In the following descriptions, “immediately previous” frame means a frame whose reception concluded within the SIFS interval preceding the start of the current frame.
The subfields within the Frame Control field of control frames are set as illustrated in Figure 7-5.
7.2.1.1 RTS frame format
The frame format for the RTS frame is as defined in Figure 7-6.
The RA field of the RTS frame is the address of the STA, on the WM, that is the intended immediate recipient of the pending directed data or management frame.
The TA field is the address of the STA transmitting the RTS frame.
For all RTS frames sent by non-QoS STAs, the duration value is the time, in microseconds, required to transmit the pending data or management frame, plus one CTS frame, plus one ACK frame, plus three SIFS intervals. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer. For all RTS frames sent by STAs under EDCA, following a contention access of the channel, the duration value is set in the following manner:
— If the NAV protection is desired for only the first or sole frame in the TXOP, the duration value is set to the time, in microseconds, required to transmit the pending frame, plus one CTS frame, plus one ACK frame if required, plus three SIFS intervals.
— Otherwise, the duration value is set to the remaining duration of the TXOP. For all RTS frames sent under HCCA, the duration value is set to one of the following values:
— If the pending frame is the final frame, the duration value is set to the time, in microseconds, required to transmit the pending frame, plus one CTS frame, plus one ACK frame if required, plus three SIFS intervals.
— If the pending frame is not the final frame in the TXOP, the duration value is set to the remaining duration of the TXOP.
7.2.1.2 CTS frame format
The frame format for the CTS frame is as defined in Figure 7-7.
When the CTS frame follows an RTS frame, the RA field of the CTS frame is copied from the TA field of the immediately previous RTS frame to which the CTS is a response. When the CTS is the first frame in a frame exchange, the RA field is set to the MAC address of the transmitter.
For all CTS frames sent in response to RTS frames, the duration value is the value obtained from the Duration field of the immediately previous RTS frame, minus the time, in microseconds, required to transmit the CTS frame and its SIFS interval. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer.
At a non-QoS STA, if the CTS is the first frame in the exchange and the pending data or management frame requires acknowledgment, the duration value is the time, in microseconds, required to transmit the pending data or management frame, plus two SIFS intervals plus one ACK frame. At a non-QoS STA, if the CTS is the first frame in the exchange and the pending data or management frame does not require acknowledgment, the duration value is the time, in microseconds, required to transmit the pending data or management frame, plus one SIFS interval. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer.
For all CTS frames sent by STAs as the first frame in the exchange under EDCA, the duration value is set in the following manner:
— If the NAV protection is desired for only the first or sole frame in the TXOP the duration value is set to
— The time, in microseconds, required to transmit the pending frame, plus one SIFS interval, plus the response frame (ACK or Block Ack), plus an additional SIFS interval, if there is a response frame, or
— The time, in microseconds, required to transmit the pending frame, plus one SIFS interval, if there is no response frame.
— Otherwise, the duration value is set to the remaining duration of the TXOP. For CTS frames sent under HCCA, the duration value is set to one of the following values:
— If the pending frame is the sole frame in the TXOP, the duration value is set to
— The time, in microseconds, required to transmit the pending frame, plus one SIFS interval, plus the response frame (ACK or Block Ack), plus an additional SIFS interval, if there is a response frame, or
— The time, in microseconds, required to transmit the pending frame, plus one SIFS interval, if there is no response frame.
— If the pending frame is not the final frame in the TXOP, the duration value is set to the remaining duration of the TXOP.
7.2.1.3 ACK frame format
The frame format for the ACK frame is as defined in Figure 7-8.
The RA field of the ACK frame is copied from the Address 2 field of the immediately previous directed
data, management, BlockAckReq control, BlockAck control, or PS-Poll control frame.
For ACK frames sent by non-QoS STAs, if the More Fragments bit was set to 0 in the Frame Control field of the immediately previous directed data or management frame, the duration value is set to 0. In all other ACK frames, the duration value is the value obtained from the Duration/ID field of the immediately previous data, management, PS-Poll, BlockAckReq, or BlockAck frame minus the time, in microseconds, required to transmit the ACK frame and its SIFS interval. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer.
7.2.1.4 PS-Poll frame format
The frame format for the PS-Poll frame is as defined in Figure 7-9.
The BSSID is the address of the STA contained in the AP. The TA field is the address of the STA transmitting the frame. The AID is the value assigned to the STA transmitting the frame by the AP in the association response frame that established that STA’s current association.
The AID value always has its two MSBs each set to 1.
7.2.1.5 CF-End frame format
The frame format for the CF-End frame is as defined in Figure 7-10.
The BSSID field is the address of the STA contained in the AP. The RA field is the broadcast group address. The Duration field is set to 0.
7.2.1.6 CF-End+CF-Ack frame format
The frame format for the CF-End+CF-Ack frame is as defined in Figure 7-11.
The BSSID field is the address of the STA contained in the AP. The RA field is the broadcast group address. The Duration field is set to 0.
7.2.1.7 Block Ack Request (BlockAckReq) frame format
The frame format of the BlockAckReq frame is defined in Figure 7-12.
The Duration/ID field value is greater than or equal to the time16, in microseconds, required to transmit one ACK or BlockAck frame, as applicable, plus one SIFS interval. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer.
The RA field of the BlockAckReq frame is the address of the recipient STA.
The TA field is the address of the STA transmitting the BlockAckReq frame.
The BAR Control field is shown in Figure 7-13.
16To allow the possibility of time remaining in the TXOP, which the sender may use to schedule other transmissions.
The TID subfield of the BAR Control field contains the TID for which a BlockAck frame is requested.
The Block Ack Starting Sequence Control field is shown in Figure 7-14. The Starting Sequence number subfield is the sequence number of the first MSDU for which this BlockAckReq is sent. The Fragment Number subfield is always set to 0.
7.2.1.8 Block Ack (BlockAck) frame format
The frame format of the BlockAck frame is defined in Figure 7-15.
If the BlockAck frame is sent in response to the BlockAckReq frame, the Duration/ID field value is the value obtained from the Duration/ID field of the immediate BlockAckReq frame, minus the time, in microseconds, required to transmit the BlockAck frame and its SIFS interval. If the BlockAck frame is not sent in response to the BlockAckReq, the Duration/ID field value is greater than (subject to the TXOP limit) or equal to the time17 for transmission of an ACK frame plus a SIFS interval. If the calculated duration includes a fractional microsecond, that value is rounded to the next higher integer.
The RA field of the BlockAck frame is the address of the recipient STA that requested the Block Ack.
The TA field is the address of the STA transmitting the BlockAck frame.
The BA Control field defined in Figure 7-16 consists of the TID subfield.
The Block Ack Starting Sequence Control field is defined in 7.2.1.7 and is set to the same value as in the immediately previously received BlockAckReq frame.
The Block Ack Bitmap field is 128 octets in length and is used to indicate the receiving status of up to 64 MSDUs. Bit position n of the Block Ack bitmap, if set to 1, acknowledges receipt of an MPDU with an 17The default values for TXOP limit are expressed in milliseconds and are multiples of 32 μs.
MPDU sequence control value equal to (Block Ack Starting Sequence Control + n). Bit position n of the Block Ack bitmap, if set to 0, indicates that an MPDU with MPDU sequence control value equal to (Block Ack Starting Sequence Control + n) has not been received. For unused fragment numbers of an MSDU, the corresponding bits in the bitmap are set to 0.
7.2.2 Data frames
The frame format for a data frame is dependent on the QoS subfield of the Subtype field and is as defined in Figure 7-17.
Data frames with a value of 1 in the QoS subfield of the Subtype field are collectively referred to as QoS data frames. Each of these data subtypes contains QoS in their names, and this frame format is distinguished by the presence of a QoS Control field in the MAC header. Data frames with a value of 0 in the QoS subfield of the Subtype field do not have the QoS Control field.
A QoS STA always uses QoS data frames for data transmissions to other QoS STAs. A QoS STA uses frames with the QoS subfield of the Subtype field set to 0 for data transmissions to non-QoS STAs. A non- QoS STA always uses frames with the QoS subfield of the Subtype field set to 0 for data transmissions to other STAs. All STAs use frames with the QoS subfield of the Subtype field set to 0 for broadcast data frames unless a transmitting STA knows that all STAs in a BSS have QoS capability, in which case the transmitting STAs use QoS data frames. All STAs use frames with the QoS subfield of the Subtype field set to 0 for multicast data frames unless it is known to the transmitter that all STAs in the BSS that are members of the multicast group have QoS capability, in which case STAs use QoS data frames.
The content of the address fields of data frames are dependent upon the values of the To DS and From DS fields in the Frame Control field and are defined in Table 7-7. Where the content of a field is shown as not applicable (N/A), the field is omitted. Note that Address 1 always holds the receiver address of the intended receiver (or, in the case of multicast frames, receivers), and that Address 2 always holds the address of the STA that is transmitting the frame.
A STA uses the contents of the Address 1 field to perform address matching for receive decisions. In cases where the Address 1 field contains a group address, the BSSID also is validated to ensure that the broadcast or multicast originated from a STA in the BSS of which the receiving STA is a member.
A STA uses the contents of the Address 2 field to direct the acknowledgment if an acknowledgment is necessary.
The DA field is the destination of the MSDU (or fragment thereof) in the Frame Body field.
The SA field is the address of the MAC entity that initiated the MSDU (or fragment thereof) in the Frame Body field.
The RA field is the unicast address of the STA that is the immediate intended receiver of the frame or the multicast or broadcast address of the STAs that are the immediate intended receivers of the frame.
The TA field is the address of the STA that is transmitting the frame.
The BSSID of the Data frame is determined as follows:
a) If the STA is an AP or is associated with an AP, the BSSID is the address currently in use by the STA contained in the AP.
b) If the STA is a member of an IBSS, the BSSID is the BSSID of the IBSS.
The Sequence Control field is defined in 7.1.3.4. The Sequence Control field for QoS (+)Null frames is ignored by the receiver upon reception.
The QoS Control field is defined in 7.1.3.5.
The frame body consists of the MSDU, or a fragment thereof, and a security header and trailer (if and only if the Protected Frame subfield in the Frame Control field is set to 1). The frame body is null (0 octets in length) in data frames of subtype Null (no data), CF-Ack (no data), CF-Poll (no data), and CF-Ack+CF-Poll (no data), regardless of the encoding of the QoS subfield in the Frame Control field.
For data frames of subtype Null (no data), CF-Ack (no data), CF-Poll (no data), and CF-Ack+CF-Poll (no data) and for the corresponding QoS data frame subtypes, the Frame Body field is omitted; these subtypes are used for MAC control purposes. For data frames of subtypes Data, Data+CF-Ack, Data+CF-Poll, and Data+CF-Ack+CF+Poll and for the corresponding four QoS data frame subtypes, the Frame Body field contains all of, or a fragment of, an MSDU after any encapsulation for security.
The maximum length of the Frame Body field can be determined from the maximum MSDU length plus any overhead from encapsulation for encryption (i.e., it is always possible to send a maximum length MSDU, with any encapsulations provided by the MAC layer within a single data MPDU).
Within all data frames sent by STAs during the CFP under PCF, the Duration/ID field is set to 32 768.
Within all data frames sent by the QoS STA, the Duration/ID field contains a duration value as defined in 7.1.4. Within all data frames sent during the CP by non-QoS STAs, the Duration/ID field is set according to the following rules:
— If the Address 1 field contains a group address, the duration value is set to 0.
— If the More Fragments bit is set to 0 in the Frame Control field of a frame and the Address 1 field
contains an individual address, the duration value is set to the time, in microseconds, required to
transmit one ACK frame, plus one SIFS interval.
— If the More Fragments bit is set to 1 in the Frame Control field of a frame and the Address 1 field
contains an individual address, the duration value is set to the time, in microseconds, required to
transmit the next fragment of this data frame, plus two ACK frames, plus three SIFS intervals.
The duration value calculation for the data frame is based on the rules in 9.6 that determine the data rate at which the control frames in the frame exchange sequence are transmitted. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer. All STAs process Duration/ID field values less than or equal to 32 767 from valid data frames (without regard for the RA, DA, and/or BSSID address values that may be present in these frames) to update their NAV settings as appropriate under the coordination function rules.
7.2.3 Management frames
The frame format for a management frame is independent of frame subtype and is as defined in Figure 7-18.
A STA uses the contents of the Address 1 (DA) field to perform the address matching for receive decisions. In the case where the Address 1 (DA) field contains a group address and the frame type is other than Beacon, the BSSID also is validated to ensure that the broadcast or multicast originated from a STA in the BSS of which the receiving STA is a member. If the frame type is Beacon, other address matching rules apply, as specified in 11.1.2.3. Frames of type Probe Request with a group address in the Address 1 field are processed as described in 11.1.3.2.1.
The address fields for management frames do not vary by frame subtype.
The BSSID of the management frame is determined as follows:
a) If the STA is an AP or is associated with an AP, the BSSID is the address currently in use by the STA contained in the AP.
b) If the STA is a member of an IBSS, the BSSID is the BSSID of the IBSS.
c) In management frames of subtype Probe Request, the BSSID is either a specific BSSID, or the wildcard BSSID as defined in the procedures specified in 11.1.3.
The DA field is the destination of the frame.
The SA field is the address of the STA transmitting the frame.
Within all management frames sent by STAs during the CFP under PCF, the Duration field is set to the value 32 768. Within all management frames sent by the QoS STA, the Duration field contains a duration value as defined in 7.1.4. Within all management frames sent during the CP by non-QoS STAs, the Duration field is set according to the following rules:
— If the DA field contains a group address, the duration value is set to 0.
— If the More Fragments bit is set to 0 in the Frame Control field of a frame and the DA field contains an individual address, the duration value is set to the time, in microseconds, required to transmit one ACK frame, plus one SIFS interval.
— If the More Fragments bit is set to 1 in the Frame Control field of a frame, and the DA field contains an individual address, the duration value is set to the time, in microseconds, required to transmit the next fragment of this management frame, plus two ACK frames, plus three SIFS intervals.
The duration value calculation for the management frame is based on the rules in 9.6 that determine the data rate at which the control frames in the frame exchange sequence are transmitted. If the calculated duration includes a fractional microsecond, that value is rounded up to the next higher integer. All STAs process Duration field values less than or equal to 32 767 from valid management frames to update their NAV settings as appropriate under the coordination function rules.
The frame body consists of the fields followed by the information elements defined for each management frame subtype. All fields and information elements are mandatory unless stated otherwise and appear in the specified, relative order. STAs that encounter an element ID they do not recognize in the frame body of a received management frame ignore that element and continue to parse the remainder of the management frame body (if any) for additional information elements with recognizable element IDs. A STA receiving a vendor-specific IE that it does not support shall ignore the vendor-specific IE. Unused element ID codes are reserved.
Gaps may exist in the ordering of fields and elements within frames. The order that remains shall be
ascending.
7.2.3.1 Beacon frame format
The frame body of a management frame of subtype Beacon contains the information shown in Table 7-8. If the dot11MultiDomainCapabilityEnabled attribute is true, a STA shall include a Country information element in the transmission of Beacon frames. Optionally, the Beacon frame format may also include the information described in either or both of FH Parameters and FH Pattern Table elements. If both FH Parameters and FH Pattern Table elements are sent, they shall describe the same hopping pattern. Note that the information described in FH Parameters and FH Pattern Table elements also may be contained in the Probe Response frame.
Table 7-8—Beacon frame body (continued)
7.2.3.2 IBSS ATIM frame format
The frame body of a management frame of subtype ATIM is null.
7.2.3.3 Disassociation frame format
The frame body of a management frame of subtype Disassociation contains the information shown in Table 7-9.
7.2.3.4 Association Request frame format
The frame body of a management frame of subtype Association Request contains the information shown in Table 7-10.
7.2.3.5 Association Response frame format
The frame body of a management frame of subtype Association Response contains the information shown in Table 7-11.
7.2.3.6 Reassociation Request frame format
The frame body of a management frame of subtype Reassociation Request contains the information shown in Table 7-12.
7.2.3.7 Reassociation Response frame format
The frame body of a management frame of subtype Reassociation Response contains the information shown in Table 7-13.
7.2.3.8 Probe Request frame format
The frame body of a management frame of subtype Probe Request contains the information shown in Table 7-14. If the dot11MultiDomainCapabilityEnabled attribute is true, a STA may include a Request information element in the Probe Request frame. The format of the Request information element is specified in 7.3.2.12.
7.2.3.9 Probe Response frame format
The frame body of a management frame of subtype Probe Response contains the information shown in Table 7-15. If the dot11MultiDomainCapabilityEnabled attribute is true, the Probe Response frame contains a Country information element and all information elements identified by the Requested Element IDs of a Request information element. Note that the information returned as a result of a Probe Request frame with a Request information element may include the FH parameters and/or the FH Pattern Table possibly replicating optional elements identified by orders 12 and 13.
A STA shall return only the 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 as requested in the Request information element.
Table 7-15—Probe Response frame body
7.2.3.10 Authentication frame format
The frame body of a management frame of subtype Authentication contains the information shown in Table 7-16. Only Authentication frames with the authentication algorithm set to Open System authentication may be used within an RSNA. RSNA STAs shall not associate if shared authentication was invoked prior to RSN association.
7.2.3.11 Deauthentication
The frame body of a management frame of subtype Deauthentication contains the information shown in Table 7-18.
7.2.3.12 Action frame format
The frame body of a management frame of subtype Action contains the information shown in Table 7-19.
