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With no intent to open a conversational can 'o worms, I'm curious if anyone is running a 4-channel plan on their production WLANs, that is willing to share their opinions and experiences on the topic.

Thanks-

Lee

Lee H. Badman
Wireless/Network Engineer, ITS
Adjunct Instructor, iSchool
Syracuse University
315.443.3003
********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Comments

I’m interested in any real-world results as well.

 

 

Thanks,

Brian

 

Message from ssmith@siu.edu

I've been using 4 channels in the 2.4GHz for years.  I've seen and tested heavily when we first switched to that idea, but since then I've more advanced RF technologies and other research that has shown that 1, 6, 11, and 1 in the same area is better than 4 unique channels.

I've been doing RF since 1997 and have had lots of field experience trying lots of combinations like this.  I'd glad discuss further, but for a more detailed conversation a phone call might be better.

Cisco has released a third party guide stating this same topic and it's supposed to be a non-Cisco document but it certainly has some marketing in it as well.

Lee H Badman wrote:
With no intent to open a conversational can 'o worms, I'm curious if anyone is running a 4-channel plan on their production WLANs, that is willing to share their opinions and experiences on the topic.

Thanks-

Lee

Lee H. Badman
Wireless/Network Engineer, ITS
Adjunct Instructor, iSchool
Syracuse University
315.443.3003
********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.


--

Scott Smith 

Network Engineering

Information Technology

Southern Illinois University Carbondale 

Redhat Certified Engineer

ssmith@siu.edu


********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Message from r_harris@culinary.edu

We ran a 4 channel plan for a couple years on our aruba system. Very dense ap deployment, lots of interference (necessary evil for the # of users and solid construction of buildings). Worked fine till we swapped to code 3.x.x.x, we were told that the ARM features all were tuned for the 3 channel plan and that we should swap back. We've found that using aruba arm and fine tuning it you'll be fine and not need to do any hacks like this. (Not that 4 channel is really a hack, but letting arm do what it wants gave us way better results once we learned to fine tune it).


Robert Harris
Manager of Network
and Audio/Video

Culinary Institute of America
1946 Campus Drive
Hyde Park, NY
845-451-1681
www.ciachef.edu

Food is Life, Create and Savor Yours.?

Please consider the environment before printing this e-mail.

>>> Lee H Badman 05/08/12 10:35 AM >>>
With no intent to open a conversational can 'o worms, I'm curious if anyone is running a 4-channel plan on their production WLANs, that is willing to share their opinions and experiences on the topic.

Thanks-

Lee

Lee H. Badman
Wireless/Network Engineer, ITS
Adjunct Instructor, iSchool
Syracuse University
315.443.3003
********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Good morning - 

I can't speak for our on campus network, as that is all managed by wireless lan controllers.  But I can speak about a different experience - 

As a consultant for NANOG, we would set up wireless networks in conference centers across the country.  The wireless space would be pretty saturated by hotel equipment, and neighboring networks.  For the conference, we would use up to 20 Cisco 1200 series APs with 2.4 and 5ghz radios.

To get our signal through mess, we'd use channels  1 4 6 8 11.

In order to figure out where to place our APs channel-wise, we would use a WiSpy analyzer.

With this tactic, we were able to successfully support upwards of 250 users on 4 access points in the general sessions

Lee,

Univ. of TN Knoxville still runs 4 channels (1-4-8-11) and has been doing so since 2000!
This said, we had a long discussion with Aruba Networks engineers about 3 VS 4 and they mentioned that
their algorithms are better tuned for 3 channels (I suspect that it is the case for most vendors that provide managed APs).
The reasoning is that an AP (or controller) can more easily detect and deal with co-channel interference
than it can with adjacent channel interference (not as detectable).
So, we have tested a dormitory  with 3 channels, and are very pleased with the results. The throughput increased sightly, which
is not a small thing. We plan to convert the whole campus to 3 channels.

In the world of human managed APs it made more sense to us to have 4 channels. Easier graph coloring and we also measured
a true benefit in high density environments. But we didn't change channels all the time and didn't play with power!

In the world of managed APs, and if you don't plan to tweak settings from the manufacturer, I would say, stick
with standards, in this case 3 channels, just because most of those systems are designed to do so.

Sorry, no cool graphs with measured differences, just a discussion ;-)

Best,

Philippe

Philippe Hanset
Univ. of TN, Knoxville


With the 3 channel system rouges are less likely to cause issues I’d think.  A rouge is likely to use 1 6 or 11 as that is the standard.  If you have a 4 channel system a rouge is going to be a huge problem where it is only an annoyance in a 3 channel system.  I have found that co-channel interference is not that big of a deal.  The protocol still works if clients are connecting to different APs on the same channel.  However adjacent channel interference is another matter.  That ends up just being noise.

 

John Kaftan

IT Infrastructure Manager

Utica College

315.792.3102

 

From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:WIRELESS-LAN@listserv.educause.edu] On Behalf Of Hanset, Philippe C
Sent: Tuesday, May 08, 2012 11:10 AM
To: WIRELESS-LAN@listserv.educause.edu
Subject: Re: [WIRELESS-LAN] 4-channels in 2.4 GHz

 

Lee,

 

Univ. of TN Knoxville still runs 4 channels (1-4-8-11) and has been doing so since 2000!

This said, we had a long discussion with Aruba Networks engineers about 3 VS 4 and they mentioned that

their algorithms are better tuned for 3 channels (I suspect that it is the case for most vendors that provide managed APs).

The reasoning is that an AP (or controller) can more easily detect and deal with co-channel interference

than it can with adjacent channel interference (not as detectable).

So, we have tested a dormitory  with 3 channels, and are very pleased with the results. The throughput increased sightly, which

is not a small thing. We plan to convert the whole campus to 3 channels.

 

In the world of human managed APs it made more sense to us to have 4 channels. Easier graph coloring and we also measured

a true benefit in high density environments. But we didn't change channels all the time and didn't play with power!

 

In the world of managed APs, and if you don't plan to tweak settings from the manufacturer, I would say, stick

with standards, in this case 3 channels, just because most of those systems are designed to do so.

 

Sorry, no cool graphs with measured differences, just a discussion ;-)

 

Best,

 

Philippe

 

Philippe Hanset

Univ. of TN, Knoxville

 

 

  Our pilot deployment included four APs in a single fairly-small building.  If I recall correctly, I put the two in the middle of the building on channels 1 and 11, with the two further out, one on ch8 (nearest the AP on ch1) and one on ch4 (nearest the AP on ch11).  I'm pretty sure these were only doing 802.11b, so even where the interference was low, the performance was modest, and nobody yet expected anything better....  Essentially, I tried to take advantage of physical separation where I couldn't rely on channel separation.
 
  (These days, we use Aruba, and generally let it try to find a selection of channels for minimal interference.)
 
David Gillett, CISSP CCNP
 

Message from jcoehoorn@york.edu

I looked into this about 18 months ago for our campus. It never made it to the point of a trial: I learned enough to stop the project before it made it that far, and I think I can summarize here what I found. 

I'll start by going back to basics: we all know that wireless channels overlap. A graph of signal from a wireless access point typically takes the shape of a parabola, or cone, with the open end pointed down and centered on the channel used by the access point. An example can be found at the following link found via quick Google Images search:


That image (from an app I'd used with great success on iOS before it was pulled from the Apple App Store for using undocumented APIs) clearly shows overlapping signals. The wider portion as a signal flares out towards the bottom is often referred to as a signal's "skirt"... this term "skirt" will be important later. The common best practice to avoid overlap (and thus avoid interference and improve performance) is to only use channels 1,6, and 11.  That much I think everyone here understands very well. 

Now let's move on to a 4-channel scenario. If you put four access points right up next to each other on channels 1,4,8,and 11, you *will* have interference. Channel 1 signals will collide with Channel 4, 4 will collide with 1 and 8, 8 will collide 4 and 11, and 11 will collide with 8, resulting in reduced performance throughout the spectrum. This is also not in question.

But what if you separate these four access points... put some distance between them? Simplistic graphs such as from my earlier link imply that as the power level of the signal falls over distance you will have a shorter and therefore narrower "skirt". Could careful planning allow you to place access points so that channel 1 APs are never near channel 4 APs, 4 APs are never near 1s or 8s, 8s are never near 4s or 11s, and 11s are never near 8s, and in this way increase AP density beyond what you could do with only three channels, all while still avoiding interference? 

The short answer is "no". It comes down to the skirts again. Most low-end tools to measure wireless coverage do a poor job of showing this, but my understanding is that wifi RF is such that the skirts "flare out" quickly, and you have nearly all of the signal overlap even at fairly low power levels. These wide skirts makes it impractical to try for four channels... you're almost as bad off as if you tried to use all eleven.


Joel Coehoorn
IT Director
York College, Nebraska
402.363.5603
jcoehoorn@york.edu


     




Message from jcoehoorn@york.edu

Phillippe, this is something I would **love** to be shown to be wrong about. 

I think all of us could benefit from a 4th channel (I know I would), if it comes with clear guidelines for when and how to use it in a way that will increase rather than decrease throughput. Right now, the best guidelines we have say, "Stick with 1,6, and 11." Deviation from that is more likely than not to result in pain.

Perhaps what is needed is more successful 4 channel implementations for study, but I think we're likely to see mainstream 5ghz make this all obsolete by then.


Joel Coehoorn
IT Director
York College, Nebraska
402.363.5603
jcoehoorn@york.edu


     



I believe Ruckus is working on something called ChannelFly that will utilize more than the standard 1, 6, and 11 2.4Ghz channels. 

 

Fyi,

Brian

 

From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU] On Behalf Of Hanset, Philippe C
Sent: Tuesday, May 08, 2012 3:20 PM
To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU
Subject: Re: 4-channels in 2.4 GHz

 

 

Message from reuss@umd.edu

Cisco has a paper on this with some graphs showing "energy overlap" on 4 channel deployments for both 802.11b and 802.11g. The 802.11g OFDM signal seemed more prone to interference in a 4 channel setup so we stuck with 1,6,11. > http://www.cisco.com/en/US/docs/wireless/technology/channel/deployment/g... -Karl Reuss University of Maryland, College Park ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
Joel,

You last comment hit the nail on the head.  We have been advising clients to migrate to 5.8 Ghz ASAP for years.  2.4 Ghz is a garbage band and all the rogues make it impossible to gain any density and throughput.  While you may be adhering to 1-6-11, the rogues may not be, and many enterprise installations just set the wireless management to "auto" not realizing that many APs will end up on odd channels to avoid rogues that are on 1-6-11.  You just cannot win in 2.4 Ghz.  If your wireless management has band steering - use it to push clients to the higher band.  Also, if you limit 2.4 Ghz associations to the higher connection speeds - you will at least help to force your clients to the best connection

Ron Walczak
PMP, CWNA, RCDD

I had some students do a project this semester where they compared aggregate throughput on a standard 3-channel model and two alternative 4-channel models. This was Cisco 2-stream 11n, a single client running iXChariot downstream throughput test.

3-Channel (1,6,11) 185 Mbps 
4-Channel (1,4,7,11) 153 Mbps
4-channel (1,4,8,11) 98 Mbps

They also ran a 3-channel test, 4 AP's with two AP's on Channel 1, the other two on 6 and 11. The goal here was to assess the incremental improvement in capacity when two AP's are contending for use of a common channel. Aggregate throughput in that scenario was 160 Mbps but the thing that was most interesting about that test was that the two AP's did not share the channel evenly. One AP on Channel 1 got 58 Mbps of throughput while the other got 12 Mbps. These tests appear to support the hypothesis that adding more AP's in a dense configuration in the 2.4 Ghz band does not result in significant added capacity when AP's are experiencing co-channel interference. It is important to note that our tests focused on downstream throughput, which would probably be the worst-case scenario for co-channel interference.

I had another team perform some testing of Ruckus' ChannelFly technology, which often uses non-standard channels. In that testing, we have noted modest improvements in performance compared to the classic 3-channel model.

I'd be happy to share the report with people who are interested.

Dave Molta


From: Lee Badman <lhbadman@syr.edu>
Reply-To: The EDUCAUSE Wireless Issues Constituent Group Listserv <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>
Date: Tue, 8 May 2012 14:34:19 +0000
To: <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>
Subject: [WIRELESS-LAN] 4-channels in 2.4 GHz

With no intent to open a conversational can 'o worms, I'm curious if anyone is running a 4-channel plan on their production WLANs, that is willing to share their opinions and experiences on the topic.

Thanks-

Lee

Lee H. Badman
Wireless/Network Engineer, ITS
Adjunct Instructor, iSchool
Syracuse University
315.443.3003
********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Message from ha.nguyen@unil.ch

I am highly interested in the report and would appreciate receiving the mentionned report.

Thanx in advance,

Ha Nguyen
Univeristy of Lausanne

On 05/10/2012 09:10 PM, David J Molta wrote:
I had some students do a project this semester where they compared aggregate throughput on a standard 3-channel model and two alternative 4-channel models. This was Cisco 2-stream 11n, a single client running iXChariot downstream throughput test.

3-Channel (1,6,11) 185 Mbps 
4-Channel (1,4,7,11) 153 Mbps
4-channel (1,4,8,11) 98 Mbps

They also ran a 3-channel test, 4 AP's with two AP's on Channel 1, the other two on 6 and 11. The goal here was to assess the incremental improvement in capacity when two AP's are contending for use of a common channel. Aggregate throughput in that scenario was 160 Mbps but the thing that was most interesting about that test was that the two AP's did not share the channel evenly. One AP on Channel 1 got 58 Mbps of throughput while the other got 12 Mbps. These tests appear to support the hypothesis that adding more AP's in a dense configuration in the 2.4 Ghz band does not result in significant added capacity when AP's are experiencing co-channel interference. It is important to note that our tests focused on downstream throughput, which would probably be the worst-case scenario for co-channel interference.

I had another team perform some testing of Ruckus' ChannelFly technology, which often uses non-standard channels. In that testing, we have noted modest improvements in performance compared to the classic 3-channel model.

I'd be happy to share the report with people who are interested.

Dave Molta


From: Lee Badman <lhbadman@syr.edu>
Reply-To: The EDUCAUSE Wireless Issues Constituent Group Listserv <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>
Date: Tue, 8 May 2012 14:34:19 +0000
To: <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>
Subject: [WIRELESS-LAN] 4-channels in 2.4 GHz

With no intent to open a conversational can 'o worms, I'm curious if anyone is running a 4-channel plan on their production WLANs, that is willing to share their opinions and experiences on the topic.

Thanks-

Lee

Lee H. Badman
Wireless/Network Engineer, ITS
Adjunct Instructor, iSchool
Syracuse University
315.443.3003
********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.


********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.

Message from kevin.semrau@millersville.edu

Dave,

I would appreciate a copy of the report.

Thanks in advance,

Kevin

 

Kevin Semrau

Network Specialist

Communications & Network Services

Millersville University

37 W. Frederick Street

Millersville, PA 17551

Office: (717) 871-5883

Fax: (717) 871-2048

www.millersville.edu

 

Message from avoelker@email.wcu.edu

I’d love a copy.  avoelker@wcu.edu

 

-- Andy Voelker

Manager of Student Computing in the Technology Commons

WCU Staff Senator

Western Carolina University

Check the status of your IT requests at any time at http://help.wcu.edu/ !

 

Message from bjohnson5@partners.org

Hi David, Please forward me a copy of your research report. Thanks, Bruce Johnson | Network Engineering Partners Healthcare | 617.726.9662 bjohnson5@partners.org

I’d like to see this as well and thank you.

 

Thanks,

Brian bkellogg@sbu.edu

 

 

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