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Could Ethernet AVB Displace CobraNet?

When baseball's New York Mets opened their brand-new Citi Field stadium last month, it included a sizeable fixed sound installation. The system, integrated by St. Charles, Mo.-based TSI Global, was networked using CobraNet, the set of hardware, software, and networking protocols that enable digital audio to travel over Ethernet.

When baseball's New York Mets opened their brand-new Citi Field stadium last month, it included a sizeable fixed sound installation comprising, among other things, 240 Crown amplifiers and 52 BSS Audio Soundweb London processors from the Harman International family of pro AV brands. The sound system, integrated by St. Charles, Mo.-based TSI Global, was networked using CobraNet, the set of hardware, software, and networking protocols that enable digital audio to travel over Ethernet.

Credit: Harman International

Later that month, on another continent, Harman engineers demonstrated what the company and others believe could take the place of CobraNet and other audio networking flavors, including EtherSound. At Pro Light & Sound in Germany, Harman previewed products streaming end-to-end Ethernet AV audio.

Another digital audio technology? That's the question Rick Kreifeldt, vice president of Harman's System Development and Integration Group, gets a lot when he talks about Ethernet AV to industry professionals. "People are fatigued by new networks," he says.

But as Kreifeldt points out, Ethernet AV is something different. It's an emerging standard hammered out through the Institute of Electrical and Electronics Engineers (IEEE), which brought us 802.11 wireless networking and the 802.3 Ethernet standard itself. What's more, the task force working on the IEEE 802.1 Ethernet Audio/Video Bridging (AVB) specifications, as they're called, includes makers of nearly all the world's Ethernet silicon, plus Harman, Apple, Cisco, Intel, Pioneer, and others.

"Five years ago we started looking for next-generation networking technology," Kreifeldt told Pro AV. "Until now we've never gotten audio networking out of the top end. We want to get it down into PA, nightclubs, and other installations."

CobraNet was designed initially for large-scale installations such as stadiums, amusement parks, and other places where audio had to travel long distances. EtherSound, developed and licensed by Digigram, has made in-roads in live sound applications. Both are proprietary ways of prioritizing audio streams over standards-based Ethernet.

Residential Beginnings

Ethernet AV started out as a residential standard. Its aim is to improve delivery of streaming media over a network and to minimize the pops and clicks that come when network traffic interferes with AV traffic. AVB-compliant devices, when connected, create a "defended cloud," Kreifeldt explains. "Inside the cloud, we can guarantee performance."

Bandwidth necessary for carrying the AV stream is reserved throughout the entire path. Devices are divided into "talkers" and "listeners." When a listener wants to tap into an audio stream, it sends a reservation back to the switch, and then on to the talker. If the bandwidth is available, it's locked in. Up to 75 percent of a network's bandwidth can be reserved, and the AV flow remains constant. Separate queues carry high-priority and low-priority traffic, with streaming AV going into the high-priority queue.

To ensure synchronization, AVB uses a time-stamping protocol. Devices are synchronized by time of day and every media packet carries a "time to play," which lets multiple speakers play back a stream at the same time. Proponents say the performance safeguards in Ethernet AV mean it experiences just 2 milliseconds of latency over seven 1 Gbps switch hops. In comparison, CobraNet averages 5.33 milliseconds over five 100 Mbps switch hops.

Perhaps more importantly, says Kreifeldt, because Ethernet AV is a non-proprietary, IEEE standard that takes pains to manage bandwidth, IT organizations find it more palatable than other audio schemes. "It's a world of difference for them," he says.

Ethernet AV has not been formally ratified by the IEEE, but Kreifeldt expects it to be finalized in a year. In the meantime, expect to see companies release "pre-standard" Ethernet AV products, much the way wireless vendors began selling pre-802.11n products while that standard awaited ratification. Kreifeldt also expects there to be a manufacturer organization for Ethernet AV that will provide compatibility testing, much the way the Wi-Fi Alliance certifies 802.11-compliant products.

Harman will show Ethernet AV in action during InfoComm '09, but Kreifeldt knows audio networking won't change overnight. "CobraNet is very bread-and-butter and we're going to support our customers with it," he says. "But we see Ethernet AV as the future."



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