Cisco Cisco 2125 Wireless LAN Controller Folheto
............................................. 104,108,112,116,132,136,140,
............................................. 149,153,157,161
Auto-RF Unused Channel List.................... 165,20,26
............................................. 149,153,157,161
Auto-RF Unused Channel List.................... 165,20,26
Interval
—The interval value, with the units defined in hours, allows the users to have a predictable
network and the channel plan assessments are only computed at the configured intervals. For example,
if the configured interval is 3 hours, the DCA computes and assesses a new channel plan every 3
hours.
if the configured interval is 3 hours, the DCA computes and assesses a new channel plan every 3
hours.
Sensitivity
—As described in the
DCA Algorithm
section, the 5dB hysteresis that is accounted for in the
algorithm to assess if the channel plan is improved by running the algorithm is now user-tunable.
Allowed configurations are Low, Medium or High Sensitivity with a setting of low indicating the algorithm
being very insensitive and a setting of high indicating the algorithm being extremely sensitive. The
default sensitivity level is Medium for both bands.
Allowed configurations are Low, Medium or High Sensitivity with a setting of low indicating the algorithm
being very insensitive and a setting of high indicating the algorithm being extremely sensitive. The
default sensitivity level is Medium for both bands.
For 802.11a, the sensitivity values equate to: Low (35dB), Medium (20dB) and High (5dB).
For 802.11b/g, the sensitivity values equate to: Low (30dB), Medium (15dB) and High (5dB)
Tx Power Control Algorithm
Default Transmit Power Control Threshold
The transmit power control threshold has always carried the responsibility of how APs hear their neighbors,
which, in due course is used to decide the transmit power of the AP. As a result of the overall enhancements
that have been made to the RRM algorithms in WLC software’s 4.1 maintenance release, the default value of -
65dBm has also been reconsidered. Therefore, the default which was deemed too hot for most deployments,
has been adapted to -70dBm. This results in better cell overlap in most indoor deployments out of the box.
However, this default only impacts new installations as the controller maintains the previously configured value
if being upgraded from 4.1.171.0 or earlier.
which, in due course is used to decide the transmit power of the AP. As a result of the overall enhancements
that have been made to the RRM algorithms in WLC software’s 4.1 maintenance release, the default value of -
65dBm has also been reconsidered. Therefore, the default which was deemed too hot for most deployments,
has been adapted to -70dBm. This results in better cell overlap in most indoor deployments out of the box.
However, this default only impacts new installations as the controller maintains the previously configured value
if being upgraded from 4.1.171.0 or earlier.
Coverage Hole Algorithm
Minimum Clients
Up until the 4.1.185.0, only one client needed to have met the condition (worse SNR threshold than the
configured value, or the defaults of 16dB for 802.11a or 12dB for 802.11b/g) for a coverage hole to be
detected and the mitigation mechanisms to be kicked in. The Client Minimum Exception Level field is now
directly tied to the CHA (and appropriately positioned in the newly created sub-section for the CHA) where the
configured value will define how many clients have to meet the SNR threshold for the coverage hole mitigation
mechanisms (increasing AP Transmit power) will kick in. It must be noted that most deployments should begin
with the defaults (12dB for 802.11b/g and 16dB for 802.11a, and Client minimum exception level of 3) and
adjusted only if necessary.
configured value, or the defaults of 16dB for 802.11a or 12dB for 802.11b/g) for a coverage hole to be
detected and the mitigation mechanisms to be kicked in. The Client Minimum Exception Level field is now
directly tied to the CHA (and appropriately positioned in the newly created sub-section for the CHA) where the
configured value will define how many clients have to meet the SNR threshold for the coverage hole mitigation
mechanisms (increasing AP Transmit power) will kick in. It must be noted that most deployments should begin
with the defaults (12dB for 802.11b/g and 16dB for 802.11a, and Client minimum exception level of 3) and
adjusted only if necessary.
Figure 19: Coverage Hole Algorithm Sub-section, separated from the Profile Thresholds, with the
default values that provide optimum results in most installations
default values that provide optimum results in most installations
Tx-Power-Up Control
In addition to allowing the number of clients that need to be in violation for coverage hole mitigation to kick in,
the algorithm has also been improved to consider AP transmit power increase in an intelligent manner. While
increasing the transmit power to the maximum might have been the safe bet to ensure sufficient mitigation and
overlap, it does have adverse effects with the presence of clients with poor roaming implementations. Instead
of changing its association to a different AP, typically the one that provides the strongest signal, the client
keeps associating to the same old AP that it has moved farther away from. As a consequence, this client is no
longer receiving a good signal from the associating AP. A failed client that is a consequence of poor roaming is
an example of a possible false positive coverage hole scenario. Poor roaming is not an indication that a
genuine coverage hole exists. The potential coverage hole is genuine if:
the algorithm has also been improved to consider AP transmit power increase in an intelligent manner. While
increasing the transmit power to the maximum might have been the safe bet to ensure sufficient mitigation and
overlap, it does have adverse effects with the presence of clients with poor roaming implementations. Instead
of changing its association to a different AP, typically the one that provides the strongest signal, the client
keeps associating to the same old AP that it has moved farther away from. As a consequence, this client is no
longer receiving a good signal from the associating AP. A failed client that is a consequence of poor roaming is
an example of a possible false positive coverage hole scenario. Poor roaming is not an indication that a
genuine coverage hole exists. The potential coverage hole is genuine if:
It is located within the intended coverage area, and
Even if the client in this coverage hole were to change its association to any other available AP, the
downlink signal the client would receive and the uplink signal at such an alternative AP from the client
would still be below the coverage threshold.
downlink signal the client would receive and the uplink signal at such an alternative AP from the client
would still be below the coverage threshold.
In order to avoid and mitigate such scenarios, the AP transmit power is only raised one level at a time (per
iteration), which allows genuine coverage holes to benefit from the power increase without running the network
hot (avoiding co-channel interference as a result).
iteration), which allows genuine coverage holes to benefit from the power increase without running the network
hot (avoiding co-channel interference as a result).