Link Quality Operations

Link quality is a metric that defines the throughput quality over the data link between the 802.11 station and an access point (AP) or peer station. The 802.11 station measures the link quality as a value ranging from zero through 100, with 100 indicating the highest link quality.

This range of values is divided into 5 groups: [0-19], [20-39], [40-59], [60-79], and [80-100].

The link quality measurement is specific to the implementation by the independent hardware vendor (IHV). It is recommended that the 802.11 station represent the link quality value as the percentage of the highest possible throughput over the data link to the AP or peer station.

When measuring the link quality to an associated AP or peer station, the 802.11 station must use the following guidelines:

  • The 802.11 station measures link quality during periodic sampling periods. The length and intervals of the sampling periods are specific to the IHV implementation.

  • During the sampling period, the 802.11 station must measure the link quality to the associated AP or one peer station. If the 802.11 station is connected to an independent basic service set (IBSS) network, the station must determine the link quality for each associated peer station during different sampling periods.

    Note  IBSS (Ad hoc) and SoftAP are deprecated. Starting with Windows 8.1 and Windows Server 2012 R2, use Wi-Fi Direct.

  • The link quality must have a value of 100 when the 802.11 station can communicate with the AP or peer station during the sampling period at the highest possible throughput. A link quality of 100 is defined when all of the following occur during the sampling period:
    1. A unicast data packet is transmitted or received at the highest PHY data rate.
    2. Packets are sent without any retransmission.
    3. Packets are received without frame check sequence (FCS) errors.
    4. The 802.11 station does not perform any transmit deferrals due to a busy media.
  • The link quality must have a value of zero if the 802.11 station cannot transmit to or receive from the associated AP or peer station during the sampling period.

The miniport driver reports link quality through any of the following:

NDIS_STATUS_DOT11_LINK_QUALITY Status Indications

The miniport driver makes the Native 802.11 NDIS_STATUS_DOT11_LINK_QUALITY indication whenever the 802.11 station determines the link quality to an associated AP or peer station has changed significantly since the last NDIS_STATUS_DOT11_LINK_QUALITY indication.

The determination for when to make this indication is specific to the IHV implementation. However, the miniport driver should implement some threshold mechanism to avoid making frequent indications.

The miniport driver should make an NDIS_STATUS_DOT11_LINK_QUALITY indication whenever the link quality changes from one group to another. For example, the driver should make this indication if the link quality changes from a value of 39 to 45. Once again, the miniport driver must avoid making frequent indications and must implement a damping algorithm to avoid thrashing when the link quality quickly changes groups.

If the 802.11 station is connected to an IBSS network, the miniport driver must make NDIS_STATUS_DOT11_LINK_QUALITY indications so that the operating system can determine the overall quality of the IBSS network. The algorithm for calculating the link quality for each associate peer station is specific to the implementation of the IHV.

Note  IBSS (Ad hoc) and SoftAP are deprecated. Starting with Windows 8.1 and Windows Server 2012 R2, use Wi-Fi Direct.

For more information about Native 802.11 indications, see Native 802.11 Status Indications.

OID_DOT11_ENUM_BSS_LIST Query Requests

The miniport driver returns the link quality of each AP or peer station detected during the last scan operation when the OID_DOT11_ENUM_BSS_LIST object identifier (OID) is queried. The driver returns the link quality through the uLinkQuality member of each DOT11_BSS_ENTRY structure that represents an AP or peer station detected by the 802.11 station.

For the currently associated AP or peer stations detected during the scan operation, the miniport driver must determine the link quality value using the same criteria that was used to make an NDIS_STATUS_DOT11_LINK_QUALITY indication.

For each AP or peer station that the 802.11 station is not associated with, the determination of the link quality value is specific to the implementation of the IHV.

For more information about scan operations, see Native 802.11 Scan Operations.

 

 

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