Wireless Access

Hi community,

 

The clients in one of our offices are mostly made up of 2.4Ghz (802.11g) laptops that are yet to be refreshed. We have a relatively high-density of APs at this particular office and as such are experiencing performance issues. There are a lot of things I know I can't overcome because of the limited availability of none overlapping channels, but I wondered what else I could do to improve the experience. I've already switched off the 1, 2, 5, 11 data rates. Max Tx EIRP is set to 127, Min Tx EIRP is set to 9. I've checked in the AP database and most APs are using 9 excluding one or two that are using 15 and 21. I've attached the output of the ARM history for the APs, as you can see, a lot of the APs are adjusting themselves based on environmental power/interference/error threshold being breached.

 

Any further recommendations?

I would definitely bring your power levels down. You can also consider disabling some of the 2.4 radios. You may be oversaturating the air and causing performance issues.


Thanks,
Tim

Hi Tim,

 

I agree, with respect to the power levels, my understanding is that is you don't specify the Tx Max the AP will support up to the maximum supported for the regulatory domain of the AP which is 21 in this particular case. When I have checked the active APs all but three of the 26 APs are operating at 9, with the three that aren't, operating at 21. With this in mind, what would you recommend adjusting the Max and Min to? We have another ARM profile defined for when we optimise the environment with additional APs for a Lync deployment, with the Max and Min set to 9 and 6 for the 2.4 radio. Would it be reasonable to use these values now? Or consider something different. We had considered using enabling 'mode aware' but read various posts in the forum that advised against doing this.

 

Thanks

The VRD for ac has some good tips for adjusting the ARM settings in HD environments.

 

http://community.arubanetworks.com/aruba/attachments/aruba/Aruba-VRDs/61/1/Aruba%20802.11ac%20Networks%20VRD.pdf

 

dazc

please do take a read of the VRD that Michael Clarke posted.

 

questions... many questions....

> What model of APs do you have ?

> whats the typical spacing ?

> What is the kind of problem being observed (high latency, packet loss, slow throughput, all) ? 

> Does it work well at night when no one is there ?

 

Also, when you said "I've already switched off the 1, 2, 5, 11 data rates"

> you did this for all SSID profiles that are active ?

> that you applied the changes to basic rates,not just tx rates ?

> if you have quite high density, then you may as well remove 1,2,5,6,9,11 and start with 12, i.e.

 

g-basic  12 18

g-tx 12 18 24 36 48 54

 

do this in conjuction with a max tx power of around 12 to maybe 15 in the ARM profile. This should be quite ok for an office type deployment with an AP every 20m or so. If you have higher density than that, it may require more agressive rate cuts (also may depend the model of AP you have)

 

When your office is empty, what does the controller Dashboard->Performance tab show for the bottom right hand corner of the graph page (noise/ch busy/interference).

 

regards

-jeff

Hi Michael/Jeff,

 

Thanks for the pointer to the VRD and the comments.

 

To answer your questions Jeff...

 

- AP-225

- 15 - 20m between APs

- Low data connection, generally poor performance (majority of clients are 802.11g)

- Need to confirm how well it works of an evening when nobody is there...

- Low data rates are off for all active SSIDs both Basic and Transmit

- We have all off now up to 12

- Of the 26 APs, 45 radios have 0 - 10%, 4 have 10 - 20% and 3 have 20 - 30% - these are with no users connected.

 

Thanks,

Darren

hi Darren

thats quite short spacing, especially with AP225. As suggested in the thread, you may wish to reduce the number of APs transmitting, but for sure

 

a> you must get the tx power down to perhaps 9 - 12

b> you could probably go more agressive with rate cuts

c> check the channel distribution - make sure it makes sense and isn't lopsided/unbalanced.

 

In a typical office space with that density there is going to be no RF reuse on 2.4ghz, the best you can hope for is to ensure that devices get what they want to get done, as fast as possible (highest rate) and on the nearest AP.

 

Ensure also

> all bcast filtering enabled (VAP -> Drop Broadcast and Unknown Multicast)

> ssid mcast rate opt is turned on (ssid profile -> BC/MC Rate Optimization)

> tweak arm profile to stop 2.4ghz channel thrashing

 

The VRD will suggest you split the ARM profiles in two with two different power ranges for each. The below tweaks would apply to the "arm-g" or whatever ARM profile you create for your 11g radio profile.

 

rf arm-profile “sample-arm-g"

   ideal-coverage-index 2                  // reduce for dense deployment

   free-channel-index 40                   // make higher for dense deployment

   backoff-time 1800                         // reduce channel change freq.

   error-rate-threshold 75                  // tolerate more error

   error-rate-wait-time 90                   // tolerate more error   

!

 

Also probably worth to investigate a bit on why those 3 are 20-30%

 

regards

-jeff

Hi Jeff,

 

Regarding the spacing, the AP-225 replaced in the equivalnet locations the AP-135. Just picking up on this comment and wanting to explore this a little more, what is your specific concern regarding the AP-225? Just curious to know if this is something specific to this AP.

 

We've now reduced the power settings down as detailed below.

 

With respect to the rate cuts, and this is an interesting one, we have lots of people complaining about their connection speed, event though they are only pushing Kbps on the average device. The site want to see a better connected rate, so we are considering, as you have suggested below, being more aggresive with this. With the density we have, do you think there are any risks in going as high as 36, 48 and 54 only?

Channel distribution is a little bit uneven, but I'm not sure if this is to do with other factors, there are lots of other APs from other providers nearby.

 

We have all the optimisations enabled in the VAP, etc.

 

We do split our profiles for 802.11a and 802.11g radio/arm. I'll look into adjusting these if necessary after the data rate changes.

 

Lastly, we did some further analysis regarding the three APs with high interference and found that the APs were deployed by cellphone antennas on the floor. Whilst they operate on different frequencies it appears that they were interfering with the APs. We are investigating this more.

 

Thanks for all of your input.

hi Darren

 

Quote "

Regarding the spacing, the AP-225 replaced in the equivalnet locations the AP-135. Just picking up on this comment and wanting to explore this a little more, what is your specific concern regarding the AP-225? Just curious to know if this is something specific to this AP."

 

I mentioned this only because the AP225 tends to have more coverage outwards from the AP than the AP135. In other words, 1:1 replacement at the the same power level, would provide a bit more coverage per AP. From a 2.4ghz perspective with just 3 channels, this means we may need to counter for that a little.

 

Quote " With the density we have, do you think there are any risks in going as high as 36, 48 and 54 only?"

 

The risks are likely low, but I would say probably cap it around 24, i.e. basic 24,36 and tx 24,36,48,54 - try that first and see how it works. Be mindful of the impact this may have on any APs that have to provide coverage to the edge of the network or in unexpected low signal areas (photocopy room, bathroom, lift lobby etc.)

 

Quote "

 Lastly, we did some further analysis regarding the three APs with high interference and found that the APs were deployed by cellphone antennas on the floor. Whilst they operate on different frequencies it appears that they were interfering with the APs. We are investigating this more."

 

Yes, celluar can affect APs in the 2.4GHz band. How close to the DAS antenna is the AP ? The APs do have filtering for the common celluar frequencies like 1.8, 1.9, 2.1 GHz etc., although we generally recommend that even with this, the AP should be at least 30cm/1ft away from a DAS antenna.  Also, what celluar frequencies are typical at your location?

 

regards

-jeff

 

Thanks Jeff, applying some of what you have suggested has helped to improve the environment considerably. The frequencies of the cellphone antennas are as you have suggested below. We will continue to monitor for a while and look to apply other tweaks if deemed necessary.

 

Thanks again,

 

Darren

hi Darren

no problem, glad to hear it's working a bit better now; post back to this thread if you want to revisit it again later or after you move the APs away from the DAS antennas a bit.

regards

-jeff