ABGN - controlling allowed protocols - IOS based 1140 ap

Unanswered Question
Apr 13th, 2010

So I wonder if someone has done all this leg work yet and if so could you give us your impressions... I am waiting for a new network card for my laptop so I can do some N testing.  We have a mix of 1100,1130 and some 1140 access points with all of them eventually being upgraded to 1140s.

What I want to do is give the N users the best chance to have great throughput. I figure the best way to do this is allow N on the 5.8Ghz radio and allow G and N on the 2.4Ghz radio. With that in mind I have the following questions.  We have a WLSE and are still using IOS mode for our access points.

I know the easy way to disable B on the 2.4Ghz radio is not allow 11mbps or lower.

No problem ... I don't want B anymore. Is there a different command to do this?

Also what IOS command do I use to determine if there are any people using B?

If G and N are allowed on the 2.4Ghz radio do they both work at the  same time?

If there are G connections does it change the modulation away from  the best/N modulation?

If I want N only on 2.4Ghz do I disable every speed below 54 mbps?  Is there a better way to disable G?

If A and N are allowed on the 5.8Ghz radio do they both work at the  same time?

If there are A connections does it change the modulation away from  the best/N modulation?

If I want N only on 5.8Ghz do I disable every speed below 54 mbps?

Thanks

Joe

I have this problem too.
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jbarger Tue, 04/13/2010 - 09:53

There are plenty of places to find this information and I was able to go read up on it before anyone gave impressions.

Here are the answers I have found.

Basically disabling the rate of the protocol you don't want to use seems to be the best way to eliminate that protocol altogether.  For example you can disable N on the 2.4 ghz radio by not allowing speed m0-m15 (I guess ).

If you enable N on the 2.4ghz radio you can't enable bonding so there is no need to worry about enhanced troughput on 2.4.

Althoug you will experience better throughput since N interacts with the radio and other clients in such a way that it will perform better when connected at 2.4.

The same is not true of the 5.8ghz radio you can enable bonding so you will get better throughput.  I still have not found out exactly how A interferes with N but I am not going to worry about it since new devices will have N.

I have configured my access point identically as before but enabled the 5.8ghz radio, enabled beam forming on both radios and allowed bonding on the 5.8ghz radio.

I supposed I was confused on the modulation and speed thing, they go hand in hand, so if your N client is sharing the radio with a G client you will be stuck using the modulation and speed of the G client.  (I may still be confused, someone clarify this for me?)  Although N supports High Throughput (HT) in all cases which makes it interact with the AP better?

Anyhow no matter how confused I am the bottom line that I understand is "Don't try to do anything special with your 2.4ghz radio (except for beamform) and do it all on the 5.8 radio since it has so many more channels you can now bond a couple of them" (I originally thought N on 2.4 would allow G to work on a single channel and N to bond and still interoperate).  When upgrading access points with the improved antenna MIMO 5.8ghz will work almost exactly as good as the old 2.4 and 2.4 will have about 20% better coverage. Previously I found that 5.8ghz was useless and never used it.  The design guide seems to skim over A interfereing with N on 5.8 except for saying there are not enough A clients to worry about, througput will still be better and A is on it's way out...

Lastly bonding on 2.4 is not supported by any of the new N chipsets even intel.

Message was edited by: jbarger  add one more comment...

rdvorak Tue, 04/13/2010 - 15:10

Hi,

you should take a look into the "Cisco 802.11n Design and Deployment Guidelines" as they give a good overview about the basic topics...

http://www.cisco.com/en/US/solutions/collateral/ns340/ns394/ns348/ns767/white_paper_80211n_design_and_deployment_guidelines.html

So the thing is "protection" = whether you enable or disable backward compatibility to the 802.11abg clients or run your network in 802.11n only mode.

As you've wrote channel bonding in 2.4GHz makes no sense as you've only one channel but running a 20MHz channel (+protection) with 150Mb is better then only 54Mb in 802.11g only, so turn it on and your 2.4GHz 802.11n stations should get better performance and your 802.11bg clients will still work.

Thanks,

Ron

jbarger Wed, 04/14/2010 - 06:55

Hi Ron,

So just to be certain I am not missing something is "protection" automatic?

AND

To enable or disable B protocol the only way I know of is to enable or disable 11Mbps speed and everything below that.

So if I wanted to disable G would I disable 54Mbps and below on the 2.4 radio?

So On the flip side I am assuming as long as those speeds are available and the N speeds are available "protection" will kick in?

Thanks,

Joe

jbarger Wed, 04/14/2010 - 09:04

When looking at the 2.4 radio and the allowed rates "show controller dot11radio 0"  there is some interesting things to be found like...

HT protection: HT mixed mode.

Legacy Beamforming: Configured Yes, Active Yes, RSSI Threshold -50 dBm

You will see the active and current rates and allowed rates like...

basic-1.0 basic-2.0 basic-5.5 basic-11.0

6.0 9.0 12.0 18.0 24.0 36.0 48.0 54.0

m0. m1. m2. m3. m4. m5. m6. m7. m8. m9. m10. m11. m12. m13. m14. m15.

I have not seen anywhere that explains "rate 6.0 is a G rate and B will not  connect at 6.0" (I believe I am incorrect in that previous statement and will test)  Also there is not yet an IOS configuration guide for ap1142 to get a better understanding of what is going on.

There is a nice table of datarates and dBm.

If you are connected at 6.0Mbps you are at -89 signal.  I didn't see this table for N rates... 

Funny I designed this networks so that -75 is the lowest acceptable signal.

Data Rate Sensitivity (rate, SNR dB, Contention dBm)
( 1.0, 10, -93)   ( 2.0, 10, -92)   ( 5.5, 11, -90)   (11.0, 14, -90)  
( 6.0, 15, -89)   ( 9.0, 16, -88)   (12.0, 18, -88)   (18.0, 19, -86)  
(24.0, 20, -85)   (36.0, 24, -81)   (48.0, 27, -78)   (54.0, 31, -77)

At this point I am just using this forum to keep notes and maybe help others think through how they want to setup their access points.

jbarger Wed, 04/14/2010 - 09:46

So as a test I disabled the rates

basic-1.0 basic-2.0 basic-5.5 basic-11.0

My 7920 802.11B IP phone would not connect, even though rates below 11mbps were available...

Here was the int d0 speed settings... edited for readability.

speed  6.0 9.0 basic-12.0 basic-18.0 basic-24.0 basic-36.0 basic-48.0 basic-54.0 m0. m1. m2. m3....m15.

So it seems that speeds 6.0 and 9.0 are G rates and not B rates...

The point is if you want to disable B and still give G the longest range possible you can leave 6.0 and 9.0 enabled.

Of course this is just one test and this should be verified by reading the specification.

Still more to learn   The reason this even occured to me to test was when looking at the HTTP setup for the ap you see the first 4 rates are seperated from the other rates, they are not in order if you examine the attached graphic...  In the graphic you see the "default" settings and not the test settings.

Thanks,

Joe

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