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June 1999

Microphone, Camera, Action! IP Video Conferencing Meets The Desktop

By Fran�ois Desloges

IP-based video conferencing promises as many benefits as its predecessor, Voice over IP (VoIP). However, both solutions rely on the deployment of a quality of service (QoS) IP network to succeed. Solutions exist today that facilitate the upgrading of the data network to add QoS capabilities, and unleash the full potential of IP video conferencing.

For a few years now, different vendors have offered interoperable video conferencing systems compliant with the ITU H.320 standard. These systems rely on the worldwide ISDN network to offer good end-to-end video conferencing solutions — comparable to traditional voice services.

Since H.320 video conferencing systems hinge on the same circuit-switched network as the legacy voice industry, they suffer from the same limitations that justified the creation of VoIP and Internet telephony. The intrinsic inefficiencies of circuit-switched voice networks generally cause services to be expensive, especially long-distance calls. And the traditional model of the intelligent, circuit-switched network is limiting the deployment of new applications as well.

Video conferencing systems using the IP network, based on the ITU H.323 standard, offer the same advantages as VoIP in terms of cost savings and applications. Cost savings are made directly by eliminating circuit-switched long-distance fees. The merging of the two distinct circuit-switched and packet-switched corporate networks in a single, simple, and scalable IP network also promises significant savings in infrastructure and management costs. The other benefit is the new applications that would be developed around the model of an efficient "dumb" IP network, with very powerful and versatile computing end nodes. Applications integrating voice, video, and the Web in a powerful collaboration tool promise significant day-to-day productivity gains to work groups.

All the benefits of IP-based H.323 video conferencing come at a cost. Indeed, the legacy packet-switched IP network is as inadequate to carry voice and video as a circuit-switch voice network is at transporting data. IP networks must therefore be upgraded to offer QoS to video streams. However, this entry cost may not be as high as it seems at first. Contrary to circuit-switched equipment, packet-switched equipment follows a tradition of simplicity, scalability, and bandwidth inexpensiveness that stems from the necessity to follow a historic 1,000-percent annual bandwidth growth.

However, QoS enabling an IP network implies two new capabilities. First, the IP network must be able to sustain guaranteed bandwidth through time to Real-Time Protocol (RTP)-based video sessions that do not adapt to bandwidth bottlenecks the way legacy TCP data sessions do. Indeed, for interactivity purposes, RTP sessions do not retransmit video frames if they’re dropped in an IP network bottleneck — they are lost forever. Guaranteeing bandwidth to video sessions ensures that as few RTP frames as possible get dropped, and that the quality of the video session will not suffer.

Second, the QoS IP network must offer minimal latency and jitter (latency variation) to delay-sensitive RTP video streams. Again, for end-user interactivity purposes, video streams should offer end-to-end transport latencies of less then 100 ms and as little jitter as possible. This is a challenge, considering a latency of over 120 ms is introduced by a single, traditional 10 Mbps Ethernet switch with 100 frames of 1.5 KB waiting in queue. Low latency and jitter are normally achieved by forwarding the frames belonging to an RTP video session in high priority. By and large, voice streams used in Internet telephony and H.323 video streams require the same QoS from the IP network. However, video sessions typically use much higher bandwidth than voice sessions. That characteristic requires special care be given in certain areas of the IP network.

Considering the benefits associated with IP-based H.323 video conferencing, it is very likely that H.323 systems will be used instead of H.320 ISDN ones, everywhere IP networks have become QoS-enabled. And as the IP infrastructure evolves over time, there is a clear potential for H.323 to take over the world. Unsurprisingly, this will not happen overnight, and each portion of the IP network will show a different upgrade agenda.

On the public Internet, H.323 will not really be usable until a critical mass of Internet service providers (ISPs) have implemented QoS in their backbones. History will tell if the traditional carriers will rush to convert the huge circuit-switched network they’ve invested heavily in, or if only new competitive carriers will build such QoS IP backbones.

Utilization of H.323 over the wide-area network (WAN) will be limited by the bandwidth available from different access technologies for the last mile as well. Indeed, video conferencing sessions, commonly using 128, 384, and 768 Kbps, are much more bandwidth-hungry than typical voice sessions at 10 Kbps. Although legacy 56K modems and 64 Kbps ISDN access lines were enough for a mix of VoIP and data, broadband access services (xDSL, cable modem, etc.) providing more than 1 Mbps of bandwidth will be essential to deploy H.323 video conferencing on the WAN.

However, corporations can start benefiting right now from H.323 advantages by bringing video conferencing out of the local conference room — where it normally sits directly on an H.320 ISDN connection — to the desktops of everyday users.

Typically, only a few groups of users may need desktop video conferencing (DVC) at first, and chances are that the corporate backbone and part of the networking infrastructure will not need to be QoS-enabled for a while.

A good immediate solution consists of:

� Regrouping the DVC users on a single LAN subnet (using DHCP for easy adds, moves, and changes).

� QoS-enabling that LAN for all DVC users.

� Using an H.323/H.320 gateway to provide the group with top quality point-to-point WAN connections over ISDN, until the Internet upgrades to QoS capabilities.

New Ethernet equipment exists today that provides QoS to voice and video streams on the LAN, and takes care of both the guaranteed bandwidth and the latency and jitter issue, while minimizing the impact of video addition on legacy data applications.

It is important to understand how guaranteed bandwidth is essential to providing QoS to video sessions, since a video stream can easily require 12 to 76 times more bandwidth than an IP voice stream. Video session bandwidth usage can quickly sum up to a large part of the total available bandwidth on a pipe.

Fortunately, on the LAN, intense competition among equipment manufacturers has reduced the price of bandwidth for a while. This very low LAN bandwidth price can be leveraged to offer guaranteed bandwidth through the creation of a full bandwidth hierarchy, where typically no more than 10 full duplex links of 10 Mbps share a full-duplex 100 Mbps uplink in an Ethernet switch.

Although such bandwidth provisioning was overkill in the TCP-data-only era, it isn’t anymore with RTP video sessions that do not adapt to bottlenecks. Besides, Ethernet bandwidth has become so inexpensive that it now makes business sense to create a full bandwidth network on the LAN, since it avoids the costs of RTP bandwidth micro-management. Indeed, with such a simple solution, there is no costly management of bandwidth required, since the network topology guarantees full bandwidth to all desktops on the LAN subnets.

On a LAN where bandwidth bottlenecks have been eliminated, the issue of minimizing the latency and jitter of video stream can be fixed today. Indeed, the only thing Ethernet equipment must do is to retransmit in high priority the delay-sensitive packets belonging to RTP video sessions in front of the legacy TCP data frames.

New QoS Ethernet equipment performs this type of prioritization, with automatic queuing. Video prioritization is achieved by performing deep inspections on each frame in order to identify if it belongs to an RTP video session. The RTP information that is used for time-stamping purposes by voice or video sessions is encapsulated at the fifth ISO layer inside an Ethernet frame

Although five-layer deep inspection involves huge processing power, this prioritization mechanism requires no special management software or Ethernet adapter drivers to be deployed, resulting in a very low upgrade cost. It is also totally transparent to any other managed prioritization mechanism, and therefore, avoids being locked with a single vendor solution. RTP auto-prioritization modularity and simplicity allow progressive QoS-enabling of the network. There is no need to replace the entire existing infrastructure, and users simply add QoS-Ethernet switches along the path between the video conferencing desktops and the H.323/H.320 gateway.

It is also a good idea to use an H.323 gatekeeper on a QoS-enabled subnet to limit the bandwidth that the video sessions will use on your LAN so that your legacy data application will still have bandwidth space to move. Beginning to deploy QoS equipment on LANs today makes business sense. Since it locally connects video conferencing desktops, only the corporate backbone will need to be upgraded when enough ISPs offer the QoS Internet access that will give its full value to DVC.

Fran�ois Desloges is director of technology for VIPswitch, Inc. of Brossard (Montreal), Qu�bec, Canada. VIPswitch is the developer and marketer of video and voice QoS Ethernet switches. The VIPswitch family of non-blocking switches automatically prioritizes delay sensitive video and voice to the desktop with QoS and 100 percent throughput. The products are performance enhancers to all H.323 systems, and are fully compatible with existing software, hardware, and networks from Cisco, Nortel, 3Com, and Lucent. For more information, visit the company’s Web site at www.vipswitch.com.

The Case For H.323 In Video Conferencing


Corporations today are leveraging their existing local- and wide-area networks (LANs/WANs) as well as the Internet to bring voice, video, and data conferencing to their workforce partners and customer base. With the H.323 protocol, real-time multimedia applications are being delivered on computer desktops over the same packet-based networks as more traditional LAN applications such as e-mail and file transfer.

The H.323 standard offers a common protocol that allows communications products offered by different vendors to work together. While this sounds simple on the surface, its impact on the video conferencing market should not be underestimated. With users from around the globe communicating via hardware and software from a variety of vendors, industry standards are required to ensure interoperability. Without a comprehensive standard such as H.323, many customers would not be willing to deploy conferencing on their IP networks.

In addition to providing essential interoperability between communication endpoints, real-time H.323 conferencing over IP networks provides the following key benefits:

  • The ability to integrate multimedia communications directly with other IP applications. H.323 allows the integration of T.120 data conferencing, creating new ways to collaborate in the corporate world. Users can share applications, mark up shared whiteboard documents, and perform file transfers during the course of an H.323 video conference. Work can be done in real time instead of being delayed until participants return to their offices.
  • New ways to use the technology, including distance learning, home-office meetings, face-to-face customer support, and direct sales expansion. Users are analyzing their current business practices and discovering new applications for this communications medium every day.
  • Protection of investment in legacy conference systems. H.320-to-H.323 gateway products bridge ISDN (circuit-switched) and IP (packet-based) networks. Conference systems that reside on H.320 networks can now conference with H.323 systems.
  • Leveraged investment in existing corporate network infrastructure. Traditional H.320 conferencing systems require dedicated ISDN for each conference room or office. H.323 can be deployed wherever IP is supported. Corporations are increasingly migrating communications onto a single IP-based network, eliminating the cost and complexity of maintaining multiple communication networks.
  • Scalability. H.323 software performance takes advantage of increased hardware performance and faster connectivity. A user can upgrade to a faster network connection or faster CPU and get a better video conferencing experience from existing H.323 software.

  • Long-distance savings. H.323 allows you to place long distance video conferencing calls over fixed-cost IP networks. Traditional H.320 conferencing requires dial-up ISDN service with incremental usage charges.
  • Convenience to the user. H.320 has traditionally meant expensive, room-based systems, requiring the user to go to the technology. H.323 can be integrated cost effectively into users’ existing desktop computers. The technology is only a button-click away.
  • Increased productivity. H.323 desktop systems are used throughout the day for general business purposes when users are not participating in video conferencing calls. Dedicated H.320 conferencing systems sit idle when there is no videoconference in session.

Through up-front evaluation and planning, corporations are successfully integrating H.323 conferencing into their existing networks — providing a valuable new method of communication for their employees, partners, and customer base. By embracing H.323 technology, businesses are able to increase communication and productivity now, while protecting their investment for the future as improved conferencing and collaboration applications become available.

As businesses recognize the value of meeting face-to-face with key customers, suppliers, and employees without leaving the office, desktop conferencing and collaboration will continue to become more widespread. These benefits can effectively be achieved using an organization’s existing IP infrastructure. Desktop conferencing solutions offer communication at a reasonable price, all within the framework of a standard that will continue to grow and evolve.

Roger Wallman is senior product manager for core technologies at White Pine Software. White Pine develops, markets and supports multi-platform browser-based internetworking software that facilitates worldwide audio and video communication, and data collaboration across the Internet, intranets, extranets, and other networks that use IP. White Pine’s video conferencing software products — CU-SeeMe Pro and MeetingPoint, create a client-server solution that allows users to participate in real-time, multipoint video, audio, and data conferences over the Internet and intranets. For more information visit White Pine’s Web site at www.wpine.com

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