Wireless Access

Hi,

I'm having trouble getting a 315 access point running in instant AP mode (I'm not using a controller) to transmit multicast at high throughput.

Its probably just some bad configuration / setup of the AP on my part so hopefully this is easy to resolve. I cant however find whats wrong so any assistance or pointers on what to do would be appreciated. Thanks!

Here are some details of what I have done / am trying to do.

• ArubaOS version: 8.3
• ssid-profile: see attached
• My use case requires the AP to transmit multicast video data at several Mbps, any where in the range 1 - 20 Mbps. I'm currently using a 10 Mbps stream.
• I have set the multicast rate following the guide Support for high multicast rate on Instant Access Points
• The multicast stream has the DSCP set to 40
• Have tried setting the multicast rate to mcs3 or above. These should give sufficient throughput for a 10 Mbps stream
• I can see in wireshark that the MCS used for transmitting the multicast is what was set by the multicast-rate knob
• On starting the multicast stream I can see on the receiving device and in wireshark that the for about the first couple of seconds the multicast rate is roughly as expected
• After that the throughput settles down at approx. 700 kbps and is stable at this rate. In wireshark I can also see that after each beacon frame only 6 multicast packets are transmitted.
• Changing the MCS does not effect this behaviour. Its 6 packets after the beacon frame and then stop until the next one.
• I'm operating the AP in a relatively clean environment. No other WiFi or interference around.
• I'm suspecting there is some bandwidth limiting or traffic shaping configuration enabled which needs to be adjusted or disabled but I cant figure out what.

Attachment(s)

ssid-profile.txt   353 B 1 version

There is quite some complexity with WLAN and Multicast as with real multicast you use the spectrum on each AP regardless if there are clients connected, and you need to do it on a data-rate that all clients understand and that also implies you need to fallback to single stream operations.

When dealing with multicast, in general, the multicast optimization feature in Aruba is something you want to deploy. It converts the Multicast stream into (L2) unicast streams, is the system can benefit from client features and run on the highest link speed. That on its turn depends/assumes that there are not so many clients that consume the stream as at a certain tipping point it is better to switch to actual multicast.

An issue there is that in larger networks, you run into capacity issues when all APs are transmitting a 20Mbps multicast stream as the stream itself and the co-channel interference from neighboring APs fill up your airtime pretty quickly. That means that it is important to carefully design in such environments, and it may not even be possible to implement.

It's probably best to work with Aruba TAC as what you see with only 6 multicast frames after each beacon sounds like 'intentional'. TAC can verify and see if there is a way to change that behavior.

Thanks for the reply Herman. Will contact Aruba TAC as you suggest.