On Cross-Layer Routing in Wireless Multi-Hop Networks

International audienc

Aspects of proactive traffic engineering in IP networks

To deliver a reliable communication service over the Internet it is essential for the network operator to manage the traffic situation in the network. The traffic situation is controlled by the routing function which determines what path traffic follows from source to destination. Current practices for setting routing parameters in IP networks are designed to be simple to manage. This can lead to congestion in parts of the network while other parts of the network are far from fully utilized. In this thesis we explore issues related to optimization of the routing function to balance load in the network and efficiently deliver a reliable communication service to the users. The optimization takes into account not only the traffic situation under normal operational conditions, but also traffic situations that appear under a wide variety of circumstances deviating from the nominal case. In order to balance load in the network knowledge of the traffic situations is needed. Consequently, in this thesis we investigate methods for efficient derivation of the traffic situation. The derivation is based on estimation of traffic demands from link load measurements. The advantage of using link load measurements is that they are easily obtained and consist of a limited amount of data that need to be processed. We evaluate and demonstrate how estimation based on link counts gives the operator a fast and accurate description of the traffic demands. For the evaluation we have access to a unique data set of complete traffic demands from an operational IP backbone. However, to honor service level agreements at all times the variability of the traffic needs to be accounted for in the load balancing. In addition, optimization techniques are often sensitive to errors and variations in input data. Hence, when an optimized routing setting is subjected to real traffic demands in the network, performance often deviate from what can be anticipated from the optimization. Thus, we identify and model different traffic uncertainties and describe how the routing setting can be optimized, not only for a nominal case, but for a wide range of different traffic situations that might appear in the network. Our results can be applied in MPLS enabled networks as well as in networks using link state routing protocols such as the widely used OSPF and IS-IS protocols. Only minor changes may be needed in current networks to implement our algorithms. The contributions of this thesis is that we: demonstrate that it is possible to estimate the traffic matrix with acceptable precision, and we develop methods and models for common traffic uncertainties to account for these uncertainties in the optimization of the routing configuration. In addition, we identify important properties in the structure of the traffic to successfully balance uncertain and varying traffic demands

Combinatorics-based energy conservation methods in wireless sensor networks

Ph.DDOCTOR OF PHILOSOPH

An Autonomous Channel Selection Algorithm for WLANs

IEEE 802.11 wireless devices need to select a channel in order to transmit their packets. However, as a result of the contention-based nature of the IEEE 802.11 CSMA/CA MAC mechanism, the capacity experienced by a station is not fixed. When a station cannot win a sufficient number of transmission opportunities to satisfy its traffic load, it will become saturated. If the saturation condition persists, more and more packets are stored in the transmit queue and congestion occurs. Congestion leads to high packet delay and may ultimately result in catastrophic packet loss when the transmit queue’s capacity is exceeded. In this thesis, we propose an autonomous channel selection algorithm with neighbour forcing (NF) to minimize the incidence of congestion on all stations using the channels. All stations reassign the channels based on the local monitoring information. This station will change the channel once it finds a channel that has sufficient available bandwidth to satisfy its traffic load requirement or it will force its neighbour stations into saturation by reducing its PHY transmission rate if there exists at least one successful channel assignment according to a predicting module which checks all the possible channel assignments. The results from a simple C++ simulator show that the NF algorithm has a higher probability than the dynamic channel assignment without neighbour forcing (NONF) to successfully reassign the channel once stations have become congested. In an experimental testbed, the Madwifi open source wireless driver has been modified to incorporate the channel selection mechanism. The results demonstrate that the NF algorithm also has a better performance than the NONF algorithm in reducing the congestion time of the network where at least one station has become congested

JTP, an energy-aware transport protocol for mobile ad hoc networks (PhD thesis)

Wireless ad-hoc networks are based on a cooperative communication model, where all nodes not only generate traffic but also help to route traffic from other nodes to its final destination. In such an environment where there is no infrastructure support the lifetime of the network is tightly coupled with the lifetime of individual nodes. Most of the devices that form such networks are battery-operated, and thus it becomes important to conserve energy so as to maximize the lifetime of a node. In this thesis, we present JTP, a new energy-aware transport protocol, whose goal is to reduce power consumption without compromising delivery requirements of applications. JTP has been implemented within the JAVeLEN system. JAVeLEN [RKM+08], is a new system architecture for ad hoc networks that has been developed to elevate energy efficiency as a first-class optimization metric at all protocol layers, from physical to transport. Thus, energy gains obtained in one layer would not be offset by incompatibilities and/or inefficiencies in other layers. To meet its goal of energy efficiency, JTP (1) contains mechanisms to balance end-toend vs. local retransmissions; (2) minimizes acknowledgment traffic using receiver regulated rate-based flow control combined with selected acknowledgments and in-network caching of packets; and (3) aggressively seeks to avoid any congestion-based packet loss. Within this ultra low-power multi-hop wireless network system, simulations and experimental results demonstrate that our transport protocol meets its goal of preserving the energy efficiency of the underlying network. JTP has been implemented on the actual JAVeLEN nodes and its benefits have been demonstrated on a real system

Contributions to the routing of traffic flows in multi-hop IEEE 802.11 wireless networks

The IEEE 802.11 standard was not initially designed to provide multi-hop capabilities. Therefore, providing a proper traffic performance in Multi-Hop IEEE 802.11 Wireless Networks (MIWNs) becomes a significant challenge. The approach followed in this thesis has been focused on the routing layer in order to obtain applicable solutions not dependent on a specific hardware or driver. Nevertheless, as is the case of most of the research on this field, a cross-layer design has been adopted. Therefore, one of the first tasks of this work was devoted to the study of the phenomena which affect the performance of the flows in MIWNs. Different estimation methodologies and models are presented and analyzed. The first main contribution of this thesis is related to route creation procedures. First, FB-AODV is introduced, which creates routes and forwards packets according to the flows on the contrary to basic AODV which is destination-based. This enhancement permits to balance the load through the network and gives a finer granularity in the control and monitoring of the flows. Results showed that it clearly benefits the performance of the flows. Secondly, a novel routing metric called Weighted Contention and Interference routing Metric (WCIM) is presented. In all analyzed scenarios, WCIM outperformed the other analyzed state-of-the-art routing metrics due to a proper leveraging of the number of hops, the link quality and the suffered contention and interference. The second main contribution of this thesis is focused on route maintenance. Generally, route recovery procedures are devoted to the detection of link breaks due to mobility or fading. However, other phenomena like the arrival of new flows can degrade the performance of active flows. DEMON, which is designed as an enhancement of FB-AODV, allows the preemptive recovery of degraded routes by passively monitoring the performance of active flows. Results showed that DEMON obtains similar or better results than other published solutions in mobile scenarios, while it clearly outperforms the performance of default AODV under congestion Finally, the last chapter of this thesis deals with channel assignment in multi-radio solutions. The main challenge of this research area relies on the circular relationship between channel assignment and routing; channel assignment determines the routes that can be created, while the created routes decide the real channel diversity of the network and the level of interference between the links. Therefore, proposals which join routing and channel assignment are generally complex, centralized and based on traffic patterns, limiting their practical implementation. On the contrary, the mechanisms presented in this thesis are distributed and readily applicable. First, the Interference-based Dynamic Channel Assignment (IDCA) algorithm is introduced. IDCA is a distributed and dynamic channel assignment based on the interference caused by active flows which uses a common channel in order to assure connectivity. In general, IDCA leads to an interesting trade-off between connectivity preservation and channel diversity. Secondly, MR-DEMON is introduced as way of joining channel assignment and route maintenance. As DEMON, MR-DEMON monitors the performance of the active flows traversing the links, but, instead of alerting the source when noticing degradation, it permits reallocating the flows to less interfered channels. Joining route recovery instead of route creation simplifies its application, since traffic patterns are not needed and channel reassignments can be locally decided. The evaluation of MR-DEMON proved that it clearly benefits the performance of IDCA. Also, it improves DEMON functionality by decreasing the number of route recoveries from the source, leading to a lower overhead.El estándar IEEE 802.11 no fue diseñado inicialmente para soportar capacidades multi-salto. Debido a ello, proveer unas prestaciones adecuadas a los flujos de tráfico que atraviesan redes inalámbricas multi-salto IEEE 802.11 supone un reto significativo. La investigación desarrollada en esta tesis se ha centrado en la capa de encaminamiento con el objetivo de obtener soluciones aplicables y no dependientes de un hardware específico. Sin embargo, debido al gran impacto de fenómenos y parámetros relacionados con las capas físicas y de acceso al medio sobre las prestaciones de los tráficos de datos, se han adoptado soluciones de tipo cross-layer. Es por ello que las primeras tareas de la investigación, presentadas en los capítulos iniciales, se dedicaron al estudio y caracterización de estos fenómenos. La primera contribución principal de esta tesis se centra en mecanismos relacionados con la creación de las rutas. Primero, se introduce una mejora del protocolo AODV, que permite crear rutas y encaminar paquetes en base a los flujos de datos, en lugar de en base a los destinos como se da en el caso básico. Esto permite balacear la carga de la red y otorga un mayor control sobre los flujos activos y sus prestaciones, mejorando el rendimiento general de la red. Seguidamente, se presenta una métrica de encaminamiento sensible a la interferencia de la red y la calidad de los enlaces. Los resultados analizados, basados en la simulación de diferentes escenarios, demuestran que mejora significativamente las prestaciones de otras métricas del estado del arte. La segunda contribución está relacionada con el mantenimiento de las rutas activas. Generalmente, los mecanismos de mantenimiento se centran principalmente en la detección de enlaces rotos debido a la movilidad de los nodos o a la propagación inalámbrica. Sin embargo, otros fenómenos como la interferencia y congestión provocada por la llegada de nuevos flujos pueden degradar de forma significativa las prestaciones de los tráficos activos. En base a ello, se diseña un mecanismo de mantenimiento preventivo de rutas, que monitoriza las prestaciones de los flujos activos y permite su reencaminamiento en caso de detectar rutas degradadas. La evaluación de esta solución muestra una mejora significativa sobre el mantenimiento de rutas básico en escenarios congestionados, mientras que en escenarios con nodos móviles obtiene resultados similares o puntualmente mejores que otros mecanismos preventivos diseñados específicamente para casos con movilidad. Finalmente, el último capítulo de la tesis se centra en la asignación de canales en entornos multi-canal y multi-radio con el objetivo de minimizar la interferencia entre flujos activos. El reto principal en este campo es la dependencia circular que se da entre la asignación de canales y la creación de rutas: la asignación de canales determina los enlaces existentes la red y por ello las rutas que se podrán crear, pero son finalmente las rutas y los tráficos activos quienes determinan el nivel real de interferencia que se dará en la red. Es por ello que las soluciones que proponen unificar la asignación de canales y el encaminamiento de tráficos son generalmente complejas, centralizadas y basadas en patrones de tráfico, lo que limita su implementación en entornos reales. En cambio, en nuestro caso adoptamos una solución distribuida y con mayor aplicabilidad. Primero, se define un algoritmo de selección de canales dinámico basado en la interferencia de los flujos activos, que utiliza un canal común en todos los nodos para asegurar la conectividad de la red. A continuación, se introduce un mecanismo que unifica la asignación de canales con el mantenimiento preventivo de las rutas, permitiendo reasignar flujos degradados a otros canales disponibles en lugar de reencaminarlos completamente. Ambas soluciones demuestran ser beneficiosas en este tipo de entornos.Postprint (published version

Survivable virtual topology design in optical WDM networks using nature-inspired algorithms

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Bilişim Enstitüsü, 2012Thesis (PhD) -- İstanbul Technical University, Institute of Informatics, 2012Günümüzde bilgisayar ağları hayatımızın önemli bir parçası ve ihtiyaç haline gelmiştir. İstediğimiz veriye, istediğimiz anda, daha hızlı, daha güvenli ve kesintisiz olarak erişme isteğimiz aslında ağ altyapısının nasıl tasarlanacağını belirlemektedir. Kullanıcıların istekleri sürekli artarken, teknolojik gelişmelerle birlikte yeni yöntem ve algoritmalarla bu istekleri karşılamanın yolları aranmaktadır. Ağdaki aktarım hızı, aktarım ortamından doğrudan etkilenmektedir; bugün uzak mesafelere en yüksek kapasiteli ve hızlı aktarımın yapılabileceği ortam ise fiberdir. Fiber optik ağlar, fiberin üstün özelliklerini (hız, düşük bit hata oranı, elektromanyetik ortamlardan etkilenmeme, düşük işaret zayıflaması, fiziksel dayanıklılık, ucuzluk, güvenlilik, vs.) en iyi kullanacak şekilde tasarlanan ağlardır. Günümüzde dünyadaki iletişim ağ altyapısı, omurga ağlardan erişim ağlarına kadar, hızla fiber optik ağlara dönüşmektedir. Optik ağların en önemli özelliklerinden biri veri aktarım hızıdır, tek bir fiberden teorik olarak 50 Tb/s veri aktarımı yapılabileceği hesaplanmaktadır. Bugün, lider iletişim firmaları 100 Gb/s ya da 1 Tb/s hızda veri aktarımı yapacak kanalllardan bahsedebiliyorsa, bu, fiziksel altyapı optik bir omurgadan oluştuğu içindir. Dalgaboyu bölmeli çoğullama (WDM) teknolojisi sayesinde bir fiber üzerinde aynı anda kurulabilecek kanal sayısı, günümüz teknolojisiyle yüzler mertebesine çıkabilmektedir. Dalgaboyu bölmeli çoğullama teknolojisi ile, optik aktarım birbiriyle çakışmayan dalgaboyu bantlarına bölünür ve her bir dalgaboyu istenen hızda çalışan, ışıkyolu olarak adlandırılan, bir iletişim kanalını destekler. Böylece, yakın gelecek için öngörülen çok yüksek hızlara çıkmadan bile, bir fiberden herbiri birkaç on Gb/s hızda çalışan yüz dolayında ışıkyolu geçebilmektedir. Bu kadar yüksek hızlarda veri aktarımı, özellikle her bir fiberinde çok sayıda kanalın taşındığı omurga ağlarda bir konuya büyük önem kazandırmaktadır: Hataya bağışıklık. En sık rastlanan hata olan, bir fiberin, herhangi bir nedenle kesilmesi (çoğunlukla inşaat makineleri tarafından, ya da doğal afetlerce), fiber tamir edilene kadar, her saniyede birkaç terabitlik veri kaybı anlamına gelecektir. Örnek olarak 10 km uzunlukta bir fiberin kopma sıklığı 11 yılda birdir. Omurga ağlarda yüzlerce, bazen binlerce, kilometrelik fiberler döşendiği gözönüne alındığında, böyle bir hata durumu için tedbir alınmaması düşünülemez. Optik ağ üzerindeki herhangi bir fibere zarar gelmesi demek bu fiber üzerinden yönlendirilmiş olan tüm ışıkyollarının kopması demektir. Her bir ışıkyolu üzerinden yüksek miktarda (40 Gb/s) veri aktarımı yapıldığından, böyle bir zarar ciddi veri kayıplarına neden olabilir. Temel olarak fiber kopmasına karşı geliştirilen iki yaklaşım vardır. Birinci yaklaşımda fiber üzerinden geçen her bir bağlantının, yani ışıkyolunun, yedek yollarla korunmasıdır. İkinci yaklaşım ise, özellikle birçok internet uygulamasına da uygun ve yeterli olacak şekilde, ışıkyollarının oluşturduğu sanal topolojinin bağlı kalmasının sağlanmasıdır. Bu ikinci yaklaşımda herbir ışıkyoluna ayrı ayrı yedek koruma yollarının atanması yerine, sanal topolojinin korunması dikkate alınarak, üst katmanların (paket katmanları) koruma mekanizmalarının devreye girebilmesi için gereken minimum koşulların sağlanması amaçlanmaktadır. Birinci yaklaşım belirli düzeylerde garantili bir koruma sağlarken yüksek miktarda ağ kaynağının atıl durmasına neden olmakta, dolayısıyla bu kadar üst düzey koruma gerektirmeyen uygulamalar için pahalı bir çözüm sunmaktadır. Son yıllarda özellikle dikkat çeken ikinci yaklaşım ise, daha ekonomik bir yöntemle iletişimin kopmaması garantisini vermekte, ancak daha yavaş bir düzeltme sağlamaktadır. Günümüzde birçok uygulama bağlantı kopmadığı sürece paket katmanının, yeni yol bulma gibi hata düzeltme mekanizmalarının devreye girmesi için gerekli olan, dakikalar mertebesindeki gecikmelere toleranslıdır (web dolaşımı, dosya aktarımı, mesajlaşma, uzaktan erişim gibi). Bu yaklaşım ilkine göre daha az ağ kaynağının atıl kalmasına neden olarak kullanıcıya daha ekonomik hizmet verilmesini sağlayacaktır. Bu çalışmada üzerinde durduğumuz hataya bağışık sanal topoloji tasarımı problemi de bu ikinci yaklaşımı benimsemektedir. Hataya bağışık sanal topoloji tasarımı problemi kendi içinde dört alt probleme ayrılmaktadır: ışıkyollarının belirlenmesi (sanal topolojiyi oluşturma), bu ışıkyollarının herhangi bir fiber kopması durumunda bile sanal topolojinin bağlı kalmasını sağlayacak sekilde fiziksel topoloji üzerinde yönlendirilmesi, dalgaboyu atanması, ve paket trafiğinin yönlendirilmesi. Bu alt problemler ayrı ayrı çözülebilir. Ancak, bunlar bağımsız problemler değildir ve bunları tek tek çözmek elde edilen çözümün kalitesinin çok düşük olmasına neden olabilir. Bununla birlikte, hataya bağışık sanal topoloji tasarımı problemi NP-karmaşıktır. Karmaşıklığı nedeniyle bu problemin, gerçek boyutlu ağlar için, klasik optimizasyon teknikleriyle kabul edilebilir zamanda çözülmesi mümkün değildir. Bu çalışmada, fiziksel topolojinin ve düğümler arası paket trafiği yoğunluğunun bilindiği durumlar için, hataya bağışık sanal topoloji tasarımı problemi bütün halinde ele alınmaktadır. Tezin ilk aşamasında, hataya bağışık sanal topoloji tasarımı probleminin alt problemi olan hataya bağışık sanal topoloji yönlendirmesi problemi ele alınmıştır. Verilen bir sanal topoloji için en az kaynak kullanarak hataya bağışık yönlendirme yapmak için iki farklı doğa-esinli algoritma önerilmektedir: evrimsel algoritmalar ve karınca kolonisi optimizasyonu. Öncelikle önerilen algoritmaların problem için uygun parametre kümesi belirlenmiş, daha sonra, algoritmaların başarımını ölçmek için, deneysel sonuçlar tamsayı doğrusal programlama (ILP) ile elde edilen sonuçlarla karşılaştırılmışır. Sonuçlar göstermektedir ki; önerdiğimiz iki algoritma da, tamsayı doğrusal programlama ile uygun bir çözüm bulunamayan büyük ölçekli ağlar için dahi, problemi çözebilmektedir. Bunun yanında, doğa-esinli algoritmalar çok daha az CPU zamanı ve hafıza kullanmaktadır. Elde edilen çözüm kalitesi ve çözüm için kullanılan CPU zamanının kabul edilebilir düzeyde olması, her iki doğa-esinli algoritmanın da gerçek boyutlu ağlar için kullanılabileceğini doğrulamaktadır. İkinci aşamada, hataya bağışık sanal topoloji tasarımı problemini bir bütün halinde çözmek için dört farklı üst-sezgisel yöntem önerilmektedir. Önerilen üst-sezgisel yöntemler alt seviyedeki sezgiselleri seçme asamasında dört farklı yöntem kullanmaktadır: evrimsel algoritmalar, benzetimli tavlama, karınca kolonisi optimizasyonu ve uyarlamalı yinelenen yapıcı arama. Deneysel sonuçlar tüm üst-sezgisel yöntemlerin hataya bağışık sanal topoloji tasarımı problemini çözmede başarılı olduğunu göstermektedir. Ancak, karınca kolonisi optimizasyonu tabanlı üst-sezgisel diğerlerine göre daha üstün sonuçlar vermektedir. Işıkyolları üzerindeki trafik akışını dengelemek için, karınca kolonisi optimizasyonu tabanlı üst-sezgisele akış deviasyonu yöntemi de eklenmiştir. Literatürde hataya bağışık sanal topoloji tasarımı problemini ele alan tüm çalışmalar çift fiber kopması durumunu gözardı etmektedir. Bu çalışmada, önerdiğimiz üst-sezgisel yöntemin başarımını hem tek hem de çift fiber kopması durumları için değerlendirdik. Önerdiğimiz yöntem çoklu fiber kopması durumları için çok kolay şekilde adapte edilebilmektedir. Tek yapılması gereken hataya bağışıklık kontrolünü yapan yordamın değiştirilmesidir. Deneysel sonuçlar göstermiştir ki, önerdiğimiz karınca kolonisi optimizasyonu tabanlı üst-sezgisel hataya bağışık sanal topoloji tasarımı problemini hem tek hem de çift fiber kopması durumları için kabul edilebilir bir sürede çözebilmektedir. Üst-sezgisel yöntemlerin hataya bağışık sanal topoloji tasarımı çözmedeki başarımını değerlendirebilmek amacıyla, karınca kolonisi optimizasyonu tabanlı üst-sezgiselle elde edilen sonuçlar, literatürde bu problem için önerilmiş başka bir yöntemle karşılaştırılmıştır. Sonuçlar üst-sezgisel yöntemlerin, çok daha az CPU zamanı kullanarak, problem için daha kaliteli çözümler verdiğini göstermektedir.Today, computer networking has become an integral part of our daily life. The steady increase in user demands of high speed and high bandwidth networks causes researchers to seek out new methods and algorithms to meet these demands. The transmission speed in the network is directly affected by the transmission medium. The most effective medium to transmit data is the fiber. Optical networks are designed for the best usage of the superior properties of the fiber, e.g. high speed, high bandwidth, low bit error rate, low attenuation, physical strength, cheapness, etc. The world's communication network infrastructure, from backbone networks to access networks, is consistently turning into optical networks. One of the most important properties of the optical networks is the data transmission rate (up to 50 Tb/s on a single fiber). Today, with the help of the wavelength division multiplexing (WDM) technology, hundreds of channels can be built on a single fiber. WDM is a technology in which the optical transmission is split into a number of non-overlapping wavelength bands, with each wavelength supporting a single communication channel operating at the desired rate. Since multiple WDM channels, also called lightpaths, can coexist on a single fiber, the huge fiber bandwidth can be utilized. Any damage to a physical link (fiber) on the network causes all the lightpaths routed through this link to be broken. Since huge data transmission (40 Gb/s) over each of these lightpaths is possible, such a damage results in a serious amount of data loss. Two different approaches can be used in order to avoid this situation: 1. Survivability on the physical layer, 2. Survivability on the virtual layer. The first approach is the problem of designing a backup link/path for each link/path of the optical layer. The second approach is the problem of designing the optical layer such that the optical layer remains connected in the event of a single or multiple link failure. While the first approach provides faster protection for time-critical applications (such as, IP phone, telemedicine) by reserving more resources, the second approach, i.e. the survivable virtual topology design, which has attracted a lot of attention in recent years, aims to protect connections using less resources. The problem that will be studied in this project is to develop methods for survivable virtual topology design, that enables effective usage of the resources. Survivable virtual topology design consists of four subproblems: determining a set of lightpaths (forming the virtual topology), routing these lightpaths on the physical topology (routing and wavelength assignment (RWA) problem), so that any single fiber cut does not disconnect the virtual topology (survivable virtual topology mapping), assigning wavelengths, and routing the packet traffic. Each of these subproblems can be solved separately. However, they are not independent problems and solving them one by one may degrade the quality of the final result considerably. Furthermore, the survivable virtual topology design is known to be NP-complete. Because of its complexity, it is not possible to solve the problem optimally in an acceptable amount of time using classical optimization techniques, for real-life sized networks. In this thesis, we solve the survivable virtual topology design problem as a whole, where the physical topology and the packet traffic intensities between nodes are given. In the first phase, we propose two different nature inspired heuristics to find a survivable mapping of a given virtual topology with minimum resource usage. Evolutionary algorithms and ant colony optimization algorithms are applied to the problem. To assess the performance of the proposed algorithms, we compare the experimental results with those obtained through integer linear programming. The results show that both of our algorithms can solve the problem even for large-scale network topologies for which a feasible solution cannot be found using integer linear programming. Moreover, the CPU time and the memory used by the nature inspired heuristics is much lower. In the second phase, we propose four different hyper-heuristic approaches to solve the survivable virtual topology design problem as a whole. Each hyper-heuristic approach is based on a different category of nature inspired heuristics: evolutionary algorithms, ant colony optimization, simulated annealing, and adaptive iterated constructive search. Experimental results show that, all proposed hyper-heuristic approaches are successful in designing survivable virtual topologies. Furthermore, the ant colony optimization based hyper-heuristic outperforms the others. To balance the traffic flow over lightpaths, we adapt a flow-deviation method to the ant colony optimization based hyper-heuristic approach. We explore the performance of our hyper-heuristic approach for both single and double-link failures. The proposed approach can be applied to the multiple-link failure problem instances by only changing the survivability control routine. The experimental results show that our approach can solve the problem for both single-link and double-link failures in a reasonable amount of time. To evaluate the quality of the HH approach solutions, we compare these results with the results obtained using tabu search approach. The results show that HH approach outperforms tabu search approach both in solution quality and CPU time.DoktoraPh

A Dynamically Refocusable Sampling Infrastructure for 802.11 Networks

The edge of the Internet is increasingly wireless. Enterprises large and small, homeowners, and even whole cities have deployed Wi-Fi networks for their users, and many users never need to--- or never bother to--- use the wired network. With the advent of high-throughput wireless networks (such as 802.11n) some new construction, even of large enterprise build- ings, may no longer be wired for Ethernet. To understand Internet traffic, then, we need to understand the wireless edge. Measuring Wi-Fi traffic, however, is challenging. It is insufficient to capture traffic in the access points, or upstream of the access points, because the activity of neighboring networks, ad hoc networks, and physical interference cannot be seen at that level. To truly understand the MAC-layer behavior, we need to capture frames from the air using Air Monitors (AMs) placed in the vicinity of the network. Such a capture is always a sample of the network activity, since it is physically impossible to capture a full trace: all frames from all channels at all times in all places. We have built a monitoring infrastructure that captures frames from the 802.11 network. This infrastructure includes several channel sampling strategies that will capture repre- sentative traffic from the network. Further, the monitoring infrastructure needs to modify its behavior according to feedback received from the downstream consumers of the captured traffic in case the analysis needs traffic of a certain type. We call this technique refocusing . The coordinated sampling technique improves the efficiency of the monitoring by utilizing the AMs intelligently. Finally, we deployed this measurement infrastructure within our Computer Science building to study the performance of the system with real network traffic

JTP, an energy-aware transport protocol for mobile ad hoc networks

Wireless ad-hoc networks are based on a cooperative communication model, where all nodes not only generate traffic but also help to route traffic from other nodes to its final destination. In such an environment where there is no infrastructure support the lifetime of the network is tightly coupled with the lifetime of individual nodes. Most of the devices that form such networks are battery-operated, and thus it becomes important to conserve energy so as to maximize the lifetime of a node. In this thesis, we present JTP, a new energy-aware transport protocol, whose goal is to reduce power consumption without compromising delivery requirements of applications. JTP has been implemented within the JAVeLEN system. JAVeLEN~\cite{javelen08redi}, is a new system architecture for ad hoc networks that has been developed to elevate energy efficiency as a first-class optimization metric at all protocol layers, from physical to transport. Thus, energy gains obtained in one layer would not be offset by incompatibilities and/or inefficiencies in other layers. To meet its goal of energy efficiency, JTP (1) contains mechanisms to balance end-to-end vs. local retransmissions; (2) minimizes acknowledgment traffic using receiver regulated rate-based flow control combined with selected acknowledgments and in-network caching of packets; and (3) aggressively seeks to avoid any congestion-based packet loss. Within this ultra low-power multi-hop wireless network system, simulations and experimental results demonstrate that our transport protocol meets its goal of preserving the energy efficiency of the underlying network. JTP has been implemented on the actual JAVeLEN nodes and its benefits have been demoed on a real system