Causal Message Ordering Research Articles

An Efficient Causal Group Communication Protocol for Free Scale Peer-to-Peer Networks

In peer-to-peer (P2P) overlay networks, a group of n (≥2) peer processes have to cooperate with each other. Each peer sends messages to every peer and receives messages from every peer in a group. In group communications, each message sent by a peer is required to be causally delivered to every peer. Most of the protocols designed to ensure causal message order are designed for networks with a plain architecture. These protocols can be adapted to use in free scale and hierarchical topologies; however, the amount of control information is O(n), where n is the number of peers in the system. Some protocols are designed for a free scale or hierarchical networks, but in general they force the whole system to accomplish the same order viewed by a super peer. In this paper, we present a protocol that is specifically designed to work with a free scale peer-to-peer network. By using the information about the network’s architecture and by representing message dependencies on a bit level, the proposed protocol ensures causal message ordering without enforcing super peers order. The designed protocol is simulated and compared with the Immediate Dependency Relation and the Dependency Sequences protocols to show its lower overhead.

QoS Guaranteed Causal Ordering Group Communication for Cognitive Radio Ad Hoc Networks

In this paper, we discuss the QoS guaranteed causal ordering group communication for cognitive radio (CR) ad hoc networks. The issue of causal ordering has been studied extensively by previous works. However, these works considered the problem at the transport layer and the methods in the works incurred high communication overhead and the long latency for message delivery. In this paper, we discuss the causal ordering at the network layer. The problem of our concern is: given a QoS group communication request in a CR ad hoc network, how to set up the connection so that the causal ordering of the group communication can be preserved, and the bandwidth consumption of the communication is minimized under the condition that the QoS requirement is satisfied. In this paper, we focus on the bandwidth requirement. We propose a two-phase method to solve the problem. In the method, we first construct a multicast tree for the communication, and then assign slots for all tree links. It is proved that the method can preserve the causal ordering of messages without extra communication overhead nor the latency for delivering messages. Simulations are conducted to show the performance of our proposed method.

Causal Order Protocol Based on Virtual Synchronous Group Membership in Wireless Sensor Networks

Many distributed applications require cooperating to fuse their data in those WSNs in real time. Some of these WSNs allow interacting with publishers and subscribers (P/S) sensors. But, there exist little research works on development of causal ordering based on virtual synchronous group membership of these P/S systems, one of mandatory properties for this kind of application fields. In this paper, we propose a novel approach based on gossip protocols and virtual synchronous group membership, guaranteeing the causal message ordering in those WSNs. In the proposed protocol, a broker gossips about FLUSH including the whole set of vectors to subscribers for virtual synchronous group membership. The protocol does not end based on the acknowledgement of FLUSH, but on the maximum gossip rounds of gossip disseminations. Therefore, this protocol is appropriate for sensor networks configured with active and passive sensors in real time synchronization. Its features might result in very low cost communication overhead between brokers and subscribers with flexible consistency by cooperating to fuse their data. Simulation results show that our gossip-style dissemination protocol outperforms the previous one in terms of virtual synchronous group membership.

Necessary and sufficient conditions on information for causal message ordering and their optimal implementation

This paper formulates necessary and sufficient conditions on the information required for enforcing causal ordering in a distributed system with asynchronous communication. The paper then presents an algorithm for enforcing causal message ordering. The algorithm allows a process to multicast to arbitrary and dynamically changing process groups. We show that the algorithm is optimal in the space complexity of the overhead of control information in both messages and message logs. The algorithm achieves optimality by transmitting the bare minimum causal dependency information specified by the necessity conditions, and using an encoding scheme to represent and transmit this information. We show that, in general, the space complexity of causal message ordering in an asynchronous system is Ω(n2), where n is the number of nodes in the system. Although the upper bound on space complexity of the overhead of control information in the algorithm is O(n2), the overhead is likely to be much smaller on the average, and is always the least possible.

An Adaptive Causal Ordering Algorithm Suited to Mobile Computing Environments

Causal message ordering is required for several distributed applications. In order to preserve causal ordering, only direct dependency information between messages, with respect to the destination process(es), need be sent with each message. By eliminating other kinds of control information from the messages, the communication overheads can be significantly reduced. In this paper we present an algorithm that uses this knowledge to efficiently enforce causal ordering of messages. The proposed algorithm does not require any prior knowledge of the network topology or communication pattern. As computation proceeds, it acquires knowledge of the communication pattern and is capable of handling dynamically changing multicast communication groups, and minimizing the communication overheads. With regard to communication overheads, the algorithm is optimal for the broadcast communication case. Extensive simulation experiments demonstrate that the algorithm imposes lower communication overheads than previous causal ordering algorithms. The algorithm can be employed in a variety of distributed computing environments. Its energy efficiency and low bandwidth requirement make it especially suitable for mobile computing systems. We show how to employ the algorithm for causally ordered multicasting of messages in mobile computing environments.

A total ordering multicast protocol using propagation trees

The paper discusses a multicast mechanism using propagation trees. It guarantees the total ordering (including causal ordering) of messages in multiple groups. The mechanism introduces a concept of meta-groups (a subset of a multicast group) and organizes meta-groups into propagation trees. Compared with the existing propagation tree mechanisms, this mechanism has the following advantages: 1) Greater parallelism. Messages can be sent to destinations by using broadcast networks. 2) Less message cost and less latency time. It takes less network communication to multicast a message and less time to have the message delivered to all the destinations. 3) More flexibility to dynamic membership changes and higher reliability for message propagation. It does not need to restructure propagation trees when there is a change in membership, and a site failure does not stop the message propagation to its descendants in the tree.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An optimal algorithm for distributed snapshots with causal message ordering

We present an optimal distributed algorithm to record a global state of a distributed system with causally ordered message delivery. The message complexity of our algorithm is O( n) bits where n is the number of processes in the system.