Controller Based WLANs

This article is to help understand the default values of 802.11ac parameters and also help understand the other configurable options.

802.11ac is a feature introduced in AOS 6.3. This feature is hardware specific and is supported by AP 225/ 224 to start off with.

Environment : 802.11ac deployments using default setting or where these parameters need to be tweaked.

Network Topology : Mobility Controller (AOS 6.3) ------ AP 225s )) (( Clients (802.11ac capable) + Non 802.11ac clients.

Below are the sections of config that hold important 802.11ac configuration parameters.

1. HT SSID Profile (mapped into ssid profile)
2. dot11a radio profile (mapped to ap group)

Below are the parameters related to 802.11ac in HT SSID Profile:

Below is the screen shot in dot11a-radio-profile, where Very High Throughput (802.11ac) is enabled for the radio.

Following are details for parameters in HT ssid profile:

Knobs in HT SSID profile:

• Very High Throughput enable - can be enabled or disabled on a per VAP basis using this knob in HT SSID profile. Enabled by default.
• 80 MHz channel usage - can be enabled or disabled on a per VAP basis using this knob in HT SSID profile. Enabled by default.
• VHT Supported MCS Map - Modulation and coding scheme decide on the QAM and convolution coding schemes to be used. MCS 8 and 9 are introduced with Modulation technique 256 QAM and 3/4 and 5/6 convolution coding respectively. MCS 9 (highest rate) is enabled for all the 3 spatial streams.
• VHT Explicit Transmit beamforming - Enables or disables TxBF in a SSID. This enabled by default. If clients support TxBF, then periodic measurements are taken to identify the phase change that needs to be done to the transmitted signal so that the signal on reception on the client will be maximum amplitude and all symbols are in-phase. Enabled by default.
• VHT TxBF Sounding Interval - The AP sends Null Data Packet Announcement, followed by Null Data packets and Beacon report from client on a periodic basis. This is done every 25 msec by default.
• Max VHT MPDU size - has been increased to11454 in VHT (also default).
• Max number of MSDUs in an AMSDU can be specified on a per WMM traffic class basis. The default value is 3 for all traffic classes except voice.

Knobs in dot11a radio profile:

• VHT enable - this is a radio level enable/ disable knob for VHT.
• Channel - ARM is allowed to define the channel. when statically assigning channels, this value is selected. using this we can specify the channel size and the primary channel. Example - 44E would represent 80 MHz channel with 44 as the primary channel. 44+ would represent 40 MHz channel with 44 as the primary channel. 44 would represent 20 MHz channel.