Ask the Expert: Deploying and Troubleshooting Wireless Networks

[Monica Lluis]

Welcome to this Cisco Support Community Ask the Expert conversation. This is an opportunity to learn and any ask questions about how to configure and troubleshoot a wireless network with Cisco expert  Alexander De Menezes.

Ask questions from Monday February 22 to Friday March 4, 2016

Wireless networks have became pervasive in today's world. Cisco offers very strong wireless porfolio that helps business to connect to the Internet anywhere anytime. 

This session will focus on answering question regarding how to deploy a wireless network and also, the common pitfalls and issues that might happen in an installed wireless network. 

Alexander De Menezes  is a Technical Support engineer in the Cisco Technical Assistance Center in Cisco Brussels.  He is expert on any wireless products, including Wireless LAN controllers and Access Points. He also has in-depth knowledge of AAA and IBNS technologies. Alexander joined Cisco in 2007. He holds a Master in Sciences in Advanced Electronic Engineering from the University of Warwick, UK. 

Alexander  might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation on the Getting Started with Wireless Community

Find other  https://supportforums.cisco.com/expert-corner/events.

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[khinminn1181]

Thank you ,Alex ,for your reply!

But I don't have any hardware devices.I am network engineering student.In this academic year,we each have to do mini thesis in respective major subjects.I choosed the title"Networked Control System for a Wireless Lan" as my mini thesis.I will implement this network in Cisco Packet Tracer simulation tool version 6.2.

Therefore ,it is better if you can direct what devices can be supported to configure remote devices in a wireless lan and how to control network speed with which protocols?

To be more thinkable,my desired network design sketch is in below attachment.I bet This sketch is quite disordered and cluttered :D

Plz,what can i used which device and which protocol in the place of admin in the sketch?

SNMP protocol is suitable for network management but i have no idea to solve network speed control problem!!!

-No No

[Eric Marshott]

Hello Alex,

I am concerned with the deployment of 3702i wireless APs and the dynamic channel assignment in my environment.

The controller (8510/7.6.130) is configured with the default settings for RRM and DCA, and the APs in dense areas (such as ED in the hospital) will select a channel other than the global default. For APs in less dense areas, the channel of the AP is dynamically being assigned to the global default.

In one instance, an AP had no "Nearby APs" on their neighbor list, but a 7925g wireless phone held directly underneath the AP (which is hanging in a ceiling tile) shows 3 or 4 APs in the area (~-75 dBm).

Due to the lack of a populated neighbor list, the AP chose the default channel which was the same channel as other APs in the area.

Is there something that can be configured on a WLC to increase the sensitivity for listening to these RRM neighbor packets? How could I be sure that RRM/DCA is working correctly in my environment?

Regards,

Eric

[Alexander De Menezes]

Hi Eric,

I see you refer to a hospital environment and voice deployments commonly need detailed troubleshooting.
So incase of urgent/critical needs, you will want to raise a TAC SR for this.
I end up with spare time following my end of business day, so my responses are getting delayed on this session.

For some action plan:

The issue you describe is mainly pointing towards point 3 below:

1)Just for info ,7.6.130.0 release is deferred on Cisco.com
Is there a specific reason you run with this release,Cisco suggested releases are marked on Cisco.com.For any specific bug fix or feature info, please refer to the release notes:
https://software.cisco.com/download/release.html?mdfid=284493532&flowid=34542&softwareid=280926587&release=7.4.140.0&relind=AVAILABLE&rellifecycle=MD&reltype=latest

http://www.cisco.com/c/en/us/support/wireless/wireless-lan-controller-software/products-release-notes-list.html

2)This is a useful tool to check on the configuration,You need to use the WLC "show run-config" and can also run a voice deployment check with the tool.
For example:

Are you using 5Ghz and the voice deployment guide recommendations?

Are you disabling lower data rates to avoid channel util issues on 2.4Ghz?

https://supportforums.cisco.com/community/12168506/wireless-lan-controller-config-analyzer-wlcca

https://supportforums.cisco.com/document/7711/wlc-config-analyzer

There are some important points and recommendations for voice deployments mentioned in the Cisco live session:
BRKEWN-3012 - Advanced - Troubleshooting Voice over Wireless LAN deployments:

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=2595&tclass=popup

3)Was a wireless site survey done while considering the 3702i APs across the floor area?

For example, in some cases a site survey is done in past while considering AP model xxxx, but over time the APs get replaced with new AP models and everything can then get messed up if the site  survey is not redone.As change in AP models can alter coverage.

Problems can also occur if APs are randomly added or removed from the floor area to maintain coverage.

Also was the site survey done considering the lowest client Tx power and 7925 Tx power levels?
We will need to verify for channel overlap across the whole floor area during the survey, as this is crucial for client roaming with phone needing a minimum number of Aps at -67dBm as per the 792x voice deployment guides.
To avoid asymmetric RF and signal drop, we also need to have AP and client power match so that the AP can listen to the Phone (otherwise the Phone may hear the AP well, but the AP may not hear the phone with weak signal), so Please refer to page 44 &45 which mentions about DTPC/AP placement/Data Rates and Transmit Power:

http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7925g/7_0/english/deployment/guide/7925dply.pdf

Here is a brief example on site survey procedure:
http://airmagnet.flukenetworks.com/assets/flash/survey/demo/

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=4211

4)On latest WLC releases, there are no critical bugs with RRM, and RRM will work fine provided the AP placement/positioning is correctly done as per the wireless site surveys.

TPC/DCA is basically occurring on every configured RRM cycle,wherein Aps adjust their channel/power based on its neighbouring Aps list.

TPC calculation happens like:

-From given AP neighbour list, do we have 3 neighbours at –70dBm or greater.
-If yes, then Tx power is determined via:
Tx_Max for given AP + (Tx Power Control threshold – RSSI of third highest neighbour)
(RSSI of third highest neighbour is basically how the third AP is hearing the current given AP).TPC hysteresis is 3bB for increase/decrease decisions.

So in short RRM should work correctly, provided the wireless survey was correctly done while considering your AP model selection.
RF profiles and overriding the TPC algorithm is only done after detailed troubleshooting, there is no fixed parameters and this can defer for sites and is really dependant on how far the Aps are from each other, what do they listen as their neighbouring Aps.Any abrupt changes can cause more harm:

http://www.cisco.com/c/en/us/td/docs/wireless/controller/8-0/configuration-guide/b_cg80/b_cg80_chapter_01111110.html#ID40

5)To correlate with the site survey we have a couple of useful tools from WCS/NCS/PI:

-Real time heat maps to determine AP-AP RSSI and coverage holes from Cisco Prime infrastructure.

-Voice Audit and Voice diagnostic tool:
http://www.cisco.com/c/en/us/td/docs/net_mgmt/prime/infrastructure/3-0/user/guide/pi_ug/mon-tools.html#pgfId-1059493

-For further info on AP to client and client to AP RSSI/SNR, you can use the WLC link test for CCx clients:
http://www.cisco.com/c/en/us/td/docs/wireless/controller/8-0/configuration-guide/b_cg80/b_cg80_chapter_01110111.html

Do let me know for any further concern.

-Alex

[STEPHEN POLZIN]

Hi Alex,

I wanted to ask about what channels I can use from the UNNI 2 extended band in Australia. I am referring to and quoting from the document;

Cisco 5760 IOS Wireless LAN Controller Configuration Best Practices September 2014

http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/5700/software/release/ios_xe_33/5760_IOS_WLC_Configuration_Best_Practices.html

Quoting from that document;

“Dynamic Frequency Selection (DFS)

Dynamic Frequency Selection was created to increase the availability of more channels in the 5 GHz spectrum. Depending on regulatory domain this can mean from 4 to 12 additional channels.”

Am I right that the terms dca and DFS are referring to the same thing?

As in the document the “show ap dot11 5ghz channel” command on my 5760 controller output shows

WLC#show ap dot11 5ghz channel

Automatic Channel Assignment

  Channel Assignment Mode                    : AUTO

  Channel Update Interval                    : 600 seconds

  Anchor time (Hour of the day)              : 0

  Channel Update Contribution                : SNI..

  Channel Assignment Leader                  : BT-BC-2-4-WLC (10.208.224.10)

  Last Run                                   : 407 seconds ago

  DCA Sensitivity Level                      : MEDIUM (15 dB)

  DCA 802.11n/ac Channel Width                  : 80 MHz

  Channel Energy Levels

      Minimum                                : -95

      Average                                : -73

      Maximum                                : -50

  Channel Dwell Times

      Minimum                                : 4 hours 37 minutes 46 seconds

      Average                                : 26 days 23 hours 9 minutes 26 seconds

      Maximum                                : 53 days 1 hour 50 minutes 3 seconds

  802.11a 5 GHz Auto-RF Channel List

    Allowed Channel List                     : 36,40,44,48,52,56,60,64,149,153,157,161

  Unused Channel List                        : 100,104,108,112,116,120,124,128,132,136,140,165

  802.11a 4.9 GHz Auto-RF Channel List

  Allowed Channel List                       :

  Unused Channel List                        :

So if I understand then this means DFS is enabled on the “Allowed Channel List”?

The document goes on to say;

“Enable the U-NII-2e channels for more channels in your regulatory domain using this command: WLC5760(config)#ap dot11 5ghz rrm channel dcl add <channel>

Available channels in North America and Europe are 100 - 140 (8 additional channels). Channels 120, 124, and 128 are disabled in the US, and severely penalized in ETSI DFS rules and are not supported.”

I am in Australia so can you tell me the permitted channels in my regulatory domain that I can add to the allowed channel list? 

Would the addition of more available channels for dynamic selection mostly be useful for improving high density deployments by reducing co-channel interference?

Thanks,

Steve

[Alexander De Menezes]

Hi Stephen,

Available channels for UNII-2 extended band in Australia seems to be similar to US as per the FCC rules and regulations:

Attached screenshots from the below mobility enterprise doc.

So from:

UNII-2 Extended (5.470 to 5.725 GHz) Non-overlapping channels 100, 104, 108, 112, 120, 124, 128, 136, 140

Channels 120,124,128 not permitted in the US, and severely penalized in ETSI DFS rules and are not supported.

Some info on page 4:

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob41dg/emob41dg-wrapper/ch3_WLAN.pdf

FCC Rule # 15.407(h)(2) requires that products operating in the UNII-2 and UNII-2 extended bands (5.25-5.35 GHz and 5.47-5.725 GHz) must support Dynamic Frequency Selection (DFS), to detect and automatically adjusts channels to protect WLAN communications from interfering with military or weather radar systems. All WLAN products that ship in Canada and the US on or after July 20, 2007 must meet the DFS for FCC requirements.

http://www.cisco.com/c/en/us/products/collateral/wireless/aironet-1300-series/prod_white_paper0900aecd801c4a88.html

http://www.cisco.com/c/en/us/td/docs/wireless/access_point/channels/lwapp/reference/guide/lw_chp2.html

Old clients pre-2007 will have issues with communicating on UNII2 extended channels since those FCC rules took effect in July 2007.

Yes, DFS is under DCA list, for further info:
http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/5700/software/release/ios_xe_33/5760_IOS_WLC_Configuration_Best_Practices.html#pgfId-45142

UNII-2 extended can help when facing issues with interference ,but if you have low channel util of <5% then i dont see much to benefit with UNII-2 extended, some useful 5760 cli commands to check on interference:
show ap dot11 5ghz load-info
show tech-support wireless

-Alex

[STEPHEN POLZIN]

Thanks for the information Alex.