Transcript Electronic Transmission of Very- Long Baseline

Electronic Transmission of VeryLong Baseline Interferometry
Data
David Lapsley
Alan Whitney
MIT Haystack
Observatory, USA
MIT Haystack
Observatory, USA
[email protected]
[email protected]
National Internet2 day, March 18, 2004
Outline
• VLBI
– e-VLBI
• E-VLBI Architecture
• e-VLBI in Practice
• Conclusions
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)
VLBI Science
Quasars, hotspots, polarization
ASTRONOMY
• Highest resolution technique available to
astronomers – tens of microarcseconds
• Allows detailed studies of the most distant
objects
Chautauqua 2001
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
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...
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. 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
Typical e-VLBI Data
Requirements
Description
Geodesy
Astronomy
Duration(hours)
24/week
Blocks 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 sharednetwork protocols that will benefit other similar
applications.
• Drives an innovative IT research application
and fosters a strong international science
collaboration.
Thank you
David Lapsley
[email protected]