by A.B. Covell  Designing a Videoconferencing Solution Network Considerations Acquiring and implementing one or two videoconference systems won't require a major overhaul of your network infrastructure. However, if you plan to ramp up to deploy more than a few systems, you'll want to think through the implications for your WAN, LAN or Intranet infrastructure. Performance, flexibility, pricing and staff support are the key factors that you'll need juggle when arriving at an effective configuration. Videoconferencing based on today's data networks poses serious challenges, and only those organizations with the staff resources and commitment to state-of-the-art network technologies will be up to the task. Most of the rest of us will roll out videoconferencing more slowly, with ISDN playing a central role. Successful videoconferencing depends on the underlying network to deliver three important performance characteri stics: 1. Isochronous transmission Video and audio delivery must be sent and received continuously and in a synchronized fashion. Any irregularities in the transmission of either or both media streams will have a perceptible negative impact on the quality of the video and audio at the end points. 2. Bandwidth For any reasonable quality video and audio, a sizable chunk of bandwidth is required. 128 Kbps is probably the minimum threshold for achieving any degree of audio/video quality. 3. Low Latency Because a conference is interactive, any delay in the transmission of audio and video is quite noticeable. This is different from some audio/video broadcast applications, which are much less sensitive to transmission delays. Given the requirement and demands of videoconferencing on the network, the availability of a QoS guarantee in the network transport is the single most compelling network characteristic when it comes to videoconferencing support. Packet switched networks, which have historically provided best-effort packet delivery mechanism fall short, though the new IETF Resource Reservation Protocol (RSVP) aims to address this deficiency for IP networks. The ISDN network does offer QoS and is available globally. Single line ISDN with two-channel 128 Kbps is adequate for decent quality conferences, and channels can be aggregated to deliver higher-quality conferencing, with 384-Kbps connections becoming a standard for 30 frames-per-second conferencing. ATM, which has yet to make serious inroads in the network environment, serves as a WAN transport that facilitates videoconferencing through the creation of private virtual circuits with guaranteed bandwidth QoS. At this point in time, circuit-switched ISDN has the edge at many sites, given ISDN's bandwidth guarantees and the wide availability of public-switched services, enabling seamless callout to anyone else with ISDN connectivity. Cost is also quite reasonable, with monthly charges for a single BRI at well under $100 in most cities. Connect charges vary, given the nature of the call, but they are modest enough that they can be covered handily in most organizations. ISDN's costs seem to mount only when you begin to consider a significant rollout of videoconferencing to the desktop via ISDN. Since most offices and desktops are LAN connected, you may need to implement H.320 LAN tunneling from desktop to an ISDN switch or an H.323 to H.320 gateway to limit the number of ISDN connections (and costs) needed to serve the enterprise. Expect the preference for ISDN at many sites to change as packet-switched networks, most particularly the Internet/intranet, gain bandwidth allocation via RSVP and protocol support for real-time synchronous media with the recently ratified IETF Real-Time Transport Protocol (RTP). It may take years for RSVP/RTP to be widely deployed, making anytime anywhere Internet conferencing viable. The intranet will see full implementation of these protocols sooner. Many organizations have complete control over their intranet infrastructure. And there are communications carriers and Internet service providers (ISPs) that offer intranet services for smaller, geographically dispersed organizations -- look for them to upgrade to RSVP-capable routers soon. The POTS alternative may gain some momentum with consumers, but video/audio quality limitations will hinder their acceptance for business use. Technology managers running low-bandwidth, shared networks, such as 10-Mbps Ethernet, should be very wary of introducing any videoconferencing solutions to network desktops. Even with low-bandwidth packages such as Enhanced CU-SeeMe, the traffic generated by a growing number of videoconferences can eat into the bandwidth needed by an ever-increasing array of bursty, network-centric desktop applications. The result can set the network manager's hair on fire. Some vendors of desktop packet-based solutions now offer videoconference network management packages to help you manage videocon ference traffic if you do go the LAN/intranet route (e.g., PictureTel's LiveManager). Network managers with Switched Ethernet (especially those with full-duplex) or 100-Mbps Ethernet are in much better shape. Then the bottlenecks are likely to occur in the backbone or WAN links. WAN links are particularly susceptible, since the high cost of dedicated WAN connections often keeps transmission rates relatively low. Videoconferences are very likely to occur across WAN links since co-located workers are more likely to meet in a conference room or at the coffee pot. Network managers eyeing ATM networks are also in position to consider videoconferencing, and certainly there are many organizations that are being driven by this application to ATM or other proprietary LAN technologies that offer QoS. Products are now becoming available, like those emerging from the PictureTel-First Virtual partnership, which offer H.323 videoconferencing over 25-Mbps ATM networks. One serious limitation of enterprise network packet-based solutions is an inability to conference with colleagues and customers outside the enterprise. One solution is a gateway to the ISDN network. For example, RadVision has developed two such gateways: One tunnels H.320 videoconference data across packet networks while the other converts the video and audio stream between H.320 and H.323. Internet videoconferencing provides another alternative solution, though it is not yet viable for most businesses since bandwidth allocation has not yet been implemented on the Internet. Once RSVP and RTP are implemented in combination with the ITU's H.323 protocols, the Internet will become a very attractive solution, indeed, combining the benefits of the packet-switched system (a single network connection for data, voice and video) and the global accessibility and QoS of the public ISDN network. Designing a Videoconferencing Solution Typical Videoconferencing Applications Characteristics Of A Successful Videoconference Solution Summary of ITU Videoconferencing Standards Videoconference System Alternatives Network Considerations Mix and Match Sample Scenarios Putting It All Together Videoconferencing Web Resources Print This Page E-mail this URL