Reliable Broadcast

Orca is a language for implementing parallel applications on loosely coupled distributed systems. Unlike most languages for distributed programming, it allows processes on different machines to share data. Such data are encapsulated in data-objects, which are instances of user-defined abstract data types. The implementation of Orca takes care of the physical distribution of objects among the local memories of the processors. In particular, an implementation may replicate and/or migrate objects in order to decrease access times to objects and increase parallelism. This paper gives a detailed description of the Orca language design and motivates the design choices. Orca is intended for applications programmers rather than systems programmers. This is reflected in its design goals to provide a simple, easy to use language that is type-secure and provides clean semantics. The paper discusses three example parallel applications in Orca, one of which is described in detail. It also describes one of the existing implementations, which is based on reliable broadcasting. Performance measurements of this system are given for three parallel applications. The measurements show that significant speedups can be obtained for all three applications. Finally, the paper compares Orca with several related languages and systems. † A preliminary version of this paper appeared in the proceedings of the First Usenix/SERC Workshop on Experiences with Building Distributed and Multiprocessor Systems, Ft. Lauderdale, Oct. 1989. * This research was supported in part by the Netherlands organization for scientific research (N.W.O.) under grant 125-30-10.

Inter-vehicle communication (IVC) protocols have the potential to increase the safety, efficiency, and convenience of transportation systems involving planes, trains, automobiles, and robots. The applications targeted include peer-to-peer networks for web surfing, coordinated braking, runway incursion prevention, adaptive traffic control, vehicle formations, and many others. The diversity of the applications and their potential communication protocols has challenged a systematic literature survey. We apply a classification technique to IVC applications to provide a taxonomy for detailed study of their communication requirements. The applications are divided into type classes which share common communication organization and performance requirements. IVC protocols are surveyed separately and their fundamental characteristics are revealed. The protocol characteristics are then used to determine the relevance of specific protocols to specific types of IVC applications.

Unlike many other operating systems, Amoeba is a distributed operating system that provides group communication (i.e., one-to-many communication). We will discuss design issues for group communication, Amoeba's group system calls, and the protocols to implement group communication. To demonstrate that group communication is a useful abstraction, we will describe a design and implementation of a fault-tolerant directory service. We discuss two versions of the directory service: one with Non-Volatile RAM (NVRAM) and one without NVRAM. We will give performance figures for both implementations.

Application-independent Redundancy Elimination (RE), or identifying and removing repeated content from network transfers, has been used with great success for improving network performance on enterprise access links. Recently, there is growing interest for supporting RE as a network-wide service. Such a network-wide RE service benefits ISPs by reducing link loads and increasing the effective network capacity to better accommodate the increasing number of bandwidth-intensive applications. Further, a networkwide RE service democratizes the benefits of RE to all end-to-end traffic and improves application performance by increasing throughput and reducing latencies.

In Journal of Cryptology 1/1 (1988) 65-75 (= [Chau_88]), David Chaum describes a beautiful technique, the DC-net, which should allow participants to send and receive messages anonymously in an arbitrary network. The untraceability of the senders is proved to be unconditional, but that of the recipients implicitly assumes a reliable broadcast network. This assumption is unrealistic in some networks, but it can be removed completely by using the fail-stop key generation schemes by Waidner (these proceedings, = [Waid_89]). In both cases, however, each participant can untraceably and permanently disrupt the entire DC-net.

Parallel computers come in two varieties: those with shared memory and those without. The former are hard to build; the latter are hard to program. In this paper we propose a hybrid form that combines the best properties of each. The basic idea is to allow programmers to define objects upon-which userdefined operations are performed, in effect, abstract data types. Each object is replicated on each machine that needs it. Reads are done locally, with no network traffic. Writes are done by a reliable broadcast algorithm. A language for parallel programming, Orca, based on distributed shared objects has been designed, implemented, and used for some applications. Its implementation uses the reliable broadcast mechanism. For applications with a high read/write ratio to the shared objects, we show that our approach can frequently achieve close to linear speedup with up to 16 processors. BLURB FOR CENTER COLUMN Parallel computers come in two varieties: those with shared memory and those without. The former are hard to build; the latter are hard to program. In this paper we propose a hybrid form that combines the best properties of each.

Mobile ad-hoc networks are making a new class of mobile applications feasible. They benefit from the fast deployment and reconfiguration of the networks, are mainly characterized by the need to support many-to-many interaction schema within groups of cooperating mobile hosts and are likely to use replication of data objects to achieve performances and high data availability. This strong group orientation requires specialized solutions that combine adaptation to the fully mobile environment and provide the adequate level of fault tolerance. In this paper, we present the reliable broadcast protocol that has been purposely designed for mobile ad-hoc networks. The reliable broadcast service ensures that all the hosts in the network deliver the same set of messages to the upper layer. It represents the building block to obtain higher broadcast and multicast services with stronger guarantees and is an efficient and reliable alternative to flooding. The protocol is constructed on top of the wireless MAC protocol, which in turn sits over the clustering protocol. It provides an exactly once message delivery semantics and tolerates communication failures and host mobility. Temporary disconnections and network partitions are also tolerated under the assumption that they are eventually repaired, as specified by a Liveness property. The termination of the protocol is proved and complexity and performance analyses are also provided.

This paper proposes a stack of three Byzantine-resistant protocols aimed to be used in practical distributed systems: multi-valued consensus, vector consensus and atomic broadcast. These protocols are designed as successive transformations from one to another. The first protocol, multi-valued consensus, is implemented on top of a randomized binary consensus and a reliable broadcast protocol. The protocols share a set of important structural properties. First, they do not use digital signatures constructed with public-key cryptography, a well-known performance bottleneck in this kind of protocols. Second, they are time-free, i.e. they make no synchrony assumptions, since these assumptions are often vulnerable to subtle but effective attacks. Third, they are completely decentralized, thus avoiding the cost of detecting corrupt leaders. Fourth, they have optimal resilience, i.e. they tolerate the failure of f = (n − 1)/3 out of a total of n processes. In terms of time complexity, the multi-valued consensus protocol terminates in a constant expected number of rounds, while the vector consensus and atomic broadcast protocols have O(f ) complexity. The paper also proves the equivalence between multivalued consensus and atomic broadcast in the Byzantine failure model without signatures. A similar proof is given for the equivalence between multi-valued consensus and vector consensus. These two results have theoretical relevance since they show once more that consensus is a fundamental problem in distributed systems.

Mobile ad hoc networks (MANETs) suffer from high transmission error rate because of the nature of radio communications. The broadcast operation, as a fundamental service in MANETs, is prone to the broadcast storm problem if the forward nodes are not carefully designated. The objective of reducing the broadcast redundancy while still providing high delivery ratio for each broadcast packet is a major challenge in a dynamic environment. In this paper, we propose a simple reliable broadcast algorithm, called double-covered broadcast (DCB), that takes advantage of the broadcast redundancy to improve the delivery ratio in the environment that has rather high transmission error rate. Among 1-hop neighbors of the sender, only selected forward nodes retransmit the broadcast message. Forward nodes are selected in such a way that (1) the sender's 2-hop neighbors are covered and (2) the sender's 1hop neighbors are either a forward node, or a non-forward node but covered by at least two forwarding neighbors. The retransmissions of the forward nodes are received by the sender as confirmation of their receiving the packet. The non-forward 1-hop neighbors of the sender do not acknowledge the reception of the broadcast. If the sender does not detect all its forward nodes' retransmissions, it will resend the packet until the maximum times of retry is reached. Simulation results show that the algorithm provides good performance for a broadcast operation under high transmission error rate environment.

Wireless communications are becoming an important part of our everyday lifestyle. One major area that will have an enormous impact on the performance of wireless ad hoc networks is the medium access control (MAC) layer. Current random access MAC protocols for ad hoc networks support reliable unicast but not reliable broadcast. In this paper, we proposed a random access MAC protocol, Broadcast Support Multiple Access (BSMA), which improves broadcast reliability in ad hoc networks.

Orca is a language for programming parallel applications on distributed computing systems. Although processors in such systems communicate only through message passing and not through shared memory, Orca provides a communication model based on logically shared data. Programmers can define abstract data types and create instances (objects) of these types, which may be shared among processes. All operations on shared objects are executed atomically. Orca's shared objects are implemented by replicating them in the local memories of the processors. Read operations use the local copies of the object, without doing any interprocess communication. Write operations update all copies using an efficient reliable broadcast protocol. In this paper, we briefly describe the language and its implementation and then report on our experiences in using Orca for three parallel applications: the Traveling Salesman Problem, the All-pairs Shortest Paths problem, and Successive Overrelaxation. These applications have different needs for shared data: TSP greatly benefits from the support for shared data; ASP benefits from the use of broadcast communication, even though it is hidden in the implementation; SOR merely requires point-to-point communication, but still can be implemented in the language by simulating message passing. We discuss how these applications are programmed in Orca and we give the most interesting portions of the Orca code. Also, we include performance measurements for these programs on a distributed system consisting of 10 MC68020s connected by an Ethernet. These measurements show that significant speedups are obtained for all three programs. * We will sometimes use the term "object" as a shorthand notation for data-objects. Note, however, that unlike in most parallel object-based systems, objects in our model are purely passive.

A noteworthy advance in distributed computing is due to the recent development of peer-to-peer systems. These systems are essentially dynamic in the sense that no process can get a global knowledge on the system structure. They mainly allow processes to look up for data that can be dynamically added/suppressed in a permanently evolving set of nodes. Although protocols have been developed for such dynamic systems, to our knowledge, up to date no computation model for dynamic systems has been proposed. Nevertheless, there is a strong demand for the definition of such models as soon as one wants to develop provably correct protocols suited to dynamic systems.

This work investigates reliable wireless broadcast with asynchronous data access. A wireless broadcast system based on LT-codes, a realization of the recently introduced Fountain codes, is introduced. We review the traditional problem formalization for Fountain codes operating on erasure channels and generalize the framework to arbitrary types of channels coining the terminology and the concept of information collecting. The sum-product algorithm in order to exploit soft-information available at the wireless receiver for decoding of LT codes is applied. Simulation results on the AWGN, as well as the fading channel, show remarkable performance gains compared to traditional erasure decoding.

... atomic broadcast protocol that is suitable for building highly available and intrusion-tolerantservices in the ... system that the adversary can exploit, for example, through denial-of-service attacks. ... polynomial-time feasibility of randomized agreement [5,6,7] and atomic broadcast [8 ...

Reliable broadcast is a basic service for many collaborative applications as it provides reliable dissemination of the same information to many recipients. This paper studies three common approaches for achieving scalable reliable broadcast in ad hoc networks, namely probabilistic flooding, counter-based broadcast, and lazy gossip. The strength and weaknesses of each scheme are analyzed, and a new protocol that combines these three techniques, called RAPID, is developed. Specifically, the analysis in this paper focuses on the trade-offs between reliability (percentage of nodes that receive each message), latency, and the message overhead of the protocol. Each of these methods excel in some of these parameters, but no single method wins in all of them. This motivates the need for a combined protocol that benefits from all of these methods and allows to trade between them smoothly. Interestingly, since the RAPID protocol only relies on local computations and probability, it is highly resilient to mobility and failures and even selfish behavior. By adding authentication, it can even be made malicious tolerant. Additionally, the paper includes a detailed performance evaluation by simulation. The simulations confirm that RAPID obtains higher reliability with low latency and good communication overhead compared with each of the individual methods.

Due to scarce resources, such as transmission power, storage space and communication bandwidth, current broadcast approaches for general ad hoc networks can not be applied to IEEE 802.15.4 based ad hoc networks (e.g., ZigBee networks). This paper proposes a forward node selection algorithm that significantly reduces broadcast redundancy. The algorithm exploits the hierarchical address space in ZigBee networks. Only one-hop neighbor information is needed: a partial list of two-hop neighbors is derived at a node without exchanging messages between neighboring nodes. The complexity of the proposed algorithm is polynomial in terms of both computation time and memory space. The localized algorithm provides an optimal and feasible solution of selecting the minimum number of rebroadcast nodes in ZigBee networks, which is an NP-hard problem for general ad hoc networks. The proposed algorithm is extended to deal with packet loss during data transmission. A ZigBee rebroadcast algorithm is also proposed to further reduce the number of rebroadcast nodes and cover the whole network faster by assigning a non-random rebroadcast timer determined by the number of neighbors to be covered, distance and link quality. Simulations are conducted to evaluate the broadcast redundancy, coverage time, and coverage ratio.

We propose a single source reliable broadcasting algorithm for linear grid-based networks where a message is guaranteed to be delivered to all the nodes of the network. The nodes are mobile and can move from one grid point to another. The solution does not require the nodes to know the network size or its diameter. The only information a node has is its identity and its position. On average, only a subset of nodes transmit and they transmit only once to achieve reliable broadcast. The protocol is contention-free and energy-efficient. We show that reliable broadcast can be achieved in O(D log n) time-slots despite node mobility, where D is the diameter of the network and n the number of nodes.

This paper introduces a new IEEE standard, IEEE 802.15.5,which provides mesh capability for wireless personal area network (WPAN) devices. The standard provides an architectural framework enabling WPAN devices to promote interoperable, stable, and scalable wireless mesh topologies. It is composed of two parts: low-rate WPAN mesh and high-rate WPAN mesh. In this paper, we present only low-rate WPAN mesh because it is designed to support wireless sensor networks. IEEE 802.15.5 low-rate part is a lightweight scalable mesh routing protocol that caters well to the requirements of resource-constrained wireless sensor networks. By binding logical addresses to the network topology, IEEE 802.15.5 obviates the need for route discovery. This eliminates the initial route discovery latency, saves storage space and reduces the communication overhead and energy consumption. A distributed link state scheme is further built atop the block addressing scheme to improve the quality of routes, robustness, and load balancing. The routing scheme scales well with regard to various performance metrics. The standard also provides enhanced functions such as multicast, reliable broadcast, power saving, time synchronization, route tracing and portability. We also present the performance evaluation of major functions performed with a 50-nodes tested deployed over a whole floor (100 x 140 ft2) at CUNY Engineering building. The results testify that the IEEE 802.15.5 will serve well for wireless personal area networks and wireless sensor networks.

Pease et al. introduced the problem of Byzantine Generals (BGP) to study the effects of Byzantine faults in distributed protocols for reliable broadcast. It is well known that BGP among n players tolerating up to t faults is (efficiently) possible if and only if n > 3t. To overcome this severe limitation, Pease et al. introduced a variant of BGP, Authenticated Byzantine General (ABG). Here players are supplemented with digital signatures (or similar tools) to thwart the challenge posed by Byzantine faults. Subsequently, they proved that with the use of authentication, fault tolerance of protocols for reliable broadcast can be amazingly increased to n > t (which is a huge improvement over the n > 3t).

A robust group key agreement protocol (GKA) allows a set of players to establish a shared secret key, regardless of network/node failures. Current constant-round GKA protocols are either efficient and nonrobust or robust but not efficient; assuming a reliable broadcast communication medium, the standard encryption-based group key agreement protocol can be robust against arbitrary number of node faults, but the size of the messages broadcast by every player is proportional to the number of players. In contrast, nonrobust group key agreement can be achieved with each player broadcasting just constant-sized messages. We propose a novel 2-round group key agreement protocol, which tolerates up to T node failures, using OðT Þ-sized messages for any T. We show that the new protocol implies a fully-robust group key agreement with logarithmic-sized messages and expected round complexity close to 2, assuming random node faults. The protocol can be extended to withstand malicious insiders at small constant factor increases in bandwidth and computation. The proposed protocol is secure under the (standard) Decisional Square Diffie-Hellman assumption.

Considerations of the real-time self-organization of neural networks for speech recog- nition and production have lead to a new understanding of several key issues in such networks, most notably a definition of new processing units and functions of hierarchical levels in the auditory system. An important function of a particular neural level in the auditory system is to provide a

The purpose of a reliable broadcast protocol is to allow groups of nodes on unreliable broadcast networks to reliably broadcast messages. A reliable broadcast protocol must guarantee two properties: (1) all of the receivers in a group receive the broadcast messages, and (2) each of the receivers orders the messages in the same sequence. In an optimistic approach to reliable broadcast protocol, a batch acknowledgement is employed for a sequence of broadcast messages, instead of one or more acknowledgements per broadcast message used in the pessimistic approach. In this paper, based on the optimistic approach, we have proposed a counter-based reliable broadcast protocol. In this protocol, the unique token ownership is circulated among all the nodes in an order specified by a token-passing-list. The system state which records related information about messages broadcast by each node is included in the token message. By appropriately updating the counter information recorded in the system state included in the token message, instead of using explicit acknowledgement messages, the proposed protocol needs fewer control messages to commit a broadcast message than other protocols, no matter whether the rate of transmission errors is high or low. Moreover, we show how to handle the flow control problem and describe the token update technique.

In this paper, we propose a novel approach for solving the reliable broadcast problem in a probabilistic unreliable model. Our approach consists in first defining the optimality of probabilistic reliable broadcast algorithms and the adaptiveness of algorithms that aim at converging toward such optimality. Then, we propose an algorithm that precisely converges toward the optimal behavior, thanks to an adaptive strategy based on Bayesian statistical inference. We compare the performance of our algorithm with that of a typical gossip algorithm through simulation. Our results show, for example, that our adaptive algorithm quickly converges toward such exact knowledge.

This paper is an introduction to oracles the aim of which is to help solving distributed computing problems in asynchronous distributed systems prone to process crash failures and fair lossy channels. Actually, the combination of asynchrony and failures makes a lot of problems impossible to solve in unreliable asynchronous distributed systems. Hence, those systems have to be extended with appropriate oracles in order these problems become solvable. Using two such problems (namely, the design of a quiescent uniform reliable broadcast facility, and the consensus problem), this paper presents appropriate oracles allowing to solve these problems. In that sense, the paper is a guided tour to the definition of oracles suited to unreliable asynchronous distributed systems.

We consider the broadcasting problem in sensor networks where the nodes have no prior knowledge of their neighborhood. That is, to preserve power and bandwidth, no beacons or ’hello’ messages are sent. We describe several Area based Beaconless Broadcasting Algorithms (ABBAs). In 2D, upon receiving the packet, each node calculates the ratio P of its perimeter, along the circle of transmission radius, that is not covered by this and previous transmissions of the same packet. The node then sets or updates its timeout to be inversely proportional to P. We also consider an alternative random timeout function. If the perimeter becomes fully covered, the node cancels retransmissions. The protocol is reliable, assuming an ideal MAC layer. We also describe three 3D ABBAs, one of them being reliable, each with two choices of timeouts.These three protocols are based on covering three projections, covering particular points on intersection circles, and covering intersection points of three spheres. Our protocols are the first reliable broadcasting protocols, other than blind flooding. We compare 2D ABBAs with two other existing beaconless protocols, BPS and Geoflood, showing its superiority. We also consider a MAC layer with collisions and show that all of our methods still remain very robust, showing high delivery ratio during the broadcast.

One way to efficiently disseminate information in a P2P overlay is to rely on a spanning tree. However, in a tree, interior nodes support a much higher load than leaf nodes. Also, the failure of a single node can break the tree, impairing the reliability of the dissemination protocol. These problems can be addressed by using multiple trees, such that each node is interior in just a few trees and a leaf node in the remaining; the multiple trees approach allows to achieve load distribution and also to send redundant information for fault-tolerance. This paper proposes Thicket, a decentralized algorithm to efficiently build and maintain such multiple trees over a single unstructured overlay network. The algorithm has been implemented and is extensively evaluated using simulation in a P2P overlay with 10.000 nodes.

Replication protocols using an eager update propagation strategy commonly need a reliable broadcast service; i.e., a broadcast primitive with atomic delivery and, in some cases, also with total order. This communication service provides some appropriate features for the recovery tasks, although in some cases this leads to partial blocking of the replica taken as the source in the updating process. CLOB is a framework for reliable broadcast protocols that log the missed update messages in case of failure, being able to automatically resend these updates when the faulty destinations recover. This behaviour is easily configurable and allows an efficient recovery mechanism in case of short-term failures, which can be combined with other version-based recovery protocols in order to manage long-term outages.

Wireless Sensor Networks (WSNs) have been the focal point of research over the last several years. Broadcast communication is a key requirement for WSNs since many tasks in the network depend on broadcasting, including critical tasks like querying. Consequently, securing broadcast communication over sensor networks has become an important research challenge.

Broadcasting is a process of information dissemination in a communications network whereby a message, originated by one member, is transmitted to all members of the network. By adding some redundant calls to the broadcasting scheme, the completion of the broadcast can be guaranteed in the presence of faulty components. We investigate the implications of transmission failures on broadcasting. In particular, we consider broadcasting when the number of transmission failures is bounded by a constant. We determine the time required to guarantee a broadcast in this model. We also study the number of links required in networks which allow reliable broadcasting.

We consider message-efficient broadcast tolerating Byzantine faults in a multi-hop wireless sensor network. Assuming a grid network where all nodes have a communication range of r, and a single neighborhood contains at most t dishonest and collision-capable (bad) nodes, each with a message budget m f , we investigate the minimum message budget m that each honest (good) node must have in order to achieve reliable broadcast. We consider three cases: (1) m f is known in advance and m is homogeneous among all good nodes; (2) m f is known in advance and m is heterogeneous among good nodes; (3) m f is unknown. For the first two cases, we present possibility results and broadcast protocols that have message costs within twice the lower bound. For the third case, we present a coding scheme that helps verify the integrity of messages at a receiving node without using any cryptographic techniques. This code leads to a reactive local broadcast primitive that has probabilistic reliability guarantees. Combined with a previously proposed scheme, it results in a broadcast protocol for t < 1 2 r(2r + 1) that guarantees reliability with high probability.

This letter proposes a busy-tone based scheme for reliable and efficient broadcasting in mobile ad hoc networks. Control packets such as RTS, CTS and ACK are ignored in the broadcast scheme, and two busy tones are used, one for channel reservation and the other for negative acknowledgement. Unlike traditional schemes for reliable broadcasting, the proposed scheme is highly efficient as

Résumé: $\ Diamond {\ cal W} $ is the class of failure detectors that ensure that every crashed process is eventually suspected by a correct process, and eventually there is correct process that is never suspected. $\ Omega $ is the class of failure detectors that ...

This paper is on the Consensus problem, in the context of asynchronous distributed systems made of n processes, at most f of them may crash. A family of failure detector classes satisfying a Perpetual Accuracy property is first defined. This family includes the failure detector class S (the class of Strong failure detectors defined by Chandra and Toueg) central to the definition of a class (Sx) where x is the minimum number (x 1) of correct processes that can never be suspected to have crashed.

We consider the challenges of supporting collaborative decision making and applications requiring coordinated interaction in mobile ad hoc networks. This environment makes group coordination difficult due to relatively high packet loss and the presence of a continuously evolving network topology that leads to a changing set of participants. We describe and evaluate an application-level mobile reliable broadcast protocol (M-RBP) that provides applications with network characteristics well-suited to supporting coordinated interaction, such as reliable broadcast with data consistency and global ordering. The protocol is time-, rather than event-driven, providing it with unique, deterministic operational characteristics that can be verified in a relatively straightforward manner.

We consider asynchronous distributed systems with message losses and process crashes. We study the impact of finite process memory on the solution to consensus, repeated consensus and reliable broadcast. With finite process memory, we show that in some sense consensus is easier to solve than reliable broadcast, and that reliable broadcast is as difficult to solve as repeated consensus: More precisely, with finite memory, consensus can be solved with failure detector S, and P − (a variant of the perfect failure detector which is stronger than S) is necessary and sufficient to solve reliable broadcast and repeated consensus.

Broadcast is the fundamental collective communication routine in which the same message is delivered from a single source to all the nodes in a network. The most efficient way to implement broadcast is through the construction of a broadcast tree.

A group key agreement protocol (GKA) allows a set of players to establish a shared secret key which can be used to secure a subsequent communication. Several efficient constantround GKAs have been proposed. However, their performance degrades if some players fail during protocol execution. This is a problem in practice, e.g. for mobile nodes communicating over wireless media, which can loose connectivity during the protocol execution. Current constantround GKA protocols are either efficient and non-robust or robust but not efficient: Assuming a reliable broadcast communication medium, the standard encryption-based group key agreement protocol can be robust against arbitrary number of node faults, but the size of the messages broadcast by every player is proportional to the number of players. In contrast, non-robust group key agreement can be achieved with each player broadcasting just constant-sized messages. We propose a novel 2-round group key agreement protocol which tolerates up to T node failures using O(T)-sized messages, for any T. To exemplify the usefulness of this flexible trade-off between message size and fault tolerance, we show that the new protocol implies a fully-robust group key agreement with O(log n)-sized messages and expected round complexity close to 2, assuming random node faults. The proposed protocol is secure under the (standard) Decisional Square Diffie-Hellman assumption.

Securing broadcast communication over sensor networks is an important research challenge. In general, broadcast communication has two important metrics: security and reliability. Though the reliability metric has drawn sufficient attention in the research community, the security metric has failed to do so. In this paper we address both these metrics with more emphasis on the former and address the Denial-of-Broadcast Message attacks (DoBM) in sensor networks. We propose a tree based model called the k-parent Flooding Tree Model (k-FTM) and present algorithms for the construction of k-FTM. The proposed k-FTM is robust against DoBM and enables the base station to detect DoBM very efficiently even in the presence of a prudent adversary who focuses on remaining undetected by causing damage below the detection threshold. k-FTM is, to our best knowledge, the first fault tolerant tree model, that is both secure and reliable. We confirm through simulations that our model achieves detection rates close to a static tree and a broadcast reliability close to blind flooding.

Gossip, or epidemic, protocols have emerged as a powerful strategy to implement highly scalable and resilient reliable broadcast primitives on large scale peer-to-peer networks. Epidemic protocols are scalable because they distribute the load among all nodes in the system and resilient because they have an intrinsic level of redundancy that masks node and network failures. This chapter provides an introduction to gossip-based broadcast on largescale unstructured peer-to-peer overlay networks: it surveys the main results in the field, discusses techniques to build and maintain the overlays that support efficient dissemination strategies, and provides an in-depth discussion and experimental evaluation of two concrete protocols, named HyParView and Plumtree.

Database replication protocols based on a certification approach are usually the best ones for achieving good performance when an eager update everywhere technique is being considered. The weak voting approach achieves a slightly longer transaction completion time, but with a lower abortion rate. So, both techniques can be considered as the best ones for eager replication when performance is a must, and both of them need atomic broadcast. We propose a new database replication strategy that shares many characteristics with such previous strategies. It is also based on totally ordering the application of writesets, using only an unordered reliable broadcast, instead of an atomic broadcast. Additionally, the writesets of transactions that are aborted in the final validation phase need not be broadcast in our strategy. Thus, this new approach always reduces the communication traffic and also achieves a good transaction response time (even shorter than those previous strategies in some system configurations).

Database replication protocols based on a certification approach are usually the best ones for achieving good performance. The weak voting approach achieves a slightly longer transaction completion time, but with a lower abortion rate. So, both techniques can be considered as the best ones for replication when performance is a must, and both of them take advantage of the properties provided by atomic broadcast. We propose a new database replication strategy that shares many characteristics with such previous strategies. It is also based on totally ordering the application of writesets, using only an unordered reliable broadcast, instead of an atomic broadcast. Additionally, the writesets of transactions that are aborted in the final validation phase are not broadcast in our strategy. Thus, this new approach reduces the communication traffic and also achieves a good transaction response time (even shorter than those previous strategies in some system configurations).

In a wireless ad-hoc network environment, it is important for a mobile host to be able to broadcast control information within a team of nodes in a bandwidth-efficient and timely manner. Although the classical flooding strategy is the only reliable broadcast method for high rates of topology change, it leads to unnecessary bandwidth consumption for low rates of topology change.

In this paper, we consider best-effort broadcast service (BEBS) in wireless cellular networks, which can be used for location-based advertising or real-time multimedia broadcasting. Contrary to the conventional broadcasting service that aims to assure reliable data delivery to all users, we establish the objective of BEBS to maximize the effective capacity of wireless resource at the cost of reliability. In this context, we introduce the notion of target reliability and formulate the problem of maximizing the capacity of BEBS under a constraint of reliability. We derive the analysis model to investigate the effect of target reliability on the achievable capacity and validate the analysis model by comparing the analysis results with the simulation results. Both analysis and simulation results confirm that the BEBS significantly improves the effective capacity by relaxing the reliability constraint, compared to the conventional reliable broadcasting.

A reliable broadcast is communication primitive used to develop fault tolerant distributed applications. It in due course delivers messages to all participating sites irrespective of their ordering. Total order broadcast impose restriction on message ordering and satisfies total order requirement.

A clear specifications, rigorous validation and verification is key to obtain better design of dependable services in such applications. With the help of formal methods one can specify and verify systems in systematic rather than ad hoc manner. It reveals ambiguities, incompleteness, and inconsistencies in a
system by facilitating clear specification, rigorous validation and verification.

In this paper, we present a formal development of total order broadcast. The model have been developed and checked by using event-B techniques supported by the RODIN tool. Event-B is a formal technique that supports the incremental design of a distributed applications using notion of refinements.

This paper presents an evaluation of several communication-optimal algorithms implementing the 3P class of failure detectors. The first algorithm is based on a Reliable Broadcast primitive, involving a quadratic number of messages to manage a suspicion. The second algorithm uses exclusively one-to-one communication, involving a linear number of messages to manage a suspicion, but with a higher latency to propagate the suspicion to the rest of processes. A third algorithm reduces this latency using an additional one-to-all communication mechanism. We evaluate the quality of service provided by these algorithms, in terms of the capability of the failure detector to provide right answers and the reaction time after a failure.

Using IP addresses in limited devices provides many benefits, but the big size of the addresses becomes a problem when resources are bounded. In order to send data to all its neighbors in an Ad-Hoc Network, a node must know all their identities, which can have a severe impact on available resources. Then, a link layer reliable broadcast emerges as a necessary feature. In this paper we present a protocolo named LLRB (Link Layer Reliable Broadcast) that extends the RTS/CTS/ACK mechanism to be used when the data is sent not only to a single node but to the whole neighborhood.