Network managers, fearful that videoconferencing would consume excessive amounts of network bandwidth, have relegated this function to specialized-room systems with ISDN connections. But now, thanks to faster networks and the new H.323 videoconferencing interoperability standard, videoconferencing is coming to the desktop.
Although desktop ISDN systems have been available for a while, IS managers have been reluctant to spend money to bring in additional ISDN lines. But things are changing: LANs are much faster, and LAN switching systems allow administrators to segment traffic, isolating videoconferencing data so that it has less impact on the network.
In addition, the international videoconferencing standard H.323, which recently became available, is designed for use over packet networks such as LANs and the Internet. With H.323, packet-based backbones, such as the Internet or a private corporate intranet, can accommodate videoconferencing, eliminating the need for a specialized ISDN network.
H.323’s architecture also allows network managers to control the impact of videoconferencing on corporate LANs. These gatekeeper functions include limiting the number of users and the amount of bandwidth an H.323 conference can consume.
“We’re at the beginning of a fundamental change in the business of how working together happens,” said Bob Castle, president of VideoServer Inc., a Lexington, Mass., provider of multipoint conferencing systems.
H.323 rolls out
H.323-based conferencing systems already have begun rolling out to the consumer market, and Microsoft Corp. plans to bundle the standard into future releases of Windows 95 and Windows NT. Microsoft also is distributing a free H.323-compatible collaboration tool called NetMeeting. Most of the current H.323 tools are slated for use on the Internet, where H.323 will be useful because it’s designed to accommodate bandwidth as low as 28.8K bps.
H.323 will be implemented in a variety of ways, with differing levels of performance. Software-based systems, where audio and video compression and decompression are performed by the PC microprocessor, will have relatively slow frame rates and small video screen sizes. For example, Microsoft’s NetMeeting displays up to 10 fps (frames per second) and a small video screen size known as QCIF (Quarter Common Intermediate Format), which has half the resolution of the full CIF. QCIF is 176 by 144 pixels; the higher-quality full CIF is 352 by 288 pixels.
Specialized videoconferencing add-on hardware is required for larger screen sizes. “Hardware accelerators will help make desktop video with H.323 more attractive,” said Walt Jones, vice president of R&D at VideoServer. “NetMeeting is a good product, but the size of the video it displays is discouraging. A third party could add an adapter card that would use the great NetMeeting interface but increase the frame rate.”
Such specialized hardware likely will be found in corporate-oriented H.323 systems that are slated to roll out during the next year. For example, PictureTel Corp. plans to introduce an H.323-compatible version of its LiveLAN videoconferencing system next month.
PictureTel officials claim the H.323 system will rival the company’s ISDN-based systems for picture quality, delivering a full CIF screen at 15 fps. According to Peter Mahoney, director of marketing at PictureTel, the company’s system will allow users to adjust the quality of the conference by choosing their transmission speeds (ranging from 64K bps to 384K bps). Generally, the higher the bandwidth, the better the quality of video.
PictureTel and other videoconferencing vendors expect corporations and other H.323 users to begin pilot testing the technology this year before rolling out larger implementations next year.
Such evolutionary growth is necessary because all of the tools needed for corporate use of H.323 are not yet in place. Current H.323-compatible products, including NetMeeting and Intel Corp.’s ProShare, can handle only single, point-to-point conferences. For multipoint conferencing, products must connect to an MCU (multipoint control unit), which links several conference participants. MCU vendors, such as Videoserver and RADVision Ltd., now are developing H.323-compatible systems.
Because of the hurdles still remaining (and their investment in existing equipment), many organizations likely will have both an ISDN-based system, which uses the H.320 videoconferencing standard, and new H.323 systems.
MCU manufacturers are currently working on ways to link the two systems, which use different addressing schemes: H.320 systems use telephone numbers, and H.323 uses IP addresses. “We’ll try to adopt a standard authentication and naming service, but this is an area where services still have to be invented,” said VideoServer’s Jones, noting that H.323 also must be made to work with existing addressing services such as Domain Naming System and directories using the Lightweight Directory Access Protocol.
In addition, gatekeeper functions will need to be enhanced to work with new Internet mechanisms for reserving bandwidth. These mechanisms, such as the Resource Reservation Protocol, are designed to reserve bandwidth for multimedia applications. The two standards will need to work together in order to avoid access problems.
Videoconferencing systems with dedicated hardware can send larger images by tapping the Full Common Intermediate Format (left). Software-based H.323 systems transmit small images using the Quarter Common Intermediate Format (right).