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Radio Policy 802.11g only vs 802.11b/g only

What is the difference?  I tried 802.11g only and it still sends out beacons with the B rates listed (send at 1mbps also).

CCNP - Wireless
CWNE #136
38 REPLIES 38
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thefranmanatt wrote:

People are reviewing data rates and saying to turn that off to disable B, etc...  I just want to know what really happens when you change that option. 

You are right about the reason code 17 for max users.   

turn what off ? The DSSS rates ?

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________
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The b/g policy allows both .11b and .11g clients to associate.

The g only policy rules out any .11b clients from joining.

I’m not sure why we have this policy setting on the network when you can accomplish the same thing by disabling all the .11b rates and keeping the .11g rates enabled. Changing the policy causes all the APs to reboot and rejoin. Changing just the rates does not require a reboot or rejoin of the AP.

A clarification: There is no such thing as a “g only” client. All .11g clients must also work on .11b only APs or using only .11b rates. So a .11b device is a subset of a .11g device.

Any rates you set as mandatory on the network must be supported by all clients you expect to join the network.

Scenario:1 I’ve one data rate set as mandatory on b and g rate. -> Both b only and g clients can connect.

Scenario:2 have one data rate set as mandatory on b rates only -> all clients can join, .11b and .11g.

Scenario:3 have one data rate set mandatory on g rates only. -> only .11g clients can join.

Supported rates are rates that the client and AP can actually send data packets between each other (directed traffic), depending on how good the link is currently.

Saravanan,

In trying to get a B only client to  on my network to test I was unable to get my 7920 phone to join. Yes I re-enabled all the B rates with a man rate of 1Mbps. The phone was giving me an auth error.  So I found an old 350 card and put it in to the PCMCIA slot of my old laptop running windows 7.   Windows 7 showed the WLAN but it had a red X next to it.  When you click it says the following.

"The capablity of your network adapter does not match the requirements of this network."

At the time I had a second mandatory rate of 18Mbps.  In setting all the G rates to supported the both clients were able to join.  So both of my B clients did NOT like a mandatory G rate and would NOT connect.  Can you retest your Scenario:1?

CCNP - Wireless
CWNE #136
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Why do you state this ..

I want to know what exactly happens when selecting G only on the WLAN.  From what I have seen It still uses the B rates so clearly it isn't disabling the B rates in order to make it G only.  Does it just ignore B clients trying to join, does it tell the B client it can't join?

What have you seen that shows B rates when B is off?

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________
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shocking I still have this screenshot from 10 months ago...

Alright,  I am going to find a B client now...

CCNP - Wireless
CWNE #136
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Ill add my 2 cents ..

The beacons will show supported rates...

As Scott mentioned the lowest mandatory rate you set will be the rate the beacons will come out as ..

When you disable 11 , 5 , 2 and 1 802.11b clients will not even be able to see these beacons because the beacon will be sent at ofdm rates which is a different modulation one that 802.11b clients can't understand.

Sent from Cisco Technical Support iPhone App

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________
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Hey George,

 

Just ran into something strange here. I have SSID set to G only. I have 1,2,5.5, and 11 disabled and only G rates as mandatory. I still have b clients joining the WLC (8.0.120.0). I go to highthroughput section and disable the MCS0 rate and then the B clients can no longer join. Have you seen this?

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Cisco Employee

G is backward compatible with B, disable all b rates if you don't have b only clients. And make one of the lower datarate as mandatory from g rates.

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Hall of Fame Master

I want to know what exactly happens when selecting G only on the WLAN. From what I have seen It still uses the B rates so clearly it isn't disabling the B rates in order to make it G only. Does it just ignore B clients trying to join, does it tell the B client it can't join?

It doesn't allow 'B' clients to join.

These are two separate things. Radio policy and data rates. With the newer code you can specify the data rates in the rf profile and apply that to the ap group. Default group will of course default using the global data rates configured. Well all ap groups unless you specify another rf profile. So if you have a b client roam from on ap on an ap group that has b rates to another ap on a different ap group that has 11 Mbps and lower disabled, the client will drop of course. So just remember that the radio policy and the data rates are two different functions.

Sent from Cisco Technical Support iPhone App

-Scott
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I digress but the word "policy" apears in MANY places in the controller config........anyway.

The Radio Policy in the WLAN configuration is the sum of the General, Security, QOS and Advanced parameters you have configured for that particular WLAN.  Specifically, the controller will apply that policy to All (802.11a/b/g/n), 802.11a only etc...

Given that there are no actual 802.11a RADIO parameters in the WLAN Policy, I don't know why it would affect connectivity outside of what's configured in the WLAN specifically.

Under the Wireless Configuration, we are given the oportunity to configure Radio Policy.  For example under 802.11b/g we can set specific data rates.  If we disable 1,2,5.5 and 11, we know that only OFDM modulation is being used.

So if we think about a linear flow: The WLAN Policy is used "on top" of the Radio Policy.  With all the confusion around this (myself included) as well as the inherint limitations, newer controller code allows up to build specific RF Profiles now that can be aplied at an AP Group level allowing us to control the RF energy, modulation and performance to specific areas rather than at a Global Controller level.

I still don't like the way it's done simply because of the "Verbiage on the screen" but we can at least control the RADIO policy allot better.  Screen shot below from version 7.4.100:

//art

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When set to G only, during the assoc rsp the STA is denied because it doesn't support all rates.  It also looks like it changes the G slot times from 20 microseconds to 9 microseconds (G mode short slot time bit set to 1).

I set the profile back to B/G and made 1Mbps and 18Mbps mandatory. Again the 7920 won't join.  It gets the same deny because it doesn't support all the data rates.  It also sets the G mode short slot time bit.

This pretty good information.  I have a lot of sites stuck on WiSM1s and 4404s so I can't use RF groups (don't support 7.2 code).  We normally have one WLAN that has some B only hand scanners.  It looks like if I set the WLANs that don't need B to G only I can use the better slot time.

I have the captures, I'll post them if anyone wants to look at them.

Here is some more in on the topic.

http://www.oreillynet.com/pub/a/wireless/2003/08/08/wireless_throughput.html?page=2

CCNP - Wireless
CWNE #136
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Cool - I'd like to see one of your captures with the WLAN Radio Policy set to 802.11g only.  Can you also confirm how you had the data rates set during the capture as well as if you had 802.11nHT enabled?  Did you by chance get a quick spectrum snapshot of what RF looks like/modulation wise?

Thx! //art

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http://boostedmopar.com/temp2/Playing_with_BG_wlan.zip

I don't have a screenshot of the rates but they will be in the beacons. HT rates are on.  I didn't do a spectrum capture.  The wasn't much going on though.

CCNP - Wireless
CWNE #136
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thinking, are 7920 is still cisco supported.

check the mandatory and supported datarate config on wlc for 7920 phone.

To testing Radio policy with b only clients - on g adapter from w.less client, select b only. it is possible the 7920 that you're using could be faulty. symbol b only clients works with the unified.

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when the 7920 didn't work what B rates were set as mandatory and supported on 2.4 radio.

the issue is phone not working and not about b client unable to connect.

i think you're mixing multiple things here.

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It is a bunch of different B devices.  A Windows 7 laptop with a cisco 350 pcmcia card, a Sony PSP, and a 7920.  The packet capture I posted shows why it can't join.

Here is a video of it.  Switch to 1080p HD

http://www.youtube.com/watch?v=VDXE2pTO0eQ

CCNP - Wireless
CWNE #136