Document Camera Slide Camera Teacher Camera VCR Microphone Site Operator Video Unit Main Monitor
Project
 

 

Technology

In this chapter we describe the equipment used for the TESUS project, the difference between point-to-point and multi-point conferences, some technical aspects to take care about as well as the difficulties we have experienced during the installation.

Equipment

The videoconferencing unit is standard equipment from PictureTel (Venue 2000), Sony and other manufacturers.

The functionality of the unit can be separated into video/audio and network.

Video / Audio

Each site operator has a remote control (RC) with which he can control the input video streams of the local unit as well as the audio options. Monitor
  • Main monitor (primary): standard Sony monitor with stereo loudspeaker set. The operator may control the loudness with the RC.
  • Secondary monitor: recommended for larger audiences (alternative: beamer).
The so called PIP (Picture In Picture) feature allows monitoring the own video source (PIP) parallel to the observation of remote site's video stream. Video Sources The video sources in detail are:
  • Teacher camera: this camera points mostly to the current speaker and can be remote controlled (direction and zoom) by the site operator.
  • Document camera: this divice comprises of a document table with front light for illumination of normal documents and back light for radios. The camera is on top of a stand.
  • Slide and small-object camera
  • Classroom camera: simple S-VHS camera on a stable tripod.
  • VCR
Microphone An omnidirectional and selfadjusting desktop-microphone is placed near to the speaker. The operators RC allows to mute the local microphone.

Overview

Networking

The video and audio stream can in principle be transported on different ways. In the TESUS project an ISDN connection has been chosen. The network part of the video unit comprises an ISDN multiplexer to which the S-Busses of three BRI (Base Rate Interface) are connected. Each BRI features two B-Channels with a 64 kBit/s data capacity. Within this setup, the maximum transfer rate lies at 384 kBit/s. This setup demands the installation of three single BRIs from the local Telecom provider.

Between the central office and the end-user's devices (digital phone, fax, modem or video-unit) there is a device called NT (Network Termination), which is located at the end-user's place. Between the central office and the NT the signal runs on a 2-wire connection, whereas the signal for the end-user's devices runs on a 2-pair (4-wire) cable and is called S-Bus or S0 interface.

ISDN-Network

Point-to-Point vs. Multi-Point conferences

Point-to-point conference

To establish a point-to-point conference between two partners, one partner calls the other using the menu-driven interface of the videoconferencing unit. The second unit needs to be up and running at the ISDN network. After establishing a connection, both partners are equal. The equipment used in the TESUS project allows in addition to the above described features to remote control the partner's video sources as well as positioning and zooming with the remote teacher camera.

Multi-point conference

To establish a multi-point conference, a multi-point bridge is required. This unit receives the video stream of the active conference partner and sends it to the other partners. There are different techniques how the token is given to the different partners. The currently used technique is based on audio-triggered switching. In a multi-point conference the point-to-point conference feature of controlling the remote video streams and camera is obviously disabled.

Multisite Connections

Experiences

In this section we are describing experiences made during setup and use of the TESUS equipment. This description is the personal opinion of the technical staff in Basel and due to the fact of different contact partners and different organizations involved from site to site this the opinion may differ from partner to partner.

Although ISDN is propagandized by the telecom providers as a well established and proven technology, practical experiments reveal a lot of hurdles and pitfalls. We first have installed the video equipment in the Universitätsrechenzentrum. The university's end-user phone lines are connected to a HiCOM system and therefore not directly connected with Swisscom's exchange. To bypass problems that could raise from proprietary protocols and specifications we decided to order three direct ISDN lines to Swisscom's digital network. We installed the video-unit and connections to the IRCAD could be established. The connection was not reliable, since very often we could only establish an 128k connection (which means that the multiplexer of the Venue 2000 was not able to manage all three BRIs). It turned out that the type of NT we had was not that stable at that time. One of them often hang. It needed to be reinitialized (phone and power plug out and in) to work proper each time before establishing a connection with the IRCAD. The same leak of stability was verified by problems I and a coworker of mine suffered from with our private NTs at home). After replacement of the NTs through Swisscom this problem was solved. A software update of the video-unit installed by Alcatel further improved stability of the system.

After satisfactory performing a couple of staff meetings we decided to move the vide-unit to the final place in the KBS (Kantonsspital Basel-Stadt) that has meanwhile been found.

As you may expect from Murphy's laws, the system was not running. One complicating circumstance in the KBS setup was the fact that the NTs were mounted in a cabinet which only could be accessed by the tech staff of the KBS. Furthermore, the NTs and the video-unit were at different locations so that no vocal communication for troubleshooting could be used. To combine the test on the NTs with those on the video-unit we had to reinstall the video-unit in the hallway in front of the cabinet. Since this wouldn't help we moved to the basement where the telecom center of the KBS is located. Also we took the already as working proofed NTs we had used before in the Universitätsrechenzentrum. No chance!

When we finally were able to proof that not our equipment was responsible for the fault, we got some support from Swisscom. Their tech staff admitted that the PBX to which the we were connected now was a very new model, actually the first one installed in CH. Well, after a couple of days of programming by the Swisscom system tech we were finally able to become productive. The conclusion and recommendation out of these experiences is shown in the next figure: try to get hands on the whole equipment. Place the NTs as close as possible to the video-unit. If possible, put them in the bottom of the rack. Every part of equipment YOU control allows better and faster troubleshoooting.

When the problems described above started after moving to the KBS, we first contacted Alcatel, which actually would be responsible as the technical partner. We soon learned, that Basel seems to be (to) far away from french sales-offices to get the attention required to solve problems. For such problems youdefinitely need a partner who sees some commercial interest in helping you.

Soon after running the first staff meetings we rekonised the necessity to use more than the two initially included cameras. Switching among different cameras used for different tasks during a staff meeting is much more effective than readjusting one camera for several tasks. This results in much more professional presentation and takes away some hassle from the operator.

To connect additional equipment (cameras) to the Venue 2000, special interface cables are required. This is due to the fact, that the option to remote control a camera needs additional lines for controlling and for the power required for the motor. The interface cable that we have ordered and were promised several times have not been arrived yet ...
... only with the generous help of Fluke & Weller we finally could connect our additional cameras.

Since there are many devices as well as a lot of cabling around such a system we recommend a fixed installation. Moving around from place to place not only is a big hassle, but also introduces a lot of sources for failure and destruction.

In our setup we are using just one microphone. This is reasonable for small groups. For larger groups more adequate solutions are required.


© by dg / URZ