Regularity is a shared memory consistency condition that has received considerable attention, notably in connection with quorum-based shared memory. Lamport's original definition of regularity assumed a single-writer model, however, and is not well defined when each shared variable may have multiple writers. In this thesis, we address this need by formally extending the notion of regularity to a multi-writer model. We have shown that the extension is not trivial. While there exist various ways to extend the single-writer definition, the resulting definitions will have different strengths. Specifically, we give several possible definitions of regularity in the presence of multiple writers. We then present a quorum-based algorithm to implement each of the proposed definitions and prove them correct. We study the relationships between these definitions and a number of other well-known consistency conditions, and give a partial order describing the relative strengths of these consistency conditions. Finally, we provide a practical context for our results by studying the correctness of two well-known algorithms for mutual exclusion under each of our proposed consistency conditions.

Regularity is a shared memory consistency condition that has received considerable attention, notably in connection with quorum-based shared memory. Lamport's original definition of regularity assumed a single-writer model, however, and is not well defined when each shared variable may have multiple writers. In this thesis, we address this need by formally extending the notion of regularity to a multi-writer model. We have shown that the extension is not trivial. While there exist various ways to extend the single-writer definition, the resulting definitions will have different strengths. Specifically, we give several possible definitions of regularity in the presence of multiple writers. We then present a quorum-based algorithm to implement each of the proposed definitions and prove them correct. We study the relationships between these definitions and a number of other well-known consistency conditions, and give a partial order describing the relative strengths of these consistency conditions. Finally, we provide a practical context for our results by studying the correctness of two well-known algorithms for mutual exclusion under each of our proposed consistency conditions.

In order to save energy consumption in idle states, low duty-cycled operation is widely used in Wireless Sensor Networks (WSNs), where each node periodically switches between sleeping mode and awake mode. Although efficient toward saving energy, duty-cycling causes many challenges, such as difficulty in neighbor discovery due to asynchronous wakeup/sleep scheduling, time-varying transmission latencies due to varying neighbor discovery latencies, and difficulty on multihop broadcasting due to non-simultaneous wakeup in neighborhood. This dissertation focuses on this problem space. Specifically, we focus on three co-related problems in duty-cycled WSNs: wakeup scheduling, routing and broadcasting. We propose an asynchronous quorum-based wakeup scheduling scheme, which optimizes heterogenous energy saving ratio and achieves bounded neighbor discovery latency, without requiring time synchronization. Our solution is based on quorum system design. We propose two designs: cyclic quorum system pair (cqs-pair) and grid quorum system pair (gqs-pair). We also present fast offline construction algorithms for such designs. Our analytical and experimental results show that cqs-pair and gqs-pair achieve better trade-off between the average discovery delay and energy consumption ratio. We also study asymmetric quorum-based wakeup scheduling for two-tiered network topologies for further improving energy efficiency. Heterogenous duty-cycling causes transmission latencies to be time-varying. Hence, the routing problem becomes more complex when the time domain must be considered for data delivery in duty-cycled WSNs. We formulate the routing problem as time-dependent Bellman-Ford problem, and use vector representation for time-varying link costs and end-to-end (E2E) distances. We present efficient algorithms for route construction and maintenance, which have bounded time and message complexities in the worst case by ameliorating with beta-synchronizer. Multihop broadcast is complex in duty-cycled WSNs due to non simultaneous wakeup in neighborhoods. We present Hybrid-cast, an asynchronous multihop broadcast protocol, which can be applied to low duty-cycling or quorum-based duty-cycling schedules, where nodes send out a beacon message at the beginning of wakeup slots. Hybrid-cast achieves better tradeoff between broadcast latency and broadcast count compared to previous broadcast solutions. It adopts opportunistic data delivery in order to reduce the broadcast latency. Meanwhile, it reduces redundant transmission via delivery deferring and online forwarder selection. We analytically establish the upper bound of broadcast count and the broadcast latency under Hybrid-cast. To verify the feasibility, effectiveness, and performance of our solutions for asynchronous wakeup scheduling, we developed a prototype implementation using Telosb and TinyOS 2.0 WSN platforms. We integrated our algorithms with the existing protocol stack in TinyOS, and compared them with the CSMA mechanism. Our implementation measurements illustrate the feasibility, performance trade-off, and effectiveness of the proposed solutions for low duty-cycled WSNs. / Ph. D.

Lock-based synchronization on multiprocessors is inherently non-scalable, non-composable, and error-prone. These problems are exacerbated in distributed systems due to an additional layer of complexity: multinode concurrency. Transactional memory (TM) is an emerging, alternative synchronization abstraction that promises to alleviate these difficulties. With the TM model, code that accesses shared memory objects are organized as transactions, which speculatively execute, while logging changes. If transactional conflicts are detected, one of the conflicting transaction is aborted and re-executed, while the other is allowed to commit, yielding the illusion of atomicity. TM for multiprocessors has been proposed in software (STM), in hardware (HTM), and in a combination (HyTM). This dissertation focuses on supporting the TM abstraction in distributed systems, i.e., distributed STM (or D-STM). We focus on three problem spaces: cache-coherence (CC), conflict resolution, and replication. We evaluate the performance of D-STM by measuring the competitive ratio of its makespan --- i.e., the ratio of its makespan (the last completion time for a given set of transactions) to the makespan of an optimal off-line clairvoyant scheduler. We show that the performance of D-STM for metric-space networks is O(N^2) for N transactions requesting an object under the Greedy contention manager and an arbitrary CC protocol. To improve the performance, we propose a class of location-aware CC protocols, called LAC protocols. We show that the combination of the Greedy manager and a LAC protocol yields an O(NlogN s) competitive ratio for s shared objects. We then formalize two classes of CC protocols: distributed queuing cache-coherence (DQCC) protocols and distributed priority queuing cache-coherence (DPQCC) protocols, both of which can be implemented using distributed queuing protocols. We show that a DQCC protocol is O(NlogD)-competitive and a DPQCC protocol is O(log D_delta)-competitive for N dynamically generated transactions requesting an object, where D_delta is the normalized diameter of the underlying distributed queuing protocol. Additionally, we propose a novel CC protocol, called Relay, which reduces the total number of aborts to O(N) for N conflicting transactions requesting an object, yielding a significantly improvement over past CC protocols which has O(N^2) total number of aborts. We also analyze Relay's dynamic competitive ratio in terms of the communication cost (for dynamically generated transactions), and show that Relay's dynamic competitive ratio is O(log D_0), where D_0 is the normalized diameter of the underlying network spanning tree. To reduce unnecessary aborts and increase concurrency for D-STM based on globally-consistent contention management policies, we propose the distributed dependency-aware (DDA) conflict resolution model, which adopts different conflict resolution strategies based on transaction types. In the DDA model, read-only transactions never abort by keeping a set of versions for each object. Each transaction only keeps precedence relations based on its local knowledge of precedence relations. We show that the DDA model ensures that 1) read-only transactions never abort, 2) every transaction eventually commits, 3) supports invisible reads, and 4) efficiently garbage collects useless object versions. To establish competitive ratio bounds for contention managers in D-STM, we model the distributed transactional contention management problem as the traveling salesman problem (TSP). We prove that for D-STM, any online, work conserving, deterministic contention manager provides an Omega(max[s,s^2/D]) competitive ratio in a network with normalized diameter D and s shared objects. Compared with the Omega(s) competitive ratio for multiprocessor STM, the performance guarantee for D-STM degrades by a factor proportional to s/D. We present a randomized algorithm, called Randomized, with a competitive ratio O(sClog n log ^{2} n) for s objects shared by n transactions, with a maximum conflicting degree C. To break this lower bound, we present a randomized algorithm Cutting, which needs partial information of transactions and an approximate TSP algorithm A with approximation ratio phi_A. We show that the average case competitive ratio of Cutting is O(s phi_A log^{2}m log^{2}n), which is close to O(s). Single copy (SC) D-STM keeps only one writable copy of each object, and thus cannot tolerate node failures. We propose a quorum-based replication (QR) D-STM model, which provides provable fault-tolerance without incurring high communication overhead, when compared with the SC model. The QR model stores object replicas in a tree quorum system, where two quorums intersect if one of them is a write quorum, and ensures the consistency among replicas at commit-time. The communication cost of an operation in the QR model is proportional to the communication cost from the requesting node to its closest read or write quorum. In the presence of node failures, the QR model exhibits high availability and degrades gracefully when the number of failed nodes increases, with reasonable higher communication cost. We develop a protoytpe implementation of the dissertation's proposed solutions, including DQCC and DPQCC protocols, Relay protocol, and the DDA model, in the HyFlow Java D-STM framework. We experimentally evaluated these solutions with respective competitor solutions on a set of microbenchmarks (e.g., data structures including distributed linked list, binary search tree and red-black tree) and macrobenchmarks (e.g., distributed versions of the applications in the STAMP STM benchmark suite for multiprocessors). Our experimental studies revealed that: 1) based on the same distributed queuing protocol (i.e., Ballistic CC protocol), DPQCC yields better transactional throughput than DQCC, by a factor of 50% - 100%, on a range of transactional workloads; 2) Relay outperforms competitor protocols (including Arrow, Ballistic and Home) by more than 200% when the network size and contention increase, as it efficiently reduces the average aborts per transaction (less than 0.5); 3) the DDA model outperforms existing contention management policies (including Greedy, Karma and Kindergarten managers) by upto 30%-40% in high contention environments; For read/write-balanced workloads, the DDA model outperforms these contention management policies by 30%-60% on average; for read-dominated workloads, the model outperforms by over 200%. / Ph. D.

Este trabalho estuda a implementação do sistema de Quorum associado ao algoritmo epidêmico Gossip, a implementação de um novo algoritmo de economia de energia - o PWSave - e o protocolo de roteamento AODV em um cenário com e sem falhas de uma rede ad hoc com mobilidade. Optou-se por implementar este trabalho em um ambiente de simulação, dado que a modelagem matemática da associação do Gossip, Quorum e PWSave com os 80 nós - quantidade de nós escolhida para o ambiente de simulação - apresentaria maior complexidade e demora ao abranger todas as variáveis de ambiente desse conjunto de soluções para cada nó presente na rede. A rotina de programação - com o uso de loops para os trabalhos repetitivos - presente no ambiente de simulação permite que os experimentos sejam efetuados mais rapidamente e com menor probabilidade de erros. Os estudos [1], [2] demonstraram, respectivamente, que soluções abrangendo o algoritmo epidêmico Gossip e o sistema de compartilhamento de dados Quorum apresentam resultados favoráveis para uma rede ad hoc com alta mobilidade. Em [1] é apresentado um cenário muito próximo ao implementado neste trabalho, com a utilização do algoritmo Gossip ao protocolo de roteamento Ad-Hoc On-Demand Distance Vector (AODV). Os parâmetros analisados foram os mesmos, a saber: routes requests (RREQ), perda de pacote, vazão e latência. Os resultados do cenário simulado mostram uma diminuição no número de RREQs em uma rede ad hoc, e os demais parâmetros, medidos no ambiente de simulação, são pouco afetados. De acordo com [2] constata-se que há um aumento da resiliência e da vazão da rede e uma menor sobrecarga causada pela distribuição da informação na rede ad hoc pelo sistema de Quorum. A associação do algoritmo Gossip com o sistema de Quorum resultou em uma diminuição considerável de RREQs e perda de pacotes, mas o parâmetro de consumo de energia, que deve ser um fator importante em uma rede ad hoc e/ou uma rede sensor, não apresentou nenhuma melhora. Portanto, foi implementada uma solução adicional ao Gossip e ao Quorum, com o desenvolvimento de um novo algoritmo de economia de energia denominado de PWSave, no simulador Glomosim com o protocolo de roteamento AODV. O PWSave é responsável pelo adormecimento dos nós da rede que não estejam processando informações, ou seja, os nós, no momento do adormecimento, não poderão trocar dados ou auxiliar na formação de rotas da rede. O PWSave associado ao Gossip e ao sistema de Quorum apresenta resultados que refletem ma diminuição no consumo de energia próxima a 10% em comparação com a solução da associação do Gossip com o sistema de Quorum sem a implementação de PWSave. Os resultados da simulação mostram que a associação de Gossip, Quorum e PWSave acarreta uma redução no número de RREQs e na taxa de perda de pacotes sem degradar muito características de fluxo e latência, além de propiciar uma considerável economia no consumo de energia. / This work studies the implementation of the Quorum system associated with the Gossip algorithm, the implementation of a new power saving algorithm - the PWSave - and the routing protocol AODV in a scenario with and without failures of an ad hoc network with mobility. It has been chosen to implement this work in an environment of simulation, because the mathematical modeling of the association of Gossip, Quorum and PWSave with 80 nodes - number of nodes that has been chosen for the simulation environment - would present a higher complexity and delay to address all environment variables of the solutions set for each node present in the network. The programming routine - with the use of loops for the repetitive works - present in the simulation environment allows the experiments to be performed faster and with less probability of errors. The studies [1], [2] have shown, respectively, that solutions covering the Gossip epidemic algorithm and the system for sharing data Quorum show favorable results for an ad hoc network with high mobility. In [1] is presented a scenario very close to that implemented in this work, using the Gossip algorithm associated to the routing protocol Ad-Hoc On-Demand Distance Vector (AODV). The parameters analyzed were the same: routes requests (RREQ), packet loss, throughput and latency. The simulated scenario results show a decrease in the number of RREQs in an ad hoc network, and the other parameters, measured in the simulation environment, are little afected. According to [2] it is noted that there is an increase in the resilience and throughput of the network and a lower overload caused by the distribution of the information in the ad hoc network by the Quorum system. The association of the Gossip algorithm with the Quorum system resulted in a considerable decrease of RREQs and packet loss, but the parameter of energy consumption, which is an important factor in an ad hoc network and/or a sensor network, shows no improvement. Therefore, an additional solution was associated to the Gossip and to the Quorum, with the development of a new power saving algorithm named PWSave, in the simulator Glomosim with the routing protocol AODV. The PWSave is responsable for the sleeping state of the network nodes when they are not processing information: the nodes at the time of sleep cannot exchange data or assist in the building of network routes. The PWSave associated with the Gossip and Quorum system provides a decrease of the energy consumption close to 10% compared to the association solution of the Gossip with the Quorum system without the PWSave implementation. The results of simulation show that the association of the Gossip, Quorum and PWSave produces a reduction in the number of RREQs and in the rate of packets loss without degrading much the throughput and latency characteristics, providing a considerable energy consumption economy.

Este trabalho estuda a implementação do sistema de Quorum associado ao algoritmo epidêmico Gossip, a implementação de um novo algoritmo de economia de energia - o PWSave - e o protocolo de roteamento AODV em um cenário com e sem falhas de uma rede ad hoc com mobilidade. Optou-se por implementar este trabalho em um ambiente de simulação, dado que a modelagem matemática da associação do Gossip, Quorum e PWSave com os 80 nós - quantidade de nós escolhida para o ambiente de simulação - apresentaria maior complexidade e demora ao abranger todas as variáveis de ambiente desse conjunto de soluções para cada nó presente na rede. A rotina de programação - com o uso de loops para os trabalhos repetitivos - presente no ambiente de simulação permite que os experimentos sejam efetuados mais rapidamente e com menor probabilidade de erros. Os estudos [1], [2] demonstraram, respectivamente, que soluções abrangendo o algoritmo epidêmico Gossip e o sistema de compartilhamento de dados Quorum apresentam resultados favoráveis para uma rede ad hoc com alta mobilidade. Em [1] é apresentado um cenário muito próximo ao implementado neste trabalho, com a utilização do algoritmo Gossip ao protocolo de roteamento Ad-Hoc On-Demand Distance Vector (AODV). Os parâmetros analisados foram os mesmos, a saber: routes requests (RREQ), perda de pacote, vazão e latência. Os resultados do cenário simulado mostram uma diminuição no número de RREQs em uma rede ad hoc, e os demais parâmetros, medidos no ambiente de simulação, são pouco afetados. De acordo com [2] constata-se que há um aumento da resiliência e da vazão da rede e uma menor sobrecarga causada pela distribuição da informação na rede ad hoc pelo sistema de Quorum. A associação do algoritmo Gossip com o sistema de Quorum resultou em uma diminuição considerável de RREQs e perda de pacotes, mas o parâmetro de consumo de energia, que deve ser um fator importante em uma rede ad hoc e/ou uma rede sensor, não apresentou nenhuma melhora. Portanto, foi implementada uma solução adicional ao Gossip e ao Quorum, com o desenvolvimento de um novo algoritmo de economia de energia denominado de PWSave, no simulador Glomosim com o protocolo de roteamento AODV. O PWSave é responsável pelo adormecimento dos nós da rede que não estejam processando informações, ou seja, os nós, no momento do adormecimento, não poderão trocar dados ou auxiliar na formação de rotas da rede. O PWSave associado ao Gossip e ao sistema de Quorum apresenta resultados que refletem ma diminuição no consumo de energia próxima a 10% em comparação com a solução da associação do Gossip com o sistema de Quorum sem a implementação de PWSave. Os resultados da simulação mostram que a associação de Gossip, Quorum e PWSave acarreta uma redução no número de RREQs e na taxa de perda de pacotes sem degradar muito características de fluxo e latência, além de propiciar uma considerável economia no consumo de energia. / This work studies the implementation of the Quorum system associated with the Gossip algorithm, the implementation of a new power saving algorithm - the PWSave - and the routing protocol AODV in a scenario with and without failures of an ad hoc network with mobility. It has been chosen to implement this work in an environment of simulation, because the mathematical modeling of the association of Gossip, Quorum and PWSave with 80 nodes - number of nodes that has been chosen for the simulation environment - would present a higher complexity and delay to address all environment variables of the solutions set for each node present in the network. The programming routine - with the use of loops for the repetitive works - present in the simulation environment allows the experiments to be performed faster and with less probability of errors. The studies [1], [2] have shown, respectively, that solutions covering the Gossip epidemic algorithm and the system for sharing data Quorum show favorable results for an ad hoc network with high mobility. In [1] is presented a scenario very close to that implemented in this work, using the Gossip algorithm associated to the routing protocol Ad-Hoc On-Demand Distance Vector (AODV). The parameters analyzed were the same: routes requests (RREQ), packet loss, throughput and latency. The simulated scenario results show a decrease in the number of RREQs in an ad hoc network, and the other parameters, measured in the simulation environment, are little afected. According to [2] it is noted that there is an increase in the resilience and throughput of the network and a lower overload caused by the distribution of the information in the ad hoc network by the Quorum system. The association of the Gossip algorithm with the Quorum system resulted in a considerable decrease of RREQs and packet loss, but the parameter of energy consumption, which is an important factor in an ad hoc network and/or a sensor network, shows no improvement. Therefore, an additional solution was associated to the Gossip and to the Quorum, with the development of a new power saving algorithm named PWSave, in the simulator Glomosim with the routing protocol AODV. The PWSave is responsable for the sleeping state of the network nodes when they are not processing information: the nodes at the time of sleep cannot exchange data or assist in the building of network routes. The PWSave associated with the Gossip and Quorum system provides a decrease of the energy consumption close to 10% compared to the association solution of the Gossip with the Quorum system without the PWSave implementation. The results of simulation show that the association of the Gossip, Quorum and PWSave produces a reduction in the number of RREQs and in the rate of packets loss without degrading much the throughput and latency characteristics, providing a considerable energy consumption economy.

Les réseaux de capteurs acoustiques sous-marins (UW-ASN) sont les plus nouveaux achèvements technologiques en termes de communication. Les UW-ASN visent à observer et à explorer les lacs, les rivières, les mers et les océans. Récemment, ils ont été soumis à une attention particulière en raison de leur grand potentiel en termes d'applications prometteuses dans divers domaines (militaires, environnementaux, scientifiques ...) et aux nouvelles questions scientifiques qu'ils suscitent. Un problème majeur dans les UW-ASN est l'épuisement rapide de l'énergie, car une grande puissance est nécessaire pour la communication acoustique, tandis que le budget de la batterie des capteurs est limité. Par conséquent, les protocoles de communication énergétiques revêtent une importance primordiale pour faire usage judiciaire du budget énergétique disponible. Dans ce contexte, cette thèse vise à étudier les principales caractéristiques des capteurs acoustiques sous-marins difficiles afin de concevoir des protocoles de communication énergétiques, plus spécifiquement au niveau routage et MAC. Tout d'abord, nous abordons le problème des trous énergétiques dans UW-ASN. Le problème du « sink-hole » se produit lorsque les capteurs les plus proches du sink épuisent leur énergie plus rapidement en raison de leur charge plus lourde. En effet, ces capteurs, en particulier ceux qui sont à un seul saut du sinkstatique, agissent comme des relais pour tous les autres capteurs, ce qui leur épuise sévèrement l’énergie.A la couche de routage,en particulier, nous proposons de distribuer la charge transmise par chaque capteur parmi plusieurs voisins potentiels, en supposant que les capteurs peuvent ajuster leur gamme de communication entre deux niveaux lorsqu'ils envoient ou transmettent des données. Plus précisément, nous déterminons pour chaque capteur l'ensemble des prochains sauts avec les poids de charge associés qui entraînent un épuisement équitable d'énergie entre tous les capteurs du réseau. Ensuite, nous étendons notre stratégie de routage équilibrée en supposant que chaque capteur n'est pas seulement capable d'ajuster sa puissance d'émission à 2 niveaux mais aussi jusqu'à n niveaux où n> 2. Par conséquent, à la couche de routage, pour chaque valeur possible de n, nous déterminons pour chaque capteur l'ensemble des éventuels sauts avec les poids de charge associés qui mènent à une consommation d'énergie équitable chez tous les capteurs du réseau. En outre, nous obtenons le nombre optimal de puissances de transmission n qui équilibre la consommation d'énergie de tous les capteurs pour chaque configuration de réseau. En plus de cela, il convient de souligner que notre protocole de routage étendu utilise un modèle de canal à variation de temps plus réaliste qui tient compte de la plupart des caractéristiques fondamentales de la propagation acoustique sous-marine. Les résultats analytiques montrent que notre protocole de routage assure une réduction importante de la consommation d’énergie. Deuxièmement, pour atténuer les impacts de collision spectaculaires gaspillant l’énergie, nous concevons un protocole MAC multicanal (MC-UWMAC) évitant les collisions pour les UW-ASNs. MC-UWMAC fonctionne avec un canal de contrôle (décomposé en créneaux de temps) et un ensemble de canaux de données à bande passante égale. Les créneaux du canal de contrôle sont dédiés à l’échange RTS / CTS permettant à une paire de capteurs communicants de s'accorder sur l'heure de début de la communication sur un canal de données pré-alloué. Dans cette thèse, nous proposons deux nouvelles procédures associées d'allocation des créneaux du canal de contrôle et d'attribution des canaux de données sans nécessiter de frais de négociation supplémentaires. En conséquence, chaque capteur peut initier l'échange RTS / CTS uniquement à son créneau assigné, calculé à l'aide d'une procédure d'allocation basée sur une partition virtuelle de grille de la zone de déploiement. (...) / UnderWaterAcoustic Sensor Networks (UW-ASNs) are the newest technological achievement in terms of communication. Composed of a set of communicating underwater sensors, UW-ASNs are intended to observe and explore lakes, rivers, seas and oceans. Recently, they have been subject to a special attention due to their great potential in terms of promising applications in various domains (military, environmental, scientific...) and to the new scientific issues they raise. A great challenging issue in UW-ASNs is the fast energy depletion since high power is needed for acoustic communication while sensors battery budget is limited. Hence, energy-efficient networking protocols are of a paramount importance to make judicious use of the available energy budget while considering the distinguishing underwater environment characteristics. In this context, this thesis aims at studying the main challenging underwater acoustic sensors characteristics to design energy-efficient communication protocols specifically at the routing and MAC layers. First, we address the problem of energy holes in UW-ASNs. The sink-hole problem occurs when the closest nodes to sink drain their energy faster due to their heavier load. Indeed, those sensors especially the ones that are 1-hop away from the static sink act as relays to it on behalf of all other sensors, thus suffering from severe energy depletion. In particular, at the routing layer, we propose to distribute the transmission load at each sensor among several potential neighbors, assuming that sensors can adjust their communication range among two levels when they send or forward data. Specifically, we determine for each sensor the set of next hops with the associated load weights that lead to a fair energy depletion among all sensors in the network. Then, we extend our balanced routing strategy by assuming that each sensor node is not only able to adjust its transmission power to 2 levels but eventually up to n levels where n > 2. Consequently, at the routing layer, for each possible value of n, we determine for each sensor the set of possible next hops with the associated load weights that lead to a fair energy consumption among all sensors in the network. Moreover, we derive the optimal number of transmission powers n that balances the energy consumption among all sensors for each network configuration. In addition to that, it is worth pointing out that our extended routing protocol uses a more realistic time varying channel model that takes into account most of the fundamental characteristics of the underwater acoustic propagation. Analytical results show that further energy saving is achieved by our extended routing scheme. Second, to mitigate the dramatic collision impacts, we design a collision avoidance energy efficient multichannel MAC protocol (MC-UWMAC) for UW-ASNs. MC-UWMAC operates on single slotted control and a set of equal-bandwidth data channels. Control channel slots are dedicated to RTS/CTS handshaking allowing a communicating node pair to agree on the start time of communication on a pre-allocated data channel. In this thesis, we propose two novel coupled slot assignment and data channels allocation procedures without requiring any extra negotiation overhead. Accordingly, each node can initiate RTS/CTS exchange only at its assigned slot calculated using a slot allocation procedure based on a grid virtual partition of the deployment area. Moreover, for each communicating pair of nodes, one data channel is allocated using a channel allocation procedure based on our newly designed concept of singleton- intersecting quorum. Accordingly, each pair of communicating nodes will have at their disposal a unique 2-hop conflict free data channel. Compared with existing MAC protocol, MC-UWMAC reduces experienced collisions and improves network throughput while minimizing energy consumption.