Wired Stuff
WiFi Tablet Corner
My80211 White Papers (Coming Soon!)

Cisco Wireless Compatibility Matrix (Nov. 2011)

Podcasts / Videos

My80211 Videos

Cisco: 802 11 frames with Cisco VIP George Stefanick

Fluke Networks: Minimize Wi Fi Network Downtime

Aruba: Packets never lie: An in-depth overview of 802.11 frames

ATM15 Ten Talk “Wifi drivers and devices”

Houston Methodist Innovates with Wireless Technology

Bruce Frederick Antennas (1/2)


Bruce Frederick dB,dBi,dBd (2/2)

Cisco AP Group Nugget

Revolution WiFi Capacity Planner

Anchor / Office Extends Ports


Peek Inside Cisco's Gear

See inside Cisco's latest wireless gear!

2.4 GHz Channel Overlap




  • CWSP Certified Wireless Security Professional Official Study Guide: Exam PW0-204
    CWSP Certified Wireless Security Professional Official Study Guide: Exam PW0-204
    by David D. Coleman, David A. Westcott, Bryan E. Harkins, Shawn M. Jackman

    Shawn Jackman (Jack) CWNE#54 is a personal friend and has been a mentor to me for many years.  I've had the pleasure and opportunity to work with Jack for 4 years. Jack is a great teacher who takes complex 802.11 standards and breaks them down so almost anyone can understand the concept at hand. I'm excited for you brother. Great job and job well done! Put another notch in the belt!

IEEE 802.11a/g/n Reference Sheet


LWAPP QoS Packet Tagging



Interference Types


Microwave Oven

Cordless Phone



bUG CSCtn75346: 7925 phone loses 5 GHz connection intermittently with OEAP600

My 2 second sales pitch

Cisco Office Extends is a very powerful enterprise tool to have in your arsenal. It is changing the way we look at remote workers enterprise wide. The ease of installation and seamless mobility from enterprise to home is changing the way we do business.  It helps with users who are technically challenged and at times have issues with the simplest of VPN clients. Most notable in healthcare remote coders. 

On a recent trip to South America I packed my AP600 and Cisco 7925 and conducted long distance testing from Chile to Houston. The calls where remarkably good and my connection was better then some hotel connections with VPN. 

Cisco Office Extends AP600 Bug -

After completing our Office Extends design I had issues connecting my Cisco 7925 Wireless Phone to my Office Extends access point (AP600). The 7925 would cycle on and off the wireless network while constantly displaying the “locating network services” on the handset. 


After a packet capture, it was very apparent the issue was the NAV timer. The phone would regularly send a CTS-SELF with a NAV timer set at 18,800us. Normally you might see a NAV at a value of 44us or there around.  

By triggering a frame with a NAV timer set to 18,800us, the Cisco phone was telling everyone on the channel not to communicate because the phone had data to send and it would take 18,800us. Clearly the payload didnt warrent that amount of time.


For the non 802.11 readers -- What does this all mean ?

802.11 wireless networks are a half duplex medium, meaning only 1 device can transmit a frame on the medium at a time. In this case, the medium is a channel for example <1, 6 or 11>. 

802.11 use Carrier Sense Multiple Access - Collision Avoidance (CSMA-CA). The Collision Avoidance is particularly interesting. 802.11 uses protocols to sense the wireless medium to determine if the medium is busy or idle. It does this with CSMA-CA. CSMA-CA uses 2 protocols. 

They are Physical Carrier Sense (CCA) and Virtual Carrier Sense (NAV). 

Physical Carrier Senses uses Clear Channel Assessment (CCA). Think of CCA like a pair of ears attached to your head.  Always listening to the medium to determine if other device(s) are on channel trigger frame transmissions. If it senses frame transmissions or elevated levels of non 802.11 interference it will determine the medium as busy. 

Virtual Carrier Sense uses Network Allocation Vector (NAV). When a frame marks the duration with a specific value, in our case 18,800us. Other devices within range of this frame will read this duration value. These devices will then BACKOFF for this set amount of time. This includes access points.

You can see, the Cisco phone was telling all other devices on the channel not to communicate for 18,800us. Normally, most client reserve the medium for 60 - 200us to send traffic. This is why I think the phone would go into locating network services. The access point read the NAV and wasn't allowed to trigger a beacon. No beacon no network. Phone drops and then tries to find the network again.

Upgrade to 1.4.3SR1 fixed the issue

CSCtn75346 Bug Details

7925 phone loses 5 GHz connection intermittently with OEAP600
7925 phone loses 5 GHz connection intermittently with OEAP600.
No connectivity issues when using 2.4 GHz.

Using an OEAP600, or certain third-party 802.11n APs, and 7925 on 5 GHz.

Use 2.4 GHz or an alternate AP platform.
Status Status 

Severity Severity 
3 - moderate 

Last Modified Last Modified 
In Last Year 

Product Product 
Cisco Unified IP Phone 7900 Series 

Technology Technology 
Wireless, Mobile 

1st Found-In 1st Found-in 

Fixed-In Fixed-in 


“While others may cringe at complex issues. I look at it from a different pair of glasses. The glasses called opportunity to learn something new”.  ~ George Stefanick


Cisco Wireless Phone Deployment Guide Update 1.4(2) - 8/14/2012

UPDATED Cisco Wireless Handset Deployment Guide


7921G Deployment Guide – 1.4(2) Update

7925G, 7925G-EX, and 7926G Deployment Guide – 1.4(2) Update





Voice Over Wireless LAN (VoWLAN) Troubleshooting Checklist

Cisco VoWLAN checklist is a great way to plan your config and to reference when you are having voice issues.


Best Practice
May Consider

Verify an AP can be seen from the phone at -67 dBm or better in all areas to be covered. You also need to verify that the AP sees the phone at -67 dBm or better in all areas as well.



Ensure that the SNR is always 25 dB or higher in all areas to provide coverage.



Verify that channel utilization is under 50%.



Configure voice WLAN to use the 802.11a band.




If using EAP authentication, ensure that fast roaming is supported such as CCKM.



WMM should be allowed or required for the voice WLAN.



Voice WLAN should be marked with Platinum QoS.



Platinum QoS profile should have the 802.1p bits set to 6.



Verify the switch ports used to connect to the controller are set to trust CoS and ports to APs and uplinks are set to trust DSCP.



Verify that Call Admission Control is enabled globally for the radios.



Verify that Load-based CAC is enabled under Call Admission Control.



Ensure that Load Based CAC (7920 AP CAC) under the WLAN is enabled for the voice WLAN if the network has a mix of 7920 and 792xG Series wireless IP phones.



Ensure that Client Based CAC (7920 Client CAC) under the WLAN is disabled for the voice WLAN.



Verify that the EDCA profile on the controller is set to Voice Optimized.



Verify that Low Latency MAC is disabled.



Verify that the 12 Mbps data rate is enabled (default PHY rate of the phone).



If using 802.11b/g disable the 1, 2, 5.5, 6, and 9 Mbps data rates if possible.



If using 802.11a disable the 6 and 9 Mbps data rates if possible.



Verify coverage is designed for 24 Mbps to maximize throughput. Optionally disable 36-54 Mbps.




Optionally disable 36-54Mbps


Verify that Aggressive Load Balancing is disabled.




Disabled ARP unicast if running a pre-4.2 image on the controller.



Verify that DTPC is enabled so that the client and AP match tx power levels.



Verify the Beacon interval is set to 100 ms.



A DTIM of 2 is recommended.



Ensure DHCP required is not enabled for the voice WLAN.




Ensure that Aironet IE is enabled for the voice WLAN.



Verify that Client MFP is set to Optional or Disabled.



Session timeout for the WLAN should not be too short (300 seconds or more).



Verify that peer-to-peer blocking is disabled.



If using TKIP encryption, disable the hold down timer on the voice WLAN to prevent MIC errors from disrupting voice.



Verify that the radio of the AP has multiple antennas and that diversity is enabled.



Ensure controllers are configured for Symmetric Mobility if phones will be roaming between controllers.




Validate the virtual interface address is the same across all controllers in the same mobility group.



Validate that the mobility status shows as UP between all controllers in the same mobility group.



Enable Traffic Stream Metrics collection on the controller.



DCA Channel Sensitivity set to High to reduce chance of channel changes during business hours.