Out of the Past

Jan. 24, 2007
AV looks back and gains better control

By Chuck Wilson, Executive Director, National Systems Contractors Association (NSCA)

In these heady days of convergence among technologies on all levels, the marriage of entertainment technology and building technology has created some pretty odd bedfellows. Take, for example, the trend among audiovisual systems designers toward embracing SNMP (Simple Network Management Protocol) for control. Perceived by the benighted as an outdated, vestigial old control system, SNMP is the hot ticket for those in the know these days who regularly use it to place in a browser window a complete template of AV commands that can be accessed via any PC.

In one sense, the benighted are right: SNMP is old. But despite first being developed in 1988, it is still the de facto standard for controlling things over the Internet. Over the last decade, SNMP slowly came into the forefront of AV control based upon a growing number of disgruntled PC-savvy users, programmers, and designers who wanted not only to control their systems in a browser window but also to network AV over the same Cat-5 cables carrying data traffic. They also wanted to reduce installation times and costs, the need for maintenance, and the real estate required to house control of their systems. Once they networked AV control with LAN and regular Internet activity, they also could forget about RS232 and other controls based around hardwired connections.

Sure, there are other protocols that can accomplish some or even most of these things, but SNMP has emerged as a logical choice based on its reliability, well-established history, and familiarity. SNMP is straightforward in design and function. There are only a handful of commands that can be given to any connected device and one vehicle for transmitting unsolicited information. To receive information from an SNMP device, "get," "get next," "get bulk," or "set" commands are sent to an SNMP server, which then either sends back the desired information or an error message. "Get" commands retrieve information on a device's status (whether the device is on or off). "Get next" commands take the equation to the next level (discovering whether or not individual components within a device are operating). "Get bulk" commands retrieve large blocks of data that would, for example, tell you everything about the status of a connected device. "Set" commands make changes in a device's function.

SNMP systems also can send messages about the function of the network system back to its user. These messages are called "traps." Traps often appear on start-up, after changes made to a system's status, or to report an error. Traps are unsolicited and occasionally unreliable. Those not fond of SNMP love to cast a critical eye upon traps, but they can be easily dealt with. A device could send a trap to a system manager and say that it's turned on. If that data arrives safely, it is put to use. If not, the server receives a "get" command, and all continues without a glitch.

Within AV applications, about 90 percent of the time SNMP is used to make devices turn on or off. The remaining 10 percent of SNMP power is dedicated to ensuring devices are working properly. This last 10 percent of SNMP function requires the most system development time and effort, for while not much usually goes wrong in an SNMP-networked system, individual functions must be checked frequently, and that means the management system has to be "smart" enough to know everything about the devices under its control.

As recently as 2 years ago, the AV world still had its doubts about SNMP. In fact, Crestron's technology vice president at the time, Fred Bargetzi, made a huge effort to build SNMP into Crestron products. He discovered, however, that "the industry didn't care."

These days that's no longer true, and a lot of this is because AV systems managers typically either work with or for an IT manager. Now that both have a voice in building AV systems, together they have brought one of the industry's latest networking innovations out of the past, into the present, and along for the ride into the foreseeable future.

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