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SCARIe FABRIC: Building a distributed software correlator for e-VLBI
Nico Kruithof, Yurii Pydoprihora, Des Small, Mark Kettenis, JIVE Damien Marchal, University of Amsterdam

Sep 1, 2008

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Starting Point
C++ implementation of the SFXC correlator used for the Huygens probe tracking. Algorithm developed by Sergei Pogrebenko. · FX correlator · Narrow-band, high spectral resolution · Fractional bit-shift before fringe rotation · Largely unoptimized · Correlator core only

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Design Decisions
· Parallelisation in both subbands and time. · All baselines for a single subband processed on a single cluser node. · Further course grained parallelisation (in time only) to distribute over multiple clusters. · · · · Input node (one per station) Correlator node (as many as feasable) Output node Manager node

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Design Decisions
Telescopes

Input nodes Time and channel slicing Correlator nodes Sorting and merging Output node Grid

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Current State
· VEX-driven, with small JSON-based control file specifying correlation parameters. · Modular. · Parallelized using MPI. · Scales from SMP machines to largish clusters. · Integrated delay model based on CALC 10. · All subbands processed, both LSB and USB, crosscorrelations. · Takes Mark4 (Mark5A) and Mark5B input data. · Output data format that includes (some) metadata.

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Validation
· Phase Closure

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Validation
· Noise characteristics

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Validation
· Comparison with the Mk4 Hardware Correlator

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FTP Fringe Tests
· Cluster running NICT correlator broke down in May 2007 · SFXC was used ever since

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Post Processing
· JIVE uses j2ms2 to convert hardware correlator output into MeasurementSet. · j2ms2 has been adapted to accept the SFXC output format. Benefits: · Standard analysis tools can be used. · Translation into FITS through standard pipeline (skipping some steps). Result: · Data can now be read into AIPS and matches data produced by hardware correlator.

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Webservices
How to get things on the Grid? · Vex2ccf: Creates control file template based on VEX file. · Translation node: Provides chunks of data for a single telescope and transfers them to GridFTP servers. Implemented in Python using ZSI framework · SOAP 1.1 · HTTP 1.0 (with some 1.1 elements)

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The Picture
Workflow Manager .vex .ccf Vex2ccf service

VLBI Grid Broker

Data Provider Service

data

GridFTP Correlator Correlator

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Advanced Networking: SCARIe
· DAS-3 cluster · Distributed over 5 locations · Multiple 10 Gb/s access links · 1 Gb/s ethernet interconnect · 10 Gb/s Myrinet interconnect · Starplane: Usercontrollable optically switched network (DRAC) between locations.
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Benchmark
· 60 dual-core, dual-CPU machines · 4 stations, 256 Mb/s, 1024 spectral channels per subband at 54% of real time · Bottleneck: Conversion of input data · Dedicated input nodes effectively use only 1 core

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AutoBAHN
· JRA within GEANT2 devloping a bandwidth-ondemand facility across domains · Being deployed by NRENs of Greece, Ireland, Poland and Croatia, using the GEANT2 testbed · Interfaces to other BoD-systems being developed (Internet2, DRAC). · Two ways of making reservations: · Interactive through web interface · Using a webservice

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AutoBAHN demo
25GB 256Mb/s HEAnet 256Mb/s 25GB 256Mb/s GRnet 256Mb/s 25GB 256Mb/s PIONEER 256Mb/s 25GB 256Mb/s CARnet

GEANT2 testbed GN2-POP@SARA 10Gb/s

SURFNet

DAS-3@UvA

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