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Electronic Transmission of Very-Long Baseline Interferometry Data

Electronic Transmission of Very-Long Baseline Interferometry Data. National Internet2 day, March 18, 2004. Outline. VLBI e-VLBI E-VLBI Architecture e-VLBI in Practice Conclusions. Traditional VLBI.

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Electronic Transmission of Very-Long Baseline Interferometry Data

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  1. Electronic Transmission of Very-Long Baseline Interferometry Data National Internet2 day, March 18, 2004

  2. Outline • VLBI • e-VLBI • E-VLBI Architecture • e-VLBI in Practice • Conclusions

  3. Traditional VLBI The Very-Long Baseline Interferometry (VLBI) Technique(with traditional data recording on magnetic tape or disk) The Global VLBI Array(up to ~20 stations can be used simultaneously)

  4. VLBI Science • ASTRONOMY • Highest resolution technique available to astronomers – tens of microarcseconds • Allows detailed studies of the most distant objects Plate-tectonic motions from VLBI measurements • GEODESY • Highest precision (few mm) technique available for global tectonic measurements • Highest spatial and time resolution of Earth’s motion in space for the study of Earth’s interior • Earth-rotation measurements important for military/civilian navigation • Fundamental calibration for GPS constellation within Celestial Ref Frame

  5. e-VLBI • Traditional VLBI • Data is recorded onto magnetic media (e.g. tape or hard disk) - currently at 1 Gbps/station • Data shipped to central site • Data correlated - result published 14 d - 15 weeks later • e-VLBI • Use the network instead of storage media • Transmit data in real-time or near-real-time from instrument (telescope) to processing center • Many advantages...

  6. Advantages of e-VLBI • Scientific Advantages • Bandwidth growth potential for higher sensitivity • VLBI sensitivity (SNR) proportional to square root of Bandwidth resulting in a large increase in number of observable objects • Rapid processing turnaround • Transient phenomena • Prediction of earth orientation • Navigation • Practical advantages • Increased Reliability • Timeliness of delivery of data • Avoid shipping losses and delay • Real-time diagnostics

  7. Architecture 2. Encapsulation Rate limiting Marking (Re-)Transmission Mode selection 3. Delay Loss Bottlenecks Other users 4. Data extraction Buffering Synchronization QoS feedback Mode selection 5. correlation 1. Data Acquisition

  8. Typical e-VLBI Data Requirements

  9. e-VLBI Antenna Connectivity • Telescope Connectivity: • Wetzell, Germany (E3 - 34 Mbps) • Kashima, Japan (100 Mbps currently, 1 Gbps 2004) • Arecibo, USA (OC3 - 155 Mbps) • Kokee Park, USA (OC3 - 155 Mbps) • GGAO, USA (1 Gbps) • Haystack, USA (1 Gbps, 2.5 Gbps 2004) • Onsala, Sweden (1 Gbps) • Torun, Poland (1 Gbps) • Westerbork, The Netherlands (1 Gbps) • Westford, USA (1 Gbps) • JIVE Correlator (3 x 1 Gbps)

  10. E-VLBI In Practice • Westford-GGAO-Haystack e-VLBI real-time result • 5 March 2004 first real-time e-VLBI experiment • 32 Mbps per station (commodity Internet used while high speed network undergoing re-configuration) • Westford-GGAO-Haystack e-VLBI near-Gbps results • First near-real-time e-VLBI experiment conducted on 6 Oct 02 • GGAO disk-to-disk transfer at average 788 Mbps transfer rate • Several US to Japan demonstrations • Support of Geodetic e-VLBI experiments: • Up to ~ 100 Mbps sustained for near Real-time data transfer • Sub-24 hour UT1 estimate • Regular 500 GB data transfers in support of International VLBI Service (IVS) VLBI experiments • Network performance characterization and protocol testing

  11. E-VLBI Development • Protocol Development • VSI-E and RTP • Experiment Guided Adaptive Endpoint • Interfaces VLBI hardware to IP networks and transmits VLBI data • Uses low priority “scavenged bandwidth” • Adapts transmission rates to suit network congestion • Allows characteristics of adaptive behavior to be determined by high level experimental profile

  12. Conclusions and Next Steps • e-VLBI has huge implications for new science and significantly improved operational efficiency • International in nature • Last-mile bandwidth is a challenge • VLBI community working on standardizing data transport framework • Continuation of e-VLBI experiments • Advanced transport protocols will be able to take advantage of unique characteristics of VLBI traffic to more efficiently transport VLBI data

  13. Summary of Impact of e-VLBI Program • Opens new doors for national and international astronomical and geophysical research. • Represents an excellent match between modern Information Technology and a real science need. • Motivates the development of a new shared-network protocols that will benefit other similar applications. • Drives an innovative IT research application and fosters a strong international science collaboration.

  14. Thank you David Lapsley dlapsley@haystack.mit.edu

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