Enablers for IP videoconferencing.
One-way video streaming is already commonplace on the Internet, and some take this as a sign that two-way videoconferencing will follow soon. Others argue that the exacting bandwidth, latency, and jitter requirements for live video will delay its widespread use for three years or more, even over the relatively controlled environment of corporate intranets.
Videoconferences that adhere to the H.323 specification generally require a line speed of at least 512 kbps and maybe as much as 1.544 Mbps (see sidebar, "Standards drive IP videoconferencing"). For high-quality video, the latency, or delay, should be less than 150 msec each way. Jitter, which occurs when the delay varies, must also be kept to a minimum; otherwise, it will cause distortion and unstable images and may even disrupt the image completely.
However long it takes to meet these specifications, the leading videoconferencing vendors are striving to do the work in "Internet time," where a period of seven years in human terms translates into about 12 months.
Network service providers are also helping to speed the process by constructing optical IP backbones that are capable of supporting live, two-way videoconferences. AT&T, for instance, plans to offer dedicated OC-3 and OC-12 Internet access services with a round-trip latency guarantee of no more than 80 msec and packet loss of 1% or less.
Among equipment vendors, PictureTel has announced one of the more ambitious plans to provide live, real-time videoconferences and other video-based services over IP networks. Known as Visual Collaboration for the Net (VCN), the strategy combines the firm's full range of desktop and group videoconferencing products and services with network access and transport capabilities delivered through major network service providers. It foresees applications ranging from e-commerce, Web hosting, and distance learning and training, to interactive customer meetings and broadcasts of corporate events.
A major component of VCN is PictureTel's Visual Collaboration Application Service (VCAS), which allows for collaborative conferencing, streaming, and broadcasting of events via a Web video portal.
Accessing VCAS via an Internet service provider and standard browser, users can schedule and conduct live videoconferences over IP and ISDN networks. They can also deliver integrated briefings with streaming video and slides to a dispersed audience, conduct distance-learning sessions using experts and stored video on demand, or view a previously broadcast event stored in a company archive.
To support the service, PictureTel has established alliances with a number of network service suppliers, including Nippon Telegraph and Telephone in Japan, Deutsche Telekom in Germany, and Enron Communications, whose high-bandwidth, low-latency Enron Intelligent Network is designed for delivering rich media content over the Internet.
PictureTel has also formed an alliance with fellow videoconferencing pioneer, Intel Corp., to jointly develop a new line of PC-based multimedia products to take advantage of the Internet, cable modems, xDSL, and other broadband facilities. Scheduled to debut in 2000, the products will support multimedia collaboration, streaming audio and video, and real-time conferencing.
Meanwhile, PictureTel recently announced a Windows NT-based application server for creating, distributing, and managing streaming video applications over IP networks. The eVideo Application Server synchronizes video, PowerPoint slides, and interactive chat for live and on-demand broadcast over corporate intranets and extranets to PCs running Internet Explorer or Netscape browsers.
The Andover, Mass. firm has also expanded its IP videoconferencing solutions with a gateway to connect ISDN and IP videoconferencing systems, along with new gatekeeper and IP network management software and multipoint server software that enables multiple sites to participate in the same conference.
VTEL Corp. is also collaborating with networking companies to enhance its visual communications solutions. Cisco Systems and GTE Network Services are joining with the Austin, Texas, firm to provide IP-based, H.323 video solutions using VTEL's desktop and small-group videoconferencing systems.
VTEL SmartStation desktop and WG500 workgroup videoconferencing systems allow point-and-click connections to both digital and IP networks on a call-by-call basis. In June, the company introduced an Internet-streaming software suite for standalone use and to enhance its videoconferencing systems.
Called TurboCast, the server-based package was the first product to result from the company's acquisition of Vosaic LLC in March. It features a Java encoder, reflector, and player applet so users can view video on PC, Macintosh, and Unix systems, as well as some Java-based handheld devices.
White Pine Software's chief executive officer believes the rapid rise in corporate Internet videoconferencing will help the company turn profitable by year's end for the first time since it went public in 1996.
The Nashua, N.H. firm's software products, including MeetingPoint and CU-SeeMe, when used in conjunction with computers equipped with mini-cameras, microphones, and a soundcard, allow users to participate in real-time, multilocation videoconferences via the Internet.
MeetingPoint Conference Server, which runs on both Sun Solaris and Windows NT, enables users to create and mediate multi-user videoconferences via the corporate network or Internet. It supports H.323 for videoconferencing and T.120 for data collaboration. Among its features are a built-in H.323 gatekeeper that lets an administrator set bandwidth limits per conference and per user, and a bandwidth pruning capability to accommodate users with different connection speeds.
Given the popularity of streaming video and its increasing convergence with interactive videoconferencing, there's a good chance that intranet video will be replacing some of your meetings and corporate training sessions before year-end 2000, closely followed by mainstream video applications over the Internet.
Standards drive IP videoconferencing
Standards, and their acceptance, will be the driving force in spurring the growth of videoconferencing over IP networks. That's why equipment vendors are lining up to support the H.323 specification adopted by the International Telecommunications Union (ITU) for transmitting voice, data, and video traffic over IP and other packet-based networks that don't offer a guaranteed quality of service (QoS).
H.323 grew out of the H.320 standard, which the ITU approved in 1990 to support videoconferencing over ISDN and other types of circuit-switched networks. The H.323 standard does not address the network type being used and is not dependent on any particular hardware or operating system.
For data traffic, H.323 uses the transmission control protocol (TCP), which is highly reliable though prone to delay. For data traffic, though, the delay is not critical, as it is with voice and video. For data conferencing, H.323 also supports the ITU's T. 120 standard, which accommodates whiteboarding and slidepresentation functions, as well as file transfer and application sharing.
For voice and video traffic, H.323 makes use of the user datagram protocol (UDP), which routes packets in sequence and with "best effort." UDP is less reliable than TCP, but its lower latency makes it better suited for the more time-sensitive traffic. H.323 also supports IP multicast, a way of sending UDP packets to multiple parties without repeating the information being transmitted.
To keep the voice and video traffic synchronized, H.323 employs the real time protocol (RTP), which effectively time stamps outgoing packets so they can be reconstructed and resynchronized at the receiving end. To guarantee bandwidth for the conferencing sessions, users can also employ the Internet Engineering Task Force's resource reservation protocol (RSVP), which provides a mechanism for reserving the required bandwidth.
H.323 defines a number of new network components, including terminals, gateways, multipoint control units, and gatekeepers, and the protocols used to communicate with them. Terminals are the devices that handle the compression/decompression functions for voice and video, either in special hardware or in software running on general-purpose processors.
Gateways connect H.323 terminals to other endpoints that do not support the standard-generally on ISDN and other circuit-switched networks. They provide the needed protocol translation for interoperability and for transferring information between the different networks.
Multipoint control units are needed when the conference involves three or more endpoints. They can be implemented in software running on other network components, but dedicated hardware is better if multipoint conferences are common.
Gatekeepers are the most important part of an H.323 network, since they limit bandwidth consumption, including the bandwidth used per call and the number of calls on any routed segment. Once the preset threshold for the number of simultaneous conferences is reached, the gatekeeper can refuse to make any further connections, effectively reserving some bandwidth for e-mail, file transfers, and other data transactions. Gatekeepers also provide address translation between LAN aliases for terminals and gateways to IP addresses.
In January 1998, the ITU ratified version 2 of the H.323 specification, which provides a means for encrypting Internet calls and makes them faster and easier to set up. The new version also allows users to transfer and forward Internet calls and perform other functions common to regular telephone service.
Other enhancements include the support of URL-style addresses, the ability for endpoints to set QoS levels through RSVP, and the ability for gateways to notify a gatekeeper about their currently available resources.
Standards have also emerged for streaming video, including Apple Computer's QuickTime, RealNetworks' Real-Time Streaming Protocol (RSTP), which has been endorsed by the Internet Engineering Task Force, and the burgeoning MPEG-4 standard developed by the Motion Picture Experts Group. Gradually, the standards are fusing and broadening the scope and usefulness of streaming video.
Apple's QuickTime file format has been adopted as the basic reference file format for MPEG-4. Besides this tie-in, Apple has made QuickTime more compatible across different types of computers.
For instance, the Apple software now includes a streaming component that relies on RealNetworks' streaming transport protocol. This makes streamed QuickTime files available to the large numbers of users who have RSTP-based plug-in client software installed in their PCs.
In another advance, MPEG-4 allows the instructions that represent the execution of user commands to be separated from the delivery of the content. This means the graphic components can be delivered in occasional bursts and stored in memory at the user's computer before they are needed. Then, only instructions need to be sent to set the graphics in motion.
Edwards is a data communications consultant who writes about network computing technology and its business use.
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|Date:||Dec 1, 1999|
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