2,038 research outputs found
Impact of Processing-Resource Sharing on the Placement of Chained Virtual Network Functions
Network Function Virtualization (NFV) provides higher flexibility for network
operators and reduces the complexity in network service deployment. Using NFV,
Virtual Network Functions (VNF) can be located in various network nodes and
chained together in a Service Function Chain (SFC) to provide a specific
service. Consolidating multiple VNFs in a smaller number of locations would
allow decreasing capital expenditures. However, excessive consolidation of VNFs
might cause additional latency penalties due to processing-resource sharing,
and this is undesirable, as SFCs are bounded by service-specific latency
requirements. In this paper, we identify two different types of penalties
(referred as "costs") related to the processingresource sharing among multiple
VNFs: the context switching costs and the upscaling costs. Context switching
costs arise when multiple CPU processes (e.g., supporting different VNFs) share
the same CPU and thus repeated loading/saving of their context is required.
Upscaling costs are incurred by VNFs requiring multi-core implementations,
since they suffer a penalty due to the load-balancing needs among CPU cores.
These costs affect how the chained VNFs are placed in the network to meet the
performance requirement of the SFCs. We evaluate their impact while considering
SFCs with different bandwidth and latency requirements in a scenario of VNF
consolidation.Comment: Accepted for publication in IEEE Transactions on Cloud Computin
Astrophysical code migration into Exascale Era
The ExaNeSt and EuroExa H2020 EU-funded projects aim to design and develop an
exascale ready computing platform prototype based on low-energy-consumption
ARM64 cores and FPGA accelerators. We participate in the application-driven
design of the hardware solutions and prototype validation. To carry on this
work we are using, among others, Hy-Nbody, a state-of-the-art direct N-body
code. Core algorithms of Hy-Nbody have been improved in such a way to
increasingly fit them to the exascale target platform. Waiting for the ExaNest
prototype release, we are performing tests and code tuning operations on an
ARM64 SoC facility: a SLURM managed HPC cluster based on 64-bit ARMv8
Cortex-A72/Cortex-A53 core design and powered by a Mali-T864 embedded GPU. In
parallel, we are porting a kernel of Hy-Nbody on FPGA aiming to test and
compare the performance-per-watt of our algorithms on different platforms. In
this paper we describe how we re-engineered the application and we show first
results on ARM SoC.Comment: 4 pages, 1 figure, 1 table; proceedings of ADASS XXVIII, accepted by
ASP Conference Serie
Virtual-Mobile-Core Placement for Metro Network
Traditional highly-centralized mobile core networks (e.g., Evolved Packet
Core (EPC)) need to be constantly upgraded both in their network functions and
backhaul links, to meet increasing traffic demands. Network Function
Virtualization (NFV) is being investigated as a potential cost-effective
solution for this upgrade. A virtual mobile core (here, virtual EPC, vEPC)
provides deployment flexibility and scalability while reducing costs,
network-resource consumption and application delay. Moreover, a distributed
deployment of vEPC is essential for emerging paradigms like Multi-Access Edge
Computing (MEC). In this work, we show that significant reduction in
networkresource consumption can be achieved as a result of optimal placement of
vEPC functions in metro area. Further, we show that not all vEPC functions need
to be distributed. In our study, for the first time, we account for vEPC
interactions in both data and control planes (Non-Access Stratum (NAS)
signaling procedure Service Chains (SCs) with application latency requirements)
using a detailed mathematical model
A Scalable Approach for Service Chain (SC) Mapping with Multiple SC Instances in a Wide-Area Network
Network Function Virtualization (NFV) aims to simplify deployment of network
services by running Virtual Network Functions (VNFs) on commercial
off-the-shelf servers. Service deployment involves placement of VNFs and
in-sequence routing of traffic flows through VNFs comprising a Service Chain
(SC). The joint VNF placement and traffic routing is called SC mapping. In a
Wide-Area Network (WAN), a situation may arise where several traffic flows,
generated by many distributed node pairs, require the same SC; then, a single
instance (or occurrence) of that SC might not be enough. SC mapping with
multiple SC instances for the same SC turns out to be a very complex problem,
since the sequential traversal of VNFs has to be maintained while accounting
for traffic flows in various directions. Our study is the first to deal with
the problem of SC mapping with multiple SC instances to minimize network
resource consumption. We first propose an Integer Linear Program (ILP) to solve
this problem. Since ILP does not scale to large networks, we develop a
column-generation-based ILP (CG-ILP) model. However, we find that exact
mathematical modeling of the problem results in quadratic constraints in our
CG-ILP. The quadratic constraints are made linear but even the scalability of
CG-ILP is limited. Hence, we also propose a two-phase column-generation-based
approach to get results over large network topologies within reasonable
computational times. Using such an approach, we observe that an appropriate
choice of only a small set of SC instances can lead to a solution very close to
the minimum bandwidth consumption. Further, this approach also helps us to
analyze the effects of number of VNF replicas and number of NFV nodes on
bandwidth consumption when deploying these minimum number of SC instances.Comment: arXiv admin note: substantial text overlap with arXiv:1704.0671
Service Chain (SC) Mapping with Multiple SC Instances in a Wide Area Network
Network Function Virtualization (NFV) aims to simplify deployment of network
services by running Virtual Network Functions (VNFs) on commercial
off-the-shelf servers. Service deployment involves placement of VNFs and
in-sequence routing of traffic flows through VNFs comprising a Service Chain
(SC). The joint VNF placement and traffic routing is usually referred as SC
mapping. In a Wide Area Network (WAN), a situation may arise where several
traffic flows, generated by many distributed node pairs, require the same SC,
one single instance (or occurrence) of that SC might not be enough. SC mapping
with multiple SC instances for the same SC turns out to be a very complex
problem, since the sequential traversal of VNFs has to be maintained while
accounting for traffic flows in various directions. Our study is the first to
deal with SC mapping with multiple SC instances to minimize network resource
consumption. Exact mathematical modeling of this problem results in a quadratic
formulation. We propose a two-phase column-generation-based model and solution
in order to get results over large network topologies within reasonable
computational times. Using such an approach, we observe that an appropriate
choice of only a small set of SC instances can lead to solution very close to
the minimum bandwidth consumption
DBBC3: AntArr Project
Low frequency bands in a traditional VLBI networks suffer not only from RFI but also from the
low efficiency of the radio telescopes. Dedicated arrays have to be used which have to maintain
all the constraints of a VLBI station, e.g., phase stability. With this aim a project with an
alternative application of the DBBC3 was set up and is presented, where a set of antennas
operating at frequencies lower than 1 GHz are combined into an array. The individual antennas
cover the broadband frequency range from 10 MHz to 1000 MHz
PMD Analysis Center 2013 Annual Report
This report summarizes the activities of the
Politecnico diMilano (PMD) IVS Analysis Center during
the year 2013 and outlines the planned aspects
of work for 2014. The main focuses in 2013 were in
the framework of the IAG WG 1.4.2 on Co-location
on Earth and in Space for the determination of the
Celestial Reference Frame. Studies carried out concern
e.g. simulations for some European VLBI antennas
performed to investigate if the VLBI phase referencing
technique can be used for precise determination
of GNSS state vectors. Furthermore, investigations
into possible deformations introduced by the change to
ICRF2 [1] were also made for the processing of 24-
hour observational session
The Stellar Initial Mass Function at the Epoch of Reionization
I provide estimates of the ultraviolet and visible light luminosity density
at z~6 after accounting for the contribution from faint galaxies below the
detection limit of deep Hubble and Spitzer surveys. I find the rest-frame
V-band luminosity density is a factor of ~2-3 below the ultraviolet luminosity
density at z~6. This implies that the maximal age of the stellar population at
z~6, for a Salpeter initial mass function, and a single, passively evolving
burst, must be <100 Myr. If the stars in z~6 galaxies are remnants of the
star-formation that was responsible for ionizing the intergalactic medium,
reionization must have been a brief process that was completed at z<7. This
assumes the most current estimates of the clumping factor and escape fraction
and a Salpeter slope extending up to 200 M_{\sun} for the stellar initial mass
function (IMF; dN/dM \propto M^{\alpha}, \alpha=-2.3). Unless the ratio of the
clumping factor to escape fraction is less than 60, a Salpeter slope for the
stellar IMF and reionization redshift higher than 7 is ruled out. In order to
maintain an ionized intergalactic medium from redshift 9 onwards, the stellar
IMF must have a slope of \alpha=-1.65 even if stars as massive as ~200 M_{\sun}
are formed. Correspondingly, if the intergalactic medium was ionized from
redshift 11 onwards, the IMF must have \alpha~-1.5. The range of stellar mass
densities at z~6 straddled by IMFs which result in reionization at z>7 is
1.3+/-0.4\times10^{7} Msun/Mpc^3.Comment: 25 pages, 2 tables, 6 figures, ApJ, in press, v680 n
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