Patent Publication Number: US-2017366364-A1

Title: Multicast Packet Transmission Method, and Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/462,816 filed on Aug. 19, 2014, which a continuation of International Patent Application No. PCT/CN2013/088786 filed on Dec. 6, 2013, which claims priority to Chinese Patent Application No. 201310071466.6 filed on Mar. 6, 2013 and Chinese Patent Application No. 201310144338.X filed on Mar. 6, 2013. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     TECHNICAL FIELD 
     The present disclosure relates to the communications field, and in particular, to a multicast packet transmission method and an apparatus. 
     BACKGROUND 
     A wireless local area network (WLAN) is a computer local area network which uses a radio channel as a transmission medium, and is an important supplement and extension to wired networks. In an application scenario of 802.11ah, an access point (AP) can generally support 6000 stations (STAs). 802.11ah is a communications standard for wireless local area networks and is applied to a large number of sensor applications with low power consumption, for example, meter reading, environment monitoring, and smart household. Exemplarily, these STAs may be separately disposed on a water meter, an electricity meter, and a gas meter. The water meter, the electricity meter, and the gas meter may belong to a same company or different companies. Using a wireless AP, these companies can separately send information at a same interval or different intervals to the water meter, the electricity meter, and the gas meter, or update the water meter, the electricity meter, and the gas meter. Therefore, in the application scenario of 802.11ah, an AP can send multicast information at different intervals and of different content to different STAs. Currently, the 802.11ah standard, however, does not define how multicast data is sent to STAs using a multicast association identifier (AID). 
     SUMMARY 
     Embodiments of the present disclosure provide a multicast packet transmission method and apparatus, and define how multicast data is sent to STAs using a multicast AID. 
     The following technical solutions are used in the embodiments of the present disclosure, 
     According to a first aspect, an embodiment of the present disclosure provides a multicast packet transmission method, where the method includes allocating, by an AP, a corresponding multicast AID to at least two STAs, where the multicast AID is set in a short media access control (MAC) header of a multicast packet; and sending, by the AP, the multicast packet to the at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. 
     In a first possible implementation manner, according to the first aspect, the method further includes calculating, by the AP for the STAs, a corresponding multicast partial association identifier (PAID) of the STAs; and setting, by the AP, the multicast PAID into a physical layer convergence procedure protocol data unit (PPDU) frame of the multicast packet. 
     In a second possible implementation manner, with reference to the first aspect or the first possible implementation manner, if the PPDU frame format is a short preamble format, the multicast PAID is set in a signal field of the short preamble format; or if the PPDU frame format is a long preamble format, the multicast PAID is set in a signal A field of the long preamble format. 
     In a third possible implementation manner, with reference to the first aspect, the first possible implementation manner, or the second possible implementation manner, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field, and the multicast AID is set in the first address field. 
     In a fourth possible implementation manner, with reference to the first aspect or the first possible implementation manner to the third possible implementation manner, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is a flag bit, and the flag bit is used to indicate whether an AID is a multicast AID. 
     In a fifth possible implementation manner, with reference to the first aspect or the first possible implementation manner to the fourth possible implementation manner, before the sending, by the AP, the multicast packet to at least two STAs, the method further includes sending, by the AP, a broadcast signal to the STAs, so that the STAs learn that the AP is to send the multicast packet to the STAs. 
     According to a second aspect, an embodiment of the present disclosure provides a multicast packet transmission method, where the method includes receiving, by a STA, a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, and a multicast AID in the multicast packet is set in a short MAC header of the multicast packet; and determining, by the STA according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. 
     In a first possible implementation manner, according to the second aspect, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field, and the multicast AID is set in the first address field. 
     In a second possible implementation manner, with reference to the second aspect or the first possible implementation manner, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, and the flag bit is used to indicate whether an AID is a multicast AID. 
     In a third possible implementation manner, with reference to the second aspect, the first possible implementation manner, or the second possible implementation manner, before the receiving, by the at least two STAs, the multicast packet sent by the AP, the method further includes receiving, by the STAs, a broadcast signal sent by the AP; and learning, by the STAs, that the AP is to send the multicast packet to the STAs. 
     In a fourth possible implementation manner, with reference to the second aspect or the first possible implementation manner to the third possible implementation manner, the method further includes, if a multicast PAID is set in a multicast PPDU frame format, determining, by the STA according to the multicast PAID, whether the multicast packet is a multicast packet corresponding to the STA. 
     According to a third aspect, an embodiment of the present disclosure provides an AP, where the AP includes a processing module configured to allocate a corresponding multicast AID to at least two STAs, where the multicast AID is set in a short MAC header of a multicast packet; and a sending module configured to send the multicast packet to the at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. 
     In a first possible implementation manner, according to the third aspect, the processing module is further configured to calculate a corresponding multicast PAID of the STAs for the STAs, and set the multicast PAID into a physical layer convergence PPDU frame of the multicast packet. 
     In a second possible implementation manner, with reference to the third aspect or the first possible implementation manner, if the PPDU frame format is a short preamble format, the multicast PAID is set in a signal field of the short preamble format; or if the PPDU frame format is a long preamble format, the multicast PAID is set in a signal A field of the long preamble format. 
     In a third possible implementation manner, with reference to the third aspect, the first possible implementation manner, or the second possible implementation manner, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field, and the multicast AID is set in the first address field. 
     In a fourth possible implementation manner, with reference to the third aspect or the first possible implementation manner to the third possible implementation manner, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, and the flag bit is used to indicate whether an AID is a multicast AID. 
     In a fifth possible implementation manner, with reference to the third aspect or the first possible implementation manner to the fourth possible implementation manner, the sending module is further configured to send a broadcast signal to the STAs, so that the STAs learn that the AP is to send the multicast packet to the STAs. 
     According to a fourth aspect, an embodiment of the present disclosure provides a STA, where the STA includes a receiving unit configured to receive a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, and a multicast AID in the multicast packet is set in a short MAC header of the multicast packet; and a determining unit configured to determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. 
     In a first possible implementation manner, with reference to the fourth aspect, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field, and the multicast AID is set in the first address field. 
     In a second possible implementation manner, with reference to the fourth aspect or the first possible implementation manner, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, and the flag bit is used to indicate whether an AID is a multicast AID. 
     In a third possible implementation manner, with reference to the fourth aspect, the first possible implementation manner, or the second possible implementation manner, the STA further includes the receiving unit, further configured to receive a broadcast signal sent by the AP; and an acquiring unit configured to learn that the AP is to send the multicast packet to the STA. 
     In a fourth possible implementation manner, with reference to the fourth aspect or the first possible implementation manner to the third possible implementation manner, the determining unit is further configured to, if a multicast PAID is set in a multicast PPDU frame format, determine, according to the multicast PAID, whether the multicast packet is a multicast packet corresponding to the STA. 
     According to yet another aspect, an embodiment of the present disclosure provides a physical (PHY) layer encapsulation method for a multicast packet, where the method includes obtaining, by an AP by means of calculation according to a multicast AID of STAs, a multicast PAID of the STAs; and setting, by the AP, the multicast PAID into a physical layer convergence PPDU frame of the multicast packet. 
     According to still another aspect, an embodiment of the present disclosure further provides a multicast PPDU frame transmission method, where the method includes receiving, by a STA, a physical layer convergence PPDU frame of a multicast packet sent by an AP, where the PPDU frame includes a first multicast PAID; and calculating, by the STA, a second multicast PAID according to a multicast AID allocated by the AP, comparing whether the first multicast PAID and the second multicast PAID are the same, and determining, according to a comparison result, whether the multicast PPDU frame is a multicast PPDU frame corresponding to the STA. 
     According to yet another aspect, an embodiment of the present disclosure discloses an AP, where the AP includes a module which obtains, by means of calculation according to a multicast AID of STAs, a multicast PAID of the STAs; and a module which sets the multicast PAID into a physical layer convergence PPDU frame of the multicast packet. 
     According to still another aspect, an embodiment of the present disclosure further discloses a STA, where the STA includes a module which receives a physical layer convergence PPDU frame of a multicast packet sent by an AP, where the PPDU frame includes a first multicast PAID; and a module which calculates a second multicast PAID according to a multicast AID allocated by the AP, compares whether the first multicast PAID and the second multicast PAID are the same, and determines, according to a comparison result, whether the multicast PPDU frame is a multicast PPDU frame corresponding to the STA. 
     According to the multicast packet transmission method and apparatus provided in the embodiments of the present disclosure, an AP allocates a corresponding multicast AID to STAs, where the multicast AID is set in a short MAC header of a multicast packet; and the AP sends the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. With this solution, because an AP allocates a corresponding multicast AID to STAs and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to STAs using a multicast AID is defined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the embodiments of the present disclosure more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments. The accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is flowchart  1  of a multicast packet transmission method according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic structural diagram of a traditional MAC header; 
         FIG. 3  is schematic structural diagram  1  of a short MAC header according to an embodiment of the present disclosure; 
         FIG. 4  is schematic structural diagram  2  of a short MAC header according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic structural diagram of an AID according to an embodiment of the present disclosure; 
         FIG. 6  is flowchart  2  of a multicast packet transmission method according to an embodiment of the present disclosure; 
         FIG. 7  is a schematic structural diagram of a sketch value of an AID according to an embodiment of the present disclosure; 
         FIG. 8  is schematic structural diagram  1  of a PPDU frame format according to an embodiment of the present disclosure; 
         FIG. 9  is schematic structural diagram  2  of a PPDU frame format according to an embodiment of the present disclosure; 
         FIG. 10  is flowchart  3  of a multicast packet transmission method according to an embodiment of the present disclosure; 
         FIG. 11  is flowchart  4  of a multicast packet transmission method according to an embodiment of the present disclosure; 
         FIG. 12  is a schematic structural diagram of an AP according to an embodiment of the present disclosure; 
         FIG. 13  is schematic structural diagram  1  of a STA according to an embodiment of the present disclosure; 
         FIG. 14  is schematic structural diagram  2  of a STA according to an embodiment of the present disclosure; 
         FIG. 15  is a schematic structural diagram of an AP according to another embodiment of the present disclosure; and 
         FIG. 16  is a schematic structural diagram of a STA according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following clearly describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. The described embodiments are merely a part rather than all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure. 
     An embodiment of the present disclosure provides a multicast packet transmission method. As shown in  FIG. 1 , the method includes the following steps. 
     S 101 . An AP allocates a corresponding multicast AID to STAs. 
     The multicast AID is set in a short MAC header of a multicast packet, and optionally, a first flag is set in a flag bit of the multicast AID. 
     A WLAN is a computer local area network which uses a radio channel as a transmission medium, and is an important supplement and extension to wired networks. In an application scenario of 802.11ah, an AP can generally support 6000 STAs. 802.11ah is a communications standard for WLANs and is applied to a large number of sensor applications with low power consumption, for example, meter reading, environment monitoring, and smart household. 
     In an application scenario of 802.11ah, when an AP is to send multicast data to multiple STAs, the AP first needs to process the data to be sent. First, the data is encapsulated at a MAC layer, and meanwhile, an AID is set in a short MAC header of the packet. Then, the data encapsulated at the MAC layer is sent to a PHY layer for encapsulation, where a specific encapsulating process is described in a following embodiment, and details are not described here. 
     It should be noted that a format of a traditional MAC header is shown in  FIG. 2 ; the traditional MAC header includes a frame control field, a duration field or a flag field, a first address field, a second address field, a third address field, a sequence control field, a fourth address field, a quality of service control field, and a high throughput control field, where a length of the frame control field, a length of the duration field, a length of the sequence control field, and a length of the quality of service control field are all 2 bytes; a length of the first address field, a length of the second address field, a length of the third address field, and a length of the fourth address field are all 6 bytes; and a length of the high throughput control field is 4 bytes. 
     However, in an application scenario of 802.11ah, an application with low power consumption can be more effectively supported if the short MAC header is adopted. As shown in  FIG. 3 , the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field, where a length of the frame control field, a length of the first address field, and a length of the sequence control field are all 2 bytes, and a length of the second address field is 6 bytes. In addition, the AID is set in the first address field, and a basic service set identifier (BSSID) is set in the second address field. 
     It should be noted that, according to a user policy, the short MAC header provided in this embodiment of the present disclosure may further include a third address field, and as shown in  FIG. 4 , a length of the third address field is 6 bytes. 
     Compared with the traditional MAC header, the short MAC header does not include the duration field, the quality of service control field, the high throughput control field, and the fourth address field, which can not only reduce a length of the MAC header to improve data transmission efficiency, but also reduce power consumption of the STA to save energy. 
     It should be added that a format that the AID is set in the first address field is shown in  FIG. 5 , where the length of the first address field is 2 bytes, that is, 16 bits. According to a stipulation, starting from the least significant bit of the first address field, the first bit to the thirteenth bit are set to be a sketch value of the AID; starting from the least significant bit of the first address field, the fourteenth bit is a flag bit, where the flag bit is used to indicate whether the AID is a multicast AID; and starting from the least significant bit of the first address field, the fifteenth bit and the sixteenth bit are both set to a numeric  1 . 
     When a packet is to be sent as a multicast packet, the AP allocates a corresponding multicast AID to the STA, where the multicast AID is set in a short MAC header of the multicast packet; optionally, a first flag is set in a flag bit of the multicast AID, and a value of the first flag is 1. 
     S 102 . The AP sends a multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. 
     The at least two STAs are in a same multicast group. 
     The AP sends the multicast packet to the at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. 
     It should be noted that the AID provided in this embodiment of the present disclosure is compiled in binary format, and the first flag is used to indicate whether the packet is a multicast packet. Therefore, the value of the first flag is 1. When the first flag is not set in the flag bit, it indicates that the packet is not a multicast packet and cannot be sent to STAs in a multicast manner. 
     It should be added that the value of the first flag varies with different user policies, and the value of the first flag may be 1 or may be 0 or any other value. The present disclosure is not limited. 
     According to the multicast packet transmission method provided in this embodiment of the present disclosure, an AP allocates a corresponding multicast AID to STAs, where the multicast AID is set in a short MAC header of a multicast packet, and a first flag is set in a flag bit of the multicast AID; and the AP sends the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. With this solution, because an AP allocates a corresponding multicast AID to a STA and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to a STA using a multicast AID is defined. 
     An embodiment of the present disclosure provides a multicast packet transmission method. As shown in  FIG. 6 , the method includes the following steps. 
     S 201 . An AP allocates a corresponding multicast AID to STAs. 
     The multicast AID is set in a short MAC header of a multicast packet, and a first flag is set in a flag bit of the multicast AID. 
     A WLAN is a computer local area network which uses a radio channel as a transmission medium, and is an important supplement and extension to wired networks. In an application scenario of 802.11ah, an AP can generally support 6000 STAs. 802.11ah is a communications standard for WLANs and is applied to a large number of sensor applications with low power consumption, for example, meter reading, environment monitoring, and smart household. 
     In an application scenario of 802.11ah, when an AP is to send multicast data to multiple STAs, the AP first needs to process the data to be sent. First, the data is encapsulated at a MAC layer, and meanwhile, an AID is set in a short MAC header of the packet. Then, the data encapsulated at the MAC layer is sent to a PHY layer for encapsulation. 
     The following successively describes processes of encapsulating data at the MAC layer and at the PHY layer. 
     A traditional MAC header includes a frame control field, a duration field or a flag field, a first address field, a second address field, a third address field, a sequence control field, a fourth address field, a quality of service control field, and a high throughput control field, where a length of the frame control field, a length of the duration field, a length of the sequence control field, and a length of the quality of service control field are all 2 bytes; a length of the first address field, a length of the second address field, a length of the third address field, and a length of the fourth address field are all 6 bytes; and a length of the high throughput control field is 4 bytes. 
     However, in an application scenario of 802.11ah, adoption of the short MAC header can more effectively support an application with low power consumption. The short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field, where a length of the frame control field, a length of the first address field, and a length of the sequence control field are all 2 bytes, and a length of the second address field is 6 bytes. In addition, the AID is set in the first address field. 
     It should be noted that, according to a user policy, the short MAC header provided in this embodiment of the present disclosure may further include a third address field, and a length of the third address field is 6 bytes. 
     Compared with the traditional MAC header, the short MAC header does not include the duration field, the quality of service control field, the high throughput control field, and the fourth address field, which can not only reduce a length of the MAC header to improve data transmission efficiency, but also reduce power consumption of the STA to save energy. 
     It should be added that the AID is set in the first address field, where the length of the first address field is 2 bytes, that is, 16 bits. According to a stipulation, the first bit to the thirteenth bit of the first address field are set to be a sketch value of the AID. Because up to 6000 nodes need to be supported in the 802.11ah scenario, when the AID sketch values are allocated to a large number of nodes, the nodes are divided by layer according to three levels, that is, page, block, and sub-block, as shown in  FIG. 7 . The first address field has at most 4 pages, which occupy 2 bits; under each page, there are 32 blocks, occupying 5 bits; under each block, there are 8 sub-blocks, occupying 3 bits; and under each sub-block, there can be 8 STAs, occupying 3 bits. Therefore, each AID only needs to indicate a page, a block, and a sub-block to which a STA belongs, and a specific position in the sub-block, and then a sketch value, corresponding to the STA, of the AID can be indicated. 
     Further, starting from the least significant bit of the first address field, the fourteenth bit is a flag bit, where the flag bit is used to indicate whether the AID is a multicast AID; and starting from the significant bit of the first address field, the fifteenth bit and the sixteenth bit are both set to a numeric  1 . 
     After the AID is set in a short MAC header of a multicast packet, the AP sends the data encapsulated at the MAC layer to the PHY layer for encapsulation. 
     The 802.11ah standard supports the following several bandwidths such as 1 megahertz (MHz), 2 MHz, 4 MHz, 8 MHz, and 16 MHz, and the 802.11ah standard defines three PPDU frame formats. These three frame formats are respectively a 1 MHz frame format, a greater than or equal to 2 MHz short preamble format, and a greater than or equal to 2 MHz long preamble format, where the short preamble format can only be used for single user (SU) communication; and the long preamble format can be used for not only SU communication but also multiple user (MU) communication. 
     As shown in  FIG. 8 , the greater than or equal to 2 MHz short preamble format includes a short training field (STF) used for initial PPDU detection, automatic gain control, rough frequency offset estimation, and time synchronization; a long training field 1 (LTF1) used for channel estimation, accurate frequency offset estimation, and time synchronization; a long training field 2 (LTF2) together with the LTF1 and long training field N LTF  (LTF_N LTF ) are used for channel estimation of multiple spatial flows, accurate frequency offset estimation, and time synchronization, where N LTF  refers to the specific number of LTF fields and is related to the number of spatial flows; and a signal (SIG) used to transmit some key information, such as a bandwidth, the number of spatial flows, and a modulation scheme, required by a receive side for depacketization. 
     As shown in  FIG. 9 , the greater than or equal to 2 MHz long preamble format includes an STF; an LTF1; a signal A (SIGA) used to transmit key information required by the receive side to depacketize an SU packet, or transmit key information shared by multiple users when an MU packet is depacketized; a short training field for data (D-STF) used to improve automatic gain control; and a signal B (SIGB) which, in SU mode, is identical to a D-LTF1 and can improve performance of channel estimation, and in MU mode, is used to transmit key information specific to each user. 
     When the multicast data encapsulated at the MAC layer is encapsulated at the PHY layer, the AP first calculates a corresponding multicast PAID of the STAs for the STAs, where a length of the PAID is 9 bits and is obtained by means of calculation after the AID is compressed. A same PAID can be obtained by means of calculation after multiple AIDs are compressed, and the same PAID is used for packet address detection at the PHY layer on the receive side. The multicast PAID can be obtained by means of calculation according to formula (1), and formula (1) is as follows: 
       (dec(AID[0:8])+dec(BSSID[44:47]⊕BSSID[40:43])×2 5 )mod 2 9   Formula (1),
 
     where ⊕ represents a bitwise exclusive or (XOR) operation; mod X represents a modulo X operation; dec( ) represents a decimal conversion operation; AID[0:8] represents bits  0  to  8  of the AID; and BSSID[44:47] represents bits  44  to  47  of a BSSID. 
     After the PAID to be set in the PPDU frame format is obtained by means of calculation, if the multicast PAID meets a preset condition, the AP sets the multicast PAID into the physical layer convergence PPDU frame format of the multicast packet. If the multicast PAID does not meet the preset condition, the AP does not set the multicast PAID into the PPDU frame format of the multicast packet. The preset condition means that the PAID obtained by means of calculation according to formula (1) is not equal to a first preset value, and that the PAID obtained by means of calculation is not equal to a second preset value, where the first preset value is a value obtained by means of calculation according to formula (2), and the second preset value is a value obtained by means of calculation according to formula (3): 
       (dec(BSSID[39:47])mod(2 9 −1))+1  Formula (2), and
 
       (dec(Overlapping BSSID[39:47])mod(2 9 −1))+1  Formula (3).
 
     Overlapping BSSID refers to an identifier of an adjacent basic service set (BSS) which overlaps a current BSS in coverage, that is, a MAC address of an adjacent AP. 
     Correspondingly, after the PAID to be set in the PPDU frame format is obtained by means of calculation, if the PAID does not meet the preset condition, the PAID is not to be set in the PPDU frame format. 
     It should be added that, if the PPDU frame format is the short preamble format, the multicast PAID is set in the signal field SIG (a portion indicated by an arrow in  FIG. 8 ) of the short preamble format; or, if the PPDU frame format is the long preamble format, the multicast PAID is set in the signal A field SIGA (a portion indicated by an arrow in  FIG. 9 ) of the long preamble format. 
     When a packet after being encapsulated at the MAC layer and the PHY layer is to be sent as a multicast packet, the AP allocates a corresponding multicast AID to the STA, where the multicast AID is set in a short MAC header of the multicast packet, a first flag is set in a flag bit of the multicast AID, and a value of the first flag is 1. 
     S 202 . The AP sends a broadcast signal to the STAs, so that the STAs learn that the AP is to send a multicast packet to the STAs. 
     Before the AP sends the multicast packet to at least two STAs, the AP sends, to the STAs, the broadcast signal which carries delivery traffic indication map information, so that the STAs learn that the AP is to send the multicast packet to the STAs. 
     The broadcast signal is sent using a delivery traffic indication map (DTIM) broadcast signal of a beacon frame, where the beacon is a management frame which is periodically broadcast by the AP, and the DTIM is a field of the broadcast signal of the beacon frame sent by the AP. 
     S 203 . The AP sends the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. 
     The at least two STAs are in a same multicast group. 
     The AP sends the multicast packet to the at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. 
     It should be added that the value of the first flag varies with different user policies, and the value of the first flag may be 1 or may be 0 or any other value. The present disclosure is not limited. 
     According to the multicast packet transmission method provided in this embodiment of the present disclosure, an AP allocates a corresponding multicast AID to STAs, where the multicast AID is set in a short MAC header of a multicast packet, and a first flag is set in a flag bit of the multicast AID; and the AP sends the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. With this solution, because an AP allocates a corresponding multicast AID to STAs and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to STAs using a multicast AID is defined. 
     An embodiment of the present disclosure provides a packet transmission method. As shown in  FIG. 10 , the method includes the following steps. 
     S 301 . A STA receives a multicast packet sent by an AP. 
     The STA receives the multicast packet sent by the AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID. 
     S 302 . The STA determines, according to a multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. 
     The STA determines, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA; if the multicast packet is a multicast packet corresponding to the STA, the STA continues to receive the multicast packet; and if the multicast packet is not a multicast packet corresponding to the STA, the STA discards the multicast packet. 
     It should be noted that a PAID is set in a PPDU frame format, and therefore the STA may also determine, according to the PAID, whether a packet is a packet corresponding to the STA. The present disclosure is not limited. 
     According to the multicast packet transmission method provided in this embodiment of the present disclosure, a STA receives a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID; and the STA determines, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. With this solution, because an AP allocates a corresponding multicast AID to STAs and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to STAs using a multicast AID is defined. 
     An embodiment of the present disclosure provides a packet transmission method. As shown in  FIG. 11 , the method includes the following steps. 
     S 401 . A STA receives a broadcast signal sent by an AP. 
     S 402 . The STA learns that the AP is to send a multicast packet to the STA. 
     S 403 . The STA receives the multicast packet sent by the AP. 
     The multicast packet is sent by the AP to at least two STAs which include the STA, and a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID. 
     The short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field; and the multicast AID is set in the first address field. A length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, where the flag bit is used to indicate whether an AID is a multicast AID. 
     S 404 . The STA determines, according to a multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. 
     The STA determines, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA; if the multicast packet is a multicast packet corresponding to the STA, the STA continues to receive the multicast packet; and if the multicast packet is not a multicast packet corresponding to the STA, the STA discards the multicast packet. 
     It should be noted that a PAID is set in a PPDU frame format, and therefore the STA may also determine, according to the PAID, whether a packet is a packet corresponding to the STA. The present disclosure is not limited. 
     According to the multicast packet transmission method provided in this embodiment of the present disclosure, a STA receives a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID; and the STA determines, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. With this solution, because an AP allocates a corresponding multicast AID to STAs and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to STAs using a multicast AID is defined. 
     An embodiment of the present disclosure provides an AP. As shown in  FIG. 12 , the AP includes a processing module  10  configured to allocate a corresponding multicast AID to STAs, where the multicast AID is set in a short MAC header of a multicast packet, and a first flag is set in a flag bit of the multicast AID; and a sending module  11  configured to send the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. 
     Further, the processing module  10  is further configured to calculate a corresponding multicast PAID of the STAs for the STAs, and set the multicast PAID into a physical layer convergence PPDU frame format of the multicast packet. 
     Further, if the PPDU frame format is a short preamble format, the multicast PAID is set in a signal field of the short preamble format; or if the PPDU frame format is a long preamble format, the multicast PAID is set in a signal A field of the long preamble format. 
     Further, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field; and the multicast AID is set in the first address field. 
     Further, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, where the flag bit is used to indicate whether an AID is a multicast AID. 
     Further, the sending module  11  is further configured to send a broadcast signal to the STAs, so that the STAs learn that the AP is to send the multicast packet to the STAs. 
     The AP provided in this embodiment of the present disclosure includes a processing module configured to allocate a corresponding multicast AID to STAs, where the multicast AID is set in a short MAC header of a multicast packet, and a first flag is set in a flag bit of the multicast AID; and a sending module configured to send the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. With this solution, because an AP allocates a corresponding multicast AID to STAs and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to STAs using a multicast AID is defined. 
     An embodiment of the present disclosure provides a STA. As shown in  FIG. 13 , the STA includes a receiving unit  20  configured to receive a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID; and a determining unit  21  configured to determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. 
     Further, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field; and the multicast AID is set in the first address field. 
     Further, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, where the flag bit is used to indicate whether an AID is a multicast AID. 
     Further, as shown in  FIG. 14 , the STA further includes the receiving unit  20  further configured to receive a broadcast signal sent by the AP; and an acquiring unit  22  configured to learn that the AP is to send the multicast packet. 
     Further, the determining unit  21  is further configured to determine, according to a multicast PAID if the multicast PAID is set in a multicast PPDU frame format, whether the multicast packet is a multicast packet corresponding to the STA. 
     The STA provided in this embodiment of the present disclosure includes a receiving unit configured to receive a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID; and a determining unit configured to determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. With this solution, because an AP allocates a corresponding multicast AID to STAs and sends a multicast packet to at least two STAs, the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs. In this way, how multicast data is sent to STAs using a multicast AID is defined. 
     An embodiment of the present disclosure provides an AP. As shown in  FIG. 15 , the AP includes a processor  30  configured to allocate a corresponding multicast AID to STAs, where the multicast AID is set in a short MAC header of a multicast packet, and a first flag is set in a flag bit of the multicast AID; and a sending circuit  31  configured to send the multicast packet to at least two STAs, so that the at least two STAs determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the at least two STAs, where the at least two STAs are in a same multicast group. 
     The processor  30  may also be referred to as a central processing unit (CPU). The methods disclosed in the foregoing embodiments of the present disclosure may be applied to the processor  30 , or implemented by the processor  30  in cooperation with functional circuits or devices. The processor  30  may be an integrated circuit chip and has a signal processing capability. In an implementation process, the steps in the foregoing methods may be completed using an integrated logic circuit of hardware in the processor  30  or instructions in the form of software. The processor  30  may be a general processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or another programmable logic component, a discrete gate or a transistor logic component, or a discrete hardware component, which can implement or control the execution of the methods, steps, and logical block diagrams disclosed in the embodiments of the present disclosure. The general processor may be a microprocessor, or the processor may also be any conventional processor or the like. The steps of the methods disclosed in the embodiments of the present disclosure may be directly executed by a hardware decoding processor, or executed by a combination of hardware and software modules in a decoding processor. The software module may be located in a mature storage medium in the art, such as a random access memory, a flash memory, a read-only memory, a programmable read-only memory or an electrically erasable programmable memory, or a register. 
     Further, the processor  30  is further configured to calculate a corresponding multicast PAID of the STAs for the STAs, and set the multicast PAID into a physical layer convergence PPDU frame format of the multicast packet. 
     Further, if the PPDU frame format is a short preamble format, the multicast PAID is set in a signal field of the short preamble format; or if the PPDU frame format is a long preamble format, the multicast PAID is set in a signal A field of the long preamble format. 
     Further, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field; and the multicast AID is set in the first address field. 
     Further, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, where the flag bit is used to indicate whether an AID is a multicast AID. 
     Further, the sending circuit  31  is further configured to send a broadcast signal to the STAs, so that the STAs learn that the AP is to send the multicast packet to the STAs. 
     An embodiment of the present disclosure further provides a STA. As shown in  FIG. 16 , the STA includes a receiver  40  configured to receive a multicast packet sent by an AP, where the multicast packet is sent by the AP to at least two STAs which include the STA, a multicast AID in the multicast packet is set in a short MAC header of the multicast packet, and a first flag is set in a flag bit of the multicast AID; and a processor  41  configured to determine, according to the multicast AID, whether the multicast packet is a multicast packet corresponding to the STA. 
     The methods disclosed in the foregoing embodiments of the present disclosure may be applied to the processor  41 , or implemented by the processor  41  cooperating with each functional circuit or device. The processor  41  may be an integrated circuit chip and has a signal processing capability. In an implementation process, the steps in the foregoing methods may be completed using an integrated logic circuit of hardware in the processor  41  or an instruction in the form of software. The processor  41  may be a general processor, a DSP, an ASIC, a FPGA or another programmable logic component, a discrete gate or a transistor logic component, or a discrete hardware component, which can implement or control the execution of the methods, steps, and logical block diagrams disclosed in the embodiments of the present disclosure. The general processor may be a microprocessor, or the processor may also be any conventional processor and the like. The steps of the methods disclosed in the embodiments of the present disclosure may be directly executed by a hardware decoding processor, or executed by a combination of hardware and software modules in a decoding processor. The software module may be located in a mature storage medium in the art, such as a random access memory (RAM), a flash memory, a read-only memory (ROM), a programmable read-only memory or an electrically erasable programmable memory, or a register. 
     Further, the short MAC header includes a frame control field, a first address field, a second address field, and a sequence control field; and the multicast AID is set in the first address field. 
     Further, a length of the first address field is 16 bits, where starting from the least significant bit of the first address field, the fourteenth bit is the flag bit, where the flag bit is used to indicate whether an AID is a multicast AID. 
     Further, the receiver  40  is further configured to receive a broadcast signal sent by the AP. 
     The processor  41  is further configured to learn that the AP is to send the multicast packet. 
     Further, the processor  41  is further configured to determine, according to a multicast PAID if the multicast PAID is set in a multicast PPDU frame format, whether the multicast packet is a multicast packet corresponding to the STA. 
     A person of ordinary skill in the art may understand that all or a part of the steps of the method embodiments may be implemented by a program instructing relevant hardware. The program may be stored in a computer readable storage medium. When the program runs, the steps of the method embodiments are performed. The foregoing storage medium includes any medium that can store program code, such as a ROM, a RAM, a magnetic disk, or an optical disc. 
     The foregoing descriptions are merely specific implementation manners of the present disclosure, and are not intended to limit the protection scope of the present disclosure. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present disclosure shall fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.