Clients keep roaming although they are not moving

[c.ong]

Hi Sir,

I have deployed a LWAPP-based wireless LAN recently in one of my customer office. Here is a brief description of the setup.

2 WLC 4404-100, one acts as a Pri Controller, the other as a backup. We have tested APs failover to the Sec WLC and vice versa. Dynamic Channel Assignment and Transmit Power Management is handled by the WLC. Most clients are laptop with built-in Wifi card. PEAP MS-CHAPv2 is enabled on all client. Machine Authetication is enabled too. ACS 4.0 as the authentication server. 3 SSID ae created on 802.11g radio module.

Below is some of the symptomps we encountered,

- Clients keep roaming from one AP to the other as indicated in XP WZC, low signal to high then falls back to low signal then to excellent again, though they are stationary

- Clients are not connected to the nearest/strongest APs

- Clients are not connected to least busy AP, e.g 11th floor users tends to connect to 12th floor AP although 11th floor AP has 0 client whereas 12th floor AP is serving 10 users

I would like to know how can I force the client to connect to the nearest/ strongest APs and reduce the client roaming. Can any fine tuning be done on the WLC?

Thank you.

Delon

[frankzehrer]

Hi Delon,

a few questions ahead

- what wireless client chipsets have you running?

- do you use divertisity antennas?

- what WLC version have you installed?

Best regards,

Frank

[limtohsoon]

Hi Frank,

I'm working with Delon on this project. Please see below answers to your questions:

(1) Intel(R) PRO/Wireless LAN 2100 3A Mini PCI Adapter (please see attached). Users has upgraded to latest driver version from Dell website, about one month ago.

(2) Lightweight AP model is AIR-LAP1242AG-C-K9. Using diversity antennas AIR-ANT4941, ceiling mounted.

(3) WLC4404-100 software version is 4.0.179.8.

802.11a is disabled globally.

Please provide us further advice.

Thank you.

B.Rgds,

Lim TS

[wififofum]

Lim,

Have you tried tweaking Roaming Aggressiveness in the Intel PROSet client utility? You may also want to try turning off Auto-RF just to see if it makes any difference.

Please let us know what you try and what results you get.

Thanks

[netmasque]

I have some follow-on questions to Franks..

Are your clients using CCX, if so, what version?

Do they support E2E?

Have you tweaked the client roaming details on the WLC (If you're running 4.x code) or running default?

Have you run debugs to see if these clients are having issues during a an AutoRF/RRM job?

Might try enabling 'Avoid Cisco AP Load' as well, which make RRM be a little smarter about updating to not drop clients.

And as always. check the nearby break room for a subpar microwave :)

[wififofum]

Netmasque,

What debugs can you run on the controller to identify client disconnects/reconnects? Any particular run/notification level?

Thanks,

[frankzehrer]

Hi all,

@ Bruce

I guess Eric (netmasque) thinks about the command "debug client ".

@ Lim

Thanks for the information.

Bruce tips are worth a try!

The Intel Wireless NIC have actual some issues with the Cisco environment.

Some examples from the forum:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Wireless%20-%20Mobility&topic=General&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.1dd73e2f

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Wireless%20-%20Mobility&topic=Security%20and%20Network%20Management&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.ee95e05

Please check if the wireless clients you use are specified in the "Cisco Compatible Client Devices" list:

http://www.cisco.com/web/partners/pr46/pr147/partners_pgm_partners_0900aecd800a7907.html

The mentioned versions can be found here:

http://www.cisco.com/warp/public/765/ccx/versions_and_features.shtml

Maybe some debugs bring up some light:

debug dott11 state enable - debug of 802.11 mobile state transitions

debug mobility directory enable - debug of mobility error messages

Hopefully this gives some errors/messages/hints to us.

Best regards,

Frank

[c.ong]

Hi Netmasque,

Here are the answers to your questions. Sorry for the late reply. The problem still persists

Are your clients using CCX, if so, what version?

Ans: I believe is CCX4 as the latest driver from Dell website showed it. However, we did not use the IntelPROSet wireless suite to manage the client. WE used WZC from XP.

Do they support E2E?

Ans: What is E2E?

Have you tweaked the client roaming details on the WLC (If you're running 4.x code) or running default?

Ans: I planned to tweak it but not sure what values to put. So I did not tweak anything on the client roaming details. It is runnig default.

Have you run debugs to see if these clients are having issues during a an AutoRF/RRM job?

Ans: WLC is in production. I am afraid that running debug will cause further damage to the network. WLC is having 50 APs attached. Is it fine for me to run debug?

Might try enabling 'Avoid Cisco AP Load' as well, which make RRM be a little smarter about updating to not drop clients.

Ans: What is the feature ' Aviod Cisco AP Load'. I have little knowledge about it. Hope you can elaborate more. Currently is not enabled

And as always. check the nearby break room for a subpar microwave :)

Ans: Have checked the environment no microwave is found.

Additional tasks which I have carried out.

1) Update driver on the IntelPROSet for the following cards based on Intel Recommendation from this URL

http://support.intel.com/support/wireless/wlan/sb/CS-010623.htm

2100BG, 2200BG, 3945ABG

2) Disable Power Saving Pole (PSP) on clients

3) Reduce the transmit power of APs to level 4 on 3 floors to create smaller cell and higher bandwidth

However, clients still encountered disconnections.

Thanks,

Delon

[wififofum]

Eric,

You can also enable email notifications via the WCS to notify you of coverage gaps or "black holes." The APs will report when clients have reached at a low signal level, which may be their reason for roaming.

Go to the Rogue AP Alarms display in the WCS and select email notifications from the drop-down menu. Hit "Go" and you'll be taken to the notifications config page, where you can have various alerts sent to an email address. Be adbised this can generate a lot of emails so be selective.

[john.preves]

your cell sizes are too big. The client can see too many cells that are within 'range'and thus tries them all even while stationary.

The only way to combat this effectively is to survey for small cells and low power settings.

The object is for the client to only see the cell that covers the area the client is in.

How was the survey conducted? Meaning how many square feet was each cell considered and what power setting was used to achieve that.

Also keep in mind that the clients shouldn't be on full power either. Doesn't do much good to tweak all your setting on your AP's and then leave the clients wide open. Same problem in reverse.

[tmoffett]

Just a few comments...

De-tuning the roaming aggressiveness is a good move.

Also, was the placement of these APs done through any kind of site survey?

The highest power level (1) is too much for most environments. You will wind up with way too much RF interference. It would be nice if the administrator was given the opportunity to set the max acceptable power setting for RRM to use.

Also, the "avoid ap load"' option is used in environments where client load is predictable and consistent. Enabling this setting causes the RRM engine to take in consideration the APs that are servicing large amounts of clients - or seeing large volumes of data. By enabling this, the controller will "tune" the radio power and channel selection with preference for those busy cells - thus giving them better performance at the cost of the less busy cells.

Use this feature with caution. If your busiest cells vary based on time of day, etc then you may not want to enable this...

My guess is that the power is too high. You can also tilt the 4941 antennas so that each AP's antennas are not parallel to each other. This will keep the fresnel zones from directly colliding with each other.

Sounds like you have lots of multipath interference.

Also, not all client adapters are built the same...

Tim

[mmacmahon]

Yeah sounds like the cell sizes are too big. Have either you or your installer performed the RF Calibration testing yet? If you didn't do the survey simply pull up the site survey doc. It SHOULD list what power the survey was completed at per AP. Them simply apply the changes in power to the APs. Most client devices can only see 64 Ap macs at a time. therefore if you run more than 1 BSSID, the client will see multiple AP MACs (1 per SSID) and it's table will fill up. That would cause it to not roam to the AP that you want or think it should be associated to. This especially hurts when the power is set too high on the APs.