3,277 research outputs found
Design of a Hybrid Modular Switch
Network Function Virtualization (NFV) shed new light for the design,
deployment, and management of cloud networks. Many network functions such as
firewalls, load balancers, and intrusion detection systems can be virtualized
by servers. However, network operators often have to sacrifice programmability
in order to achieve high throughput, especially at networks' edge where complex
network functions are required.
Here, we design, implement, and evaluate Hybrid Modular Switch (HyMoS). The
hybrid hardware/software switch is designed to meet requirements for modern-day
NFV applications in providing high-throughput, with a high degree of
programmability. HyMoS utilizes P4-compatible Network Interface Cards (NICs),
PCI Express interface and CPU to act as line cards, switch fabric, and fabric
controller respectively. In our implementation of HyMos, PCI Express interface
is turned into a non-blocking switch fabric with a throughput of hundreds of
Gigabits per second.
Compared to existing NFV infrastructure, HyMoS offers modularity in hardware
and software as well as a higher degree of programmability by supporting a
superset of P4 language
Use of Devolved Controllers in Data Center Networks
In a data center network, for example, it is quite often to use controllers
to manage resources in a centralized man- ner. Centralized control, however,
imposes a scalability problem. In this paper, we investigate the use of
multiple independent controllers instead of a single omniscient controller to
manage resources. Each controller looks after a portion of the network only,
but they together cover the whole network. This therefore solves the
scalability problem. We use flow allocation as an example to see how this
approach can manage the bandwidth use in a distributed manner. The focus is on
how to assign components of a network to the controllers so that (1) each
controller only need to look after a small part of the network but (2) there is
at least one controller that can answer any request. We outline a way to
configure the controllers to fulfill these requirements as a proof that the use
of devolved controllers is possible. We also discuss several issues related to
such implementation.Comment: Appears in INFOCOM 2011 Cloud Computing Worksho
Identifying Proteins of High Designability via Surface-Exposure Patterns
Using an off-lattice model, we fully enumerate folded conformations of
polypeptide chains of up to N = 19 monomers. Structures are found to differ
markedly in designability, defined as the number of sequences with that
structure as a unique lowest-energy conformation. We find that designability is
closely correlated with the pattern of surface exposure of the folded
structure. For longer chains, complete enumeration of structures is
impractical. Instead, structures can be randomly sampled, and relative
designability estimated either from designability within the random sample, or
directly from surface-exposure pattern. We compare the surface-exposure
patterns of those structures identified as highly designable to the patterns of
naturally occurring proteins.Comment: 17 pages, 12 figure
Observable Properties of Orbits in Exact Bumpy Spacetimes
We explore the properties of test-particle orbits in "bumpy" spacetimes -
stationary, reflection-symmetric, asymptotically flat solutions of Einstein
equations that have a non-Kerr (anomalous) higher-order multipole-moment
structure but can be tuned arbitrarily close to the Kerr metric. Future
detectors should observe gravitational waves generated during inspirals of
compact objects into supermassive central bodies. If the central body deviates
from the Kerr metric, this will manifest itself in the emitted waves. Here, we
explore some of the features of orbits in non-Kerr spacetimes that might lead
to observable signatures. As a basis for this analysis, we use a family of
exact solutions proposed by Manko & Novikov which deviate from the Kerr metric
in the quadrupole and higher moments, but we also compare our results to other
work in the literature. We examine isolating integrals of the orbits and find
that the majority of geodesic orbits have an approximate fourth constant of the
motion (in addition to the energy, angular momentum and rest mass) and the
resulting orbits are tri-periodic to high precision. We also find that this
fourth integral can be lost for certain orbits in some oblately deformed
Manko-Novikov spacetimes. However, compact objects will probably not end up on
these chaotic orbits in nature. We compute the location of the innermost stable
circular orbit (ISCO) and find that the behavior of orbtis near the ISCO can be
qualitatively different depending on whether the ISCO is determined by the
onset of an instability in the radial or vertical direction. Finally, we
compute periapsis and orbital-plane precessions for nearly circular and nearly
equatorial orbits in both the strong and weak field, and discuss weak-field
precessions for eccentric equatorial orbits.Comment: 42 pages, 20 figures, accepted by Phys. Rev. D, v2 has minor changes
to make it consistent with published versio
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