Wireless Access

Hi,

 

We have a dense deployment at our college with AP 105 in almost every classroom. What I have noticed it since (recently)  we have mounted more APs the overall goodput has been decreased to 20 mbps or sometimes to 8 mbps even lower sometimes as more and more devices are connected. Before that we used to have goodput of upto 270 mbps sometimes.

 

Here I am looking for some good practice advice or basic tuning of network. We have couple of AP 61 in our network too but they are in different building and can't interefere with AP 105 though on the same master controller. Our controller is running OS version 6.1.3.9. and model is 3400.

 

No survey has been done and I joined this organization recently and at the moment I am not in a position to conduct survey due to work load but I have a plan to do it soon. But for now I am looking for some help from you guys to tweak my network to get better performance.

 

Thanks in anticipation.

#3400

Do you have Airwave deployed in your network?

How many wireless networks are you broadcasting?

Nope. Airwave is not deployed.

 

We have four SSIDs.

Thanks

Without Airwave we will not have any historical data to understnd where you are, and if you make changes, the result.

 

Without airwave you can look at your dashboard under channel utilization at a time when it is not busy to determine how you are doing.

 

Yeah we can't afford at the moment to have Airwave license and deploy it.

 

Actually our APs are not mounted on ceiling thus it is difficult to determine the coverage and transmit power needs. The people before me has established this network and I am trying to increase the performance of wireless.

 

Any more ideas?

You should get an evaluation version of Airwave.  It lasts for 90 ays and it is free.

 

You need to look at the dashboard on the controller under channel utilization to see what you numbers are when the building is empty to baseline the network.  4 SSIDs is too much for a dense network and will kill your throughput.

 

Please read the article here http://community.arubanetworks.com/t5/Technology-Blog/Removing-the-Bottleneck-in-Wireless/ba-p/77978 for more ideas.

 

I bet this is caused by co channel interference. The controller is good at picking channels based on current conditions, but it is better to plan out your 2.4 ghz channels manually. In every single poorly performing network that I have tuned - manual 2.4 channel selection ends up running better.

Print out your floor plans and mark all your AP locations. Then start assigning 1,6,11 channels (the only three non competing channels in 2.4) so that APs on the same channel are furthest away from each other.

Keep in mind signal bleeds up and down a floor in many cases.

You may find that turning off some of the APs will actually improve things.

If you mark all of your APs on a floorplan I would be happy to draw up a channel plan for you.

canucklehead,

 

Without knowing how many ssids, what channel utilization and what power the access points are at currently, isn't it too soon to be turning off access points or setting manual channel and power?  Wouldn't we have to make sure that drop broadcast and multicast is on, and that the access points are spaced correctly?  If the dashboard shows interference in a certain specific number of access points, shouldn't we be checking for that first, as well?

 

Very good points, and I do not disagree. And furthermore, your suggestions are easier to start off with. What stood out for me is that there is an AP is almost every classroom. In those high density setups I usually end up statically setting at least some of the radios.

Canucklehead,

 

If those classrooms have cinderblocks or brick between them and/or it is only a single story building, that might be warranted.  We have to dig deeper and find out what the true issue is and show the OP how to measure his/her progress...

We have a two story building and definately classrooms are above each other. But APs placement is different and not above eachother in most of the cases...i believe :)

Farzan Qureshi,

 

You are probably better off opening up a TAC case.  Without data to understand or support what your issues are, it is better to have TAC take look at all of your private data and come up with some suggestions.  We can come up with some suggestions here, but without a way to measure progress, we will not know what is your issue and if we have solved the problem.  Being that you just started there, you  probably know very little about what we need to be able to help you on this forum.  TAC should be able to get your logs and make some suggestions.  Otherwise, you are at the mercy of anyone here who makes a suggestion.

So I know that APs are not properly spaced and it is a better idea to shutdown few APs which are adjcent to eachother. Obviously even if i regulate transmit power it will not help because signal will still bleed. Also, if i manually assign channels 1 6 11 it will still create co channel interference because i know this wireless network is poorly designed because APs are in every classroom and affecting network performance.

 

So do you suggest first I should shutdown couple of APs where I feel the need and go from there? I have already set to drop broadcast and multicast in air.

 

Kindly advise.

What I like to do is get all the AP's on a floorplan (or multiple floorplans).  You have to consider the wireless network as a whole before you start turning off individual radios.  Generally you keep the radios that are at the edges of the building and consider turning off radios that are more in the middle. 

 

-Put all of your AP's on a floor plan

-Get an idea of how much your AP propagates (how far away from the AP is the signal -65? (assuming the radio is at at least 3/4 power)

-Get a pencil and start assigning 1,6 or 11 to each access point, making sure that AP's on the same channel so not overlap.

-If there is no way to assign a channel to an AP without interfering with another AP, consider turning it off

 

Once you get your AP channel layout right, same channel AP's will be as far apart as possible.  This in turn will cluster clients on the same channel into the same area talking to the same AP (a good thing).

 

If you go through the effort of mapping your AP's, I would be happy to have a look.

 

Cheers,

 

Tobias

 

This is what I needed :) Yes I have started doing it. We have AP in every classroom thus it will take a while before I am able to mount APs on our floor plan. And yes you are right on this that I should consider wireless network as a whole and mark APs to be shutdown which can't be moved to non overlapping channels. I might need your help then once I mark all APs on floor plan.

Can I post it here once I am done?

fqureshi@rosmi…,

 

Do you know that shutting down access points will fix your problem?

 

You first need to 

 

1.  Define your problem

2.  See what in the logs.tar can tell you why (tac can help you do this)

3.  Come up with a plan based on what tac says.

 

You seem to be coming up with a plan to disable access points when you have not asked yourself:

 

- what problem do I actually have?

- Is it limited to a specific location?

- Is it limited to a specific time?

- Is it limited to a specific device?

 

The problem with your current approach is that many users here decide not to get help from TAC and end up making their situation much worse.  When they finally go to TAC things are so bad that it becomes critical to fix it and pressures everyone involved.  Since you are new at your location, it does not hurt to have TAC look at your logs.tar based on a specific issue that you are having.  Anything is just guessing and could make your wireless worse...

 

I agree with you cjoseph.

The problem we are having just started since we have mounted more APs in our environment without considering the channel overlapping issues, adjacent channel interference and APs are also not placed properly. I am aware what are the issues in our network. I just want to get an idea from where to start that is why I posted on this forum. Before introducing more APs in our environment the datarates were very good however as there was a need to increase capacity our respective person has put APs in every classroom without planning and now it is creating an issue like high contention and frame retries and dropped.

 

I will surely open a case with TAC before making any changes to network. At the moment I am just making everything clear to communicate with TAC or people like you to actually put forward issues in our network.

 

Thanks for guiding me.

fqureshi@rosmi…

 

There is no problem with getting as much advise as possible here:  Collect all of it.  Good advise has been given by people in the thread already.  The only thing is that people on the forum only have the information that you give us....  TAC can request much much more and give you better advice.  You can even run the advice given here by TAC and see what they say, because they will have a much better picture based on your logs that you can submit to them.

 

If you want to have  90-day evaluation version of Airwave so that you can at least get more visibility with your issues, just PM me with your email address and we will get it taken care of.

Got the license details. Thanks for sending it through. I will make a plan to install it and gather more data.

Thanks again for your help.

It sounds like you have quite a significant WLAN to look after...you'd probably benefit from attending a CWNA course or, failng that, get a copy of the study guide. 

 

 

You may have to tweek your arm and rf profile to better tune your rf environnement (i.e: reduce the max tx power, disable the lower data rate 1&2 mbps, you may consider). If you don't have time for a survey you can do some CLI command to have an idea of the signal being percived between AP (show ap arm ... | include ... ). You may also enavle or try to convert one in spectrum monitor to see if you got interferer.