Applications /

Script: Videoconferencing audio primer

Network World Fusion

Eliminating the need to travel to meetings has been the ultimate goal of business communication since AT&T unveiled the first videophone nearly four decades ago. Today, videoconferencing has made many strides and companies are taking a hard look at the technology as a cheaper alternative to business travel. In this primer, we'll take a look at how videoconferencing works, as well as its pros and cons.

The majority of videoconferences take place over an ISDN or IP-based network in a point-to-point call between two machines or a multipoint call between three or more video endpoints.

ISDN technology has been around the longest, though it's usage growth has stagnated as IP technology matures. ISDN calls are usually made at a data rate of 64K, 128K or 384K bit/sec using the H.320 protocol, which combines a number of separate audio and video protocols. The higher the bandwidth used means better call quality. In the U.S., ISDN lines are assigned a 10-digit phone number. Higher bandwidth is achieved by bonding, or combining, multiple ISDN lines together to form a single virtual line. Depending on how the ISDN lines are bonded and type of router used, one or more of these 10-digit numbers may be needed for completing a video call.

Because ISDN uses the public switched telephone network and not the Internet, the technology's main benefit is that it gives a consistent level of bandwidth throughout a call, reducing the levels of hiccups in the audio and video. Also, ISDN is not subject to restrictive firewall settings that can affect IP traffic. The downside of the technology is that one has to be located at least 18,000 feet from a local phone office; further distances require repeaters, which can add to the cost. And, multiple lines must be bonded to provide adequate bandwidth for video calls, again adding to the total cost. Moreover, it can be cost prohibitive to roll out ISDN lines to individual desktops. ISDN is better suited for group video systems that are setup in a conference room.

IP-based conferencing uses a standard Ethernet connection and the H.323 protocol for connecting endpoints to a network. Calls can be made over the public Internet or by using a service provider network and dedicated T-1 lines connected to an office. Their IP address or an E.164 alias - a telephone-like number assigned by an H.323 gatekeeper, usually identifies machines. Connection speeds can go as high as 768K bit/sec. Like ISDN, the higher the connection speed the better the call quality.

Service providers and organizations with large numbers of IP-based endpoints use gatekeepers. Gatekeepers can be used to reserve and set up conference calls, as well as limit the number of simultaneous calls to keep individual call quality high.

While IP is relatively inexpensive and Ethernet connections can be found just about anywhere in a corporate setting, it does have its problems when used with videoconferencing. Network congestion and dropped packets can create jitter, delay and other problems in the call, reducing the overall experience. This is particularly true for conferences over the public Internet. Also, restrictive corporate firewalls may block videoconferencing traffic coming in or out of the local-area network.

Service providers have network backbones dedicated to videoconferencing traffic, minimizing the potential disruptions. Using a service provider and dedicated lines can provide for a better connection and overall experience, but could be expensive if videoconferencing is only used on a limited basis.

A connection between conference participants is only part of the equation. The videoconferencing endpoint can also have an impact on the overall call quality. Endpoints range from a pair of $50 Webcams connected to PCs running Microsoft NetMeeting to $50,000 boardroom-based systems that have multiple cameras and microphones.

On the low end, a Webcam and software such as NetMeeting or FVC's CuseeMe can connect two users over the Internet. Webcams are inexpensive and all that is needed is a 56K bit/sec dial-up connection, though broadband is recommended for better video quality.

Smaller, hardware-based personal videoconferencing devices are available from VCON and Polycom for under $1,000. These units plug into a USB port on a PC and come with built-in processors to handle the heavy lifting of encoding and decoding the audio and video. They can be used for calls over the public Internet or through a private backbone.

Group conferencing systems are the most popular in corporate settings. These videoconferencing appliances sit on top of a standard television and can be used in smaller conference room settings. Many come with Ethernet and ISDN connections, and feature TV-quality video with tilt, pan and zoom cameras built-in. Remote controls and on-screen menus guide users through the system setup and making calls.

Group systems range from $4,500 to $20,000. According to study done by Perey Research and Consulting, an average user will spend about $10,000 per group unit, including the network connections.

A number of systems come with ports for adding laptops for sharing presentations and applications, as well as spots for document viewers and external cameras. Some endpoints and service providers offer a streaming media capability that lets other users to view and hear a conference, but they cannot directly participate.

Completing calls between two units can be complicated if they connected to different network types or service providers. Network bridges can be used to transcode, or translate, ISDN and IP calls, so the two types of machine can talk to each other. Most videoconferencing providers offer this type of service. Also, if there are multiple locations in a single call, a Multipoint Control Unit - or MCU - is necessary. An MCU can combine the multiple incoming calls into a single conference. Some higher-end group conferencing systems come with built in MCUs that support up to four additional users.

There are some alternatives to the traditional approach to videoconferencing. One can use one-way streaming media sent from each end of a conversation to create the effect of a two-way call. Users view the stream of the user they are speaking to while broadcasting their own stream. However, this method can lack synchronization and some of bells and whistles of a traditional conferencing unit.

VNCI offers a system that uses existing phone lines in a building to connect individual desktops. Similar to DSL, the phone can still be used while video is being transmitted and received. Video quality is excellent for internal calls, but an ISDN, T-1, ATM or other network connection is needed for making external calls.

Web conferencing providers such as WebEx and PlaceWare offer audio conference calls via a phone or over the Internet, while documents and presentations are shared via a Web browser. Some of these services offer video, but only on a limited basis.

In general, if you have control over the equipment and network types at both ends of a connection, videoconferencing should be relatively simple for end users to sit down in front of a unit and make a call. Ad hoc calls made across unknown network types can be more complicated, but the technology is making strides in ease of use and quality.

Back to the main Videoconferencing primer page