15,876 research outputs found
Towards Loop-Free Forwarding of Anonymous Internet Datagrams that Enforce Provenance
The way in which addressing and forwarding are implemented in the Internet
constitutes one of its biggest privacy and security challenges. The fact that
source addresses in Internet datagrams cannot be trusted makes the IP Internet
inherently vulnerable to DoS and DDoS attacks. The Internet forwarding plane is
open to attacks to the privacy of datagram sources, because source addresses in
Internet datagrams have global scope. The fact an Internet datagrams are
forwarded based solely on the destination addresses stated in datagram headers
and the next hops stored in the forwarding information bases (FIB) of relaying
routers allows Internet datagrams to traverse loops, which wastes resources and
leaves the Internet open to further attacks. We introduce PEAR (Provenance
Enforcement through Addressing and Routing), a new approach for addressing and
forwarding of Internet datagrams that enables anonymous forwarding of Internet
datagrams, eliminates many of the existing DDoS attacks on the IP Internet, and
prevents Internet datagrams from looping, even in the presence of routing-table
loops.Comment: Proceedings of IEEE Globecom 2016, 4-8 December 2016, Washington,
D.C., US
A Light-Weight Forwarding Plane for Content-Centric Networks
We present CCN-DART, a more efficient forwarding approach for content-centric
networking (CCN) than named data networking (NDN) that substitutes Pending
Interest Tables (PIT) with Data Answer Routing Tables (DART) and uses a novel
approach to eliminate forwarding loops. The forwarding state required at each
router using CCN-DART consists of segments of the routes between consumers and
content providers that traverse a content router, rather than the Interests
that the router forwards towards content providers. Accordingly, the size of a
DART is proportional to the number of routes used by Interests traversing a
router, rather than the number of Interests traversing a router. We show that
CCN-DART avoids forwarding loops by comparing distances to name prefixes
reported by neighbors, even when routing loops exist. Results of simulation
experiments comparing CCN-DART with NDN using the ndnSIM simulation tool show
that CCN-DART incurs 10 to 20 times less storage overhead
Enabling Correct Interest Forwarding and Retransmissions in a Content Centric Network
We show that the mechanisms used in the name data networking (NDN) and the
original content centric networking (CCN) architectures may not detect Interest
loops, even if the network in which they operate is static and no faults occur.
Furthermore, we show that no correct Interest forwarding strategy can be
defined that allows Interest aggregation and attempts to detect Interest
looping by identifying Interests uniquely. We introduce SIFAH (Strategy for
Interest Forwarding and Aggregation with Hop-Counts), the first Interest
forwarding strategy shown to be correct under any operational conditions of a
content centric network. SIFAH operates by having forwarding information bases
(FIBs) store the next hops and number of hops to named content, and by having
each Interest state the name of the requested content and the hop count from
the router forwarding an Interest to the content. We present the results of
simulation experiments using the ndnSIM simulator comparing CCN and NDN with
SIFAH. The results of these experiments illustrate the negative impact of
undetected Interest looping when Interests are aggregated in CCN and NDN, and
the performance advantages of using SIFAH
Transverse oscillations of a multi-stranded loop
We investigate the transverse oscillations of a line-tied multi-stranded
coronal loop composed of several parallel cylindrical strands. First, the
collective fast normal modes of the loop are found with the T-matrix theory.
There is a huge quantity of normal modes with very different frequencies and a
complex structure of the associated magnetic pressure perturbation and velocity
field. The modes can be classified as bottom, middle, and top according to
their frequencies and spatial structure. Second, the temporal evolution of the
velocity and magnetic pressure perturbation after an initial disturbance are
analyzed. We find complex motions of the strands. The frequency analysis
reveals that these motions are a combination of low and high frequency modes.
The complexity of the strand motions produces a strong modulation of the whole
tube movement. We conclude that the presumed internal fine structure of a loop
influences its transverse oscillations and so its transverse dynamics cannot be
properly described by those of an equivalent monolithic loop.Comment: Accepted in Ap
Dark photon searches with atomic transitions
Dark matter could be made up of dark photons, massive but very light
particles whose interactions with matter resemble those of usual photons but
suppressed by a small mixing parameter. We analyze the main approaches to dark
photon interactions and how they can be applied to direct detection experiments
which test different ranges of masses and mixings. A new experiment based on
counting dark photons from induced atomic transitions in a target material is
proposed. This approach appears to be particularly appropriate for dark photon
detection in the meV mass range, extending the constraints in the mixing
parameter by up to eight orders of magnitude with respect to previous
experiments.Comment: 16 pages, 3 figure
Study of a colliding laser-produced plasma by analysis of time and space-resolved image spectra
The interaction of two counter-propagating laser-produced plasmas was studied using simultaneous
imaging and spectroscopic techniques. Spectrally-filtered time-gated ICCD imaging was used
to obtain information about the spatial dynamics and temporal evolution of the collision process.
While, time-resolved imaging spectroscopy was used to determine the spatial and temporal distributions
of electron temperature and density within the interaction region. We examine specifically
the interaction of plasmas whose parameters match those typically used in pulsed laser deposition
of thin films. These low temperature plasmas are highly collisional leading to the creation of a
pronounced stagnation layer in the interaction region
The effects of magnetic-field geometry on longitudinal oscillations of solar prominences: Cross-sectional area variation for thin tubes
Solar prominences are subject to both field-aligned (longitudinal) and
transverse oscillatory motions, as evidenced by an increasing number of
observations. Large-amplitude longitudinal motions provide valuable information
on the geometry of the filament-channel magnetic structure that supports the
cool prominence plasma against gravity. Our pendulum model, in which the
restoring force is the gravity projected along the dipped field lines of the
magnetic structure, best explains these oscillations. However, several factors
can influence the longitudinal oscillations, potentially invalidating the
pendulum model. The aim of this work is to study the influence of large-scale
variations in the magnetic field strength along the field lines, i.e.,
variations of the cross-sectional area along the flux tubes supporting
prominence threads. We studied the normal modes of several flux tube
configurations, using linear perturbation analysis, to assess the influence of
different geometrical parameters on the oscillation properties. We found that
the influence of the symmetric and asymmetric expansion factors on longitudinal
oscillations is small.}{We conclude that the longitudinal oscillations are not
significantly influenced by variations of the cross-section of the flux tubes,
validating the pendulum model in this context.Comment: Accepted for publication in Astronomy & Astrophysic
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