1,721,132 research outputs found
A Multi-Commodity Flow Model for Optimal Routing in Wireless MESH Networks
No full textWe propose a mathematical programming model
of the routing problem in multi-hop wireless networks that takes into account quality of service requirements considering bandwidth constraints. The proposed approach is suitable for Wireless MESH Networks (WMN) where topology is almost fixed and routes can be optimized based on global objectives. We then consider and solve the scheduling problem, illustrating how routing and scheduling models can be combined to route flows with guaranteed bandwidth. As an interesting application of the proposed approach, we present some numerical examples that show how our model can be used to estimate the impact of transmission range on network capacity
Multi-channel power-controlled directional MAC for wireless mesh networks
No full textWireless Mesh Networks (WMNs) have emerged recently as a technology for providing high-speed last mile connectivity in next-generation wireless networks. Several MAC protocols that exploit multiple channels and directional antennas have been proposed in the literature to increase the performance of WMNs. However, while these techniques can improve the wireless medium utilization by reducing radio interference and the impact of the exposed nodes problem, they can also exacerbate the hidden nodes problem. Therefore, efficient MAC protocols need to be carefully designed to fully exploit the features offered by multiple channels and directional antennas. In this paper we propose a novel Multi-Channel Power-Controlled Directional MAC protocol (MPCD-MAC) for nodes equipped with multiple network interfaces and directional antennas. MPCD-MAC uses the standard RTS-CTS-DATA-ACK exchange procedure. The novel difference is the transmission of the RTS and CTS packets in all directions on a separate control channel, while the DATA and ACK packets are transmitted only directionally on an available data channel at the minimum required power, taking into account the interference generated on already active connections. This solution spreads the information on wireless medium reservation (RTS/CTS) to the largest set of neighbors, while data transfers take place directionally on separate channels to increase spatial reuse. Furthermore, power control is used to limit the interference produced over active nodes. We measure the performance of MPCD-MAC by simulation of several realistic network scenarios, and we compare it with other approaches proposed in the literature. The results show that our scheme increases considerably both the total traffic accepted by the network and the fairness among competing connections
Cost-Aware Caching: Caching More (Costly Items) for Less (ISPs Operational Expenditures)
Full text linkAlbeit an important goal of caching is traffic reduction, a perhaps even more important aspect follows from the above achievement: the reduction of internet service provider (ISP) operational costs that comes as a consequence of the reduced load on transit and provider links. Surprisingly, to date this crucial aspect has not been properly taken into account in cache design. In this paper, we show that the classic caching efficiency indicator, i.e., the hit ratio, conflicts with cost. We therefore propose a mechanism whose goal is the reduction of cost and, in particular, we design a cost-aware (CoA) cache decision policy that, leveraging price heterogeneity among external links, tends to store with more probability the objects that the ISP has to retrieve through the most expensive links. We provide a model of our mechanism, based on Che's approximation, and, by means of a thorough simulation campaign, we contrast it with traditional cost-blind schemes, showing that CoA yields a significant cost saving, that is furthermore consistent over a wide range of scenarios. We show that CoA is easy to implement and robust, making the proposal of practical relevance
Joint pricing and cognitive radio network selection: A game theoretical approach
No full textThis paper addresses the joint pricing and network selection problem in cognitive radio networks, considering both the point of view of network users and the Primary Operator. The problem is formulated as a Stackelberg (leader-follower) game where first the PO sets the network subscription price to maximize its revenue. Then, users perform the network selection process, deciding whether to pay for having a guaranteed service, or use a cheaper, best-effort secondary network, where congestion and low throughput may be experienced. Such process is modeled as a population game to study the strategic interactions among a large number of agents. For our pricing and network selection game, we provide equilibrium and convergence properties, and derive optimal stable price and network selection settings. Numerical results illustrate that our game model captures the main factors behind cognitive network pricing and channel selection, thus representing a promising framework for the design and understanding of cognitive radio systems
Dynamic Online QoS Routing Schemes: Performance and Bounds
No full textSeveral dynamic QoS routing techniques have been recently proposed for new IP networks based on label forwarding. However, no extensive performance evaluation and comparison is available in the literature.
In this paper, after a short review of the major dynamic QoS routing schemes, we analyze and compare their performance referring to several networks scenarios. In order to set an absolute evaluation of the performance quality we have obtained the ideal performance of any routing scheme using a novel and flexible mathematical programming model that assumes the knowledge of arrival times and duration of the connections offered to the network. This model is based on an extension of the maximum multi-commodity flow problem. Being an integer linear programming model, its complexity is quite high and its evaluation is constrained to networks of limited size. To overcome the computational complexity we have defined an approximate model, based on the multi-class Erlang formula and the minimum multi-commodity cut problem, that provides an upper bound to the routing scheme performance. The performance presented in the paper, evaluated by measuring the connection rejection probability, shows that the schemes considered reach, in several scenarios, the ideal performance, showing that no much gain is left for alternate new schemes
Joint Routing and Scheduling Optimization in Wireless Mesh Networks with Directional Antennas
No full textMetodo di allocazione di banda, di tipo distribuito, in una rete passiva con un accesso multiplo CSMA/CD
No full textL'invenzione si riferisce ad un metodo di allocazione dinamica di banda, di tipo distribuito, in una rete passiva EPON (Ethernet Passive Optical Network) con un accesso multiplo CSMA/CD (Carrier Sense Multiple Access with Collision Detection). Una rete EPON è una rete in fibra ottica punto-multipunto con nessun elemento attivo nel percorso di trasmissione dalla sorgente alla destinazione. L’architettura più diffusa è basata su una topologia ad albero e prevede l’esistenza di un Optical Line Terminal (OLT), di un hub passivo (HUB) e di varie Optical Network Units (ONU). Nelle reti EPON, in direzione upstream, ossia dalle ONU all’OLT, le ONU condividono la capacità di canale, e possono dunque contendersi l’uso delle risorse disponibili. L’utilizzo di meccanismi di allocazione di banda risulta assolutamente necessario, in quanto in caso contrario risulta impossibile controllare la porzione di banda allocata ad ogni ONU, rendendo di conseguenza impossibile supportare criteri di qualità di servizio. Il metodo brevettato è basato su due algoritmi dinamici di distribuzione della banda, il primo dei quali distribuisce la capacità della rete fra i nodi attivi nel time slot precedente proporzionalmente al peso loro assegnato, mentre il secondo distribuisce la capacità della rete fra i nodi attivi, tenendo conto della quantità di traffico trasmessa dalle sorgenti attive nel time slot precedente
Representation Selection Problem: Optimizing Video Delivery through Caching
No full textTo cope with Internet video explosion, recent work proposes to deploy caches to absorb part of the traffic related to popular videos. Nonetheless, caching literature has mainly focused on network-centric metrics, while the quality of users' video streaming experience should be the key performance index to optimize. Additionally, the general assumption is that each user request can be satisfied by a single object, which does not hold when multiple representations at different quality levels are available for the same video.Our contribution in this paper is to extend the classic object placement problem (which object to cache and where) by further considering the representation selection problem (i.e., which quality representation to cache), employing two methodologies to tackle this challenge. First, we employ a Mixed Integer Linear Programming (MILP) formulation to obtain the centralized optimal solution, as well as bounds to natural policies that are readily obtained as additional constraints of the MILP. Second, from the structure of the optimal solution, we learn guidelines that assist the design of distributed caching strategies: namely, we devise a simple yet effective distributed strategy that incrementally improves the quality of cached objects. Via simulation over large scale scenarios comprising up to hundred nodes and hundred million objects, we show our proposal to be effective in balancing user perceived utility vs bandwidth usage
Directional MAC and Routing Schemes for Power Controlled Wireless Mesh Networks with Adaptive Antennas
No full textBandwidth estimation schemes for TCP over wireless networks
No full textThe use of enhanced bandwidth estimation procedures within the congestion control scheme of TCP was proposed recently as a way of improving TCP performance over links affected by random loss. This paper first analyzes the problems faced by every bandwidth estimation algorithm implemented at the sender side of a TCP connection. Some proposed estimation algorithms are then reviewed, analyzing and comparing their estimation accuracy and performance. As existing algorithms are poor in bandwidth estimation, and in sharing network resources fairly, we propose TIBET (time intervals based bandwidth estimation technique). This is a new bandwidth estimation scheme that can be implemented within the TCP congestion control procedure, modifying only the sender-side of a connection. The use of TIBET enhances TCP source performance over wireless links. The performance of TIBET is analyzed and compared with other schemes. Moreover, by studying TCP behavior with an ideal bandwidth estimation, we provide an upper bound to the performance of all possible schemes based on different bandwidth estimates
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