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The Memotec CX900e aced our tests, flawlessly protecting our video stream while delivering excellent data performance. Coupled with its video framer, the CX900e proves that video over frame relay not only works, but can blow you away with its performance.

No matter how badly we abused the WAN connection, our CX900e never dropped a video call. By assigning "very high" priority to the video and merely "high" priority to our LAN traffic, we blasted IP traffic at extremely high rates, much higher than the WAN could deliver. Yet this did not affect our video stream--we simply lost IP packets that overloaded the WAN, which was precisely the result we hoped we'd see.

More than a frame relay access device, the CX900e can operate in a variety of WAN applications. Unlike the ACT SDM-9300, the CX900e starts as an empty box with no I/O ports; you add the interfaces you need. The CX900e features six slots you can fill with a mix of serial data, LAN, WAN and voice interface adapters. Like the ACT unit, the CX900e can act as a frame relay switch to connect devices that expect to attach to a frame relay network, such as the VideoFramer.

This flexibility makes the CX900e's setup more difficult. Don't even think about trying to configure this unit at the command line. With its SNMP-like command syntax, the native Memotec command line interface is obtuse and unforgiving. Perhaps you can grow accustomed to typing "frsap:2 alias=frsap2, link=bopsap210,type=1,lmgt=3, iftype=2" to configure an interface, but we'd rather not.

Fortunately, Memotec provides--at no charge--Thunderview EMS, a Windows- and/or HP OpenView for Windows-based configurator that also provides some performance statistics and fault management. Configurations can be saved externally with Thunderview (or from the command line) and edited offline. These capabilities far exceed what the ACT device offers.

ACT Networks SDM-9300
The SDM-9300 disappointed us, underachieving in our tests. Despite frequent communication with ACT's tech support, we couldn't drive video at our target rate of 384 Kbps, and had to settle for 256-Kbps delivery. We attempted a variety of traffic priority settings, but even tiny amounts of data traffic disrupted the video call.

Architecturally, the Memotec and ACT units have many common elements, including a Motorola QUICC RISC processor (ACT's at 25 MHz, Memotec's at 33 MHz) and the Science Dynamics video framer. It's at the higher layers of software that the two units part company. ACT uses a simple text-menu interface from the console or via telnet, while Memotec resorts to convoluted command line or simple GUI administration utilities.

The SDM-9300 is, for all practical purposes, a fixed-configuration box, with four serial ports, two voice/fax ports and two slots for optional interfaces, such as Ethernet or token ring. The serial ports are soft-strappable to support many serial interface types (see features chart, page 48). Other configurations are available from ACT.

ABL VideoExpress VT2C Video Codec
The ABL VT2C box is built from a Pentium-class PC, so you can attach a keyboard, mouse and monitor to set up and control the videoconferencing sessions; you also can use an optional keypad panel, if you prefer. This is an ideal solution if you're new to videoconferencing and haven't already invested in a room system. You could set up a conference room with built-in cameras and mixed microphones, and feed these lines directly to the VT2C. If no more than two cameras are involved, you can use the ABL VT2C keypad for audio/video switching and volume/muting.

The output side of ABL's VT2C works like Science Dynamics' VFX-250S, but with 2-byte packet headers and 1,500-byte packet lengths. One or two camera- and audio-line inputs are connected directly to the VT2C's user-input side. An H.320 codec, which compresses video at speeds up to 15 fps, is built into this versatile unit. In addition, an audio codec supports G.711 (3.4 KHz/64 Kbps), G.722 (7 KHz/64Kbps) and G.728 (3.4 KHz/16 Kbps). We ran audio at G.722 to be consistent with the PictureTel unit used with the other framers.