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WiFi: Beamformer support for 802.11ac (VHT at 5GHz) is broken
Closed, ResolvedPublicBUG

Description

Configuring 802.11ac requires setting VHT capability flags. Technically, this is done by providing a list of features to the vht_capab variable in hostapd.conf. However, there are multiple flags which incorporate numbers whose values might depend on the presence of other flags and further settings.

The beamformer/beamformee setting is one such family of flags. Here, the numbers X in both flags [BF-ANTENNA-X] and [SOUNDING-DIMENSION-X] depends on two conditions:

a. the overall antenna count, and
b. if the single-user-beamformer capability is activated. In this case, X needs to be set to the number of antennas minus one.

The Bug:

  1. When configuring 802.11ac without beamforming, VHT flags are being created as expected.

VHT capabilities:

vht {
    antenna-count 3
    center-channel-freq {
        freq-1 42
    }
    channel-set-width 1
    max-mpdu 11454
    max-mpdu-exp 3
}

Resulting VHT flags in hostapd.conf:

vht_capab=[MAX-MPDU-11454][MAX-A-MPDU-LEN-EXP-3]

  1. When configuring 802.11ac with multi-user-beamformer capabilities, VHT flags are rendered incomplete.

VHT capabilities:

vht {
    antenna-count 3
    beamform multi-user-beamformer
    center-channel-freq {
        freq-1 42
    }
    channel-set-width 1
    max-mpdu 11454
    max-mpdu-exp 3
}

Resulting VHT flags in hostapd.conf:

vht_capab=[BF-ANTENNA-3][SOUNDING-DIMENSION-3]

Expected result:

vht_capab=[MAX-MPDU-11454][MAX-A-MPDU-LEN-EXP-3][BF-ANTENNA-3][SOUNDING-DIMENSION-3][MU-BEAMFORMER]

  1. When configuring 802.11ac with multi-user-beamformer and single-user-beamformer capabilities, VHT flags are rendered incomplete and with wrong numbers.

VHT capabilities:

vht {
    antenna-count 3
    beamform multi-user-beamformer
    beamform single-user-beamformer
    center-channel-freq {
        freq-1 42
    }
    channel-set-width 1
    max-mpdu 11454
    max-mpdu-exp 3
}

Resulting VHT flags in hostapd.conf:

vht_capab=[BF-ANTENNA-3][SOUNDING-DIMENSION-3]

Expected result:

vht_capab=[MAX-MPDU-11454][MAX-A-MPDU-LEN-EXP-3][BF-ANTENNA-2][SOUNDING-DIMENSION-2][MU-BEAMFORMER][SU-BEAMFORMER]

Pull Request: https://github.com/vyos/vyos-1x/pull/3576

References:

Details

Version
VyOS 1.5-rolling-202405262024 and VyOS 1.4.0-epa3
Is it a breaking change?
Unspecified (possibly destroys the router)
Issue type
Bug (incorrect behavior)

Event Timeline

alainlamar updated the task description. (Show Details)
alainlamar updated the task description. (Show Details)
alainlamar changed Version from VyOS 1.5-rolling-202405262024 to VyOS 1.5-rolling-202405262024 and VyOS 1.4.0-epa3.
Viacheslav triaged this task as Normal priority.May 31 2024, 9:21 AM