Information Technology Reference
In-Depth Information
Dynamic channel assignment:
WLCs automatically assign channels to avoid inter-
ference.
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Interference detection and avoidance:
As Cisco LWAPs monitor all channels, in-
terference is detected by a predefined threshold (10 percent by default). Interference
can be generated by rogue APs, microwaves, cordless telephones, Bluetooth devices,
neighboring WLANs, or other electronic devices.
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Dynamic transmit power control:
The WLCs automatically adjust power levels.
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Coverage hole detection and correction:
WLCs may adjust the power output
of APs if clients report that a low received signal strength indication (RSSI) level is
detected.
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Client and network load balancing:
Clients can be influenced to associate with
certain APs to maintain network balance.
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With AP self-healing WLCs use RRM to raise the power levels and adjust the channel se-
lection of neighbor APs to compensate for lost of coverage of a failed AP. APs report a
lost neighbor when they no longer receive neighbor messages at -70 dBm.
RF Groups
An RF group is a cluster of WLC devices that coordinate their RRM calculations. When
the WLCs are placed in an RF group, the RRM calculation can scale from a single WLC to
multiple floors, buildings, or even the campus. As shown in Figure 5-16, APs send neigh-
bor messages to other APs. If the neighbor message is above -80 dBm, the controllers
for m an RF g roup. The WLCs elec t an RF g roup leader to analy ze the RF data . The RF
group leader exchanges messages with the RF group members using UDP port 12114 for
802.11b/g/n and UDP port 12115 for 802.11a.
Key
To p i c
RF groups are formed with the following process:
1.
APs send out neighbor messages over the air. The message includes an encrypted
shared secret that is configured in the WLC and pushed to each AP.
2.
APs sharing the same secret are able to validate messages from each other. Neighbor
messages need to be over -80dBm to form a RF group.
3.
The members in the RF group elect an RF group leader to maintain a “master” power
and channel scheme for the RF group. The RF group leader analyzes real-time radio
data collected by the system and calculates the master power and channel plan.
RF Site Survey
Similar to performing an assessment for a wired network design, RF site surveys are done
to determine design parameters for WLANs and customer requirements. RF site surveys
help determine the coverage areas and check for RF interference. This helps determine the
appropriate placement of wireless APs.
The RF site survey has the following steps:
1.
devices to support, sites where wireless devices will be located.
