Cisco Wi-Fi software makes video more reliable, efficient over wireless

Cisco Tuesday announced software for its Wi-Fi products to improve video performance, reliability and scaling on 802.11n wireless networks. The new code, dubbed VideoStream, compensates for Wi-Fi weaknesses that degrade video quality as the number of streams and clients grow.

VideoStream makes three changes in handling video traffic, according to Cisco. First, it takes a new approach to video multicasting to clients, making the streams more reliable, and using bandwidth more efficiently. Second, it can assign different priorities to individual streams, so a video by the company president gets a higher priority than a clip from a sports broadcast. Finally, it can block new video requests if they will cause video quality for the new request, or for the overall network, to erode.

The new software becomes part of Cisco's system code in its access points and wireless controllers.

Today, video originates on the wired network as a multicast stream, but when it hits the Wi-Fi network it becomes a relatively slow wireless broadcast to any clients that might be within range, says David Stiff, product manager for Cisco's wireless networking business unit. From the network's perspective, the broadcast goes out with a wish: "I hope you can hear this." In addition, there is no acknowledgement from the clients, so no error-checking is done. "You can lose packets," Stiff says. "It's a horrible environment for streaming video."

Tools for testing Wi-Fi video performance are sketchy, as Network World wireless blogger Craig Mathias noted in a post about Veriwave's wireless video testing tool.

One way to improve that environment is to fiddle with how Wi-Fi networks handle multicast. Wireless multicasts are challenging because clients are at different ranges from the access point, so the network has to adjust the data rate. To ensure that more distant clients receive the packets in proper sequence and timing, the network will throttle back the rate for all clients. Both Cisco and rival Aruba Networks convert the original video multicast into separate but multiple unicasts to improve bandwidth efficiency. And Ruckus Wireless last December announced a patent on such multicast conversion.

With VideoStream, Cisco pushes this conversion from the wireless LAN controller to the access point. The Cisco WLAN controller manages the incoming video stream and passes the multicast to the LAN switch and then to the Cisco access points. The access points convert the multicast transmission into multiple, separate unicasts. The access points handle the state control, client monitoring and packet replication, and send the video unicast only to the Wi-Fi clients that request it.

According to Cisco, this new approach means that the Wi-Fi network can now handle large-scale video multicasts, and that both the wireline and wireless bandwidth between the Wi-Fi controller and the clients is used more efficiently.

In addition, Cisco exploits the 802.11e/Wireless Multimedia (WMM) quality of service standard to create more fine-grained prioritization of video streams. Until now, WMM allowed video traffic overall to be given some priority weighting relative to data, for example. Now, VideoStream lets separate video streams be given different priorities, and this can be done dynamically as network requirements change. A management video broadcast on a new company-wide project might be given a high priority on the network while other video traffic is designated only as "best effort."

The controller marks the stream with the appropriate QoS for a given access point; the access point then assigns each stream a hardware queue or path onto the network, according to Stiff.

Finally, VideoStream can treat video requests from clients as the Wi-Fi network treats VoIP requests. As the number of requests and connections increase, at some point the wireless channel fills up. The next "call" in such a case suffers from poor quality and begins to erode quality for other calls. VideoStream, through a feature dubbed Resource Reservation Control, can block that next multicast video request, sending a "video not available" message to protect overall video quality on the network.

Network administrators can set up and manage VideoStream via a new set of screens in the administrative GUI.

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John Cox

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