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It is important to note that though our testing for this project concluded on July 23, 1999, we're reporting conditions known to exist before that date. The pace of H.323-related software upgrades, patches and bug fixes is feverish. Before making purchase decisions, check with your intended supplier(s) to see if problems reported here have been, or soon will be, corrected.

Role of the H.323 Gatekeeper
Under H.323 call-setup rules, an endpoint can directly call another using its basic IP address (e.g., 100.101.102.103). But if an MCU needs to be employed, or the caller finds it easier to use a shorter telephone-extension-like phone number, or perhaps a character string that represents a terminal ID or looks like the callee's e-mail name, you must employ an Internet locator service (ILS) or an H.323 gatekeeper. We didn't test ILS servers for this project, but we did examine the gatekeeper's role by using popular implementations, the RadVision hardware GK 1.5, which is built into RadVision's MCU-323, and GK 1.3, built into the Madge LVG EN LAN Video Gateway (which is a private-labeled RadVision LIU-323).

Capabilities Exchange
During conference setup under H.323, endpoints and MCUs exchange messages that advise each other of the audio and video algorithms they propose to use. It's something like the signaling that goes on between a baseball catcher and pitcher. However, most MCUs can offer just one audio and one video algorithm, which is preset by the operator of each conference. Only VideoServer's Encounter supports mixed-mode (audio and video) conferencing. It can adapt to proposals of G.711, G.723 or G.728 from endpoints.

A problem arises with most endpoint videoconferencing systems if you want to force them to use a specific audio and video algorithm required for a given MCU conference. To keep the user interfaces simple, manufacturers usually don't provide setup mechanisms that force the audio and video algorithms. Instead, they design their software to make appropriate choices automatically, depending on the bandwidth limit selected by a user. But this leads to connection failures if the "appropriate" choices don't match algorithm choices expected by the MCU. We provide some examples in the following discussion of the endpoints we used for our MCU tests.

Intel ProShare 500 version 5.1
Deservedly, the PS 500 has become the gold standard against which other desktop PC videoconferencing systems are compared. This is a dual-mode H.320/H.323 system that uses only one PCI-slot PC plug-in board for video-frame grabbing and management of a BRI ISDN connection. (Although not heavily advertised by Intel, you can use the onboard ITK ISDN adapter for Internet access via an ISP. You can be connected to the Internet on one 64-Kbps channel and use the other channel to make voice telephone calls.)

If you install a PS 500 endpoint in anything less than a 400-MHz Pentium MMX, you may experience connection rejects or "green screen" indications that video couldn't be established. Also, don't overinstall a version of Microsoft NetMeeting that is different from the version that comes with your ProShare 500 software. Doing so may lead to mysterious calibration freeze-ups or failure to establish video.

When operating under version 5.1 software, the PS 500 obeys RAS rules, and registers correctly with every gatekeeper we tested. The audio and video bandwidth slider bar indirectly affects the choices of audio and video algorithms a PS 500 will propose during call setup. A selection of 400 Kbps will make it propose G.723.1 audio and H.261 video. A selection of 128 Kbps will make it propose G.723.1 audio and H.263 video. However, if the called endpoint can use only G.711 or G.728 audio, the PS 500 usually will adapt.

Intel TeamStation Update 6
We confirmed that a TeamStation, which runs under similar Intel software, will register and negotiate capabilities just as well as a PS 500. Teamstations have better microphones and echo-canceling sound systems than PS 500s. Although Zydacron Z350 boards are built into TeamStations to enhance performance, their chip-based audio codecs are surrounded by Intel software. We heard none of the audio garbling that we experienced with standalone Z350s running under Zydacron's 2.10 software (see below).

PolyCom ViewStation Beta 5.00
Perhaps because Intel ProShare 500 systems first propose G.723.1 audio when placing a call at 400 Kbps, and perhaps because PolyCom's new beta H.323 software makes errors during capabilities exchange, we were unable to connect these two systems. However, we had excellent results when a Zydacron Z350 system called a PolyCom at 384 Kbps. After a conference was under way, we observed that both of these systems had agreed on G.728 audio and H.261 video. This may be attributed to their H.320 heritages, where G.728 is the preferred audio algorithm. PolyCom and Zydacron both have evolved their newer H.323-capable products by re-engineering older H.320 platforms. They appear to have strong instincts to use G.728 whenever possible.

Sorenson Vision EnVision version 1.00
When we ran the EnVision desktop videoconferencing system from Sorenson Vision at full CIF, we saw performances that were no better than four frames per second.

Unlike other systems that automatically select audio and video algorithms based on selected speed, however, EnVision does let the user set a preference order for the audio algorithm proposals during call setup. We forced two flavors of G.723 to the top of that list, but observed that EnVision ignored both, and set up in G.711.

There appears to be no way to direct EnVision to register with a preferred gatekeeper; under current 1.0 software, EnVision doesn't register anywhere. However, if "automatic gatekeeper" is checked, the EnVision can accept an alias string, and will connect to another endpoint or MCU that is properly registered somewhere on the LAN segment.

Sorenson has addressed these issues in its EnVision 1.5 system, which begins beta tests this month.

Microsoft NetMeeting version 3.01
"The NetMeeting Phenomenon" (which accompanies the main article) reports that NetMeeting 3.01 is the first version to perform RAS correctly. It can register with a gatekeeper and participate in a multipoint conference if the proper audio and video algorithms are used. However, to trick NetMeeting into using G.723.1 audio and H.263 video, it must be told during setup that it is operating on a 28.8-Kbps modem.

NetMeeting 3.01 cannot make a direct call to a PS 500 with 5.1 software; it reports "other party not able to accept NetMeeting calls." This probably happens because NetMeeting 3.01 recognizes that the ProShare has NetMeeting 2.11 running at its end. A call from a PS 500 to NetMeeting 3.01 locks up the Net Meeting endpoint, apparently because NetMeeting 3.01 does not appear to correctly issue or honor bandwidth restriction instructions. When participating in a conference restricted to 384 Kbps or less, we observed that our NetMeeting endpoint often would freeze up, and report as "not responding" in the Windows Task List.

Zydacron Z350 With Version 2.10 Software
As reported above, a Z350 system with Zydacron software will look and sound great if it can negotiate G.728 audio with another party, such as the PolyCom ViewStation. However, we observed difficulties with Z350-Intel ProShare 500 connections that don't appear to be much improved since Zydacron upgraded its software for the Z340/Z350. Before concluding our testing in July 1999, we downloaded and tested version 2.10.

We observed that if a Z350 initiates a 128-Kbps call to a ProShare, it purports on its connection monitor to be using G.723.1 audio. However, the connection monitor's bandwidth consumption graph shows 117 Kbps for the H.261 video and 30 Kbps for audio. (G.723.1 should consume no more than 11 Kbps including overhead.) In this situation, the PS 500 fails to put up either audio or video.

If a PS 500 with its bandwidth slider bar set to 128 Kbps initiates a call to the Z350, we observe the slider bar pushed up to 400 Kbps, and the PS 500 purporting to be transmitting video at 330.6 Kbps. Both ends adopt G.711 audio and H.261 video. They can see each other; the Z350 can hear the PS 500, but audio coming from the Z350 contains an annoying rapid clicking sound.

extra: Microsoft Internet Information Server (IIS) 4.0
While setting up the PictureTel Web Center NC20R001 on our NT 4.0 Server, a diagnostic stated that "this program requires Microsoft IIS 4.0 or greater­abort setup." During its installation, IIS 4 warned that it had not been tested on anything newer than Service Pack 3. We found it works just fine with SP5. But after installing IIS 4 on our server computer, browser programs trying to connect would complain about corrupted scripts.

As of July 1999, there is an installation bug associated with IIS 4.0. The folks at White Pine Software had experienced it, and they helped us with the workaround: After installation, it is important to stop the IIS Administrator service before performing the required NT restart.