Wireless Access

I am currently using a 7010 controller and a AP-325 to make a local video streaming service. The video source I have puts out it's stream in multicast at 5mbps. I have configured the Aruba 7010 to enable DMO and I followed the user guide to implement the other related settings.

However when I hit around 25 active clients receiving the stream the performance tanks and the video playback becomes very poor. Adding a second AP fixes the issue and allows more clients but one of the requirements of this project is to support about 35 clients on one AP. The aggregate bandwidth is much lower than the stated specs of the AP-325.

I can support many more than 30 clients using a streaming protocol managed by a separate server. But when relying on the Aruba 7010 to perform DMO it seems severely limited. The CPU and memory usage of the controller and the APs is quite low even as frames are dropping.

I appreciate any insight you could provide. 

What value is the DMO threshold set to?

Does performance improve if you disable DMO? 

I've experimented with different values for the threshold. Too low and the problem gets worse as expected but even at maximum it can't seem to handle more than 25 users.

With DMO off multicast streaming basically unusable for all but a very small number of clients.

Thanks for taking the time to reply!

What is the minimum data rate configured for you SSID?

This seems to match with the problem you're experiencing. DMO attempts to take L3 multicast streams and converts them to wireless unicast until a threshold is reached where the airtime for multiple unicasts exceeds simply using a wireless multicast. If your data rate is too low for the multicast stream (I believe you said the stream is 5Mbps before), then this will cause a problem ... sending a 5Mbps stream on a 1 or 2 Mbps data rate isn't enough bandwidth. 

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@dottaviano wrote:

I've experimented with different values for the threshold. Too low and the problem gets worse as expected but even at maximum it can't seem to handle more than 25 users.

 

With DMO off multicast streaming basically unusable for all but a very small number of clients.

 

Thanks for taking the time to reply!

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You might get some mileage out of disabling DMO and then enabling 'BC/MC Rate Optimization' on the SSID profile. This will send multicast at the highest enabled basic rate, 24Mbps by default. Or as suggested above disable the lower data rates to force higher rates.

Hello dottaviano,

I have actually been working on a technology that streams multicast video over WiFi. I have been using Aruba mainly as my testing platform. 

There are two routes:

DMO disabled -  Multicast traffic is sent over the air to a multicast mac address. Any STA can listen that is subscribed. If there is dropped frames, then thats it, they are missed by that STA. Frames are sent only once.

DMO enabled - Multicast is converted to unicast traffic, going from a best effort connection to a guaranteed connection with acknowledgements. Each additional subscriber to the multicast group (each additional STA streaming the video) takes up more channel utilization e.g. frames are sent once for each STA and if an acknowledgement is not received it is sent again. For a small number of STAs, brilliant. Too many, well then the  channel is saturated. Once the DMO threshold is reached, it stops the conversion and the video is streamed via basic multicast. Again, If the packets are dropped along the wireless last hop, well that's missing traffic, and video is bad.

It has been pointed out in this thread that you can change the multicast rate that the AP will send at but this needs other configuration to make it work. If you are sending 5mbps of video traffic but the data link layer of the wireless when sending multicast is 1-2mbps well thats a no-go.  

On your webGUI is the DMO threshold setting a number of STAs or a percentage of channel utilization?

The solution I am working is a separate thing entirely. Its an application that sends video over multicast and also then sends Forward Error Correction frames. The video can be reconstructed by the client app in real time.