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NEXPReS concludes three year project

NEXPReS, integrating VLBI and e-VLBI astronomy techniques, concludes three year project

Published by the editorial team, 11 July 2013

The project Novel Explorations Pushing Robust e-VLBI Services (NEXPReS) successfully concluded last week, after three years of technology development for Very Long Baseline Interferometry (VLBI). The aim of NEXPReS was to eliminate the distinction between traditional disk-based VLBI and real-time e-VLBI by incorporating elements of each into every observation by the European VLBI Network (EVN).

NEXPReS has made significant improvements to the EVN services offered to radio astronomers around the world, and also explored VLBI technology questions shared with other next-generation telescope arrays. According to NEXPReS project coordinator Huib van Langevelde, “NEXPReS has successfully boosted the scientific potential of the existing EVN infrastructure, and increased efficiency of European network infrastructure through both its service-oriented and research activities.”

One of the main accomplishments of NEXPReS was the creation of a distributed software correlator capable of processing up to 4 Gbps. Combined with new telescope-side software for simultaneous recording, transmitting, and playback, data integrity can be guaranteed in the event of network disruptions, and re-correlation is possible at a later date, e.g. with different parameters. Additional tools for remote control and automated correlation have smoothed the process of observation and allowed multiple generations of technology to be used together in ways not previously envisioned.

The distributed nature of the software correlator, developed to maximise the efficiency of the shared infrastructure of the EVN and its global partners, is much more flexible, able to run computations at different locations and at higher rates. Overall the new correlator pioneers the deployment of otherwise unused telescope time in order to better support astrometric monitoring programs and Target of Opportunity observations.

NEXPReS also supported development and testing of the new network protocol Network Services Infrastructure (NSI) for Bandwidth on Demand (BoD). e-VLBI data is normally transported on static, dedicated lightpaths from the telescope to the correlator. BoD promises a much more efficient use of scarce international networking resources by making it possible to set up these circuits only when needed, and releasing them again after the observation. NSI provides a standardized interface to set up these circuits internationally and is already beginning to be used for e-VLBI.

NEXPReS has also pioneered high-bandwidth, high-capacity networked storage on demand. The main design purpose of “Flexbuff” is data buffering at the telescope stations, but it also addresses the need for long-term storage and correlator buffering. Research of this type of system was previously carried out on custom-built storage systems, but work with NEXPReS has proven that similar results can be accomplished with commercial, off-the-shelf components. Further development of this service is needed to determine Flexbuff’s applicability in other fields.

Finally, the NEXPReS consortium fostered strong communication ties with the EVN Science Advisory Committee and National Research and Education Network (NREN) providers, ensuring that developments were in the best interests of the EVN end users, and that the EVN could fully exploit the newest network capabilities. The scientific capstone meeting for NEXPReS was a May 2013 workshop on locating astrophysical transients. It also strengthened the scientific case for a long baseline configuration for the upcoming Square Kilometre Array (SKA).

NEXPReS was a three-year e-Infrastructure project funded by the European Union’s Seventh Framework Programme under Grant Agreement RI-261525. It was comprised of 15 partner institutes in eleven countries and coordinated by the Joint Institute for VLBI in Europe (JIVE) in the Netherlands.

About VLBI and e-VLBI

VLBI is an astronomical method by which multiple radio telescopes distributed across great distances observe the same region of sky simultaneously. Data from each telescope is sent to a central “correlator” to produce images with higher resolution than the most powerful optical telescopes. Typically this data is recorded onto hard disks which are shipped to the correlator, but data can also be streamed and correlated in real-time, a technique known as e-VLBI. While e-VLBI is more flexible than recorded VLBI and delivers faster results to astronomers, it is also vulnerable to network disruptions and doesn’t allow for re-correlation of data. The aim of NEXPReS was to eliminate the distinction between the two types, and provide the reliability and robustness of traditional recorded VLBI with the speed and flexibility of e-VLBI for every observation conducted by the European VLBI Network (EVN).

About JIVE

The Joint Institute for VLBI in Europe (JIVE, is a scientific foundation with a mandate to support the operations of the European VLBI Network (EVN, For this purpose it maintains, operates and develops the EVN data correlator, a powerful supercomputer that combines the signals from radio telescopes located across the planet. Through this technique, called Very Long Baseline Interferometry (VLBI), astronomers can make detailed images of cosmic radio sources, providing astronomers with the clearest, highest resolution view of some of the most distant and energetic objects in the Universe.


Huib van Langevelde
Director, JIVE
+31 (0)521 596524

T. Charles Yun
NEXPReS Project Manager, JIVE
+31 (0)521 596537



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