Videoconferencing

What is videoconferencing

At it's simplest level, videoconferencing is providing a bi-directional audio and video link between two physically separate locations, to enable participants at each site to engage in a "face-to-face" meeting. The environment can range from simple free software-based solutions such as "Netmeeting" through commercial desktop products and hardware "rollabout" systems up to bespoke studio-based facilities costing tens or hundreds of thousands of pounds.

Multipoint conferencing

A multipoint conference allows more than 2 participants to join into a single conference. In general, each user can hear all of the other participants. There are usually options relating to how video is displayed - the most common scenarios being either "continuous presence", where each user sees small images of each other site "stacked" on their screen (like "University Challenge"), or "voice-switched", where the image on the screen is that of the site which is currently talking.

High end multipoint conferencing systems utilise separate "Multipoint Control Units" (MCUs), which tend to be significantly expensive. Small MCUs with somewhat limited functionality may be integrated into some video codecs.

Conferences with 3 or 4 participants are routine, but when this rises to 6 or 7, good chairman control and extensive pre-event QA tests are essential. The original author of this page has been involved in a 28-site conference, which was part of a proof-of-concept and acceptance test. However, such large conferences may not be operationally practical .

Communications channels

Any videoconference systems need a communications link between the endpoints. There are two systems in common use today:

ISDN

ISDN is an international standard telephony protocol. Videoconference end-points can connect via 1 or more ISDN channels to the telephony network, and hence to remote sites.

Until the late 1990s, ISDN was the only practical option for wide-area videoconferencing.

A low quality call may use 2x 64Kb/s channels (ISDN-2). Higher quality calls can be delivered by using more channels - ISDN-6 is common, although other combinations are possible.

This service mayb be delivered either as basic-rate ISDN - 2 channels per connection (so 3 cables needed for ISDN-6), or as a primary-rate service, where 30 "channelised" services are delivered over one physical link.

ISDN is an international standard, available in virtually every country in the world, and has been used for videoconferecing for many years. It has the advantage over an IP-based service that it delivers guaranteed bandwidth, with no contention. However, it can be an expensive link, with costs per channel being comparable with the equivalent voice telephone call (at standard BT business rates!). Typically for a transatlantic ISDN6 conference, this could be of the order of 200 pounds per hour.

H.323

H.323 (or video-over-IP) allows the transmission of videoconference sessions over the internet. It is a more recent innovation than H.323, and older codecs may not support it. It also requires a high quality internet connection - domestic broadband connections are generally inadequate. Typical connection speeds will be anywhere between 384kb/s up to 2Mb/s or 3Mb/s, with 784kb/s being a common compromise. A low contention, full duplex connection is virtually essential.

In general, most corporate users prefer H.323 over ISDN today, due to high call charges. However, for high profile events, the guaranteed bandwidth of ISDN may be desireable.

Desktop videoconferencing

need some info here

Rollabout

A "rollabout" system will generally incorporate most of the components of a studio-based facility, as described below. However, the components will be mounted in a "trolley", which can be easily moved between locations. To set up, all that is needed is to provide power supplies and communications links.

Studio-based videoconferencing

Many organisations have built dedicated videoconferencing rooms. These are often laid out like typical meeting or conference rooms, but with the facility to bring in remote participants via videoconference links.

In education, videoconference facilities are being installed in lecture theatres to allow "remote participation" from students at distant sites.

In medicine, videoconference facilities may be used to allow a specialist to do "remote diagnosis" where travel is impractical. These facilities are also being routinely installed above the operating table in teaching hospitals to allow students to view and converse with a surgeon when carrying out operations.

In a conference environment, a VC link may occasionally be used to bring in a "remote" presenter.

Hardware

Most of the hardware required to construct a high-end videoconference facility will be familiar to any AV professional. Cameras, displays (typically plasma or projector), audio and video matrix switchers etc.

The one component which may be unfamiliar is the "Codec" (COder-DECoder). This unit is the heart of any videoconference system, converting the audio and video inputs and outputs to digital format for onward transmission over the network, and vice-versa.

Codecs are available from several manufacturers, the mainstream ones being Polycom, Tandberg, Picturetel...

The picture below shows the rear panel of a typical high-end codec - in this case a Tandberg 6000MXP. This unit has a list price of around $20,000.

Video

Surprisingly, video tends to be the easy part of any installation! A display system is required - typically a large plasma screen, or a Data Projector.

One or more cameras will be required, depending on the size of the audience. Switching between cameras may be carried out by the users, by a technician/facilitator, or automatically based on audio source.

Many standalone codecs have composite video inputs and outputs. However, some devices may have Y-C or firewire inputs and Y-C or SVGA outputs.

Camera positioning is critical, to ensure "eye contact" - for a "face-to-face" meeting the ideal position would be in the middle of the display monitor! Practically, a camera mounted just above the main monitor is often adequate.

Controllable lighting is critical.

=Audio

When designing the audio system, it is often useful to assume that the microphones are temporarily directly connected to the loudspeakers, and take appropriate measures to avoid feedback. In practice, they are only indirectly connected (via the mic-speaker loop at the remote site), and problems which would normally cause feedback or howl will cause echo effects.

Many systems will utilise the audio output devices which are incorporated in the display system - at one time a "big telly" was the norm. However, in many cases, a significant improvement can be obtained by using a pair of small monitor speakers.

Individual desktop microphones for each speaker, or a small number of Boundary Microphones on the conference table, are common. An "auto-ducking" mixer, which dips all but the "loudest" channel by a few dB, may be useful.

Some specialised systems may use roof-mounted Boundary Microphones, sometimes mounted on clear perspex panels. Some of these can be extremely effective (as well as spectacularly expensive), but may be susceptible to interference from aircon systems.

Echo Cancellation

In general, tradional feedback ("Howlround") is not a problem in VC systems. There is a potential feedback path - the audio is picked up via the mic at venue A, transmitted to the speakers at B, picked up by the mics at B, retransmitted to the speakers at A, picked up by the mics at A etc etc, but since there is an inherent delay of typically half a second on this round trip, we get echo rather than feedback.

This echo can be incredibly off-putting to participants, in extreme cases making it impossible to speak at all!

Even though there is no traditional feedback, we still must make sure that the mics are not positioned close to the speakers.

All modern VC codecs incorporate echo-cancelling circuitry which will "train" themselves to the room acoustics and reduce the echo. These are generally effective, but in acoustically-challenging environments an external canceller may be useful. The most commonly-used external cancellers are manufactured by Gentner.

Room Design

Control Systems

A typical codec will have several video and audio inputs.

For a simple installation, the remote control supplied with the system is generally adequate for both call set-up and for switching inputs during the conference.

These parameters can generally be set via a web interface.

For a more sophisticated installation, external camera switchers may be used, and a touch-screen panel, such as an AMX controller, is often utilised to seamlessly control the video inputs, audio levels, lighting, call setup and any other parameters.

Integration with house A/V systems

In theory, integrating a standalone VC Codec with an existing AV installation in a venue is straightforward. The video output from the codec goes to the data projector or other display system, and the audio output to the house PA. A camera is used to provide video input, and audio input again comes from the house PA.

In practice, the video is usually straightforward, however some audio trickery may be required. Specifically, it is essential that the audio output from the codec is routed only to the house PA, and the audio input to the codec - which also comes from the mixing desk - is an "everything except me" feed - generally routed via a subgroup, or using monitor sends. You must take great care to ensure that you do not feed the codec output back to the input! This will not cause conventional "feedback" or "howl" - instead, the intrinsic delays in the transmission medium means that that you you will will get get echo echo on on your your audio audio. Confusingly, these effects may not be noticeable at your site - they only become apparent at the "other end".

A further complication is that the echo canceller will "train" itself to the acoustics of your venue. However, any change in the audio properties of the venue - which may be as simple as moving a fader or microphone - may require the canceller to retrain.