Reliable Broadcast

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.

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.

... 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 ...

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.

Byzantine consensus in asynchronous message-passing systems has been shown to require at least 3f + 1 processes to be solvable in several system models (e.g., with failure detectors, partial synchrony or randomization). Recently a couple of solutions to implement Byzantine fault-tolerant state machine replication using only 2f + 1 replicas have appeared. This reduction from 3f + 1 to 2f + 1 is possible with a hybrid system model, i.e., by extending the system model with trusted/trustworthy components that constrain the power of faulty processes to have certain behaviors. Despite these important results, the problem of solving Byzantine consensus with only 2f + 1 processes is still far from being well understood. In this paper we present a methodology to transform crash consensus algorithms into Byzantine consensus algorithms with different characteristics, with the assistance of a reliable broadcast primitive that requires trusted/trustworthy components to be implemented. We exemplify the methodology with two algorithms, one that uses failure detectors and one that is randomized. We also define a new flavor of consensus and use it to solve atomic broadcast, showing the practical interest of the transformations.

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).

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.

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.

The paper presents the Extra-Stage Cube interconnection network reliability estimation using Stratified Sampling Monte Carlo (SSMC) method. The parameter of reliability includes terminal reliability, broadcast reliability and network reliability. The SSMC method provides approximate solutions by performing statistical sampling experiments on a computer. This method of reliability prediction is useful when system complexity makes the formulation of exact models essentially impossible. A computer program has been developed and the SSMC method was demonstrated as a good estimator for all the three types of the reliability parameter after compared with the exact reliability and reliability bounds. obtained by Matrix Enumeration (ME) method [2] for N=8 to N=32, and by Recursive Manner (RM) method [14] for N=128 to N=1024. The measure of accuracy using parameter α is defined as α = ME ME SSMC | | − for N=8 to N=32 α = RM RM SSMC | |

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.

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.

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.

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 allow 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. .

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.

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.

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 paper proposes a model for (a class of) dynamic systems. That dynamic model is defined by (1) a parameter (an integer denoted) and (2) two basic communication abstractions (query-response and persistent reliable broadcast). The new parameter is a threshold value introduced to capture the liveness part of the system (it is the counterpart of the minimal number of processes that do not crash in a static system). To show the relevance of the model, the paper adapts an eventual leader protocol designed for the static model, and proves that the resulting protocol is correct within the proposed dynamic model. In that sense, the paper has also a methodological flavor, as it shows that simple modifications to existing protocols can allow them to work in dynamic systems.

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.

Byzantine consensus in asynchronous message-passing systems has been shown to require at least 3f + 1 processes to be solvable in several system models (e.g., with failure detectors, partial synchrony or randomization). Recently a couple of solutions to implement Byzantine fault-tolerant state-machine replication using only 2f + 1 replicas have appeared. This reduction from 3f + 1 to 2f + 1 is possible with a hybrid system model, i.e., by extending the system model with trusted/trustworthy components that constrain the power of faulty processes to have certain behaviors. Despite these important results, the problem of solving Byzantine consensus with only 2f + 1 processes is still far from being well understood. In this paper we present a methodology to transform crash consensus algorithms into Byzantine consensus algorithms with different characteristics, with the assistance of a reliable broadcast primitive that requires trusted/trustworthy components to be implemented. We exemplify the methodology with two algorithms, one that uses failure detectors and one that is randomized. We also define a new flavor of consensus and use it to solve atomic broadcast, showing the practical interest of the transformations.

Conventional broadcasting protocols suffer from network congestion, frequent message losses and corruption of broadcast messages due to a vast number of duplicate packets transmitting in the network. In this paper, we propose an efficient, scalable and reliable broadcast protocol to send a message in the entire network where every node is guaranteed to receive the message with low overhead and minimal cost. The scalability and reliability of broadcast transmission is ensured by composing the entire network in a hierarchy of grids/squares. A higher order square is made up of four lower order squares forming a quad tree architecture. With this grid architecture a node does not need to flood the broadcast packet to the entire network. Rather a node exploits the Geographic Forwarding mechanism to send the packet to a particular square. The rest of the work is done by the very first node receiving the packet destined for that particular grid. This node has now the responsibility to update its own grid with the broadcast packet. The whole procedure is repeated iteratively in every grid. Simulation results show that our proposed algorithm is reliable, scalable, robust and also outperforms some other promising broadcasting protocols that exist in the current literature.

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.

Network protocol designers, both at the physical and network level, have long considered interference and simultaneous transmission in wireless protocols as a problem to be avoided. This, coupled with a tendency to emulate wired network protocols in the wireless domain, has led to artificial limitations in wireless networks.

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

Abstract This paper proposes a novel protocol for reliable broadcasting of life safety messages in Vehicular Ad-hoc Networks (VANETs) simulating reactions of car drivers. In case of any dramatic change of speed or moving direction, the vehicle is considered ...

This paper proposes a novel protocol for reliable broadcasting of life safety messages in Vehicular Ad-hoc Networks (VANETs) simulating reactions of car drivers. In case of any dramatic change of speed or moving direction, the vehicle is considered abnormal and hence it transmits an emergency warning message over the control channel of the Dedicated Short-Range Communication Protocol (DSRC). The proposed protocol gives the vehicle in the most dangerous situation the highest priority to transmit the acknowledgement signal. The choice of that vehicle is done locally based on the location, direction, and speed of the receiving vehicle. The superiority of the proposed protocol over existing protocols is highlighted conceptually and with simulations.

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

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.

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.

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.

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.

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.

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.

Traditional wireless ad hoc medium access control (MAC) protocols often utilize control frames such as Request-To-Send (RTS), Clear-To-Send (CTS) and Acknowledgement (ACK) to reliably delivery unicast data. However, little effort has been given to improve the reliable delivery of broadcast data. Often, broadcast data are transmitted blindly without any consideration of hidden terminals. In this paper, we proposed a novel MAC protocol, Broadcast Medium Window (BMW) that reliably delivers broadcast data.

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.

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.

ABSTRACT In this paper different means for adding reliability in different protocol layers are discussed, in order to reliably broadcast multimedia data within existing wireless networks. In particular, we investigate the performance of additional forward error correction in the physical layer, the radio link control layer, and the RTP layer for multimedia broadcast and multicast services over GERAN systems. Advantages and drawbacks when applying means for reliability in different layers are shown. We introduce a simple receiver modification, referred to as permeable-layer receiver (PLR), which exploits traditionally useless information at the receiver, while the transmitter is kept unchanged. Significant performance gains are reported. Finally, the application to H.264/AVC based wireless video broadcast is discussed and the performance of different system designs for video transmission is shown

Abstract-Orca is a language for implementing parallel ap- plications 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 ...

In the recent past composability has emerged as a key requirement for various distributed protocols. It is not enough for a protocol to be robust when it runs in isolation or in a “stand-alone” setting but it should be robust even in an environment where several copies of the same protocol or other protocol(s) are running simultaneously. In this work, we investigate the composability for protocols that tolerate a bounded adversary modeled as a probabilistic polynomial time Turing machine. We examine composability of protocols for two fundamental problems in distributed computing - reliable unicast and reliable broadcast. We show that any composable protocol – for reliable unicast tolerating an adversary, that corrupts up to any t nodes, requires 2t + 1 connectivity and for reliable broadcast tolerating an adversary, that corrupts up to any t nodes, requires n > 3t and 2t + 1 connectivity.

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.

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.

Many distributed and parallel applications can make good use of broadcast communication. In this paper we present a (software) protocol that simulates reliable broadcast, even on an unreliable network. Using this protocol, application programs need not worry about lost messages. Recovery of communication failures is handled automatically and transparently by the protocol. In normal operation, our protocol is more efficient than previously published reliable broadcast protocols. An initial implementation of the protocol on 10 MC68020 CPUs connected by a 10 Mbit/sec Ethernet performs a reliable broadcast in 1.5 msec.

Ensuring causal consistency in a Distributed Shared Memory (DSM) means all operations executed at each process will be compliant to a causality order relation. This paper first introduces an optimality criterion for a protocol P , based on a complete replication of memory locations at each process and propagation of write updates, that enforces causal consistency. This criterion measures the capability of a protocol to update the local copy as soon as possible while respecting causal consistency. Then we present an optimal protocol built on top of a reliable broadcast communication primitive and we show how previous protocols based on complete replication presented in the literature are not optimal. Interestingly, we prove that the optimal protocol embeds a system of vector clocks which captures the read/write semantics of a causal memory. From an operational point of view, an optimal protocol exploiting reliable broadcast strongly reduces its message buffer overhead. Simulation studies show that the optimal protocol roughly buffers a number of messages of one order of magnitude lower than non-optimal ones based on the same communication primitive.

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.

Considerations of the real-time self-organization of neural networks for speech recognition 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 partially-compressed code, mapped to the articulatory system, to permit imitation of novel sounds. Furthermore, top-down priming signals from the articulatory system to the auditory system help to stabilize the emerging auditory code. These structures help explain results from the motor theory, which states that speech is analyzed by how it would be produced. Higher stages of processing require chunking or unitization of the emerging language code, an example of a classical grouping problem. The partially compressed auditory codes are further compressed into item codes (e.g., phonemic segments), which are stored in a working memory representation whose shortterm memory pattern is its code. A masking field level receives input from this working memory and encodes this input into list chunks, whose top-down signals organize the items in working memory into coherent groupings with invariant properties. This total architecture sheds new light on key speech issues such as coarticulation, analysis-by-synthesis, motor theory, categorical perception, invariant speech perception, word superiority, and phonemic restoration.

Gossip, or epidemic, protocols have emerged as a powerful strategy to implement highly scalable and resilient reliable broadcast primitives. Due to scalability reasons, each participant in a gossip protocol maintains a partial view of the system. The reliability of the gossip protocol depends upon some critical properties of these views, such as degree distribution and clustering coefficient.

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.