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Ruckus patents technique for video over Wi-Fi

The system turns multicast video into unicast streams so it can run more smoothly

By , IDG News Service
December 07, 2009 08:10 AM ET

IDG News Service - Wi-Fi equipment vendor Ruckus Wireless has patented a technique that appears to be widely used to improve video on wireless LANs.

The company recently received patent protection in Europe after earlier having it patented in the U.S. Many other vendors seem to use a similar approach, according to industry analysts. But Ruckus said it isn't going on the warpath.

"We're not looking to go out and sue the industry," said Seamus Hennessy, Ruckus' chief financial officer.

"We want to use this to build a case and build a strong patent portfolio, so if we do need to go on the offensive, we can," Hennessy said.

The technique is a fundamental one involving a shift from one transmission protocol to another, and Ruckus said its patent is broad. In 2004, when it was trying to develop wireless LAN gear that could smoothly deliver high-definition TV, the Ruckus engineering team found a problem: Carriers used multicast to deliver IPTV (Internet Protocol TV), and multicast wasn't suited to 802.11 networks.

Multicast is an IP mechanism that sends one packet to multiple endpoints, in this case subscribers' TVs. That works on wired networks, but on wireless LANs, every endpoint needs to receive a given stream of packets at a different speed based on its distance from the access point, as well as other factors. In addition, with multicast, wireless LAN endpoints have no way of acknowledging to the access point that a packet has been received.

In response, the network slows down the multicast session to the lowest common denominator to reach the most distant endpoint. Under those circumstances, the video can be choppy or slow.

Ruckus already had special antennas and software to make high-definition video run more reliably over wireless LANs, but this problem stood in the way.

"It became clear to us that the way 802.11 handled multicast wasn't going to work at all," said Bill Kish, Ruckus co-founder and chief technology officer.

The problem could affect enterprises that distribute training videos or other content to employees over a wireless LAN, as well as any other application that uses multicast in a home or office, Kish said. That includes push-to-talk on Wi-Fi pagers such as those from Vocera, he said.

In response, Ruckus devised a way to first detect when an endpoint was trying to initiate a multicast session and then change that session to one using unicast, another IP transmission system. Unicast sends a separate stream to each endpoint, so each session can run at the correct pace for that endpoint, and sends acknowledgments for incoming packets.

Unicast puts a bigger load on the network because it sends a separate video stream to each endpoint. But even with heavier traffic, unicast delivers a better video experience than a multicast session that isn't working, Kish said.

The multicast-to-unicast conversion is the only real option for any vendor that wants to make multicast run well over its networks, and the technique is widely used, said Burton Group analyst Paul DeBeasi.

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