Posts Tagged ‘2.4 GHz’
Control roaming behavior on your Cisco wireless network.
Roaming is just another expectation from your end users. They expect to walk freely around the office to conference rooms or far off cubicles and have their laptop or handheld remain connected while downloading files or in the middle of a conversation. If the roaming process is not quick enough then you could see conversations and clients gets dropped forcing them reconnect to the WLAN, and I can guarantee you your end users will be calling.
Now, if you have done a proper site survey and have solid data to work off of, you can control the roaming behavior of your WLAN clients. The reason you need to know the details of your wireless environment is because you are going to set RSSI limits concerning when your clients should begin looking for a new AP to associate to and, how quickly they are roam between access points. Just keep in mind, making these settings will effect the entire WLAN not just individual sections.
I would also like to mention your clients should be CCXv4 or higher to take advantage of these features. To see if your clients are CCXv4 compliant go to Monitor -> Clients -> click on the client in question.
On your Cisco Wireless LAN Controller, you want to navigate to Wireless -> 802.11a/n or 802.11b/g/n (depending on which frequency you want to customize) -> Client Roaming.
The first thing you need to do when you want to customize these settings is change the mode to custom this will allow you to edit the default values for the rest of the parameters.
The next option is minimum rssi. If a clients RSSI value is below this threshold it will not associate/authenticate to the access point, instead it will continue to look for a better signal from different access points. Valid values for this field are -80 through -90. The understanding is that the signal strength/quality will be so low reliable communication will not be established.
Next we have a setting called hysteresis this value is in dB and states how much stronger the signal of another access point has to be before a client decides to roam to it. This is useful if you have multiple access points in close proximity of each other or clients are moving between the edge of coverage of different access point. The higher this value the closer a client needs to be to an access point for it to associate to the second access point. Valid ranges are from 2 through 4 dB.
Now we have the scan threshold this is another RSSI value range. When the wireless client’s RSSI drops below this threshold the client will begin actively scanning for another access point it can receive a stronger signal from. Valid values range between -70 through -77.
The last field on the page is the transition time this is the amount of a client is going to see a better signal from neighboring access, before it attempts to associate to the second access point. The client determines a better signal when its RSSI drops below the scan threshold and it sees a signal from a neighboring access point higher than the scan threshold.
So all these factors do work together and can be customized for your environment. Normal data traffic is more forgiving since it’s not as delay sensitive, but If you have voice on your WLAN you will want to fine tune these settings to avoid dropped calls.
Cisco Band Select.
Thought I would shift gears to wireless for a little bit. Cisco introduced a feature some time ago called band select were the dual band clients have a better chance at joining the 5 GHz radio compared to the 2.4 GHz range. This is mainly due to the influx of dual band clients nowadays and how the 2.4 GHz range is generally over utilized.
The Cisco accomplishes this is by ignoring/delaying the first few 802.11b/g probe frames in hopes of it accepting the 802.11a probes because it will appear to have a quicker response time. I would also like to point out that this feature only works when the client first associates to the Access Point. So this feature will not kick in on the fly when the AP notices a high client count or high channel utilization. Plus this feature only goes in one direction from the 2.4 GHz range to the 5 GHz not visa-versa. So this is not a load balance mechanism.
This feature is configured very simply all from one screen in the WLC, under Wireless -> Advanced -> Band Select:
Now you’ve only got a few settings to configure here, but you still need to take care with these settings like anything on the network you are going to configure. Probe Cycle Count, tells the AP how many probe beacons/frames to ignore/delay. Scan Cycle Period Threshold tells the AP how often in milliseconds it can expect each probe from the client, this setting can be changed depending on the client Wi-Fi cards you are using in your environment and how often the send out probe requests (Check vendor documentation for this). Age Out Suppression, this is the time-out for when the clients will be declared as “new” and may have their probe frames delayed/ignored again. Age Out Dual Band is the very similar to age out suppression, however age out dual band only applies to dual band clients so it will not effect everyone. Just keep in mind something will need to happen for the client to disassociate and re-associate with access point. Acceptable Client RSSI just states the minimum RSSI value a client registers for it to be eligible for band select.
Also keep in mind this feature can be controlled per-WLAN, under the “Advanced” tab
This can also be done via the CLI of the WLC using the following commands:
config band-select cycle-count cycle_count
config band-select cycle-threshold milliseconds
config band-select expire suppression seconds
config band-select expire dual-band seconds
config band-select client-rssi client_rssi
config wlan band-select allow {enable | disable} wlan_ID
And if you want to verify the band select configuration use the following command:
show band-select
CCIE or Null! 