65,240 research outputs found
An adaptive reliable multicast protocol in ad hoc networks
Multicasting is an essential service for ad-hoc wireless networks. In multicast communication, many reliable multicast schemes were studied in order to overcome packet losses in the network. This paper describes our effort to build a Source Tree Reliable Multicast protocol for ad-hoc networks (STRM). STRM provides the delivery of an ordered contiguous sequence of data packets from one sender to many receivers in an ad-hoc network. It is designed to support applications based on bulk data transfer, like files, images and software packages. The core to its support of node mobility, and also what makes the protocol unique, is the dynamic selection of a sub set of 1-hop neighbors from the sender as its Forward Servers (FSs). The key idea behind selecting this sub set 1-hop neighbors is to forward the retransmit lost data packets that needed by some receivers to achieve higher throughput and to receive the ACK packet from receivers to avoid the ACK-implosion problem inherent in any reliable multicast scheme. Finally, simulation results show that the protocol has high delivery ratio and low end-to-end delay comparing with ReMHoc protocol
CRDTs: Consistency without concurrency control
A CRDT is a data type whose operations commute when they are concurrent.
Replicas of a CRDT eventually converge without any complex concurrency control.
As an existence proof, we exhibit a non-trivial CRDT: a shared edit buffer
called Treedoc. We outline the design, implementation and performance of
Treedoc. We discuss how the CRDT concept can be generalised, and its
limitations
Optimistic Parallel State-Machine Replication
State-machine replication, a fundamental approach to fault tolerance,
requires replicas to execute commands deterministically, which usually results
in sequential execution of commands. Sequential execution limits performance
and underuses servers, which are increasingly parallel (i.e., multicore). To
narrow the gap between state-machine replication requirements and the
characteristics of modern servers, researchers have recently come up with
alternative execution models. This paper surveys existing approaches to
parallel state-machine replication and proposes a novel optimistic protocol
that inherits the scalable features of previous techniques. Using a replicated
B+-tree service, we demonstrate in the paper that our protocol outperforms the
most efficient techniques by a factor of 2.4 times
Scalability of broadcast performance in wireless network-on-chip
Networks-on-Chip (NoCs) are currently the paradigm of choice to interconnect the cores of a chip multiprocessor. However, conventional NoCs may not suffice to fulfill the on-chip communication requirements of processors with hundreds or thousands of cores. The main reason is that the performance of such networks drops as the number of cores grows, especially in the presence of multicast and broadcast traffic. This not only limits the scalability of current multiprocessor architectures, but also sets a performance wall that prevents the development of architectures that generate moderate-to-high levels of multicast. In this paper, a Wireless Network-on-Chip (WNoC) where all cores share a single broadband channel is presented. Such design is conceived to provide low latency and ordered delivery for multicast/broadcast traffic, in an attempt to complement a wireline NoC that will transport the rest of communication flows. To assess the feasibility of this approach, the network performance of WNoC is analyzed as a function of the system size and the channel capacity, and then compared to that of wireline NoCs with embedded multicast support. Based on this evaluation, preliminary results on the potential performance of the proposed hybrid scheme are provided, together with guidelines for the design of MAC protocols for WNoC.Peer ReviewedPostprint (published version
DTKI: a new formalized PKI with no trusted parties
The security of public key validation protocols for web-based applications
has recently attracted attention because of weaknesses in the certificate
authority model, and consequent attacks.
Recent proposals using public logs have succeeded in making certificate
management more transparent and verifiable. However, those proposals involve a
fixed set of authorities. This means an oligopoly is created. Another problem
with current log-based system is their heavy reliance on trusted parties that
monitor the logs.
We propose a distributed transparent key infrastructure (DTKI), which greatly
reduces the oligopoly of service providers and allows verification of the
behaviour of trusted parties. In addition, this paper formalises the public log
data structure and provides a formal analysis of the security that DTKI
guarantees.Comment: 19 page
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