Wireless Access

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Contributor I

Aggressive MCS rate backoff for Apple TVs

Has anyone experienced problems in their enterprise with Apple TVs having an extremely aggressive rate backoff.  I have streaming problems to them.  It was best described as things pause a lot.  When I looked into it closer, I noticed that the data rates would drive down to 39, 14, and even 7 Mbps when doing a 'show ap association'.   Those number obviously correspond with the MCS rates.  

 

Chuck L.  VHD design has recommendations to disable MCS rates 0 - 2, 8 - 10, 16 - 18.  Has anyone done this in enterprise HD environments?

 

Does anyone have any remedy or things to look at.  The AP is a 220 series and the Apple TV is about 15 feet away.  Airwave shows the airtime utilization as having lots available on transmit, receive and noise.   There is a lot of Bluetooth in the space.  

 

Guru Elite

Re: Aggressive MCS rate backoff for Apple TVs

1.  What band is the Apple TV operating on?

2.  What is the channel utilization?

3.  Are you using 20 or 40 mhz channels?

4.  What is the AP power set at?

5.  How is the AP mounted?

6.  What version of ArubaOS?

7.  How many other clients are on that AP?

 

Clients backing off is fairly typical.  We need to understand if it is justified or not.

 

 



Colin Joseph
Aruba Customer Engineering

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Contributor I

Re: Aggressive MCS rate backoff for Apple TVs

1. Apple TV 2nd Gen, 2.4 Ghz band

2. Airwave shows it maxing out at 40%, but mostly occassional spikes around 15 to 20%

3. 20 Mhz

4. 15 dB, due to the concrete wall thickness and real estate it needs to cover in the space and the room next to it (probably a bit high)

5. Wall mounted 224 with stick antennas

6.  6.4.2.8

7. 10 to 15 per band on the AP

 

Without any utilization it seems to connect up at 72 Mbps and stay there.  Once it is used for streaming the rates jump all over the place.  In the past, despite optimal SNR and CCI not being much of an issue, it would retry 10% of its packets pretty consistently.  This was observed with the 'show ap debug client-table' command.  

 

Thanks.  

Guru Elite

Re: Aggressive MCS rate backoff for Apple TVs

2.  If Airwave shows that it maxes out at 40%, plenty of times it bursts to over 60% and then drops after that.  Streaming only increases it more.

 

I see that the Apple TV's phy is a-HT-20-1ss, which means that its top association rate is 72 megs.  If you have 10 to 15 users on that access point that are even further away, the AppleTV is going to be significantly impacted when it tries to stream anything, because those users farther away on the other side of a concrete wall are probaby going to drag its performance down.  Long story short, you need to figure out how to get that AppleTV on 5ghz if it can support it, and fewer devices on that access point, otherwise it will be hard to maintain a reliable stream on it.

 

When you say CCI is not an issue, at 10% retries and 15 other users, CCI is an issue.  If you do a packet capture on that channel while the AppleTV is streaming, you will be able to see what is connecting to it and causing your problem.  Unless you figure out a way to confine the RF from that AP to be only in the space where the AppleTV is, it will continue to compete with other users on the side of the wall.  

 

It is easy for me to say based on the limited information you give me what it is, but you might have someone take a look at your deployment to see what can be done about your issue.

 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I

Re: Aggressive MCS rate backoff for Apple TVs

A follow up observation.  I am unsure if anyone else has seen this.  

 

I tried changing the G band power down to 6 dB (from 12dB) with the A band at 18 dB.  However the Apple TV still preferred the G band.  I then made A band channel 40 Mhz only, but kept VHT enabled.  Immediately the Apple TVs went to the A band.  

 

In all cases the 'show ap virtual-beacon-report client-mac'  command the G band was still the stronger signal over the A band.  Even with the G band turned way down.  

 

So now I have them on the A band.  Hopefully now I can prevent the Apple TVs from dialing back so aggressively on their data rates. 

 

Guru Elite

Re: Aggressive MCS rate backoff for Apple TVs

show ap virtual-beacon report shows how well the access point sees the client and not the other way around so turning the AP power up or down would not affect client match decision making. 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Re: Aggressive MCS rate backoff for Apple TVs

Colin has you on the right path.  Curious though about your 2.4GHz radios.  Have you trimmed lower data rates in your SSID profile?  This will help with 2.4 utilization, just in case your Apple TVs wander back to 2.4 on occasion.  Also, were you saying that you had 40MHz channels allowed on g?  If so, that would've accounted for your CCI.

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Contributor I

Re: Aggressive MCS rate backoff for Apple TVs

Ok, thanks Colin for the clarification on the ap virtual beacon command.   

 

We run 12 Mbps beacon rates and 12, 24, 36, 48, 54 Mbps g rates.  

 

I had 20 Mhz in 2.4 and 20/40/80 enabled on the 5.0 ghz.  Even the 'manual' steering command given by Colin didn't move the Apple TV to the other band.  Once 80 Mhz was removed, the Apple TVs went right to the 5 Ghz band using the 40 Mhz channel.  I was struggling with getting them to go to the a band.  So I'm happy that this is accomplished.  I hope the streaming stuff will work better now.  

 

Thanks!

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