer performance constraints. The latter are then considered together with a realistic representation of traffic patterns at the network layer to design the IP network. Examples of application of the proposed design methodology to different networking configurations show the effectiveness of our approach.

Performance of routing protocols for VANETs: a realistic analysis format

Vehicular Ad Hoc Network (VANETs) are self-configuring networks where the nodes are vehicles equipped with wireless communication technologies. In such networks, limitation of signal coverage and fast topology changes impose difficulties to the proper functioning of the routing protocols. Most applications critically rely on routing protocols. Thus in this work, we propose a methodology for investigating the performance of well established protocols for MANETs in the VANET arena. Three routing protocols are considered: AODV, DSDV and OLSR. To ensure a meaningful evaluation of the protocols, we devised a realistic simulation environment in terms of network characteristics, communications protocols and traffic patterns. We consider the VanetMobiSim software for a more realistic simulation of vehicular movements in urban environments, as well as the NS-3 package for traffic and communication emulation. Simulation results have led to conclude that the routing protocols analyzed present variable performances in the VANET scenario, with OLSR outperforming the other studied protocols.

Improving VANETs connectivity with a totally ad hoc living mobile backbone

The vehicular ad hoc network (VANET) for intelligent transportation systems is an emerging concept to improve transportation security, reliability, and management. The network behavior can be totally different in topological aspects because of the mobility of vehicular nodes. The topology can be fully connected when the flow of vehicles is high and may have low connectivity or be invalid when the flow of vehicles is low or unbalanced. In big cities, the metropolitan buses that travel on exclusive lanes may be used to set up a metropolitan vehicular data network (backbone), raising the connectivity among the vehicles. Therefore, this paper proposes the implementation of a living mobile backbone, totally ad hoc (MOB-NET), which will provide infrastructure and raise the network connectivity. In order to show the viability of MOB-NET, statistical analyses were made with real data of express buses that travel through exclusive lanes, besides evaluations through simulations and analytic models. The statistic, analytic, and simulation results prove that the buses that travel through exclusive lanes can be used to build a communication network totally ad hoc and provide connectivity in more than 99% of the time, besides raising the delivery rate up to 95%.

Increasing Connectivity in VANETs Using Public Transport Backbones

The Vehicular Ad Hoc Networks (VANETs) can be deployed in several regions of urban environments in different days and times, depending on the flow of vehicles. Because of that, the network behavior concerning topological aspects may vary considerably and the guarantee of connectivity between vehicles is a great challenge. The utilization of a fixed infrastructure can enable the use of VANETs, however, this kind of architecture presents prohibitive costs. In big cities, the metropolitan buses that travel on exclusive lanes may be used to set up a metropolitan vehicular data network (backbone). Therefore, this paper considers the implementation of a live mobile backbone, totally ad hoc (BMVA), which provide infrastructure and increase the network connectivity. In order to demonstrate the viability of the BMVA, statistical analysis were performed based on real data from express buses, which travel on exclusive lanes in the city of Curitiba (PR). Statistical, analytical and simulation results confirm that the buses that travel on exclusive lanes could be used to build a totally ad hoc data network and to provide very good network connectivity. In order to exploit the intrinsic connectivity provided by BMVA a new routing protocol, called P-AODV, is also proposed. The P-AODV aims to give priority to the nodes belonging to BMVA during the route discovery process, thereby improving the network performance.

Considering Packet Loss Probability in Fault-Tolerant OSPF Routing

Interior gateway protocols such as OSPF associate a weight with each network link and then compute shortest paths. The weights optimization is done by solving the Weight Setting Problem (WSP). One drawback of current approaches is that they disregard factors like packet loss probability. Most approaches also ignore network dynamics. When a router or link fails, there is a redistribution of traffic to alternate paths, increasing the network load and thus resulting in congestion. This paper presents a strategy for solving the WSP considering link congestion, packet loss and fault tolerance. Two meta-heuristics (simulated annealing and harmony search) are applied to yield good quality and high performance solutions. Applications under different scenarios show the effectiveness of the proposed approach.

Solving the base station placement problem by means of swarm intelligence

The base station placement problem (BSP) is characterized as the most important issue to solve in planning a wireless network. It corresponds to a constrained combinatorial optimization problem, being classified as NP-hard. This paper presents a binary PSO approach for solving BSP problems in a CDMA indoor environment (with obstructions), aiming at serving a set of users, with a minimum number of base stations. A benchmark of four maps of increasing complexity was created for testing the system. To evaluate the performance of our approach, PSO results are compared with the optimal solutions found by an exhaustive search (ES) procedure. Analytical results for a variety of problem instances suggest that the PSO algorithm presents a good tradeoff between processing times and results.