13,524 research outputs found
Reliable Messaging to Millions of Users with MigratoryData
Web-based notification services are used by a large range of businesses to
selectively distribute live updates to customers, following the
publish/subscribe (pub/sub) model. Typical deployments can involve millions of
subscribers expecting ordering and delivery guarantees together with low
latencies. Notification services must be vertically and horizontally scalable,
and adopt replication to provide a reliable service. We report our experience
building and operating MigratoryData, a highly-scalable notification service.
We discuss the typical requirements of MigratoryData customers, and describe
the architecture and design of the service, focusing on scalability and fault
tolerance. Our evaluation demonstrates the ability of MigratoryData to handle
millions of concurrent connections and support a reliable notification service
despite server failures and network disconnections
Implementation and evaluation of the sensornet protocol for Contiki
Sensornet Protocol (SP) is a link abstraction layer between the network layer and the link layer for sensor networks. SP was proposed as the core of a future-oriented sensor node architecture that allows flexible and optimized combination between multiple coexisting protocols. This thesis implements the SP sensornet protocol on the Contiki operating system in order to: evaluate the effectiveness of the original SP services; explore further requirements and implementation trade-offs uncovered by the original proposal. We analyze the original SP design and the TinyOS implementation of SP to design the Contiki port. We implement the data sending and receiving part of SP using Contiki processes, and the neighbor management part as a group of global routines. The evaluation consists of a single-hop traffic throughput test and a multihop convergecast test. Both tests are conducted using both simulation and experimentation. We conclude from the evaluation results that SP's link-level abstraction effectively improves modularity in protocol construction without sacrificing performance, and our SP implementation on Contiki lays a good foundation for future protocol innovations in wireless sensor networks
On the tradeoff between privacy and energy in wireless sensor networks
Source location privacy is becoming an increasingly important property of some wireless sensor network applica- tions. The fake source technique has been proposed as an approach for handling the source location privacy problem in these situations. However, whilst the efficiency of the fake source techniques is well documented, there are several factors that limit the usefulness of current results: (i) the assumption that fake sources are known a priori, (ii) the selection of fake sources based on an prohibitively expensive pre-configuration phase and (iii) the lack of a commonly adopted attacker model. In this paper we address these limitations by investigating the efficiency of the fake source technique with respect to possible implementations, configurations and extensions that do not require a pre-configuration phase or a priori knowledge of fake sources. The results presented demonstrate that one possible implementation, in presence of a single attacker, can lead to a decrease in capture ratio of up to 60% when compared with a flooding baseline. In the presence of multiple attackers, the same implementation yields only a 30% decrease in capture ratio with respect to the same baseline. To address this problem we investigate a hybrid technique, known as phantom routing with fake sources, which achieves a corresponding 50% reduction in capture ratio
Towards composition of verified hardware devices
Computers are being used where no affordable level of testing is adequate. Safety and life critical systems must find a replacement for exhaustive testing to guarantee their correctness. Through a mathematical proof, hardware verification research has focused on device verification and has largely ignored system composition verification. To address these deficiencies, we examine how the current hardware verification methodology can be extended to verify complete systems
Visualization of Tree-Structured Data Through a Multi Touch User Interface
This writing project examines different types of visualizations for tree-structured data sets. Visualizations discussed include link-node diagrams and treemap diagrams. Also discussed is recent innovations with regards to distinguishing multi touch from single touch technology. I explore the requirements needed to build a multi touch table top surface, and describe the process of building one. I then describe my proposed method of visualizing tree-structured data and how it can be implemented using Core Animation technology. I also propose a means of interacting with the data through a multi touch interface, and discuss which gestures can be used to navigate the visualization display
Hong-Ou-Mandel interference of polarization qubits stored in independent room-temperature quantum memories
First generation quantum repeater networks require independent quantum
memories capable of storing and retrieving indistinguishable photons to perform
quantum-interference-mediated high-repetition entanglement swapping operations.
The ability to perform these coherent operations at room temperature is of
prime importance in order to realize large scalable quantum networks. Here we
address these significant challenges by observing Hong-Ou-Mandel (HOM)
interference between indistinguishable photons carrying polarization qubits
retrieved from two independent room-temperature quantum memories. Our
elementary quantum network configuration includes: (i) two independent sources
generating polarization-encoded qubits; (ii) two atomic-vapor dual-rail quantum
memories; and (iii) a HOM interference node. We obtained interference
visibilities after quantum memory retrieval of for few-photon level inputs and for single-photon level inputs. Our prototype
network lays the groundwork for future large-scale memory-assisted quantum
cryptography and distributed quantum networks.Comment: 12 pages, 6 figure
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