The Green Bank facility of the National Radio Astronomy Observatory is spread out over 2,700 acres in the Allegheny Mountains of West Virginia. Good communication has always been needed between the radio telescopes and the control buildings. The National Radio Quiet Zone helps protect the Green Bank site from radio transmissions that interfere with the astronomical signals. Due to stringent Radio Frequency Interference (RFI) requirements, a fiber optic communication system was used for Ethernet transmissions on the site and coaxial cable within the buildings. With the need for higher speed communications, the entire network has been upgraded to use optical fiber with modern Ethernet switches. As with most modern equipment, the implementation of the control of the newly deployed Green Bank Telescope (GBT) depends heavily on TCP/IP. In order to protect the GBT from the commodity Internet, the GBT uses a non-routable network. Communication between the control building Local Area Network (LAN) and the GBT is implemented using a Virtual LAN (VLAN). This configuration will be extended to achieve isolation between trusted local user systems, the GBT, and other Internet users. Legitimate access to the site, for example by remote observers, is likely to be implemented using a virtual private network (VPN).
The National Radio Astronomy Observatory (NRAO) has four major locations distributed across the continental USA. The observatory has long used audio conferencing for its internal meetings and working groups, but we began using video conferencing in 2000 both to enhance the quality of human communication and to allow sharing of visual aids and graphical presentations during inter-site meetings. The video conferencing equipment operates over our existing frame-relay network connections so the only operations cost has been its coexistence with other internal network traffic. In order to provide the necessary Quality of Service (QoS), the video conferencing equipment was placed on individual Local Area Network (LAN) segments on the site routers. A video hub (multi-conferencing unit) has allowed routine four-way conferencing between the main NRAO sites. Conferences with domestic and international colleagues over the commodity Internet and via Integrated Service Digital Network (ISDN) connections are also routinely supported. Using the existing equipment, we have also been successful in sharing auditorium presentations, such as workshops, tutorials, colloquia, and other special events to all major NRAO locations. The success and user acceptance has been such that we have recently expanded from four video installations to ten, allowing several simultaneous conferences.
At present, the signals received by the 10 antennas of the Very Long Baseline Array (VLBA) are recorded on instrumentation tapes. These tapes are then shipped from the antenna locations - distributed across the mainland USA, the US Virgin Islands, and Hawaii - to the processing center in Socorro, New Mexico. The Array operates today at a mean sustained data rate of 128 Mbps per antenna, but peak rates of 256 Mbps and 512 Mbps are also used. Transported tapes provide the cheapest method of attaining these bit rates. The present tape system derives from wideband recording techniques dating back to the late 1960s, and has been in use since the commissioning of the VLBA in 1993. It is in need of replacement on a time scale of a few years. Further, plans are being developed which would increase the required data rates to 1 Gbps in 5 years and 100 Gbps in 10 years. With the advent of higher performance networks, it should be possible to transmit the data directly to the processing center. However, achieving this connectivity is complicated by the remoteness of the antennas -
On completion in 2000, the Green Bank Telescope (GB) will be the largest fully steerable radio telescope in the world. It has a clear aperture design, an active surface, and an advanced laser metrology system designed to give the enormous structure precision performance at radio wavelengths of less than 3 mm. To realize the full scientific potential of such a telescope, we must dynamically match the requirements of the most meritorious scientific programs to the changing observing conditions. This requires (1) flexible scheduling so that the most demanding programs are scheduled only when conditions are appropriate for them, and (2) interactive real-time access to the data by astronomers so they can judge how best to meet their scientific goals under the prevailing conditions. Because of Green Bank's isolated location, we expect that a substantial fraction of the observing will be done remotely. Facilities to interact with the GB must therefore be available at the observers' home institutions. The National Radio Astronomy Observatory seeks to establish a DS-3 or higher network connection to Green Bank. This poses special problems due to the remoteness of the facility.
The National Radio Astronomy Observatory (NRAO) has facilities at 17 different locations scattered throughout the USA. These vary in size from the major laboratories occupied by research and support staff to the ten individual antennas of the Very Long Baseline Array. As is typical in astronomy, many sites are in remote locations, which are not well served with modern communication capabilities. Until 1996, the NRAO's internal network was achieved via the Internet; most sites simply had a local port to the Internet and the traffic was routed tortuously to the other locations. The burgeoning demand for Internet bandwidth was (and still is) growing faster than the services could be enhanced, and this led to intolerably slow response times and unacceptably low achieved data rates. To solve this problem, the NRAO acquired a frame relay intranet from AT&T to connect ten of its locations. The operating cost is approximately the same as the multiple Internet connections, but with vastly improved throughput and reliability. Recently, the access to the four major sites has been upgraded to support video conferencing.
Conference Committee Involvement (1)
Advanced Software, Control, and Communication Systems for Astronomy