7.3.1.1 Authentication Algorithm Number field
The Authentication Algorithm Number field indicates a single authentication algorithm. The length of the Authentication Algorithm Number field is 2 octets. The Authentication Algorithm Number field is illustrated in Figure 7-19. The following values are defined for authentication algorithm number:
Authentication algorithm number = 0: Open System
Authentication algorithm number = 1: Shared Key
All other values of authentication number are reserved.
7.3.1.2 Authentication Transaction Sequence Number field
The Authentication Transaction Sequence Number field indicates the current state of progress through a multistep transaction. The length of the Authentication Transaction Sequence Number field is 2 octets. The Authentication Transaction Sequence Number field is illustrated in Figure 7-20.
7.3.1.3 Beacon Interval field
The Beacon Interval field represents the number of time units (TUs) between target beacon transmission times (TBTTs). The length of the Beacon Interval field is 2 octets. The Beacon Interval field is illustrated in Figure 7-21.
7.3.1.4 Capability Information field
The Capability Information field contains a number of subfields that are used to indicate requested or
advertised optional capabilities.
The length of the Capability Information field is 2 octets. The format of the Capability Information field is defined in Figure 7-22. No subfield is supplied for ERP as a STA supports ERP operation if it includes all of the Clause 19 mandatory rates in its supported rate set.
Each Capability Information subfield is interpreted according to the management frame subtype, as defined in this subclause.
APs set the ESS subfield to 1 and the IBSS subfield to 0 within transmitted Beacon or Probe Response management frames. STAs within an IBSS set the ESS subfield to 0 and the IBSS subfield to 1 in transmitted Beacon or Probe Response management frames.
STAs set the QoS, CF-Pollable, and CF-Poll Request subfields in Association and Reassociation Request management frames according to Table 7-20.
APs set the CF-Pollable and CF-Poll Request subfields in Beacon and Probe Response management frames according to Table 7-21. A non-QoS AP sets the CF-Pollable and CF-Poll Request subfield values in Association Response and Reassociation Response management frames equal to the values in the last Beacon or Probe Response frame that it transmitted.
APs set the Privacy subfield to 1 within transmitted Beacon, Probe Response, Association Response, and Reassociation Response management frames if data confidentiality is required for all data frames exchanged within the BSS. If data confidentiality is not required, the Privacy subfield is set to 0.
In an RSNA, non-AP STAs in an ESS set the Privacy subfield to 0 within transmitted Association and Reassociation Request management frames. APs ignore the Privacy subfield within received Association and Reassociation Request management frames.
STAs within an ESS set the Privacy subfield to 1 in DLS Request and DLS Response frames if encryption is required for all data frames exchanged. If encryption is not required, the Privacy subfield is set to 0.
STAs within an IBSS set the Privacy subfield to 1 in transmitted Beacon or Probe Response management frames if data confidentiality is required for all data frames exchanged within the IBSS. If data confidentiality is not required, STAs in an IBSS set the Privacy subfield to 0 within these management frames.
STAs that include the RSN information element in Beacon and Probe Response frames shall set the Privacy subfield to 1 in any frame that includes the RSN information element.
APs (as well as STAs in IBSSs) shall set the Short Preamble subfield to 1 in transmitted Beacon, Probe Response, Association Response, and Reassociation Response MMPDUs to indicate that the use of the short preamble, as described in 18.2.2.2, is allowed within this BSS. To indicate that the use of the short preamble is not allowed, the Short Preamble subfield shall be set to 0 in Beacon, Probe Response, Association Response, and Reassociation Response MMPDUs transmitted within the BSS.
ERP STAs shall set the MIB variable dot11ShortPreambleOptionImplemented to true as all ERP devices support both long and short preamble formats.
STAs shall set the Short Preamble subfield to 1 in transmitted Association Request and Reassociation Request management frames and in DLS Request and DLS Response frames when the MIB attribute dot11ShortPreambleOptionImplemented is true. Otherwise, STAs shall set the Short Preamble subfield to 0.
APs (as well as STAs in IBSSs) shall set the PBCC subfield to 1 in transmitted Beacon, Probe Response, Association Response, and Reassociation Response management frames to indicate that the packet binary convolutional code (PBCC) modulation option, as described in 18.4.6.6 and 19.6, is allowed within this BSS. To indicate that the PBCC modulation option is not allowed, the PBCC subfield shall be set to 0.
STAs shall set the PBCC subfield to 1 in transmitted Association Request, Reassociation Request, DLS Request, and DLS Response frames when the MIB attribute dot11PBCCOption-Implemented is true. Otherwise, STAs shall set the PBCC subfield to 0.
Bit 7 of the Capabilities Information field shall be used to indicate Channel Agility capability by the High
Rate direct sequence spread spectrum (HR/DSSS) PHY or ERP. STAs shall set the Channel Agility bit to 1 when Channel Agility is in use and shall set it to 0 otherwise.
A STA shall set the Spectrum Management subfield in the Capability Information field to 1 if the STA’s dot11SpectrumManagementRequired is true; otherwise, it shall be set to 0.
STAs set the QoS subfield to 1 within the Capability Information field when the MIB attribute dot11Qos-
OptionImplemented is true and set it to 0 otherwise.
STAs shall set the Short Slot Time subfield to 1 in transmitted Association Request, Reassociation Request, DLS Request, and DLS Response MMPDUs when the MIB attribute dot11ShortSlotTime-
OptionImplemented and dot11ShortSlotTimeOptionEnabled are true. Otherwise, the STA shall set the Short Slot Time subfield to 0 in transmitted Association Request and Reassociation Request MMPDUs.
If a STA that does not support Short Slot Time associates, the AP shall use long slot time beginning at the first Beacon subsequent to the association of the long slot time STA. APs shall set the Short Slot Time subfield in transmitted Beacon, Probe Response, Association Response, and Reassociation Response MMPDUs to indicate the currently used slot time value within this BSS.
STAs shall set the MAC variable aSlotTime to the short slot value upon transmission or reception of Beacon, Probe Response, Association Response, and Reassociation Response MMPDUs from the BSS that the STA has joined or started and that have the short slot subfield set to 1 when the MIB attribute dot11ShortSlotTimeOptionImplemented is true. STAs shall set the MAC variable aSlotTime to the long slot value upon transmission or reception of Beacon, Probe Response, Association Response, and Reassociation
Response MMPDUs from the BSS that the STA has joined or started and that have the short slot subfield set to 0 when the MIB attribute dot11ShortSlotTimeOptionImplemented is true. STAs shall set the MAC variable aSlotTime to the long slot value at all times when the MIB attribute dot11ShortSlotTime- OptionImplemented is false. When the dot11ShortSlotTimeOptionImplemented MIB attribute is not present, or when the PHY supports only a single slot time value, then the STA shall set the MAC variable aSlotTime to the slot value appropriate for the attached PHY.
For IBSS, the Short Slot Time subfield shall be set to 0.
APs set the APSD subfield to 1 within the Capability Information field when the MIB attribute dot11APSDOptionImplemented is true and set it to 0 otherwise. STAs always set this subfield to 0.
APs as well as STAs in IBSSs shall set the DSSS-OFDM subfield to 1 in transmitted Beacon, Probe Response, Association Response, and Reassociation Response MMPDUs to indicate that the use of direct sequence spread spectrum with orthogonal frequency division multiplexing (DSSS-OFDM), as described in 19.7, is allowed within this BSS or by STAs that want to use DSSS-OFDM within an IBSS. To indicate that the use of DSSS-OFDM is not allowed, the DSSS-OFDM subfield shall be set to 0 in Beacon, Probe Response, Association Response, and Reassociation Response MMPDUs transmitted within the BSS.
STAs shall set the DSSS-OFDM subfield to 1 in transmitted Association Request, Reassociation Request, DLS Request, and DLS Response MMPDUs when the MIB attribute dot11DSSS-
OFDMOptionImplemented and dot11DSSS-OFDMOptionEnabled are true. Otherwise, STAs shall set the DSSS-OFDM subfield to 0 in transmitted Association Request and Reassociation Request MMPDUs.
STAs set the Delayed Block Ack subfield to 1 within the Capability Information field when the MIB attribute dot11DelayedBlockAckOptionImplemented is true and set it to 0 otherwise.
STAs set the Immediate Block Ack subfield to 1 within the Capability Information field when the MIB attribute dot11ImmediateBlockAckOptionImplemented is true and set it to 0 otherwise.
Unused bits of the Capability Information field are reserved.
7.3.1.5 Current AP Address field
The Current AP Address field is the MAC address of the AP with which the STA is currently associated. The length of the Current AP Address field is 6 octets. The Current AP Address field is illustrated in Figure 7-23.
7.3.1.6 Listen Interval field
The Listen Interval field is used to indicate to the AP how often a STA in power save mode wakes to listen to Beacon management frames. The value of this parameter is the STA’s Listen Interval parameter of the MLME-ASSOCIATE.request primitive and is expressed in units of Beacon Interval. The length of the Listen Interval field is 2 octets. The Listen Interval field is illustrated in Figure 7-24.
An AP may use the Listen Interval information in determining the lifetime of frames that it buffers for a STA.
7.3.1.7 Reason Code field
This Reason Code field is used to indicate the reason that an unsolicited notification management frame of type Disassociation, Deauthentication, DELTS, DELBA, or DLS Teardown was generated. The length of the Reason Code field is 2 octets. The Reason Code field is illustrated in Figure 7-25.
The reason codes are defined in Table 7-22.
7.3.1.8 AID field
The AID field is a value assigned by an AP during association that represents the 16-bit ID of a STA. The length of the AID field is 2 octets. The AID field is illustrated in Figure 7-26.
The value assigned as the AID is in the range 1–2007 and is placed in the 14 LSBs of the AID field, with the two MSBs of the AID field each set to 1 (see 7.1.3.2).
7.3.1.9 Status Code field
The Status Code field is used in a response management frame to indicate the success or failure of a requested operation. The length of the Status Code field is 2 octets. The Status Code field is illustrated in Figure 7-27.
If an operation is successful, then the status code is set to 0. If an operation results in failure, the status code indicates a failure cause. The failure cause codes are defined in Table 7-23.
7.3.1.10 Timestamp field
This field represents the value of the timing synchronization function (TSF) timer (see 11.1) of a frame’s source. The length of the Timestamp field is 8 octets. The Timestamp field is illustrated in Figure 7-28.
7.3.1.11 Action field
The Action field provides a mechanism for specifying extended management actions. The format of the Action field is shown in Figure 7-29.
The Category field is set to one of the nonreserved values shown in Table 7-24. Action frames of a given category are referred to as <category name> Action frames. For example, frames in the QoS category are called QoS Action frames.
If a STA receives a unicast Action frame with an unrecognized Category field or some other syntactic error and the MSB of the Category field set to 0, then the STA shall return the Action frame to the source without change except that the MSB of the Category field is set to 1.
The Action Details field contains the details of the action. The details of the actions allowed in each category are described in the appropriate subclause referenced in Table 7-24.
Details on the additional fixed fields used within the Action field are given in 7.3.2.12 through 7.2.1.17.
7.3.1.12 Dialog Token field
The Dialog Token field is used for matching action responses with action requests when there are multiple, concurrent action requests. The length of the Dialog Token field is 1 octet. The Dialog Token field is illustrated in Figure 7-30. The value of the Dialog Token field in a request Action frame is arbitrary. The value of the Dialog Token field in a response frame is copied from each request Action frame.
7.3.1.13 DLS Timeout Value field
The DLS Timeout Value field is used in the DLS Request frame to indicate the timeout value for the direct link. The length of the DLS Timeout Value field is 2 octets. The DLS Timeout Value field is illustrated in Figure 7-31.
The DLS Timeout Value field contains the duration, in seconds, after which the direct link is terminated, if there are no frame exchanges within this duration with the peer. A value of 0 implies that the direct link is never to be terminated based on a timeout.
7.3.1.14 Block Ack Parameter Set field
The Block Ack Parameter Set field is used in ADDBA frames to signal the parameters for setting up a Block Ack. The length of the Block Ack Parameter Set field is 2 octets. The Block Ack Parameter Set field is illustrated in Figure 7-32.
The Block Ack Policy subfield is set to 1 for immediate Block Ack and 0 for delayed Block Ack. The Block Ack Policy subfield value assigned by the originator of the QoS data frames is advisory.
The TID subfield contains the value of the TC or TS for which the Block Ack is being requested.
The Buffer Size subfield indicates the number of buffers of size 2304 octets available for this particular TID.18
In an ADDBA Request frame, the Buffer Size subfield is intended to provide guidance for the frame
receiver to decide its reordering buffer size and is advisory only. If the Buffer Size subfield is set to 0, it implies that the originator of the Block Ack has no information to specify its value.
In an ADDBA Response frame, when the Status Code field is set to 0, the Buffer Size subfield is set to a value of at least 1.
7.3.1.15 Block Ack Timeout Value field
The Block Ack Timeout Value field is used in the ADDBA Request frame to indicate the timeout value for Block Ack. The length of the Block Ack Timeout Value field is 2 octets. The Block Ack Timeout Value field is illustrated in Figure 7-33.
The Block Ack Timeout Value field contains the duration, in TUs, after which the Block Ack setup is terminated, if there are no frame exchanges (see 11.5.3) within this duration using this Block Ack agreement. A value of 0 disables the timeout.
18For buffer size, the recipient of data advertises a single scalar number that is the number of maximum-size fragment buffers available. Every buffered MPDU will consume one of these buffers regardless of whether the frame contains a whole MSDU or a fragment of an MSDU. In other words, ten maximum-size unfragmented MSDUs will consume the same amount of buffer space at the recipient as 10 small fragments.
7.3.1.16 DELBA Parameter Set field
The DELBA Parameter Set field is used in a DELBA frame to terminate an already setup Block Ack.The length of the DELBA Parameters field is 2 octets. The DELBA Parameters field is illustrated in Figure 7-34.
The Initiator subfield indicates if the originator or the recipient of the data is sending this frame. It is set to 1 to indicate the originator and is set to 0 to indicate the recipient. The TID subfield indicates the TSID or the UP for which the Block Ack has been originally set up.
7.3.1.17 QoS Info field
The QoS Info field is 1 octet in length and contains capability information bits. The contents of the field are dependent on whether the STA is an AP or a non-AP STA.
The format of the QoS Info field, when sent by the AP, is defined in Figure 7-35.
In the Beacon frame, the EDCA Parameter Set Update Count subfield is initially set by the AP to 0 and is incremented every time any of the AC parameters changes.
APs set the Q-Ack subfield to 1 when the MIB attribute dot11QAckOptionImplemented is true and set it to 0 otherwise.
APs set the Queue Request subfield to 1 if they can process a nonzero Queue Size subfield in the QoS Control field in QoS data frames and set it to 0 otherwise.
APs set the TXOP Request subfield to 1 if they can process a nonzero TXOP Duration Requested subfield in the QoS Control field in QoS data frames and set it to 0 otherwise.
The format of the QoS Info field, when sent by the non-AP STA, is defined in Figure 7-36.
Each of the ACs U-APSD Flag subfields is 1 bit in length and set to 1 in (Re)Association Request frames to indicate that the corresponding AC (AC_BE, AC_BK, AC_VI, or AC_VO) is both trigger-enabled and delivery-enabled. It is set to 0 in (Re)Association Request frames to indicate that the corresponding AC is neither trigger-enabled nor delivery-enabled. A TSPEC as described in 11.2.1.4 is to be used to make a particular AC exclusively either trigger-enabled or delivery-enabled. These subfields are always set to 0 when the APSD subfield in the Capability Information field is set to 0.
Non-AP STAs set the Q-Ack subfield to 1 when the MIB attribute dot11QAckOptionImplemented is true and set it to 0 otherwise.
The Max SP Length subfield is 2 bits in length and indicates the maximum number of total buffered MSDUs and MMPDUs the AP may deliver to a non-AP STA during any SP triggered by the non-AP STA. This subfield is reserved when the APSD subfield in the Capability Information field is set to 0. This subfield is also reserved when all four U-APSD flags are set to 0. If the APSD subfield in the Capability Information field is set to 1 and at least one of the four U-APSD flags is set to 1, the settings of the values in the Max SP Length subfield are defined in Table 7-25.
Non-AP STAs set the More Data Ack subfield to 1 to indicate that they can process ACK frames with the More Data bit in the Frame Control field set to 1 and will remain in the Awake state. Non-AP STAs set the More Data Ack subfield to 0 otherwise. For APs, the More Data Ack subfield is reserved.
7.3.2 Information elements
Elements are defined to have a common general format consisting of a 1 octet Element ID field, a 1 octet length field, and a variable-length element-specific information field. Each element is assigned a unique Element ID as defined in this standard. The Length field specifies the number of octets in the Information field. See Figure 7-37.
The set of valid elements is defined in Table 7-26.
A STA that encounters an unknown or reserved element ID value in a management frame received without error shall ignore that element and shall parse any remaining management frame body for additional information elements with recognizable element ID values. The frame body components specified for many management subtypes result in elements ordered by ascending element ID.
7.3.2.1 SSID element
The SSID element indicates the identity of an ESS or IBSS. See Figure 7-38.
The length of the SSID information field is between 0 and 32 octets. A 0 length information field is used within Probe Request management frames to indicate the wildcard SSID.
7.3.2.2 Supported Rates element
The Supported Rates element specifies up to eight rates in the Operational-Rate-Set parameter, as described in the MLME-JOIN.request and MLME-START.request primitives. The information field is encoded as 1 to 8 octets, where each octet describes a single Supported Rate. If the number of rates in the Operational Rate Set exceeds eight, then an Extended Supported Rate element shall be generated to specify the remaining supported rates. The use of the Extended Supported Rates element is optional otherwise.
Within Beacon, Probe Response, Association Response, and Reassociation Response management frames, each Supported Rate contained in the BSSBasicRateSet parameter is encoded as an octet with the MSB (bit 7) set to 1, and bits 6 through 0 are set to the data rate, if necessary rounded up to the next 500kb/s, in units of 500 kb/s. For example, a 2.25 Mb/s rate contained in the BSSBasicRateSet parameter is encoded as X'85'. Rates not contained in the BSSBasicRateSet parameter are encoded with the MSB set to 0, and bits 6 through 0 are set to the appropriate value from the valid range column of the DATA_RATE row of the table in 10.4.4.2 (e.g., a 2 Mb/s rate not contained in the BSSBasicRateSet parameter is encoded as X'04'). The MSB of each Supported Rate octet in other management frame types is ignored by receiving STAs.
The Supported Rate information in Beacon and Probe Response management frames is delivered to the management entity in a STA via the BSSBasicRateSet parameter in the MLME-SCAN.confirm primitive. It is used by the management entity in a STA to avoid associating with a BSS if the STA cannot receive and transmit all the data rates in the BSSBasicRateSet parameter (see Figure 7-39).
If the DSSS-OFDM bit is set to 1 in the transmitted Capability Information field of an MMPDU, then any supported rates transmitted in that frame that include rates that are common to both DSSS-OFDM and ERP- OFDM shall be interpreted by receiving and transmitting STA to indicate support for both DSSS-OFDM and ERP-OFDM at the indicated rate. However, if any of those rates are indicated as basic (a rate in the BSSBasicRateSet parameter), then the basic rate designation shall be interpreted by receiving and transmitting STA to apply only for the ERP-OFDM modulation and rate. If the PBCC bit is set to 1 in the transmitted capability field of an MMPDU, then any supported rates transmitted in that frame that include rates that are common to both PBCC and CCK shall be interpreted by receiving and transmitting STA to indicate support for both PBCC and CCK at the indicated rate. However, if any of those rates are indicated as basic, then the basic rate designation shall be interpreted by receiving and transmitting STA to apply only for the CCK modulation and rate. That is, if the rate is indicated as basic, the basic designation does not apply to DSSS-OFDM, PBCC, or ERP-PBCC.
7.3.2.3 FH Parameter Set element
The FH Parameter Set element contains the set of parameters necessary to allow synchronization for STAs using an FH PHY. The information field contains Dwell Time, Hop Set, Hop Pattern, and Hop Index parameters. The total length of the information field is 5 octets. See Figure 7-40.
The Dwell Time field is 2 octets in length and contains the dwell time in TU.
The Hop Set field identifies the current set (dot11CurrentSet) of hop patterns and is a single octet.
The Hop Pattern field identifies the current pattern (dot11CurrentPattern) within a set of hop patterns and is a single octet.
The Hop Index field selects the current index (dot11CurrentIndex) within a pattern and is a single octet.
The description of the attributes used in this subclause can be found in 14.8.2.
7.3.2.4 DS Parameter Set element
The DS Parameter Set element contains information to allow channel number identification for STAs using a DSSS PHY. The information field contains a single parameter containing the dot11CurrentChannel- Number (see 15.4.6.2 for values). The length of the dot11CurrentChannelNumber parameter is 1 octet. See Figure 7-41.
7.3.2.5 CF Parameter Set element
The CF Parameter Set element contains the set of parameters necessary to support the PCF. The information field contains the CFPCount, CFPPeriod, CFPMaxDuration, and CFPDurRemaining fields. The total length of the information field is 6 octets. See Figure 7-42.
CFPCount indicates how many delivery traffic indication messages (DTIMs) (including the current frame) appear before the next CFP start. A CFPCount of 0 indicates that the current DTIM marks the start of the CFP.
CFPPeriod indicates the number of DTIM intervals between the start of CFPs. The value is an integral
number of DTIM intervals.
CFPMaxDuration indicates the maximum duration, in TU, of the CFP that may be generated by this PCF. This value is used by STAs to set their NAV at the TBTT of Beacon frames that begin CFPs.
CFPDurRemaining indicates the maximum time, in TU, remaining in the present CFP, and is set to 0 in CFP Parameter elements of Beacon frames transmitted during the CP. The value of CFPDurRemaining is referenced to the immediately previous TBTT. This value is used by all STAs to update their NAVs during CFPs.
7.3.2.6 TIM
The TIM element contains four fields: DTIM Count, DTIM Period, Bitmap Control, and Partial Virtual
Bitmap. See Figure 7-43.
The Length field for this element indicates the length of the information field, which is constrained as
described below.
The DTIM Count field indicates how many Beacon frames (including the current frame) appear before the next DTIM. A DTIM Count of 0 indicates that the current TIM is a DTIM. The DTIM count field is a
single octet.
The DTIM Period field indicates the number of beacon intervals between successive DTIMs. If all TIMs are DTIMs, the DTIM Period field has the value 1. The DTIM Period value 0 is reserved. The DTIM period field is a single octet.
The Bitmap Control field is a single octet. Bit 0 of the field contains the Traffic Indicator bit associated with Association ID 0. This bit is set to 1 in TIM elements with a value of 0 in the DTIM Count field when one or more broadcast or multicast frames are buffered at the AP. The remaining 7 bits of the field form the Bitmap Offset.
The traffic-indication virtual bitmap, maintained by the AP that generates a TIM, consists of 2008 bits, and is organized into 251 octets such that bit number N (0 ≤ N ≤ 2007) in the bitmap corresponds to bit number (N mod 8) in octet number .N / 8. where the low-order bit of each octet is bit number 0, and the high order bit is bit number 7. Each bit in the traffic-indication virtual bitmap corresponds to traffic buffered for a specific STA within the BSS that the AP is prepared to deliver at the time the Beacon frame is transmitted. Bit number N is 0 if there are no directed frames buffered for the STA whose Association ID is N. If any directed frames for that STA are buffered and the AP is prepared to deliver them, bit number N in the trafficindication virtual bitmap is 1. A PC may decline to set bits in the TIM for CF-Pollable STAs it does not intend to poll (see 11.2.1.6).
The Partial Virtual Bitmap field consists of octets numbered N1 through N2 of the traffic indication virtual bitmap, where N1 is the largest even number such that bits numbered 1 through (N1 × 8) – 1 in the bitmap are all 0 and N2 is the smallest number such that bits numbered (N2 + 1) × 8 through 2007 in the bitmap are all 0. In this case, the Bitmap Offset subfield value contains the number .N1/2., and the Length field is set to (N2 – N1) + 4.
In the event that all bits other than bit 0 in the virtual bitmap are 0, the Partial Virtual Bitmap field is
encoded as a single octet equal to 0, the Bitmap Offset subfield is 0, and the Length field is 4.
7.3.2.7 IBSS Parameter Set element
The IBSS Parameter Set element contains the set of parameters necessary to support an IBSS. The
information field contains the ATIM Window parameter. See Figure 7-44.
The ATIM Window field is 2 octets in length and contains the ATIM Window length in TU.
7.3.2.8 Challenge Text element
The Challenge Text element contains the challenge text within Authentication exchanges. The element information field length is dependent upon the authentication algorithm and the transaction sequence number as specified in 8.2.2.2. See Figure 7-45.
7.3.2.9 Country information element
The Country information element contains the information required to allow a STA to identify the regulatory domain in which the STA is located and to configure its PHY for operation in that regulatory domain. The format of this information element shall be as shown in Figure 7-46.
The element ID for this information element shall be 7. The length of the information element is variable, as the element may contain more than one triplet comprising the First Channel Number, Number of Channels, and Maximum Transmit Power Level fields and referred to as subband triplets. Alternatively, where dot11RegulatoryClassesRequired is true and the First Channel Number/Regulatory Extension Identifier octet has a positive integer value of 201 or greater, then that triplet comprises the Regulatory Extension Identifier, Regulatory Class, and Coverage Class fields. Together they are referred to as a regulatory triplet. The minimum length of the information element is 8 octets.
The Country String field of the element shall be 3 octets in length. The AP shall set this field to the value contained in the dot11CountryString attribute before transmission in a Beacon or Probe Response frame. Upon reception of this element, a STA shall set the value of the dot11CountryString to the value contained in this field.
The First Channel Number/Regulatory Extension Identifier field shall be 1 octet in length. If the field has a positive integer value less than 201, then it shall contain a positive integer value that indicates the lowest channel number in the subband described in this information element. The group of channels described by each pair of the First Channel Number and the Number of Channels fields shall not have overlapping channel identifiers. [For example, the pairs (2,4) and (5,2) overlap and shall not be used together.] The First Channel Numbers shall be monotonically increasing where dot11RegulatoryClassesRequired is not true.
Where dot11RegulatoryClassesRequired is true, consecutive subband triplets following a regulatory triplet shall have monotonically increasing First Channel Number fields.
The Number of Channels field of the subelement shall be 1 octet in length.
The Maximum Transmit Power Level field is a signed number and shall be 1 octet in length. It shall indicate the maximum power, in dBm, allowed to be transmitted. As the method of measurement for maximum transmit power level differs by regulatory domain, the value in this field shall be interpreted according to the regulations applicable for the domain identified by the Country String.
A regulatory class is an index into a set of values for radio equipment sets of rules. The Regulatory Class field shall be 1 octet in length.
A coverage class is an index into a set of values for aAirPropagationTime. The Coverage Class field shall be 1 octet in length.
The Coverage Class field of the regulatory triplet specifies the aAirPropagationTime characteristic used in BSS operation, as shown in Table 7-27. The characteristic aAirPropagationTime describes variations in actual propagation time that are accounted for in a BSS and, together with maximum transmit power level, allow control of BSS diameter.
Table 7-27—Coverage Class field parameters
The Pad field is 0 or 1 octet in length. The length of the Country information element shall be evenly divisible by 2. The Pad shall be used to add a single octet to the element if the length is not evenly divisible by 2. The value of the Pad field shall be 0.
7.3.2.10 Hopping Pattern Parameters information element
The Hopping Pattern Parameters information element contains the information necessary to allow a STA to calculate the code family using the hyperbolic congruence code (HCC) and extended HCC (EHCC) algorithms. See 9.8.2.1 for a description of the HCC and EHCC algorithms. The format of this information element shall be as shown in Figure 7-47.
The Element ID of this information element shall be 8. The length of this element is 4 octets.
The Prime Radix field of this element shall indicate the value to be used as the prime radix (N) in the HCC and EHCC algorithms. The value of this field shall be a positive integer. The size of this field is 1 octet.
The Number of Channels field of this element shall indicate the value to be used as the maximum for the family index (a) in the HCC and EHCC algorithms. The value of this field shall be a positive integer and shall not be less than the prime radix minus 3 (N–3). The size of this field is 1 octet.
7.3.2.11 Hopping Pattern Table information element
The Hopping Pattern Table information element contains the information necessary for an FH implementation to be able to create the hopping sequences necessary to operate in the regulatory domain in which the information element was received. The format of the information element shall be as shown in Figure 7-48.
The Element ID of this information element shall be 9. The information element is variable in length. The length of the information element is indicated by the Length field.
The Flag field indicates that a Random Table is present when the value is 1. When the flag value is 0, it indicates that a Random Table is not present and that the hop index method is to be used to determine the hopping sequence. The size of this field is 1 octet.
The Number of Sets field indicates the total number of sets within the hopping patterns. The size of this field is 1 octet.
The Modulus and Offset fields indicate the values to be used in the equations to create a hopping sequence from the Random Table information. The size of these fields are each 1 octet.
The Random Table field is a variable length field. It is a vector of single octet values that indicate the random sequence to be followed during a hopping sequence. The size of the Random Table field is found by subtracting 4 from the value of the Length field of this element.
Two equations are used to create a hopping sequence from the information in the Frequency Hopping information element and the Hopping Pattern Table information element. Equation (7-1), the Random Table Method, shall be used when the value of the Flag field of the Hopping Pattern Table information element is 1. Equation (7-2), the Hop Index Method, shall be used when the value of the Flag field of the Hopping Pattern Table information element is 0.
The values of i, p, and s are found in the Frequency Hopping information element. The values of m, n, and q are found in the Hopping Pattern Table information element.
7.3.2.12 Request information element
This element is placed in a Probe Request frame to request that the responding STA include the requested information in the Probe Response frame. The format of the information element shall be as shown in Figure 7-49.
The Element ID of this information element shall be 10. The information element is variable in length. The length of the information element is indicated in the Length field.
The Requested Element IDs are the list of elements that are to be included in the responding STA’s Probe Response frame. The Requested Element IDs shall be listed in order of increasing element ID.
A STA shall return only those information elements that it supports. In an improperly formed Request information element, a STA may ignore the first information element requested that is not ordered properly and all subsequent information elements requested. In the probe response frame, the STA shall return the requested information elements in the same order requested in the Request information element of the probe request frame.
7.3.2.13 ERP Information element
The ERP Information element contains information on the presence of Clause 15 or Clause 18 STAs in the BSS that are not capable of Clause 19 (ERP-OFDM) data rates. It also contains the requirement of the ERP Information element sender (AP in a BSS or STA in an IBSS) as to the use of protection mechanisms to optimize BSS performance and as to the use of long or short Barker preambles. See Figure 7-50 for a definition of the frame element.
If one or more NonERP STAs are associated in the BSS, the Use_Protection bit shall be set to 1 in
transmitted ERP Information elements.
In an IBSS, the setting of the Use_Protection bit is left to the STA. In an IBSS, there is no uniform concept of association; therefore, a typical algorithm for setting the Use_Protection bit will take into account the traffic pattern and history on the network. If a member of an IBSS detects one or more NonERP STAs that are members of the same IBSS or receives a Beacon from a member of the same IBSS with the Use_Protection bit set to 1, then the Use_Protection bit should be set to 1 in the ERP Information Element of transmitted Beacon and Probe Response frames.
The NonERP_Present bit shall be set to 1 when a NonERP STA is associated with the BSS. Examples of when the NonERP present bit may additionally be set to 1 include, but are not limited to, when
a) A NonERP infrastructure or independent BSS is overlapping (a NonERP BSS may be detected by
the reception of a Beacon where the supported rates contain only Clause 15 or Clause 18 rates).
b) In an IBSS, if a Beacon frame is received from one of the IBSS participants where the supported rate set contains only Clause 15 or Clause 18 rates.
c) A management frame (excluding a Probe Request) is received where the supported rate set includes only Clause 15 or Clause 18 rates.
ERP APs and ERP STAs shall invoke the use of a protection mechanism after transmission or reception of the Use_Protection bit with a value of 1 in an MMPDU to or from the BSS that the ERP AP or ERP STA has joined or started. ERP APs and ERP STAs may additionally invoke protection mechanism use at other times. ERP APs and ERP STAs may disable protection mechanism use after transmission or reception of the Use_Protection bit with a value of 0 in an MMPDU to or from the BSS that the ERP AP or ERP STA has joined or started.
When there are no NonERP STAs associated with the BSS and the ERP Information Element sender’s dot11ShortPreambleOptionImplemented MIB variable is set to true, then the Barker_Preamble_Mode bit may be set to 0. The Barker_Preamble_Mode bit shall be set to 1 by the ERP Information Element sender if one or more associated NonERP STAs are not short preamble capable as indicated in their Capability Information field, or if the ERP Information Element senders dot11ShortPreambleOptionImplemented MIB variable is set to false.
If a member of an IBSS detects one or more nonshort-preamble-capable STAs that are members of the same IBSS, then the Barker_Preamble_Mode bit should be set to 1 in the transmitted ERP Information Element.
ERP APs and ERP STAs shall use long preambles when transmitting Clause 15, Clause 18, and Clause 19 frames after transmission or reception of an ERP Information Element with a Barker_Preamble_Mode value of 1 in an MMPDU to or from the BSS that the ERP AP or ERP STA has joined or started, regardless of the value of the short preamble capability bit from the same received or transmitted MMPDU that contained the ERP Information Element. ERP APs and ERP STAs may additionally use long preambles when transmitting Clause 15, Clause 18, and Clause 19 frames at other times. ERP APs and ERP STAs may use short preambles when transmitting Clause 15, Clause 18, and Clause 19 frames after transmission or reception of an ERP Information Element with a Barker_Preamble_Mode value of 0 in an MMPDU to or from the BSS that the ERP AP or ERP STA has joined or started, regardless of the value of the short preamble capability bit from the same received or transmitted MMPDU. NonERP STAs and NonERP APs may also follow the rules given in this paragraph.
Recommended behavior for setting the Use_Protection bit is contained in 9.13.
The ERP Information element shall have the form shown in Figure 7-50.
Bits r3 through r7 are reserved, set to 0, and ignored on reception. Note that the length of this element is flexible and may be expanded in the future.
7.3.2.14 Extended Supported Rates element
The Extended Supported Rates element specifies the rates in the OperationalRateSet as described in the MLME_JOIN.request and MLME_START.request primitives that are not carried in the Supported Rates element. The information field is encoded as 1 to 255 octets where each octet describes a single supported rate.
Within Beacon, Probe Response, Association Response, and Reassociation Response management frames, each supported rate contained in the BSSBasicRateSet parameter, as defined in 10.3.10.1, is encoded as an octet with the MSB (bit 7) set to 1 and bits 6 through 0 are set to the appropriate value from the valid range column of the DATA_RATE row of the table in 10.4.4.2 (e.g., a 1 Mb/s rate contained in the BSSBasicRateSet parameter is encoded as X'82'). Rates not contained in the BSSBasicRateSet parameter are encoded with the MSB set to 0, and bits 6 through 0 are set to the appropriate value from the valid range column of the DATA_RATE row of the table in 10.4.4.2 (e.g., a 2 Mb/s rate not contained in the BSSBasicRateSet parameter is encoded as X'04'). The MSB of each octet in the Extended Supported Rate element in other management frame types is ignored by receiving STAs.
Extended Supported Rate information in Beacon and Probe Response management frames is used by STAs in order to avoid associating with a BSS if they do not support all the data rates in the BSSBasicRateSet parameter.
For STAs supporting eight or fewer data rates, this element is optional for inclusion in all of the frame types that include the supported rates element. For STAs supporting more than eight data rates, this element shall be included in all of the frame types that include the supported rates element.
The Extended Supported Rates element has the format shown in Figure 7-51.
7.3.2.15 Power Constraint element
The Power Constraint element contains the information necessary to allow a STA to determine the local maximum transmit power in the current channel. The format of the Power Constraint element is shown in Figure 7-52.
The Length field shall be set to 1.
The Local Power Constraint field shall be set to a value that allows the mitigation requirements to be satisfied in the current channel. The field is coded as an unsigned integer in units of decibels relative to 1mW. The local maximum transmit power for a channel is thus defined as the maximum transmit power level specified for the channel in the Country element minus the local power constraint specified for the channel (from the MIB) in the Power Constraint element.
The Power Constraint element is included in Beacon frames, as described in 7.2.3.1, and Probe Response frames, as described in 7.2.3.9. The use of Power Constraint elements is described in 11.8.2.
7.3.2.16 Power Capability element
The Power Capability element specifies the minimum and maximum transmit powers with which a STA is capable of transmitting in the current channel. The format of the Power Capability element is shown in Figure 7-53.
The Length field shall be set to 2.
The Minimum Transmit Power Capability field shall be set to the nominal minimum transmit power with which the STA is capable of transmitting in the current channel, with a tolerance ± 5 dB. The field is coded as a signed integer in units of decibels relative to 1 mW.
The Maximum Transmit Power Capability field shall be set to the nominal maximum transmit power with which the STA is capable of transmitting in the current channel, with a tolerance ± 5 dB. The field is coded as a signed integer in units of decibels relative to 1 mW.
The Power Capability element is included in Association Request frames, as described in 7.2.3.4, and
Reassociation Request frames, as described in 7.2.3.6. The use of Power Capability elements is described in 11.8.1.
7.3.2.17 TPC Request element
The TPC Request element contains a request for a STA to report transmit power and link margin information using a TPC Report element. The format of the TPC Request element is shown in Figure 7-54.
Figure 7-54—TPC Request element format
The Length field shall be set to 0.
The TPC Request element is included in TPC Request frames, as described in 7.4.1.3. The use of TPC Request elements and frames is described in 11.8.4.
7.3.2.18 TPC Report element
The TPC Report element contains transmit power and link margin information sent in response to a TPC Request element. A TPC Report element is included in a Beacon frame or Probe Response frame without a corresponding request. The format of the TPC Report element is shown in Figure 7-55.
The Length field shall be set to 2.
The Transmit Power field shall be set to the transmit power used to transmit the frame containing the TPC Report element. The field is coded as a signed integer in units of decibels relative to 1 mW. The maximum tolerance for the transmit power value reported in the TPC Response element shall be ± 5 dB. This tolerance is defined as the difference, in decibels, between the reported power value and the actual EIRP of the STA (measured when transmitting 1500 octet frames).
The Link Margin field contains the link margin at the time and for the rate at which the frame containing the TPC Request element was received. The field is coded as a signed integer in units of decibels. The Link Margin field shall be set to 0 and shall be ignored when a TPC Report element is included in a Beacon frame or Probe Response frame. The measurement method of Link Margin is beyond the scope of this standard.
The TPC Report element is included in TPC Report frames, as described in 7.4.1.4; Beacon frames, as described in 7.2.3.1; and Probe Response frames, as described in 7.2.3.9. The use of TPC Report elements and frames is described in 11.8.4.
7.3.2.19 Supported Channels element
The Supported Channels element contains a list of channel subbands (from those channels defined in 17.3.8.3.3) in which a STA is capable of operating. The format of the Supported Channels element is shown in Figure 7-56.
The Length field is variable and depends on the number of subbands, defined by a First Channel Number– Number of Channels pair, that are included in the element.
The First Channel Number field shall be set to the first channel (as defined in 17.3.8.3.3) in a subband of supported channels.
The Number of Channels field shall be set to the number of channels in a subband of supported channels.
The Supported Channels element is included in Association Request frames, as described in 7.2.3.4, and Reassociation Request frames, as described in 7.2.3.6. The use of the Supported Channels element is described in 11.9.1 and 11.9.7.
7.3.2.20 Channel Switch Announcement element
The Channel Switch Announcement element is used by an AP in a BSS or a STA in an IBSS to advertise when it is changing to a new channel and the channel number of the new channel. The format of the Channel Switch Announcement element is shown in Figure 7-57.
The Length field shall be set to 3.
The Channel Switch Mode field indicates any restrictions on transmission until a channel switch. An AP in a BSS or a STA in an IBSS shall set the Channel Switch Mode field to either 0 or 1 on transmission. A Channel Switch Mode set to 1 means that the STA in a BSS to which the frame containing the element is addressed shall transmit no further frames within the BSS until the scheduled channel switch. A STA in an IBSS may treat a Channel Switch Mode field set to 1 as advisory. A Channel Switch Mode set to 0 does not impose any requirement on the receiving STA.
The New Channel Number field shall be set to the number of the channel to which the STA is moving (as defined in 17.3.8.3.3).
The Channel Switch Count field either shall be set to the number of TBTTs until the STA sending the Channel Switch Announcement element switches to the new channel or shall be set to 0. A value of 1 indicates that the switch shall occur immediately before the next TBTT. A value of 0 indicates that the switch shall occur at any time after the frame containing the element is transmitted.
The Channel Switch Announcement element is included in Channel Switch Announcement frames, as described in 7.4.1.5, and may be included in Beacon frames, as described in 7.2.3.1, and Probe Response frames, as described in 7.2.3.9. The use of Channel Switch Announcement elements and frames is described in 11.9.7.
7.3.2.21 Measurement Request element
The Measurement Request element contains a request that the receiving STA undertake the specified measurement action. The format of the Measurement Request element is shown in Figure 7-58.
The Length field is variable and depends on the length of the Measurement Request field. The minimum value of the Length field is 3 (based on a minimum length for the Measurement Request field of 0 octets).
The Measurement Token shall be set to a nonzero number that is unique among the Measurement Request elements in a particular Measurement Request frame.
The Measurement Request Mode field (shown in Figure 7-59) is a bit field with the following bits defined:
— Enable bit (bit 1) indicates whether this element is used to request the destination STA to enable or disable the sending of measurement requests and autonomous measurement reports of a specified type to this STA. The Enable bit shall be set to 1 when the Request bit and Report bit are valid. The Enable bit shall be set to 0 when the Request bit and Report bit are invalid.
— Request bit (bit 2) indicates whether the STA receiving the request shall enable or disable measurement requests of the type specified in the Measurement Type field. The Request bit shall be set to 1 when enabling a measurement request. The Request bit shall be set to 0 when disabling a measurement request or when the Request bit is invalid (i.e., when the Enable bit is set to 0 or when the Measurement Type field contains a reserved measurement request type value).
— Report bit (bit 3) indicates whether the STA receiving the request shall enable or disable autonomous measurement reports of the type corresponding to the measurement report specified in the Measurement Type field. The Report bit shall be set to 1 when enabling an autonomous measurement report. The Report bit shall be set to 0 when disabling an autonomous measurement
report or when the Report bit is invalid (i.e., when the Enable bit is set to 0 or when the
Measurement Type field contains a reserved measurement report type value).
— All other bits are reserved and shall be set to 0.
The use of the Enable, Request, and Report bits is also summarized in Table 7-28. See 11.9.6 for the
description of how a STA shall handle requests to enable or disable measurement requests and autonomous
reports.
The Measurement Type field shall be set to a number that identifies a measurement request or a measurement report. The Measurement Types that have been allocated for measurement requests are shown in Table 7-29 and measurement reports are shown in Table 7-30 (in 7.3.2.22).
The Measurement Request field shall be null when the Enable bit is set to 1 and shall contain the specification of the measurement request, as described in 7.3.2.21.1 through 7.3.2.21.3, when the Enable bit is set to 0.
The Measurement Request element is included in a Measurement Request frame as described in 7.4.1.1. The use of Measurement Request elements and frames is described in 11.9.6.
7.3.2.21.1 Basic request
A Measurement Type in the Measurement Request element may indicate a basic request. The response to a basic request is a basic report. It is mandatory for a STA in a BSS to generate a basic report in response to a basic request if the request is received from the AP with which it is associated, except as specified in 11.9.6. The Measurement Request field corresponding to a basic request is shown in Figure 7-60.
The Channel Number field shall be set to the channel number for which the measurement request applies (as defined in 17.3.8.3.3).
The Measurement Start Time field shall be set to the TSF timer at the time (± 32 μs) at which the requested basic request measurement shall start. A value of 0 shall indicate it shall start immediately.
The Measurement Duration field shall be set to the duration of the requested measurement,expressed in TUs.
7.3.2.21.2 CCA request
A Measurement Type in the Measurement Request element may indicate a CCA request. A response to a CCA request is a CCA report. It is optional for a STA to generate a CCA report in response to a CCA Request. The Measurement Request field corresponding to a CCA request is shown in Figure 7-61.
