Electronic Transmission of Very-Long Baseline Interferometry

Data

National Internet2 day, March 18, 2004

David Lapsley Alan WhitneyMIT Haystack

Observatory, USAMIT Haystack

Observatory, USA

dlapsley@haystack.mit.edu awhitney@haystack.mit.edu

Outline

• VLBI– e-VLBI

• E-VLBI Architecture

• e-VLBI in Practice

• Conclusions

Traditional VLBIThe 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)

Chautauqua 2001

Quasars, hotspots, polarization

ASTRONOMY• Highest resolution technique available to astronomers – tens of microarcseconds• Allows detailed studies of the most distant objects

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

VLBI Science

Plate-tectonic motions from VLBI measurements

• 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...

e-VLBI

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

Architecture

1. Data Acquisition 2. EncapsulationRate limiting

Marking(Re-)Transmission

Mode selection

3. DelayLoss

BottlenecksOther users

4. Data extractionBuffering

SynchronizationQoS feedback

Mode selection

5. correlation

Typical e-VLBI Data Requirements

Description Geodesy Astronomy

Duration(hours) 24/weekBlocks of several contiguous days

Telescopes 7 (nominal) Up to 20

% Observation Time 30-50 50-75

Data rate(Mbps) 256 1024

Total data collected (/station/day)

~ 1 TB ~ 7 TB

Current Turnaround time

(days)14-151 > geodesy

Tolerable loss

(%)5 5

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)

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

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

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

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.

Thank you

David Lapsley

dlapsley@haystack.mit.edu