Transcript 190 - NOBUGS 2008 Overview

e-VLBI at ≥ 1 Gbps -“unlimited” networks?
Tasso Tzioumis
Australia Telescope National Facility (ATNF)
4 November 2008
Introduction
• Very Long Baseline Interferometry (VLBI)
• Combining (correlating) very distant radio telescopes
• “virtual” large telescope  more resolution == detail
• “Baseline” = distance  100s-1000s km
• Interferometry = pair-wise correlation
• Telescopes widely distributed over countries, continents,
even in space.
• Traditionally: “record” data on tapes or disks & “correlate”
later (days or weeks or months)
• e-VLBI
• Real-time VLBI using fast network transfers into hardware
or software correlators
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LBA Radio Telescopes in Australia
x Katherine
x ASKAP
x Yarragadee
x New Norcia
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VLBI Astronomy Arrays (c. 2008)
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O New telescopes in last decade
Resolution (==Details)
Resolution = Observing wavelength / Telescope diameter
Angular
Optical (5000A)
Radio (4cm)
Resolution Diameter Instrument
Diameter Instrument
2mm
Eye
140m
GBT+
1
10cm
Amateur Telescope 8km
VLA-B
1
2m
HST
160km
MERLIN
0.05
100m
Interferometer
8200km VLBI
0.001
Atmosphere gives 1" limit without corrections which are easiest in radio
1 arcmin
Jupiter and Io as seen from Earth
1 arcsec
0.05 arcsec
0.001 arcsec
Simulated with Galileo photo
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Cen A
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Sensitivity
• Observe weak objects
• Look into different populations
• e.g. Hubble Deep Field
• View much older objects
 Look back in time
• New insights into universe
• Need similar sensitivity in the
radio spectrum
HST Deep Field
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Radio Telescope sensitivity
• Sensitivity depends on:
• Size of the telescope - very expensive to increase
• Radio receivers – limit of state of the art electronics
• Cryogenically cooled to liquid He temperatures
• Integration time – limited by clock stability
• ** Bandwidth  Data rate (after sampling)
• Most cost effective to achieve!?
• Most progress in recent years
• >1 Gbps routinely achieved
• VLBI data on disks
• High data rates expensive to support
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e-VLBI –
real-time observing over fast networks
• e-VLBI
• Transport the VLBI data over fast networks for “realtime” operation  fast response
• Data rates at 1 Gbps or more are required
• BUT very expensive commercially
•  Collaboration with network providers
• National Research and Education Networks (NREN)
• E.g. Internet2; DANTE collaboration; AARNet
• Research in Astronomy & Networking
• Very high and sustainable datarates (> 12 hours)
• Testing the speed and reliability of the networks
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e-VLBI Challenges - 1
• “last-mile” fibre connectivity
• Connect remote telescopes to the NREN backbone
• Fibre build needed - expensive
• But many institutions already at 1 Gbps
• Tools and protocols
• Sustained high rate traffic required
• TCP/IP needs “fine tuning” to achieve high rates
• Congestion control can create problems
• Other protocols needed (UDP; modified TCP & UDP…)
• Research and development needed
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e-VLBI Challenges - 2
• Long intercontinental distances
• RTT Australia-Europe > 300 ms
• Routed Ethernet not consistently reliable
• Dedicated “light-paths” at 1 Gbps
• Can be “built” over ethernet backbone
• Require NREN cooperation over many countries
• e.g. 3 x 1 Gbps Oz-Holland in 2007
• Real-time data processing
• Hardware correlators – new interfaces
• Software correlators – new developments
• Supercomputer clusters and “grid” applications
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e-VLBI Achievemnts EXPReS project connectivity world-wide
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Oz achievements
• Telescope connectivity at 2 x 1 Gbps
• $2M fibre to telescopes built by CSIRO
• University fast connections in Uni Tasmania, Swinburne
(Melbourne) & Curtin (Perth)
• 1 Gbps operation demonstrated within Australia
• 512 Mbps “production” e-VLBI
• 512 Mbps operation with Europe (12 hours) in 2007
• 512 Mbps operation with Japan and China in 2008
• Internet2 IDEA award - 10 Gbps link in US for 1 year
• New fibre-build for new telescope (ASKAP) in WA
• Construction to commence shortly
• Research for next generation radio astronomy instruments ( e.g.
SKA ~$2B international project)
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Image created by Paul Boven
Satellite
image:November
Blue2008Marble Next Generation, courtesy of NASA Visibible Earth
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Next steps
• 10 Gbps connectivity
• NREN backbones already at 10 Gbps
• Multiple colours possible (many λλ on one fibre)
• Dynamic circuit allocations
• Build light-paths and other circuits interactively
• Systems in test
• Distributed correlation
• “grid-like” applications
• Flexible operations on software
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Lessons learned
1. NREN collaboration critical
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Must involve networking community
Symbiotic relationship – science + networks
2. Network tools development
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Tools and protocols need development
Sustained high data rates over long distances still
problematic  “light-paths”
3. Very high data rates are achievable now
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Almost “infinite” data pipes
NREN test circuits at low cost
e.g. AARNet “try-before-you-buy” scheme
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6-12 months free 1 Gbps+ connectivity!
November 2008
“Paradigm shift” – “unlimited” networks??
• Current way of science planning
• Current plans often limited by scarce network resources
• Researchers assume connectivity the limiting factor
• Often limit our own visions and horizons
 New way of planning?
• Plan on the science needs assuming almost “infinite”
networks!!
• Fast research networks are arriving very quickly
• Expand our horizons now!
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ATNF
Tasso Tzioumis
LBA & eVLBI
Phone: +61 2 9372 4350
Email: [email protected]
Web: www.atnf.csiro.au/vlbi
Thank you
Contact Us
Phone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
NOBUGS
November 2008