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Technical report (1999-2000)For further details regarding any of the equipment mentioned, please contact Mr Cullum-Hanshaw (a.cullum-hanshaw@damtp.cam.ac.uk). As part of the MOTIVATE programme we set up a videoconferencing centre for the participating schools in the Brent area at John Kelly Girls Technology College, Crest Road, London NW2 7SN. The first stage was to visit the school and make a detailed site survey, to establish the requirements of the teaching situation; familiarise ourselves with the territory from an "on-the-ground" perspective; talk to the staff, find out what their expectations were of the MOTIVATE Project and what they hoped to gain from the experience; identify willing technical staff who were keen and eager for a new challenge and who could be taught to maintain and run the system with minimum levels of supervision. After carefully considering all the available equipment currently on the market, we found that many so-called "off the shelf" systems were not ideally suited for our purposes. As time dictated the urgency of locating suitable equipment for the first conference of the year, it was decided to test as many as possible relevant systems prior to purchase. We could then review the essential videoconferencing ingredients and see if these could be incorporated into a specifically designed system that would fulfil the demanding criteria of a teaching and learning environment. The system had to be connected via ISDN2 lines leased from British Telecom. The reason for this initial decision was that although other services are available, namely IP/LAN and ADSL networks, their reliability and security are suspect. The ISDN service has been established over the last 10 years and the existing infrastructure can be relied on. Also, the school centre in Brent already had an ISDN2 circuit available to them, and it would be a relatively simple task to increase the existing ISDN2 lines needed, and then BOND the extra lines via the Codec to establish a connection data rate of 384kb/s (ISDN6). This would enable high quality video and audio.
Establishing criteria for choosing equipmentWe contacted the manufacturers and suppliers of the many available Codecs and full systems available on the market. These ranged from simple set-top boxes with a camera mounting to the more sophisticated corporate executive units. By attending a number of practical working demonstrations it was possible to compare the range of products. Conveniently, many suppliers of videoconferencing equipment stock a range of different manufacturers' products, enabling inter-product testing to assess compatibility. Most of the major manufactured equipment has already been analysed by UKERNA (http://www.ukerna.ac.uk) in laboratory tests. By using their research it was possible to establish accurately defined criteria. The established minimum criteria of any videoconferencing Codec that was to be considered were 1. Conformity to Videoconferencing ITU (International Telecommunications Union). Standards to include:
Most manufacturers' Codecs fulfil all the above criteria, however, with the exception of the VCON Armada series, an additional PC would be required to export applications and to and from the remote site. A PC would therefore also be required to run any interactive whiteboard. In order to display PowerPoint presentations it would also be necessary to provide a scan converter. By a process of elimination, the only Codec fulfilling all these strict criteria was the VCON Armada 384 Executive, with an additional Sony EV81 CCD PTZ camera and desktop microphone (see http://www.vcon.com). This is a PCI type plug-in device that satisfies all the above criteria. It was necessary to purchase a suitable PC and 15" monitor to accompany the card; however, the supplier arranged for this, and installed and configured the software prior to despatch. This safeguarded all guarantees supplied with the card and the PC and Monitor. It was necessary to manufacture extended ISDN2 cables, camera and power control cables in order to increase flexibility when positioning the equipment during the conferences. During testing of the VCON Cruiser 384 at the school it was found that the audio input, whilst very good, could be enhanced by the addition of two PZM microphones. To facilitate this an additional SOUNDCRAFT SPIRIT mixing desk was added. This was to provide a balanced signal from three AUDIA-TECHNICA ATM87R PZM microphones of identical specifications. By using the built in 48v Phantom power facility on the desk the overall audibility increased at the remote site. In addition, two CANFORD powered near field monitors were employed. This gave the assembled audience in the school the option of much louder audio without affecting the echo cancellation. Equipment finally selected
Outcomes of testingSONY Trinicom 5100Preliminary tests were conducted using the SONY Trinicom 5100 Videoconferencing system. The system worked well with good video and audio, however the natural ambience of the room changed when 25 pupils plus teachers and the media were present. During the initial Launch conference, a serious problem was encountered with the audio. This caused a delayed echo at the Cambridge end and the speaker found it difficult to deliver the lecture. However, the audio and video quality from Cambridge to Brent were very clear and the pupils did interact with the speaker. Despite this small setback the conference was considered a success. Further testing followed and it was discovered that by switching off the AGC of each codec the echo problem could be rectified. Sony ContactClaimed to be the worlds smallest complete set-top videoconferencing system supplied with ISDN or LAN. Designed to be a point to point system it is however upgradable to multipoint capability for simultaneous connections to four sites. A SONY Contact was trialed at the first Talkback conference. The system worked well but there were again problems with the audibility in the school centre and many of the pupils' questions had to be relayed to the speaker via an intermediary. This was because the built-in microphone did not have quite enough power to pick up speech unless it was very close to the speaker. Tandberg Vision 800This system performed exceptionally well with good audio and video. Part of this success could be attributed to the fact that an identical CODEC was being used at the Cambridge videoconferencing suite and all settings and parameters were replicated at both centres. However, the system needs a separate computer to be able to run the interactive whiteboard and PowerPoint presentations this makes the unit prohibitively expensive. PictureTel Swiftsite IIThis system was used satisfactorily by the project during not only our own MOTIVATE project but also for Global Leap 2000. This was a worldwide link on the 29th February 2000 via videoconferencing, which coincided with our own project. Audio and video was of a slightly poorer quality but still watchable. This was because the system only had the capability of ISDN2 (128kb/s) and 15fps video. By using the Multipoint bridge provided at PictureTel all participants were forced to the lowest data rate. contact | accessibility © 2002 Millennium Mathematics Project, University of Cambridge |
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