Performing Explicit Scan Operations

The 802.11 station performs the explicit scan operation following an OID set request of OID_DOT11_SCAN_REQUEST. The parameters for the scan operation are defined through the DOT11_SCAN_REQUEST_V2 structure, which accompanies the set request.

Following the OID set request of the OID_DOT11_SCAN_REQUEST object identifier (OID), the miniport driver invokes the 802.11 station's media access control (MAC) layer management entity (MLME) MLME-SCAN.request service primitive. For more information about this service primitive, refer to Clause 6.3.3 of the IEEE 802.11-2012 standard.

When performing the implicit scan operation, the miniport driver and 802.11 station must follow these guidelines::

  • The miniport driver must initiate the explicit scan request by the 802.11 station and complete the OID set request of the OID_DOT11_SCAN_REQUEST OID. The miniport driver must not wait for the scan operation to finish before completing the set request. The miniport driver must return NDIS_STATUS_SUCCESS from its MiniportOidRequest function after initiating the scan operation.

  • The 802.11 station must cancel any implicit scan operations that it is currently performing. The miniport driver must restrict the 802.11 station from performing implicit scan operations while the explicit scan operation is in progress.

  • The 802.11 station must perform only one explicit scan operation for each OID set request of OID_DOT11_SCAN_REQUEST. The miniport driver cannot initiate another explicit scan operation by the 802.11 station until the operating system issues another OID set request of OID_DOT11_SCAN_REQUEST.

  • If the miniport driver is operating in Extensible Station (ExtSTA) mode, retain its basic service set (BSS) network cache. The miniport driver must only clear the cache when OID_DOT11_FLUSH_BSS_LIST is set.

  • If an explicit scan operation is in progress when a method request of OID_DOT11_RESET_REQUEST is made or the MiniportResetEx function is called, cancel the scan operation.

If the 802.11 station performs an active scan, it must transmit an 802.11 Probe Request frame on every channel that it scans. The 802.11 station prepares each Probe Request frame in the following way:

  • The BSS identifier (BSSID) field of the 802.11 MAC header is set to the value of the dot11BSSID member of the DOT11_SCAN_REQUEST_V2 structure. If this member has a value of zero, the BSSID field must be set to the wildcard BSSID value of 0xFFFFFFFFFFFF.

  • The SSID IE is set to an entry from the SSID list that is defined through the udot11SSIDsOffset and uNumOfdot11SSIDs members of the DOT11_SCAN_REQUEST_V2 structure. The 802.11 station must send a Probe Request frame for each SSID entry in the list.

  • If the list is empty (as indicated by a zero value for the uNumOfdot11SSIDs member), the station must send a single Probe Request frame and set the SSID IE to the wildcard zero-length SSID.

  • If the IEEE 802.11d dot11MultiDomainCapabilityEnabled management information base (MIB) object is set to TRUE and the bUseRequestIE member of the DOT11_SCAN_REQUEST_V2 structure is set to TRUE, the 802.11 station must prepare an 802.11d Request information element (IE) at the end of the Probe Request frame. The station must set the Length subfield of the IE to the value of the uNumOfRequestIDs member and must copy the list of Request IDs after the Length subfield. For more information about the dot11MultiDomainCapabilityEnabled MIB object, see OID_DOT11_MULTI_DOMAIN_CAPABILITY_ENABLED.

    The 802.11 station can add entries to the list of Request IDs, but must insert each Request ID in the Request IE in order of increasing element ID.

    For more information about the 802.1d Request IE and Request IDs, refer to clause 7.3.2.15 of the IEEE 802.11d-2001 standard.

  • If the DOT11_SCAN_REQUEST_V2 structure defines a list of information elements (IEs), the 802.11 station must copy the list of IEs to the end of the Probe Response frame. The list of IEs is defined through the uIEsOffset and uIEsLength members.

If the miniport driver's current packet filter has enabled the NDIS_PACKET_TYPE_802_11_DIRECTED_MGMT or NDIS_PACKET_TYPE_802_11_BROADCAST_MGMT filter settings, the miniport driver must call NdisMIndicateReceiveNetBufferLists for all 802.11 Beacon and Probe Response frames received by the 802.11 station. When performing the scan operation, the miniport driver must indicate these frames regardless of whether the 802.11 station received the frames as part of the scan operation. For more information about the 802.11 packet filter settings, see OID_GEN_CURRENT_PACKET_FILTER.

The 802.11 station completes the explicit scan operation when one of the following occurs:

  • The 802.11 station has scanned all specified channels for each PHY specified in the DOT11_SCAN_REQUEST_V2 structure.

  • The scan operation is canceled through a method request of OID_DOT11_RESET_REQUEST or a call to the miniport driver's MiniportResetEx function.

  • The scan operation is canceled whenever all PHYs that are used for the scan operation are turned off through either an OID set request of OID_DOT11_NIC_POWER_STATE or through some proprietary object identifier (OID) or hardware switch developed by the independent hardware vendor (IHV). In this situation, the miniport driver must set the ndisStatus member of the NDIS_STATUS_DOT11_SCAN_CONFIRM indication to NDIS_STATUS_UNSUPPORTED_MEDIA.

After the scan operation completes, the miniport driver must make a media-specific NDIS_STATUS_DOT11_SCAN_CONFIRM indication. The miniport driver must also make this indication when the scan operation is canceled through a method request of OID_DOT11_RESET_REQUEST or a call to the miniport driver's MiniportResetEx function.

If the miniport driver is operating in ExtSTA mode, a method request of OID_DOT11_ENUM_BSS_LIST can be made to return a list of BSS networks detected during the scan operation. The OID_DOT11_ENUM_BSS_LIST OID returns the cached list regardless of the scan state and should not return NDIS_STATUS_DOT11_MEDIA_IN_USE.

 

 

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