Multicast over a Wireless Infrastructure - 5508 Controllers

[emnyman1027]

Anyone have any trouble with a video multicast stream across a wireless network? I know multicast works great on the wired infrastructure but not on the 5508 controllers. The video stream show up so multicast is working just very fragmentated. The access points are 1131's and 1142's, controllers are 5508's, and the wired infrastructure is 6500-Es. If so, were you able to find a resolution?

[Nicolas Darchis]

Hi Eric,

Multicast over wireless is adventurous by design. First of all, everything is multicasted on wire (to the APs where clients are subscribed), but over the air a multicast is identical to a broadcast (everyone receives the frames). And so you need to send the frames at the best supported rate by everyone.

So if you have 1Mbps as mandatory rate, your multicast frames are sent at 1Mbps ...

One thing is to disable low rates and set the first mandatory one at something higher.

But then since it's a broadcast there is no retransmission and you know that wireless medium has collisions by design and even in good conditions, clients WILL lose some packets.

The feature DirectStream (or VideoStream) in 7.0 WLC code was introduced for this. It unicasts the multicast stream to all subscribed clients. So you have the best data rate for that client (11n all the way) and possible retransmissions. So if only a few clients are subscribed to the stream per AP, it will increase video quality drastically. Basically, the WLC monitors all the streams (IGMP snooping) and when a client subscribes to the stream, it will unicast the packets to that client.

http://www.cisco.com/en/US/docs/wireless/controller/7.0/configuration/guide/c70cms.html

Hope this helps.

Nicolas

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[Stephen Rodriguez]

Eric,

     You may also want to check the power save settings on the client.  I worked with someone recently that no matter what we did, the stream was choppy, until he set the adapter to power management at the highest it could go.