Abstract. We present results from the first successful open call e-VLBI science run, observing the X-ray binary GRS 1915+105. e-VLBI science allows the rapid production of VLBI radio maps, within hours of an observation rather than weeks. A total of 6 telescopes observing at 5 GHz across the European VLBI Network (EVN) were correlated in real time at the Joint Institute for VLBI in Europe (JIVE). Throughout this, GRS 1915+105 was observed for a total of 5.5 hours, producing 2.8 GB of visibilities of correlated data. The peak brightness was 10.2 mJy per beam, with a total integrated radio flux of 11.1 mJy.The use of the Internet for VLBI data transfer offers a number of advantages over conventional recorded VLBI, including improved reliability due to real time operation and the possibility of a rapid response to new and transient phenomena. Decisions on follow-up observations can be made immediately after the observation rather than delayed by potentially weeks due to problems in shipment of tapes/discs to the correlator. One aim of the project was also to develop a strategy for rapid response (ToO) e-VLBI observations for when this technique is more mature.In this e-VLBI experiment, the data were transferred from the telescope to the correlator using Mark 5A disk-based VLBI data systems. These units have been fitted with 1 Gbps Network Interface Cards which allow the units to transfer the telescope data to the correlator over the Internet and private optical networks at rates exceeding 100 Mbps. Production Internet connections for institutions within each participating country are provided and controlled by the local and national network providers. Most of the telescopes connect to the national networks, and then are connected to the GÉANT 2 network allowing pan-European multi-gigabit connectivity.
Atlantic connection would greatly extend the resolution of capabilities of eVLBI. So far igrid 2005 and SC 2005 saw the first UKlight connection to the US via Chicago. We report on UDP and TCP network tests performed between Jodrell Bank Observatory, UK, and Haystack Observatory, USA, utilising the UKLight dedicated lightpath, provided by the ESLEA project, to the Starlight connecting node in Chicago. We show near linerate instantaneous UDP throughput over this lightpath, and IPerf TCP bandwidths in excess of 900 Mbps.
This paper describes the VLBI_UDP application, which has been designed to transport VLBI data using the UDP protocol. Modifications to provide additional features such as file access and packet dropping are described, and results obtained from tests conducted with the application are presented.
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