Do WLCs manage LWAPPs from using overlapping chs?

Answered Question

I'm a beginner with wireless and, even more so, the WLC. (I'm using an WLC module in a 2851 ISR). I have a couple general questions regarding the WLCM:

1) I will be deploying five LAPs off of the WLCM in one floor of one building. Is it true I will not have to worry about overlapping channels as the WLCM will detect contention and change channels? Do I not have to configure anything in particular, regarding channels, on the RF side?

2) I will also be using 7920s in my deployment and want to ensure call quality when a user walks/roams between LAPs. I will be using static WEPs and 7920s reside on the same VLAN. Since all APs are associated to the same WLCM, is it true I will not have to do any additional configuration to ensure smooth roaming?

THANKS!

I have this problem too.
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Correct Answer by john.preves about 9 years 7 months ago

greetings,

That is what it is supposed to do. It has been my experience and others as well, that this is not necessarily the case.

As far as channel allocation, this device does a poor job, although, I have many more AP's than 5, so perhaps, your mileage will vary. Be on the lookout for same channel co located devices where none need to be.

Power settings also do not get handled properly. Almost every AP in my facilities are at power level 2 (17dBm or 50mW) and that is only because I do not allow maximum power as an option. There is a wonderful document that you must download if you are going to be anywhere near LWAPP - http://www.cisco.com/warp/public/114/rrm.pdf

read the transmit power algorithm and coverage hole algorithm in particular. I took that the third AP from any AP has a default threshold of -65 meaning unless this criteria is met the power will not go down. Since my surveys are at 11Mbps at -65dBm, that would mean the location of my third AP from my first AP will be at the edge of the first AP cell. If you draw three circles on paper, your first circle is anywhere you want, the radius of the third circle must pass through the edge of the first circle...so now you have to shoehorn the second circle in there someplace. This scenario is what is known as 50% overlap - where two AP's (two 50% is 100%)overlap of another AP. So in the event of an AP failure - two other ones can pick up the slack. Well if I design my networks as such, what the hell do I need LWAPP for? I opened a TAC case and got nowhere fast actually, I got nowhere at all.

My solution for me is to redesign the existing infrastrucure so as to have 20 - 30% overlap and have 11 Mbps cell boundries at -65dBm. The only way I will be able to maintain the power and channel allocations will be to remove the auto RF capabilities from the channel and power. I will harcode that in. Maybe, once I get the design up and functional, I will experiment with sections of the facility and let auto RF have a chance in a properly designed environment and see what happens. I unfortunately am in a high-profile healthcare production environment and I am not comfortable, especially given the reuslts I have seen so far.

I hope you have determined that the 5 AP's you need was based on a valid survey, preferably using the 7920 as the survey tool.

If you have determined your coverage, throughput requirements and plans for future growth, and read about how much throughput you can get from each AP in data and voice scenarios and determined that some areas may or may not be more densely populated with users using either data or voice or both - then you should be ok.

Please think about voice being on the same vlan as data, which should be separate further still from the hardwired data people.

If you don't have many users then proceed. If you think that the user density might bite you in the pants, it will and it will not let go.

If I haven't scared the crap out of you yet, I hope to have given you things to think about and tools to use so you do not find yourself in the situation I am currently in.

On the other hand, being the cleaner pays remarkably well. I'm sort of the wireless 'Mr. Wolf' in our network movie.

Be well -

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Correct Answer
john.preves Tue, 02/06/2007 - 20:24

greetings,

That is what it is supposed to do. It has been my experience and others as well, that this is not necessarily the case.

As far as channel allocation, this device does a poor job, although, I have many more AP's than 5, so perhaps, your mileage will vary. Be on the lookout for same channel co located devices where none need to be.

Power settings also do not get handled properly. Almost every AP in my facilities are at power level 2 (17dBm or 50mW) and that is only because I do not allow maximum power as an option. There is a wonderful document that you must download if you are going to be anywhere near LWAPP - http://www.cisco.com/warp/public/114/rrm.pdf

read the transmit power algorithm and coverage hole algorithm in particular. I took that the third AP from any AP has a default threshold of -65 meaning unless this criteria is met the power will not go down. Since my surveys are at 11Mbps at -65dBm, that would mean the location of my third AP from my first AP will be at the edge of the first AP cell. If you draw three circles on paper, your first circle is anywhere you want, the radius of the third circle must pass through the edge of the first circle...so now you have to shoehorn the second circle in there someplace. This scenario is what is known as 50% overlap - where two AP's (two 50% is 100%)overlap of another AP. So in the event of an AP failure - two other ones can pick up the slack. Well if I design my networks as such, what the hell do I need LWAPP for? I opened a TAC case and got nowhere fast actually, I got nowhere at all.

My solution for me is to redesign the existing infrastrucure so as to have 20 - 30% overlap and have 11 Mbps cell boundries at -65dBm. The only way I will be able to maintain the power and channel allocations will be to remove the auto RF capabilities from the channel and power. I will harcode that in. Maybe, once I get the design up and functional, I will experiment with sections of the facility and let auto RF have a chance in a properly designed environment and see what happens. I unfortunately am in a high-profile healthcare production environment and I am not comfortable, especially given the reuslts I have seen so far.

I hope you have determined that the 5 AP's you need was based on a valid survey, preferably using the 7920 as the survey tool.

If you have determined your coverage, throughput requirements and plans for future growth, and read about how much throughput you can get from each AP in data and voice scenarios and determined that some areas may or may not be more densely populated with users using either data or voice or both - then you should be ok.

Please think about voice being on the same vlan as data, which should be separate further still from the hardwired data people.

If you don't have many users then proceed. If you think that the user density might bite you in the pants, it will and it will not let go.

If I haven't scared the crap out of you yet, I hope to have given you things to think about and tools to use so you do not find yourself in the situation I am currently in.

On the other hand, being the cleaner pays remarkably well. I'm sort of the wireless 'Mr. Wolf' in our network movie.

Be well -

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