23,148 research outputs found
libcppa - Designing an Actor Semantic for C++11
Parallel hardware makes concurrency mandatory for efficient program
execution. However, writing concurrent software is both challenging and
error-prone. C++11 provides standard facilities for multiprogramming, such as
atomic operations with acquire/release semantics and RAII mutex locking, but
these primitives remain too low-level. Using them both correctly and
efficiently still requires expert knowledge and hand-crafting. The actor model
replaces implicit communication by sharing with an explicit message passing
mechanism. It applies to concurrency as well as distribution, and a lightweight
actor model implementation that schedules all actors in a properly
pre-dimensioned thread pool can outperform equivalent thread-based
applications. However, the actor model did not enter the domain of native
programming languages yet besides vendor-specific island solutions. With the
open source library libcppa, we want to combine the ability to build reliable
and distributed systems provided by the actor model with the performance and
resource-efficiency of C++11.Comment: 10 page
Roaming Real-Time Applications - Mobility Services in IPv6 Networks
Emerging mobility standards within the next generation Internet Protocol,
IPv6, promise to continuously operate devices roaming between IP networks.
Associated with the paradigm of ubiquitous computing and communication, network
technology is on the spot to deliver voice and videoconferencing as a standard
internet solution. However, current roaming procedures are too slow, to remain
seamless for real-time applications. Multicast mobility still waits for a
convincing design. This paper investigates the temporal behaviour of mobile
IPv6 with dedicated focus on topological impacts. Extending the hierarchical
mobile IPv6 approach we suggest protocol improvements for a continuous
handover, which may serve bidirectional multicast communication, as well. Along
this line a multicast mobility concept is introduced as a service for clients
and sources, as they are of dedicated importance in multipoint conferencing
applications. The mechanisms introduced do not rely on assumptions of any
specific multicast routing protocol in use.Comment: 15 pages, 5 figure
Performance Analysis of Multicast Mobility in a Hierarchical Mobile IP Proxy Environment
Mobility support in IPv6 networks is ready for release as an RFC, stimulating
major discussions on improvements to meet real-time communication requirements.
Sprawling hot spots of IP-only wireless networks at the same time await voice
and videoconferencing as standard mobile Internet services, thereby adding the
request for multicast support to real-time mobility. This paper briefly
introduces current approaches for seamless multicast extensions to Mobile IPv6.
Key issues of multicast mobility are discussed. Both analytically and in
simulations comparisons are drawn between handover performance characteristics,
dedicating special focus on the M-HMIPv6 approach.Comment: 11 pages, 7 figure
Broadcasting in Prefix Space: P2P Data Dissemination with Predictable Performance
A broadcast mode may augment peer-to-peer overlay networks with an efficient,
scalable data replication function, but may also give rise to a virtual link
layer in VPN-type solutions. We introduce a simple broadcasting mechanism that
operates in the prefix space of distributed hash tables without signaling. This
paper concentrates on the performance analysis of the prefix flooding scheme.
Starting from simple models of recursive -ary trees, we analytically derive
distributions of hop counts and the replication load. Extensive simulation
results are presented further on, based on an implementation within the OverSim
framework. Comparisons are drawn to Scribe, taken as a general reference model
for group communication according to the shared, rendezvous-point-centered
distribution paradigm. The prefix flooding scheme thereby confirmed its widely
predictable performance and consistently outperformed Scribe in all metrics.
Reverse path selection in overlays is identified as a major cause of
performance degradation.Comment: final version for ICIW'0
Uncovering Vulnerable Industrial Control Systems from the Internet Core
Industrial control systems (ICS) are managed remotely with the help of
dedicated protocols that were originally designed to work in walled gardens.
Many of these protocols have been adapted to Internet transport and support
wide-area communication. ICS now exchange insecure traffic on an inter-domain
level, putting at risk not only common critical infrastructure but also the
Internet ecosystem (e.g., DRDoS~attacks).
In this paper, we uncover unprotected inter-domain ICS traffic at two central
Internet vantage points, an IXP and an ISP. This traffic analysis is correlated
with data from honeypots and Internet-wide scans to separate industrial from
non-industrial ICS traffic. We provide an in-depth view on Internet-wide ICS
communication. Our results can be used i) to create precise filters for
potentially harmful non-industrial ICS traffic, and ii) to detect ICS sending
unprotected inter-domain ICS traffic, being vulnerable to eavesdropping and
traffic manipulation attacks
Hypermedia Learning Objects System - On the Way to a Semantic Educational Web
While eLearning systems become more and more popular in daily education,
available applications lack opportunities to structure, annotate and manage
their contents in a high-level fashion. General efforts to improve these
deficits are taken by initiatives to define rich meta data sets and a
semanticWeb layer. In the present paper we introduce Hylos, an online learning
system. Hylos is based on a cellular eLearning Object (ELO) information model
encapsulating meta data conforming to the LOM standard. Content management is
provisioned on this semantic meta data level and allows for variable,
dynamically adaptable access structures. Context aware multifunctional links
permit a systematic navigation depending on the learners and didactic needs,
thereby exploring the capabilities of the semantic web. Hylos is built upon the
more general Multimedia Information Repository (MIR) and the MIR adaptive
context linking environment (MIRaCLE), its linking extension. MIR is an open
system supporting the standards XML, Corba and JNDI. Hylos benefits from
manageable information structures, sophisticated access logic and high-level
authoring tools like the ELO editor responsible for the semi-manual creation of
meta data and WYSIWYG like content editing.Comment: 11 pages, 7 figure
Revisiting Actor Programming in C++
The actor model of computation has gained significant popularity over the
last decade. Its high level of abstraction makes it appealing for concurrent
applications in parallel and distributed systems. However, designing a
real-world actor framework that subsumes full scalability, strong reliability,
and high resource efficiency requires many conceptual and algorithmic additives
to the original model.
In this paper, we report on designing and building CAF, the "C++ Actor
Framework". CAF targets at providing a concurrent and distributed native
environment for scaling up to very large, high-performance applications, and
equally well down to small constrained systems. We present the key
specifications and design concepts---in particular a message-transparent
architecture, type-safe message interfaces, and pattern matching
facilities---that make native actors a viable approach for many robust,
elastic, and highly distributed developments. We demonstrate the feasibility of
CAF in three scenarios: first for elastic, upscaling environments, second for
including heterogeneous hardware like GPGPUs, and third for distributed runtime
systems. Extensive performance evaluations indicate ideal runtime behaviour for
up to 64 cores at very low memory footprint, or in the presence of GPUs. In
these tests, CAF continuously outperforms the competing actor environments
Erlang, Charm++, SalsaLite, Scala, ActorFoundry, and even the OpenMPI.Comment: 33 page
Backscatter from the Data Plane --- Threats to Stability and Security in Information-Centric Networking
Information-centric networking proposals attract much attention in the
ongoing search for a future communication paradigm of the Internet. Replacing
the host-to-host connectivity by a data-oriented publish/subscribe service
eases content distribution and authentication by concept, while eliminating
threats from unwanted traffic at an end host as are common in today's Internet.
However, current approaches to content routing heavily rely on data-driven
protocol events and thereby introduce a strong coupling of the control to the
data plane in the underlying routing infrastructure. In this paper, threats to
the stability and security of the content distribution system are analyzed in
theory and practical experiments. We derive relations between state resources
and the performance of routers and demonstrate how this coupling can be misused
in practice. We discuss new attack vectors present in its current state of
development, as well as possibilities and limitations to mitigate them.Comment: 15 page
A Lesson in Scaling 6LoWPAN -- Minimal Fragment Forwarding in Lossy Networks
This paper evaluates two forwarding strategies for fragmented datagrams in
the IoT: hop-wise reassembly and a minimal approach to directly forward
fragments. Minimal fragment forwarding is challenged by the lack of forwarding
information at subsequent fragments in 6LoWPAN and thus requires additional
data at nodes. We compared the two approaches in extensive experiments
evaluating reliability, end-to-end latency, and memory consumption. In contrast
to previous work and due to our alternate setup, we obtained different results
and conclusions. Our findings indicate that direct fragment forwarding should
be deployed only with care, since higher packet transmission rates on the
link-layer can significantly reduce its reliability, which in turn can even
further reduce end-to-end latency because of highly increased link-layer
retransmissions.Comment: If you cite this paper, please use the LCN reference: M. S. Lenders,
T. C. Schmidt, M. W\"ahlisch. "A Lesson in Scaling 6LoWPAN - Minimal Fragment
Forwarding in Lossy Networks." in Proc. of IEEE LCN, 201
Optimizing Resolution and Uncertainty in Bathymetric Sonar Systems
Bathymetric sonar systems (whether multibeam or phase-differencing sidescan) contain an inherent trade-off between resolution and uncertainty. Systems are traditionally designed with a fixed spatial resolution, and the parameter settings are optimized to minimize the uncertainty in the soundings within that constraint. By fixing the spatial resolution of the system, current generation sonars operate sub-optimally when the SNR is high, producing soundings with lower resolution than is supportable by the data, and inefficiently when the SNR is low, producing high-uncertainty soundings of little value. Here we propose fixing the sounding measurement uncertainty instead, and optimizing the resolution of the system within that uncertainty constraint. Fixing the sounding measurement uncertainty produces a swath with a variable number of bathymetric estimates per ping, in which each estimate’s spatial resolution is optimized by combining measurements only until the desired depth uncertainty is achieved. When the signal to noise ratio is sufficiently high such that the desired depth uncertainty is achieved with individual measurements, bathymetric estimates are produced at the sonar’s full resolution capability. Correspondingly, a sonar’s resolution is no-longer only considered as a property of the sonar (based on, for example, beamwidth and bandwidth,) but now incorporates geometrical aspects of the measurements and environmental factors (e.g., seafloor scattering strength). Examples are shown from both multibeam and phase- differencing sonar systems
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