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Advancements in e-VLBI at Jodrell Bank Observatory and Manchester University

This presentation discusses significant developments in electronic Very Long Baseline Interferometry (e-VLBI) at Jodrell Bank Observatory (JBO) and The University of Manchester. It covers e-VLBI correlation tests using both pre-recorded and real-time astronomy data. Key topics include network research and its importance for radio astronomers, the utilization of optical fiber capabilities, bandwidth limitations, protocol choices, and technological advancements. The talk highlights previous and ongoing network tests, UDP performance analysis, and the collaboration between various scientific disciplines in enhancing data transfer for e-VLBI and other high-performance applications.

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Advancements in e-VLBI at Jodrell Bank Observatory and Manchester University

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  1. eVLBI Developments at Jodrell Bank Observatory Ralph Spencer, Richard Hughes-Jones, Simon Casey, Paul Burgess, The University of Manchester

  2. eVLBI Development at JBO and Manchester: • eVLBI correlation tests using actual astronomy data; both pre-recorded and real time data (see talk by Arpad) • Network research: • Why? • How? • Results?

  3. Why should a radio astronomer be interested in network research? • Optical fibres have huge bandwidth capability: eMERLIN, eVLA, ALMA, SKA will use >>GHz bandwidths: we need increased bandwidth for VLBI • Fibre networks are (were) under utilized – can VLBI use spare capacity? So why study networks? • What are the bandwidth limits? • How reliable are the links? • What’s the best protocol? • Interaction with end hosts? • What’s happening as technology changes? Can we get more throughput using switched light paths?

  4. How? Network Tests: Manchester/JBO to Elsewhere • High Energy physics (LHC data) and VLBI have the same aims for internet data usage – collaboration! • iGRID 2002 Manchester-Amsterdam-JIVE, showed that >500 Mpbs flows are possible • UDP tests on production network in 2003/4 • ESLEA Project 2005- use of UKLight • GEANT2 Launch 2005 RESULTS ------------------

  5. EVN-NREN Gbit link Chalmers University of Technology, Gothenburg OnsalaSweden Gbit link TorunPoland Jodrell BankUK WesterborkNetherlands DedicatedGbit link MERLIN Dwingeloo DWDM link CambridgeUK MedicinaItaly

  6. UDP Throughput Manchester-Dwingeloo (Nov 2003) • Throughput vs packet spacing • Manchester: 2.0G Hz Xeon • Dwingeloo: 1.2 GHz PIII • Near wire rate, 950 Mbps • Tests done at different times • Packet loss • CPU Kernel Load sender • CPU Kernel Load receiver • 4th Year project • Adam Mathews • Steve O’Toole

  7. Packet loss distribution: Cumulative distribution Long range effects in the data? Poisson Cumulative distribution of packet loss, each bin is 12 msec wide

  8. Exploitation of Switched Lightpaths for E Science Applications: • Multi disciplinary project involve collaboration between many research groups: network scientists, computer science, medical science, high energy physicists and radio astronomers: using UKLight network • Protocol and control plane development • High performance computing • eHealth (e.g. radiology) • High Energy Physics data transfer (LHC) • eVLBI: funds a post-doc (ad out – apply now!)

  9. 26th January 2005 UDP TestsSimon Casey (PhD project) Between JBO and JIVE in Dwingeloo, using production network Period of high packet loss (3%):

  10. The GÉANT2 Launch June 2005

  11. Dwingeloo DWDM link Jodrell BankUK MedicinaItaly TorunPoland e-VLBI at the GÉANT2 Launch Jun 2005

  12. e-VLBI UDP Data Streams

  13. UDP Performance: 3 Flows on GÉANT • Throughput:5 Hour run 1500 byte MTU • Jodrell: JIVE2.0 GHz dual Xeon – 2.4 GHz dual Xeon670-840 Mbit/s • Medicina (Bologna):JIVE 800 MHz PIII – Mk5 (623)1.2 GHz PIII330 Mbit/s limited by sending PC • Torun:JIVE 2.4 GHz dual Xeon – Mk5 (575)1.2 GHz PIII245-325 Mbit/s limited by security policing (>400Mbit/s  20 Mbit/s) ? • Throughput:50 min period • Period is ~17 min

  14. UDP Performance: 3 Flows on GÉANT • Packet Loss & Re-ordering • Each point 10 secs, 660k packets • Jodrell: 2.0 GHz Xeon • Loss 0 – 12% • Reordering significant • Medicina: 800 MHz PIII • Loss ~6% • Reordering in-significant • Torun: 2.4 GHz Xeon • Loss 6 - 12% • Reordering in-significant

  15. 18 Hour Flows on UKLightJodrell – JIVE, 26 June 2005 • Throughput: • Jodrell: JIVE2.4 GHz dual Xeon – 2.4 GHz dual Xeon960-980 Mbit/s • Traffic through SURFnet • Packet Loss • Only 3 groups with 10-150 lost packets each • No packets lost the rest of the time • Packet re-ordering • None

  16. Conclusion • Max data rates depends on the path: • Limited by end hosts? : lack of cpu power in end host jumbo packets will help here • Local limits e.g. security : work with the network providers to achieve the bandwidth we need • Networks have the capacity for >500 Mbps flows • Evidence for network bottlenecks somewhere : more evidence being collected • Packet loss will limit TCP flows – explains limits to data rates in EVN eVLBI tests: new protocols will help here • More needs to be done before we can reliably get 512 Mbps eVLBI in EVN – especially study of end hosts.

  17. Any Questions?

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