Cisco Cisco 2112 Wireless LAN Controller Folheto
(WLC) >config load-balancing window ?
<client count> Number of clients (0 to 20)
<client count> Number of clients (0 to 20)
In dense production networks, the controllers have been verified to function optimally with load-balancing ON
and window size set at 10. In practical terms, this means load-balancing behavior is only enabled when, for
example, a large group of people congregate in a conference room or open area (meeting or class). Load-
balancing is very useful to spread these users between various available APs in such scenarios.
and window size set at 10. In practical terms, this means load-balancing behavior is only enabled when, for
example, a large group of people congregate in a conference room or open area (meeting or class). Load-
balancing is very useful to spread these users between various available APs in such scenarios.
Note:
Users are never “thrown off” the wireless network. Load-balancing only occurs upon association and the
system will try to encourage a client towards a more lightly loaded AP. If the client is persistent, it will be
allowed to join and never left stranded.
allowed to join and never left stranded.
Radio Resource Management: Introduction
Along with the marked increase in the adoption of WLAN technologies, deployment issues have similarly risen.
The 802.11 specification was originally architected primarily with a home, single-cell use in mind. The
contemplation of the channel and power settings for a single AP was a trivial exercise, but as pervasive WLAN
coverage became one of users’ expectations, determining each AP’s settings necessitated a thorough site
survey. Thanks to the shared nature of 802.11’s bandwidth, the applications that are now run over the wireless
segment are pushing customers to move to more capacity-oriented deployments. The addition of capacity to a
WLAN is an issue unlike that of wired networks where common practice is to throw bandwidth at the problem.
Additional APs are required to add capacity, but if configured incorrectly, can actually lower system capacity
due to interference and other factors. As large-scale, dense WLANs have become the norm, administrators
have continuously been challenged with these RF configuration issues that can increase operating costs. If
handled improperly, this can lead to WLAN instability and a poor end user experience.
The 802.11 specification was originally architected primarily with a home, single-cell use in mind. The
contemplation of the channel and power settings for a single AP was a trivial exercise, but as pervasive WLAN
coverage became one of users’ expectations, determining each AP’s settings necessitated a thorough site
survey. Thanks to the shared nature of 802.11’s bandwidth, the applications that are now run over the wireless
segment are pushing customers to move to more capacity-oriented deployments. The addition of capacity to a
WLAN is an issue unlike that of wired networks where common practice is to throw bandwidth at the problem.
Additional APs are required to add capacity, but if configured incorrectly, can actually lower system capacity
due to interference and other factors. As large-scale, dense WLANs have become the norm, administrators
have continuously been challenged with these RF configuration issues that can increase operating costs. If
handled improperly, this can lead to WLAN instability and a poor end user experience.
With finite spectrum (a limited number of non-overlapping channels) to play with and given RF’s innate desire
to bleed through walls and floors, designing a WLAN of any size has historically proven to be a daunting task.
Even given a flawless site survey, RF is ever-changing and what might be an optimal AP channel and power
schema one moment, might prove to be less-than-functional the next.
to bleed through walls and floors, designing a WLAN of any size has historically proven to be a daunting task.
Even given a flawless site survey, RF is ever-changing and what might be an optimal AP channel and power
schema one moment, might prove to be less-than-functional the next.
Enter Cisco’s RRM. RRM allows Cisco’s Unified WLAN Architecture to continuously analyze the existing RF
environment, automatically adjusting APs’ power levels and channel configurations to help mitigate such things
as co-channel interference and signal coverage problems. RRM reduces the need to perform exhaustive site
surveys, increases system capacity, and provides automated self-healing functionality to compensate for RF
dead zones and AP failures.
environment, automatically adjusting APs’ power levels and channel configurations to help mitigate such things
as co-channel interference and signal coverage problems. RRM reduces the need to perform exhaustive site
surveys, increases system capacity, and provides automated self-healing functionality to compensate for RF
dead zones and AP failures.
Radio Resource Management: Concepts
Key Terms
Readers should fully understand these terms used throughout this document:
Signal: any airborne RF energy.
dBm: an absolute, logarithmic mathematical representation of the strength of an RF signal. dBm is
directly correlated to milliwatts, but is commonly used to easily represent output power in the very low
values common in wireless networking. For example, the value of -60 dBm is equal to 0.000001
milliwatts.
directly correlated to milliwatts, but is commonly used to easily represent output power in the very low
values common in wireless networking. For example, the value of -60 dBm is equal to 0.000001
milliwatts.
Received Signal Strength Indicator (RSSI): an absolute, numeric measurement of the strength of the
signal. Not all 802.11 radios report RSSI the same, but for the purposes of this document, RSSI is
assumed to directly correlate with received signal as indicated in dBm.
signal. Not all 802.11 radios report RSSI the same, but for the purposes of this document, RSSI is
assumed to directly correlate with received signal as indicated in dBm.
Noise: any signal that cannot be decoded as an 802.11 signal. This can either be from a non-802.11
source (such as a microwave or Bluetooth device) or from an 802.11 source whose signal has been
invalidated due to collision or any other retarding of the signal.
source (such as a microwave or Bluetooth device) or from an 802.11 source whose signal has been
invalidated due to collision or any other retarding of the signal.
Noise floor: the existing signal level (expressed in dBm) below which received signals are unintelligible.
SNR: the ratio of signal strength to noise floor. This value is a relative value and as such is measured in
decibels (dB).
decibels (dB).
Interference: unwanted RF signals in the same frequency band that can lead to a degradation or loss of
service. These signals can either be from 802.11 or non-802.11 sources.
service. These signals can either be from 802.11 or non-802.11 sources.
A Bird’s-Eye View of RRM
Before getting into the details of how RRM algorithms work, it is important to first understand a basic work-flow
of how an RRM system collaborates to form an RF Grouping, as well as understand what RF computations
happen where. This is an outline of the steps that Cisco’s Unified Solution goes through in learning, grouping,
and then computing all RRM features:
of how an RRM system collaborates to form an RF Grouping, as well as understand what RF computations
happen where. This is an outline of the steps that Cisco’s Unified Solution goes through in learning, grouping,
and then computing all RRM features:
1. Controllers (whose APs need to have RF configuration computed as a single group) are provisioned
with the same RF Group Name. An RF Group Name is an ASCII string each AP will use to determine if
the other APs they hear are a part of the same system.
the other APs they hear are a part of the same system.