Network Computingwww.networkcomputing.com

Call Management From a LiveManager console, a network manager can control the amount of network bandwidth allotted to H.323 audio and video traffic. The manager also can associate extension numbers with the IP addresses of participating H.323 terminals. When configured this way, incoming calls dialed via ISDN to the LiveGateway can furnish an additional extension and be automatically connected to the desired terminal. Or, as an option, an operator station can be configured to provide inbound call support.

To place an outbound H.320 ISDN call from an H.323 terminal, an address in the form of "918765432123,918765 432124" must be provided. In each number string, "9" is the service code that grabs the attention of the LiveGateway. The remaining digits are the prefix and area code (if necessary), plus the number(s) of the H.320 station. PictureTel restricts the service code to a single digit, but it can be redefined to whatever value you choose.

Setting up the PictureTel system is easy and intuitive. The LiveGateway card tries to automatically detect its environment, but its configuration program lets a network manager override the base address and IRQ (Interrupt Request) settings. One log file that can be viewed from the configuration screen provides a time-stamped report of relevant events that occur during the gateway card's initialization, pretesting and configuration reloading.

Pumping Frames During testing in our lab, we were pleasantly surprised to find that a LiveLAN H.323 terminal calling through the LiveGateway's single BRI connection to our H.320 room videoconferencing system achieved a video throughput of 14 fps (frames per second). When a LiveGateway system detects one of its own kind at the other end of the connection (in this case, a PictureTel Concorde), it transcodes to a proprietary audio algorithm, PT724, which releases more bandwidth for video without degrading audio quality.

However, an ISDN call placed from our Wisconsin-based LiveManager to another LiveManager unit located at PictureTel's headquarters achieved only 10 fps. In this case, the LiveGateways apparently settled on their default audio algorithm, G.711, which chews up half of the available BRI ISDN bandwidth.

We did note one behavioral problem with LiveGateway. After puzzling "connection failure" messages were repeatedly received by an H.323 terminal during call setup, we discovered that the RADVision gateway also was operating (but without active connections) on our LAN. It had to be removed before the LiveGateway would complete calls. But the converse was not true. The RADVision L2W-323 would operate without problems whether or not PictureTel's LiveGateway was present. PictureTel recognizes this problem and says it will correct it in a future software release.

But Wait, There's More In addition to H.323 to H.320 videoconferencing, the LiveGateway supports T.120-compliant collaborative connections. Microsoft's Internet-based NetMeeting system emerged from LiveShare Plus, in a joint development project with PictureTel, so LiveLAN terminals can easily interoperate with NetMeeting. The LiveGateway performs Microsoft Internet Locator Server (ILS) registration using LDAP.

PictureTel's LiveGateway does not support placement of a voice call over ISDN to a POTS telephone from the DVC workstation or H.323 multipoint conferencing, but the company says it is planning to announce these features later in the year.

Dave Brown is an independent consultant in videoconferencing and network applications. He can be reached at dave@dbec.com.