Juan J. Gálvez

Responsive on-line gateway load-balancing for wireless mesh networks

Abstract We propose an adaptive online load-balancing protocol for multi-gateway Wireless Mesh Networks (WMNs) which, based on the current network conditions, balances load between gateways. Traffic is balanced at the TCP flow level and, as a result, the aggregate throughput, average flow throughput and fairness of flows improves. The proposed scheme (referred to as Gateway Load-Balancing, GWLB) is highly responsive, thanks to fast gateway selection and the fact that current traffic conditions are maintained up-to-date at all times without any overhead. It also effectively takes into account intra-flow and inter-flow interference when switching flows between gateway domains. We have found the performance achievable by routes used after gateway selection to be very close to the performance of optimal routes found by solving a MINLP formulation under the protocol model of interference. Through simulations, we analyze performance and compare with a number of proposed strategies, showing that GWLB outperforms them. In particular, we have observed average flow throughput gains of 128% over the nearest gateway strategy.

Efficient rate allocation, routing and channel assignment in wireless mesh networks supporting dynamic traffic flows

Abstract In this paper we address the issue of joint routing, channel re-assignment and rate allocation in multi-radio multi-channel Wireless Mesh Networks (WMNs) with the goal of optimizing the performance of the current set of flows in the WMN. The objective is to balance the instantaneous traffic in the network at the flow level, optimize link-channel assignment and allocate flow rates to achieve proportional fairness given the current traffic and network constraints, including the topology, interference characteristics, number of available channels and radios. Unlike prior work, we do not assume a priori knowledge of traffic, and instead take into account the instantaneous traffic conditions to optimize performance at the flow level, taking both throughput and fairness into account. In this work we analyze the problem and, due to its hardness, propose a fast heuristic algorithm (JRCAR) to solve it. We evaluate this algorithm through numerical experiments, including comparisons against optimal solutions. In addition, we show that JRCAR can be used in a highly responsive system in practical scenarios with time-varying traffic conditions. We implement such a system under the ns-3 simulator, where the simulation results obtained corroborate the behavior observed in the numerical experiments and show that JRCAR is effective in dynamic and practical conditions.

A distributed algorithm for gateway load-balancing in Wireless Mesh Networks

Wireless Mesh Networks (WMNs) provide a cost-effective way of deploying a network and providing broadband Internet access. In WMNs a subset of nodes called gateways provide connectivity to the wired infrastructure (typically the Internet). Because traffic volume of WMNs is expected to be high, and due to limited wireless link capacity, gateways are likely to become a potential bottleneck. In this paper, we propose a distributed load-balancing protocol where gateways coordinate to reroute flows from congested gateways to under-utilized gateways. Unlike other approaches, our scheme takes into account the effects of interference. This makes it suitable for implementation in practical scenarios, achieving good results, and improving on shortest path routing. Also, it is load-sensitive and can improve network utilization in both balanced and skewed topologies. Simulation results prove the effectiveness of our approach, which outperforms all schemes tested. We have observed throughput gains of up to 80% over the shortest path algorithm.

Multipath routing with spatial separation in wireless multi-hop networks without location information

We develop an on-demand multipath routing protocol for multi-hop wireless networks (MWNs), capable of finding spatially disjoint paths (paths physically distant from each other) without the need of location information. Multipath routing can enable various applications and enhancements in MWNs, such as load balancing, bandwidth aggregation, reliability and secure communications. The use of spatially disjoint routes is important to effectively achieve these gains, due to the non-interfering nature and distance of the paths. Most of the proposed multipath protocols for MWNs focus on reliability and do not find spatially separate paths. We propose a new on-demand protocol called Spatially Disjoint Multipath Routing (SDMR), capable of finding multiple paths in one route discovery, measuring the distance between them and choosing paths with most separation. A new distance metric is presented to measure path separation, which proves to be congruent with Euclidean distance across nodes in the paths. We develop a heuristic algorithm which, given a topology graph and utilizing the proposed distance metric, can discover spatially disjoint paths between any two nodes in the graph. To evaluate the protocol, we have studied the overhead both analytically in comparison with OLSR, and by simulation. The simulations also demonstrate the effectiveness of the protocol in finding spatially separate routes.

Design and Performance Evaluation of Multipath Extensions for the DYMO Protocol

Medium sized storage area networks using fibre channel have been a common implementation for data storage in enterprise data centers. The ever increasing demand for large storage pools has paved to the idea of implementing large distributed storage area networks also known as large fabrics. The large fabrics seem to experience fabric scaling and fabric stability issues. These scaling and stability issues are related to the performance of various fabric servers of fabric services, such as fabric controller, fabric login, directory, etc., which are part of the fibre channel-2 level of the fibre channel protocol. To determine the extent of scaling and stability issues of a large fabric an adequate tool is required. The tool could be an analytical model, a hardware simulator, or a discrete event software simulator. The discrete event software simulator provides a number of benefits over the analytical model and hardware simulator. In this paper, the modeling of a fibre channel switch using the OMNeT++ discrete event simulator and simulation of large fabric are presented. As a first step, only the fibre channel-2 level of the fibre channel switch is modeled since it is the layer containing various fabric services dealing with fabric building and managing. In this paper, the process of building a fabric and managing and how it is implemented in the simulator are discussed. Also, a preliminary analysis of the results in comparison to the test bed traffic is presented showing the accuracy and representation of an actual large fabric by the simulator.In this paper we propose a multipath extension to dynamic MANET on-demand (DYMO) routing protocol. Multipath protocols have been shown to benefit on-demand routing in MANETs, where the knowledge of alternate paths allows to reduce the frequency of route discovery in the presence of link failures. Route discovery is an operation which accounts for most of the overhead of these protocols. This is specially helpful in scenarios with node mobility where link failures are frequent. Our extension is based on AOMDV. It can discover multiple disjoint paths in one route discovery with minimal additional overhead over DYMO. We analyze the performance gains of using alternate path information with DYMO. Simulation results show that multipath routing greatly benefits DYMO in reducing overhead and therefore increasing performance.

Spatially Disjoint Multipath Routing protocol without location information

Multipath routing permits the discovery and use of multiple paths between a source and a destination. We develop a distributed on-demand multipath routing protocol for MANETs capable of finding spatially disjoint paths without location information. The use of spatially disjoint routes in multipath routing is important due to the non-interfering nature of the paths. This enables applications such as load-balancing, bandwidth aggregation, secure communications and multimedia transmission. Most of the proposed multipath protocols for MANETs focus on reliability and are not adequate for these types of applications because of route coupling between alternate paths. We propose Spatially Disjoint Multipath Routing (SDMR) protocol, capable of finding multiple paths in one route discovery, measuring the distance between them and choosing paths with most separation. SDMR is evaluated through simulation.

A feedback-based adaptive online algorithm for Multi-Gateway load-balancing in wireless mesh networks

We propose an adaptive online load-balancing protocol for Multi-Gateway Wireless Mesh Networks (WMNs) which, based on the current network conditions, balances load between gateways. Our protocol (GWLB) achieves two goals: (i) alleviating congestion in affected domains and (ii) balancing load to improve flow fairness across domains. As a result of applying GWLB the throughput and fairness of flows improves. The proposed scheme effectively takes into account the elastic nature of TCP traffic, and intra-flow and inter-flow interference when switching flows between domains. Through simulations, we analyze performance and compare with a number of proposed strategies, showing that GWLB outperforms them. In particular, we have observed average flow throughput gains of 104% over the nearest gateway strategy.

Mathematical modelling and computational study of two-dimensional and three-dimensional dynamics of receptor–ligand interactions in signalling response mechanisms

Cell signalling processes involve receptor trafficking through highly connected networks of interacting components. The binding of surface receptors to their specific ligands is a key factor for the control and triggering of signalling pathways. But the binding process still presents many enigmas and, by analogy with surface catalytic reactions, two different mechanisms can be conceived: the first mechanism is related to the Eley–Rideal (ER) mechanism, i.e. the bulk-dissolved ligand interacts directly by pure three-dimensional (3D) diffusion with the specific surface receptor; the second mechanism is similar to the Langmuir–Hinshelwood (LH) process, i.e. 3D diffusion of the ligand to the cell surface followed by reversible ligand adsorption and subsequent two-dimensional (2D) surface diffusion to the receptor. A situation where both mechanisms simultaneously contribute to the signalling process could also occur. The aim of this paper is to perform a computational study of the behavior of the signalling response when these different mechanisms for ligand-receptor interactions are integrated into a model for signal transduction and ligand transport. To this end, partial differential equations have been used to develop spatio-temporal models that show trafficking dynamics of ligands, cell surface components, and intracellular signalling molecules through the different domains of the system. The mathematical modeling developed for these mechanisms has been applied to the study of two situations frequently found in cell systems: (a) dependence of the signal response on cell density; and (b) enhancement of the signalling response in a synaptic environment.

TCP Flow-Aware Channel Re-Assignment in Multi-Radio Multi-Channel Wireless Mesh Networks

We consider the traffic-aware channel assignment problem in a multi-radio Wireless Mesh Network that involves assigning channels to radio interfaces to optimize the performance of a set of TCP flows (flow throughput and fairness). The resulting optimization problem is NP-hard. At the TCP flow level, rapid traffic fluctuations are expected, imposing the need for frequent channel re-assignment to adapt to current traffic conditions. We develop a centralized greedy channel assignment algorithm suited for this task that can support frequent channel re-assignment by two properties: (i) low computational complexity, permitting it to quickly calculate a solution, and (ii) by taking into account the previous channel assignment to generate a new one with minimum variation. Focusing on the gateway access scenario, we observe an important benefit to optimizing the performance of TCP flows with the proposed algorithm.

Achieving Spatial Disjointness in Multipath Routing without Location Information

We develop an on-demand multipath routing protocol for multi-hop wireless networks (MWNs), capable of finding spatially disjoint paths without the need of location information. Multipath routing can enable various applications and enhancements in MWNs, such as load balancing, bandwidth aggregation, reliability and secure communications. The use of spatially disjoint routes is important to effectively achieve these gains, due to the non-interfering nature of the paths. Most of the proposed multipath protocols for MWNs focus on reliability and do not find spatially disjoint paths. We propose a new on-demand protocol called Spatially Disjoint Multipath Routing (SDMR), capable of finding multiple paths in one route discovery, measuring the distance between them and choosing paths with most separation. Simulations demonstrate the effectiveness of the protocol in finding spatially separate routes.