Manual Channel set vs Automatic Channel set which one is better and why?

[bhupenderrawat79]

Hello,

A lot have been said about about letting the WLC set the channels for the AP's,  in fact many so called "best practices" states that we should let the WLC do the channel assignment.

In my experience I think that this is not true, i have seen many sites where the channels are set to automatic and let me tell you, the air quality is horrible.

Yes I understand that RRM have come a long way...but what happens in environements where a customer have a mix of models, for example an office with a mix of 3502's and 3702's? how will the WLC handle this setup? and most importantly a place where it has a lot of bluetooth traffic.?

I think if the air is clean, a place where there is no third party tenants above or under your site meaning an office building and you know the behaviour of your users, then perhaps letting the WLC do the automatic channel selection may work otherwise i think it will not do any good.

Suggestions or comments? I would love to get some feedback. Thanks!

[Scott Fella]

I will never try to statically set channels for this main reason:

Majority of neighboring Wireless is configured to auto choose.

This means that you never know if a neighboring wireless network will change an AP channel to one of yours. Also, I do t care much about Bluetooth since that operates in the 2.4ghz and that band is just overloaded as it is.

With any vendors algorithm, it’s better than manually changing channels than coming up with new channel plans every day, week or month.

[bhupenderrawat79]

Scott,

I just dont agree, I have over 200 sites around the world and i can tell you that when we set the wlc to do automatic channel selection, many AP's suddenly are in the same channel now causing co-channel interference and when we go onsite and do an spectrum analyzer sweep and hard code the channels, the performance is much better.

[Scott Fella]

I work on a global deployment with over 30,000 access points from Cisco and Aruba. I will tell you that if you have a sparse deployment then yes RRM and Aruba’s ARM will not work. If you have a sense deployment and you are seeing AP’s on the same channel, then your running into a bug. I will never go without using the vendors feature to automatically change channels and power. Remember that Cisco requires three AP’s within -75 by default before RRM is used. Even with my previous customers using CIsco, Aruba or Meraki, never used static. Look at how your AP’s are deployed first and then assess if maybe that is why RRM is not working.

[Leo Laohoo]

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@bhupenderrawat79 wrote:

an office with a mix of 3502's and 3702's? how will the WLC handle this setup? and most importantly a place where it has a lot of bluetooth traffic.? 

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RRM & DCA doesn't work that way.  So what if there's BLE?  The mere presence of BLE isn't the only reason why the AP needs to take action.  The WLC needs to evaluate how strong is the BLE from the nearest AP.  If the power is low, then do nothing or ignore.  If the power is too strong then maybe it's a combination of switching channels or powering down.   

I have some controllers/APs where RRM & EDRRM is turned on while I have other WLC there this feature is turned off.  The reason why I have them turned off is because there are certain "dumb" wireless clients who are not fond of RRM & DCA.  

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@bhupenderrawat79 wrote:

 a place where there is no third party tenants above or under your site meaning an office building and you know the behaviour of your users 

---

That is incorrect.  It doesn't necessarily meant that just because there's only one tenant in a property it is synonymous to there is no co-channel interference.   Microwave ovens, non-compliant BLE clients, BYO hot spots, etc.  Need I say more?  And what about co-channel interference not just above or below?  What about the around the horizontal azimuth?

I leave RRM & DCA enabled because I don't want to be bogged down analyzing each and every one of my APs for co-channel interference and which AP should have what power and channel.  I leave that up to the controller do sort things out.  

DCA may work for some but it may/can not work for others.  YMMV

[bhupenderrawat79]

Leo,

I certainly agree with your comments indeed. Although based on what i have seen the WLC is not doing a good job setting the channels on my AP's in several sites. Yes i understand that some of these sites have a mix of AP's models. As I mentioned above, i have few sites where the previous managers have not really standardized, meaning for example in one site we have a mix of 3502i's and 3702i's and let me tell you the channel assigment is doing a horrible job setting up the channels. I am not sure if perhaps is because there is couple different models of AP's or what, but the channel assignment is really bad. 

I think that this may work well where the AP model are the same and the model of the AP supports new features such as the 3802's series, and the AP locations are the most appropriate. 

[Leo Laohoo]

Sites with mixed models don't make any significant difference. Both 3500 and 3700 support CleanAir. So it's fine.
If there is two or more APs having "horrible" DCA then post the complete output to the command "sh ap auto-rf 802.11a <AP Name>".
Another thing, software version of the controller plays significant role in this.

[bhupenderrawat79]

Scott,

The software version I am running on my WLC is 8.1.122.0. and of course now these AP's are configured manually because the kept always going to the same channel.

Number Of Slots.................................. 2
AP Name.......................................... A
MAC Address...................................... c0:8c:60
Slot ID........................................ 1
Radio Type..................................... RADIO_TYPE_80211a
Sub-band Type.................................. All
Noise Information
Noise Profile................................ PASSED
Channel 36................................... -96 dBm
Channel 40................................... -92 dBm
Channel 44................................... -95 dBm
Channel 48................................... -94 dBm
Channel 52................................... -94 dBm
Channel 56................................... -95 dBm
Channel 60................................... -94 dBm
Channel 64................................... -94 dBm
Channel 100.................................. -94 dBm
Channel 104.................................. -94 dBm
Channel 108.................................. -94 dBm
Channel 112.................................. -94 dBm
Channel 116.................................. -94 dBm
Channel 120.................................. -94 dBm

--More-- or (q)uit
Channel 124.................................. -95 dBm
Channel 128.................................. -95 dBm
Channel 132.................................. -94 dBm
Channel 136.................................. -94 dBm
Channel 140.................................. -94 dBm
Channel 149.................................. -91 dBm
Channel 153.................................. -90 dBm
Channel 157.................................. -93 dBm
Channel 161.................................. -93 dBm
Channel 165.................................. -92 dBm
Interference Information
Interference Profile......................... PASSED
Channel 36................................... -128 dBm @ 0 % busy
Channel 40................................... -128 dBm @ 0 % busy
Channel 44................................... -128 dBm @ 0 % busy
Channel 48................................... -128 dBm @ 0 % busy
Channel 52................................... -128 dBm @ 0 % busy
Channel 56................................... -128 dBm @ 0 % busy
Channel 60................................... -128 dBm @ 0 % busy
Channel 64................................... -128 dBm @ 0 % busy
Channel 100.................................. -128 dBm @ 0 % busy
Channel 104.................................. -128 dBm @ 0 % busy
Channel 108.................................. -128 dBm @ 0 % busy

--More-- or (q)uit
Channel 112.................................. -128 dBm @ 0 % busy
Channel 116.................................. -128 dBm @ 0 % busy
Channel 120.................................. -128 dBm @ 0 % busy
Channel 124.................................. -128 dBm @ 0 % busy
Channel 128.................................. -128 dBm @ 0 % busy
Channel 132.................................. -128 dBm @ 0 % busy
Channel 136.................................. -128 dBm @ 0 % busy
Channel 140.................................. -128 dBm @ 0 % busy
Channel 149.................................. -128 dBm @ 0 % busy
Channel 153.................................. -128 dBm @ 0 % busy
Channel 157.................................. -128 dBm @ 0 % busy
Channel 161.................................. -68 dBm @ 1 % busy
Channel 165.................................. -128 dBm @ 0 % busy
Rogue Histogram (20/40/80)
.............................................
Channel 36................................... 1/ 0/ 0
Channel 40................................... 1/ 0/ 0
Channel 44................................... 0/ 0/ 0
Channel 48................................... 0/ 0/ 0
Channel 52................................... 0/ 0/ 0
Channel 56................................... 0/ 0/ 0
Channel 60................................... 1/ 0/ 0
Channel 64................................... 0/ 0/ 0

--More-- or (q)uit
Channel 100.................................. 0/ 0/ 0
Channel 104.................................. 0/ 0/ 0
Channel 108.................................. 0/ 0/ 0
Channel 112.................................. 0/ 0/ 0
Channel 116.................................. 0/ 0/ 0
Channel 120.................................. 0/ 0/ 0
Channel 124.................................. 0/ 0/ 0
Channel 128.................................. 0/ 0/ 0
Channel 132.................................. 0/ 0/ 0
Channel 136.................................. 0/ 0/ 0
Channel 140.................................. 0/ 0/ 0
Channel 149.................................. 1/ 0/ 0
Channel 153.................................. 0/ 0/ 0
Channel 157.................................. 0/ 0/ 0
Channel 161.................................. 2/ 0/ 0
Channel 165.................................. 0/ 0/ 0
Load Information
Load Profile................................. PASSED
Receive Utilization.......................... 0 %
Transmit Utilization......................... 0 %
Channel Utilization.......................... 1 %
Attached Clients............................. 1 clients
Coverage Information

--More-- or (q)uit
Coverage Profile............................. PASSED
Failed Clients............................... 1 clients
Client Signal Strengths
RSSI -100 dbm................................ 0 clients
RSSI -92 dbm................................ 1 clients
RSSI -84 dbm................................ 0 clients
RSSI -76 dbm................................ 0 clients
RSSI -68 dbm................................ 0 clients
RSSI -60 dbm................................ 0 clients
RSSI -52 dbm................................ 0 clients
Client Signal To Noise Ratios
SNR 0 dB.................................. 0 clients
SNR 5 dB.................................. 0 clients
SNR 10 dB.................................. 1 clients
SNR 15 dB.................................. 0 clients
SNR 20 dB.................................. 0 clients
SNR 25 dB.................................. 0 clients
SNR 30 dB.................................. 0 clients
SNR 35 dB.................................. 0 clients
SNR 40 dB.................................. 0 clients
SNR 45 dB.................................. 0 clients
Nearby APs
Radar Information

--More-- or (q)uit
RF Parameter Recommendations
Power Level.................................. 1
RTS/CTS Threshold............................ 2347
Fragmentation Threshold...................... 2346
Antenna Pattern.............................. 0

Persistent Interference Devices
Class Type Channel DC (%%) RSSI (dBm) Last Update Time
------------------------- ------- ------ ---------- ------------------------
All third party trademarks are the property of their respective owners.

(Cisco Controller) >

Number Of Slots.................................. 2
AP Name.......................................... 
MAC Address...................................... 7c:6
Slot ID........................................ 1
Radio Type..................................... RADIO_TYPE_80211a
Sub-band Type.................................. All
Noise Information
Noise Profile................................ PASSED
Channel 36................................... -95 dBm
Channel 40................................... -94 dBm
Channel 44................................... -94 dBm
Channel 48................................... -94 dBm
Channel 52................................... -94 dBm
Channel 56................................... -95 dBm
Channel 60................................... -94 dBm
Channel 64................................... -95 dBm
Channel 100.................................. -95 dBm
Channel 104.................................. -94 dBm
Channel 108.................................. -93 dBm
Channel 112.................................. -95 dBm
Channel 116.................................. -94 dBm
Channel 120.................................. -93 dBm

--More-- or (q)uit
Channel 124.................................. -93 dBm
Channel 128.................................. -93 dBm
Channel 132.................................. -94 dBm
Channel 136.................................. -94 dBm
Channel 140.................................. -93 dBm
Channel 149.................................. -92 dBm
Channel 153.................................. -89 dBm
Channel 157.................................. -92 dBm
Channel 161.................................. -91 dBm
Channel 165.................................. -91 dBm
Interference Information
Interference Profile......................... PASSED
Channel 36................................... -128 dBm @ 0 % busy
Channel 40................................... -128 dBm @ 0 % busy
Channel 44................................... -128 dBm @ 0 % busy
Channel 48................................... -128 dBm @ 0 % busy
Channel 52................................... -128 dBm @ 0 % busy
Channel 56................................... -128 dBm @ 0 % busy
Channel 60................................... -128 dBm @ 0 % busy
Channel 64................................... -128 dBm @ 0 % busy
Channel 100.................................. -128 dBm @ 0 % busy
Channel 104.................................. -128 dBm @ 0 % busy
Channel 108.................................. -128 dBm @ 0 % busy

--More-- or (q)uit
Channel 112.................................. -128 dBm @ 0 % busy
Channel 116.................................. -128 dBm @ 0 % busy
Channel 120.................................. -128 dBm @ 0 % busy
Channel 124.................................. -128 dBm @ 0 % busy
Channel 128.................................. -128 dBm @ 0 % busy
Channel 132.................................. -128 dBm @ 0 % busy
Channel 136.................................. -128 dBm @ 0 % busy
Channel 140.................................. -128 dBm @ 0 % busy
Channel 149.................................. -128 dBm @ 0 % busy
Channel 153.................................. -128 dBm @ 0 % busy
Channel 157.................................. -128 dBm @ 0 % busy
Channel 161.................................. -128 dBm @ 0 % busy
Channel 165.................................. -128 dBm @ 0 % busy
Rogue Histogram (20/40/80)
.............................................
Channel 36................................... 0/ 0/ 0
Channel 40................................... 0/ 0/ 0
Channel 44................................... 1/ 0/ 0
Channel 48................................... 0/ 0/ 0
Channel 52................................... 0/ 0/ 0
Channel 56................................... 0/ 0/ 0
Channel 60................................... 1/ 0/ 0
Channel 64................................... 0/ 0/ 0

--More-- or (q)uit
Channel 100.................................. 0/ 0/ 0
Channel 104.................................. 0/ 0/ 0
Channel 108.................................. 0/ 0/ 0
Channel 112.................................. 0/ 0/ 0
Channel 116.................................. 0/ 0/ 0
Channel 120.................................. 0/ 0/ 0
Channel 124.................................. 0/ 0/ 0
Channel 128.................................. 0/ 0/ 0
Channel 132.................................. 0/ 0/ 0
Channel 136.................................. 0/ 0/ 0
Channel 140.................................. 0/ 0/ 0
Channel 149.................................. 1/ 0/ 0
Channel 153.................................. 0/ 0/ 0
Channel 157.................................. 0/ 0/ 0
Channel 161.................................. 1/ 0/ 0
Channel 165.................................. 0/ 0/ 0
Load Information
Load Profile................................. PASSED
Receive Utilization.......................... 0 %
Transmit Utilization......................... 0 %
Channel Utilization.......................... 0 %
Attached Clients............................. 0 clients
Coverage Information

--More-- or (q)uit
Coverage Profile............................. PASSED
Failed Clients............................... 0 clients
Client Signal Strengths
RSSI -100 dbm................................ 0 clients
RSSI -92 dbm................................ 0 clients
RSSI -84 dbm................................ 0 clients
RSSI -76 dbm................................ 0 clients
RSSI -68 dbm................................ 0 clients
RSSI -60 dbm................................ 0 clients
RSSI -52 dbm................................ 0 clients
Client Signal To Noise Ratios
SNR 0 dB.................................. 0 clients
SNR 5 dB.................................. 0 clients
SNR 10 dB.................................. 0 clients
SNR 15 dB.................................. 0 clients
SNR 20 dB.................................. 0 clients
SNR 25 dB.................................. 0 clients
SNR 30 dB.................................. 0 clients
SNR 35 dB.................................. 0 clients
SNR 40 dB.................................. 0 clients
SNR 45 dB.................................. 0 clients
Nearby APs
AP 50:17: slot 1.................. -81 dBm on 149 (10.192.73.14)

--More-- or (q)uit
AP bc:f1:f2: slot 1.................. -69 dBm on 40 (10.192.73.14)
AP e8:ed:fslot 1.................. -78 dBm on 112 (10.192.73.14)
AP e8:ed:fslot 1.................. -53 dBm on 100 (10.192.73.14)
Radar Information
RF Parameter Recommendations
Power Level.................................. 1
RTS/CTS Threshold............................ 2347
Fragmentation Threshold...................... 2346
Antenna Pattern.............................. 0

Persistent Interference Devices
Class Type Channel DC (%%) RSSI (dBm) Last Update Time
------------------------- ------- ------ ---------- ------------------------
All third party trademarks are the property of their respective owners.

[Scott Fella]

Looks like the reason might be sparse AP deployment and thus why you are having to set channels and power manually. Look at each radio output, you need to have minimum three AP’s within -75.

[bhupenderrawat79]

Scott,

I think you are correct, i dont have visibility into the site, but i suspect the AP's are here and there positioned anywhere. I believe no one ever did a survey there and hence they decided to put the ap's anywhere.

So If i am understanding correctly, it will be best to let the WLC do the channel assignment automatically IF a proper survey is done and the position of the AP's are correct. is this fair statement? otherwise then one can run into issues like the one I am seeing on this site is this correct?.

[Scott Fella]

You are correct. When I was at a Cisco partner doing design and deployment, we always recommended to have a site survey performed or else we will not guarantee the installation. This is probably and most likely the reason RRM is not working because of the existing AP placement design. We had site that previously had these very sparse deployments and we had vendors go out a redesign around 500 sites worldwide and we added around double and sometimes triple the amount of access points previously and also moved existing into better locations. Yes it is a lot of money to do, but in the end, you want your users to “Love” their wireless experience!!! Or else they will either be wired or bring in their own AP.

[bhupenderrawat79]

Scott,

By the way thank you very much for taking the time to respond to my questions, i have one last question actually two questions well three :)

I understand that the client capacity per AP is determined on the type of application or the type of traffic the user is doing, for example web and email vs video, these are two different animals and since the AP is just like computer which it needs to code and decode traffic plus WiFI is half duplex then of course the client capacity is going to vary depending on the type of traffic

But if you have an office with about 100 people doing most of the time web and email and one skype for business video call here is there, do you think a single AP can handle the load and not chocke on it? and correct me if i am wrong but, if you have an AP set to max clients to 50, when the AP reached 50 then the 51 client will go to the nearest ap? is this correct?.

Also what would you do if you have a large meeting room that can handle 200 people, and about 10 people will be doing video skype and the others will be doing web an email, how many AP's would you put on the room?. theorically speaking of course. 

[Scott Fella]

I understand that the client capacity per AP is determined on the type of application or the type of traffic the user is doing, for example web and email vs video, these are two different animals and since the AP is just like computer which it needs to code and decode traffic plus WiFI is half duplex then of course the client capacity is going to vary depending on the type of traffic
You are correct, but you also have to look at if users are uploading/downloading, doint any cloud sync, etc.  I always recommend around 30 devices per AP as that would be worst case in our environment.  You can maybe hit around 50-60 if its only email/web traffic, but you need to make sure.  Enable AVC and see what types of traffic you have or if you have netflow, you can also look at types of applications being used.
But if you have an office with about 100 people doing most of the time web and email and one skype for business video call here is there, do you think a single AP can handle the load and not chocke on it? and correct me if i am wrong but, if you have an AP set to max clients to 50, when the AP reached 50 then the 51 client will go to the nearest ap? is this correct?.
100 per AP is too high, plus you want redundancy and overlap.  When you set max client to 50, no other devices will join.  Also keep in mind that the devices makes the decision and what I have seen when setting the ma client is that the device that is not allowed, will keep trying to join that AP and will not join a different AP that is close in proximity.
Also what would you do if you have a large meeting room that can handle 200 people, and about 10 people will be doing video skype and the others will be doing web an email, how many AP's would you put on the room?. theorically speaking of course.
In our large event building and offices with MPR’s, we have high density of AP’s.  For example, if we have an MPR that can handle around 200 users ma, I would probably have 5 minimum.  I always want to be on the safe side and improving end user experience. 
What you also need to look at is the data rate you want to achieve in an ap coverage cell.  I typically only have 36mbps or even at times 48mbps as my lowest mandatory rate and the one data rate lower as supported and of course the data rates above as supported.  Using this and the lower TX power (high density), I can tweak environments if I need to.  For example, I can set the max tx on 5GHz to 17dbm and min TX to 8dbm.  Max TX on 2.4GHz would be 8dbm and min 3dbm.  With how ap’s are placed, 5GHz would be around 14dbm to 17dbm using RRM because of all the available channels (depending on country) and 2.4GHz would be around 3dbm, since there are few channels to choose.  I know that with a dense deployment, I have no issues with 5GHz and only really care about achieving -70 -72 coverage on 2.4GHz since I would disable some 2.4GHz radios.  My preference is to have more 802.11a/n/ac clients connected than 802.11g/n connection with 802.11b disabled.

[Scott Fella]

You would be better to upgrade to 8.2 from 8.1.  Here is a like to TAC recommended AireOS versions:

https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/200046-tac-recommended-aireos.html

[Leo Laohoo]

I had a look at the output and both APs are showing 0% Channel Utilization. This means the air isn't busy and ideal condition for 802.11a. Now do the same for the 802.11b radio but make sure you pull this info during business hours. Compare the output to outside business hours, like 9 pm or 10 pm.
Next, your firmware is 8.1. I wouldn't use this. Like Scott said, use either the latest 8.2, 8.3 or 8.5.