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CLI-based Configuration Guide - WLAN-AC

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document provides the concepts, configuration procedures, and configuration examples of WLAN-AC features.
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AP-based Load Balancing

AP-based Load Balancing


Load balancing can evenly distribute AP traffic loads to ensure high bandwidth for each STA. The load balancing function applies to wireless networks with high user densities to ensure access of STAs. Two load balancing technologies are available: AP-based load balancing and radio-based load balancing.

In Figure 5-7, AP1 and AP2 associate with an AC. Four users (STA1 to STA4) associate with AP1, and one user (STA5) associates with AP2. If too many users connect to the Internet through AP1, AP1 will be overloaded, whereas resources on AP2 are not used.

After load balancing is configured on an AC, the AC uses a load balancing algorithm to determine whether a new STA (STA6 in Figure 5-7) can associate with an AP. The load balancing algorithm prevents new STAs from associating with heavily-loaded APs to reduce loads on these APs.

Load balancing can be implemented among APs only when the APs are connected to the same AC and all these APs can be discovered by a STA.

Figure 5-7  WLAN load balancing


Depending on whether a load balancing group needs to be manually created, load balancing is classified as either static or dynamic load balancing:
  • Static load balancing: APs providing the same services are manually added to a load balancing group. Each AP periodically reports STA association information to the AC, and the AC distributes user traffic among APs based on received STA association information. When a STA sends an association request, the AP uses a load balancing algorithm to determine whether to accept the association request. Static load balancing can be implemented when the following conditions are met:

    • APs in Figure 5-7 are single-band APs that support only one frequency band. If dual-band APs are used, traffic is load balanced among APs working on the same frequency band.
    • Each load balancing group supports a maximum of 16 APs.
  • Dynamic load balancing: A STA sends broadcast Probe Request frames to scan available APs. The APs that receive the Probe Request frames all report the received STA information to the AC. The AC adds these APs to a load balancing group and then uses a load balancing algorithm to determine whether to permit access from the STA. Static load balancing supports a limited number of group members, and all members must be manually added to the group and work on the same frequency band. Dynamic load balancing overcomes these limitations.

Depending on the load balancing algorithm used, load balancing is classified as either traffic-based load balancing or session-based load balancing:

The AC calculates the load percentage of each radio in a load balancing group using the formula:

Load percentage of a radio = (Number of associated STAs on the radio/Maximum number of STAs allowed on the radio) x 100%

The AC compares the load percentages of all of the radios in the load balancing group and obtains the smallest load percentage value. When a STA requests to associate with an AP radio, the AC calculates the difference between the radio's load percentage and the smallest load percentage value and compares the load difference with a specified threshold.

If the load difference is smaller than the threshold, the AC allows the STA to associate with the radio. If not, the AC rejects the association request of the STA. If the STA continues sending association requests to this AP, the AC allows the STA to associate with the AP when the number of consecutive association attempts of the STA exceeds the maximum number of rejection times configured on the AC.

In the formula, the value of Maximum number of STAs allowed on the radio depends on AP types, which can be obtained using the display ap-type { id type-id | type ap-type } command. Maximum number of STAs allowed on the radio refers to the value of the field Maximum station number in the command output.

The following example explains the implementation of static load balancing.

As shown in Figure 5-7, four STAs (STA1 to STA4) are online on AP1, and only STA5 is online on AP2. Assume that AP1 and AP2 each allow a maximum of 10 users, the start threshold for load balancing is set to 5, and the load difference threshold is set to 5%. Now, STA6 requests to associate with AP1.

STA6 is the sixth STA requesting to associate, and the number exceeds the start threshold; therefore, the AC uses a load balancing algorithm to determine whether to allow STA6 to associate.

According to the load percentage calculation formula, the load percentage of AP1's radio is 40% (4/10 x 100% = 40%), and the load percentage of AP2's radio is 10% (1/10 x 100% = 10%). Therefore, the smallest load percentage value is 10%. When STA6 associates with AP1, the load percentage of AP1 will reach 50% (5/10 x 100% = 50%). The difference between this load percentage and the smallest value is 40% (50% - 10% = 40%), larger than the load difference threshold (5%). Therefore, the AC determines that traffic is not evenly distributed between the two APs and prevents STA6 from associating with AP1.

Updated: 2019-08-07

Document ID: EDOC1100033726

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