JP4521368B2 - COMMUNICATION DEVICE, COMMUNICATION METHOD, AND COMMUNICATION PROGRAM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication device which secures a communication efficiency and performs a multicast communication with high reliability. <P>SOLUTION: A communication device includes a group information storing portion 142 for storing group identifying information of a first multicast group and identifying information of another communication device which belongs to the first multicast group associated with each other, a data transmitter 121 for multicast transmitting a message to which a sequence No. is added to another communication device, a retransmitter 122 for receiving a retransmission request message of the message from the other communication device and for retransmitting the message to the other communication device received, and a group management means for updating the group information storing portion 142 by shifting identifying information of the other communication device to the second multicast group when retransmission request messages are continuously received equal to or more than a predetermined times from the same other communication device, and when it is determined that the retransmission request messages are continuously received equal to or more than the predetermined times. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a communication apparatus, a communication method, and a communication program for transmitting multicast data to external wireless terminals grouped in transmission rate units.

  Unicast, broadcast, multicast, and the like exist as transmission methods for transmitting data by wireless communication on a network. The unicast transmission method is a one-to-one communication method. When the same data is transmitted from one transmitting terminal to many receiving terminals, the load on the transmitting terminal increases and the network bandwidth is compressed. Is a problem.

  The broadcast transmission method is a method for transmitting data to all receiving terminals on the network. In the broadcast transmission method, there is a problem in that data is transmitted even to a terminal that does not want reception.

  The multicast transmission method is a method for reducing unnecessary traffic by simultaneously distributing the same data to a large number of terminals. In the multicast transmission method, data is delivered only to terminals that wish to receive data, so that data can be transmitted more efficiently than broadcast.

  In multicast transmission over TCP / IP (Transmission Control Protocol / Internet Protocol) network, which is widely used in wired LAN (Local Area Network), the router on the communication path replicates data according to the destination. Data can be distributed efficiently without having to do so. For this reason, multicast transmission using a TCP / IP network is used when Internet video distribution is performed.

  The IP multicast group address is converted into a MAC (Media Access Control) address, and the receiving terminal selects and receives only multicast data related to itself.

  IEEE 802.11, which is a typical technical standard for wireless LANs, also stipulates support for multicast, and wireless MAC frames to which a multicast address is specified are received by all terminals belonging to the multicast group.

  In IEEE 802.11, which employs CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) as medium access control, the communication speed is increased by changing the physical layer protocol. For example, the IEEE 802.11 (2 Mbps), IEEE 802.11b (11 Mbps), and IEEE 802.11g (54 Mbps) standards have been formulated for the 2.4 GHz band.

  As for the 5 GHz band, IEEE 802.11a (54 Mbps) exists at present. In addition, IEEE 802.11 TGn (Task Group n) has been established and standardization work is being carried out in order to formulate standards for different speeds in both the 2.4 GHz band and the 5 GHz band.

  When transmitting multicast data, for example, if the transmission is performed at a high transmission rate such as 54 Mbps, a reception terminal that is far from the transmission terminal has a higher probability of packet reception failure due to distance attenuation or the like. If transmission is performed at a low transmission rate, a receiving terminal far from the transmitting terminal can be stably received, but the bandwidth cannot be used effectively. Further, in wireless multicast, an acknowledgment (ACK: Acknowledgment) is not returned from the terminal, and therefore it is not possible to determine whether or not reception has been successful on the transmitting terminal side.

  Thus, in multicast communication under a wireless LAN environment, it is necessary to improve communication efficiency by setting an appropriate transmission rate and to ensure reliability by detecting and recovering packet loss.

  On the other hand, the multicast data is transmitted redundantly, and the receiving side discards and acquires the packet as necessary. The polling is sequentially transmitted to each receiving terminal to transmit a negative acknowledgment (NACK: Negative Acknowledgment). Proposals have been made for technologies that allow sequential transmission, technologies that select repeaters that retransmit multicast data within a multicast group, and determine retransmission control based on retransmissions from the repeaters. Wireless communication efficiency was not enough.

  Further, for example, Patent Document 1 proposes a technique for constructing a multicast group for each transmission rate based on channel conditions, power requirements, device capability, terminal location information, and the like, and changing the service type and quality. In the method of Patent Document 1, one wireless terminal belongs to a plurality of multicast groups, and reliability is not guaranteed using an acknowledgment or a negative response.

US Patent Application Publication No. 2005/0070256

  However, the method of Patent Document 1 cannot dynamically change a multicast group accompanying the movement of a terminal or a change in a propagation path (channel) environment. Therefore, for example, even if the terminal moves to a place where the radio wave condition is poor, it cannot move to a group with a low transmission rate that is robust (low packet error rate), and the reliability of wireless communication by multicast is sufficient There was a problem that could not be secured.

  The present invention has been made in view of the above, and an object of the present invention is to provide a communication device, a communication method, and a communication program capable of realizing wireless communication by highly reliable multicast while ensuring communication efficiency. To do.

In order to solve the above-described problems and achieve the object, the present invention provides first group identification information for identifying a first multicast group and identification for identifying other communication devices belonging to the first multicast group. Group information storage means for storing group information in association with information, and a message with a sequence number corresponding to the first multicast group added to the other communication device belonging to the first multicast group by multicast transmission And a retransmission request message for requesting retransmission of the message from the other communication device, and retransmitting the message requested for retransmission to the other communication device that has received the retransmission request message. Resending means to perform and the resending means continuously from the other communication device for a predetermined number of times. And determines whether the retransmission request message has been received, and if it is determined that the retransmission request message has been received more than the number of times, the identification information of the other communication device is set to a second multicast group. Update the group information stored in the group information storage means in association with the second group identification information for identifying the second group identification information, and send a movement request message requesting movement to the second multicast group to the other communication device Group management means for updating the group information stored in the group information storage means by associating the identification information of the other communication device that has received the transmission request message with the second group identification information. It is characterized by having these.

  The present invention also provides a communication method and a communication program that can execute the above-described apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, at the time of the multicast communication by wireless LAN, data can be delivered with the transmission rate which considered the channel state and the terminal position, and grouping can be changed dynamically based on the negative response from a terminal. For this reason, there is an effect that it is possible to execute highly reliable wireless communication while ensuring communication efficiency.

  Exemplary embodiments of a communication apparatus, a communication method, and a communication program according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
The communication apparatus according to the first embodiment transmits multicast data to which a sequence number is added, and retransmits corresponding data when a negative response is received from a receiving terminal that has detected loss of data due to lack of sequence number information. To do. In addition, the communication device according to the first embodiment changes a specific receiving terminal to a group having a low transmission rate when retransmission to the specific receiving terminal continues.

  FIG. 1 is an explanatory diagram illustrating an example of a configuration of a wireless LAN including a video distribution server 100 which is a communication device according to the first embodiment. As shown in the figure, the video distribution server 100 is connected to the Internet 500 via a router 400a. Also, wireless APs (Access Points) 200a, 200b, and 200c are connected to the Internet 500 via routers 400b, 400c, and 400d, respectively.

  The router 400a, the router 400b, and the router 400d form a multicast distribution tree using a multicast routing protocol based on a participation request from each wireless STA 300. The multicast data transmitted from the video distribution server 100 is copied by the router 400a and transmitted to the router 400b and the router 400d.

  The wireless APs 200a, 200b, and 200c transmit data received from the video distribution server 100 to the wireless STAs (Stations) 300a, 300b, 300x, and 300y using a wireless communication protocol such as IEEE802.11a.

  The wireless APs 200a, 200b, and 200c all have the same configuration, and may be simply referred to as the wireless AP 200 below. Similarly, since the wireless STAs 300a, 300b, 300x, and 300y have the same configuration, they may be simply referred to as wireless STAs 300 below. Details of the configurations of the wireless AP 200 and the wireless STA 300 will be described later.

  In the figure, it is shown that the wireless STAs 300b and 300y belong to the same multicast group. Accordingly, the multicast data transferred by the router 400b and the router 400d are transmitted on the wireless channel by the wireless APs 200a and 200c, respectively. Each wireless STA 300 that has received the wireless MAC frame confirms the multicast address, and determines whether to pass it to a higher layer than the MAC layer or to discard it as invalid. In the example shown in the figure, the wireless STA 300b and the wireless STA 300y receive multicast data from the video distribution server 100.

  FIG. 2 is a block diagram illustrating a configuration of the video distribution server 100 according to the first embodiment. As shown in the figure, the video distribution server 100 includes an application processing unit 110, a multicast processing unit 120, a wired communication processing unit 130, a retransmission data storage unit 141, and a group information storage unit 142. .

  The application processing unit 110 executes processing of data transmitted by multicast, and includes a video data generation unit 111.

  The video data generation unit 111 generates video stream data such as MPEG-2 and MPEG-4 transmitted by multicast. Note that data to be transmitted by multicast is not limited to moving image video data, and any data such as still image video data, audio data, and text data can be generated as a transmission target.

  The multicast processing unit 120 controls transmission processing by multicast, and includes a data transmission unit 121, a retransmission unit 122, a group management unit 123, and a group information notification unit 124.

  The data transmission unit 121 determines the type of data to be transmitted for each multicast group and sequentially transmits data to each group. Specifically, the data transmission unit 121 performs processing for assigning a sequence number to data passed from the video data generation unit 111, setting of a multicast address, and the like.

  The data transmission unit 121 transmits multicast data via the wired communication processing unit 130 that is a communication interface. Further, in preparation for retransmission of multicast data, the data transmission unit 121 stores a copy of the multicast data transmitted to the retransmission data storage unit 141 described later.

  The retransmission unit 122 acquires information on a sequence number to be retransmitted from the NACK received from the wireless STA 300, extracts data corresponding to the acquired sequence number from the retransmission data storage unit 141, and performs a retransmission process.

  Specifically, when the retransmission unit 122 first receives a data retransmission request corresponding to a specific sequence number from a specific wireless STA 300, the retransmission unit 122 retransmits the packet to the specific wireless STA 300 by unicast. .

  In addition, when the retransmission unit 122 receives a data retransmission request for a specific sequence number from another wireless STA 300, the retransmission unit 122 multicasts packets to all the wireless STAs 300 included in the multicast group to which the other wireless STA 300 belongs. Resend

  The group management unit 123 manages information on multicast groups created for each transmission rate and information on continuous sequence numbers added to data for each multicast group. The sequence number information is associated with each group and each data to be transmitted, and is a storage unit (FIG. 5) configured by a storage medium such as an HDD (Hard Disk Drive), an optical disk, a memory card, and a RAM (Random Access Memory). (Not shown).

  In addition, the group management unit 123 performs a process of moving the wireless STA 300 that repeatedly received the retransmission request to a group with a low transmission rate. Further, when a message requesting to move to another transmission rate group (participation request) is received from the wireless STA 300, processing for moving the wireless STA 300 to the high transmission rate group is performed.

  The group information notification unit 124 periodically transmits group information indicating information indicating how many sequence numbers of data transmitted to each multicast group are currently advanced.

  For example, when transmission of the high transmission rate group is completed up to the sequence number 1000 and data transmission of the robust transmission rate group is completed up to the sequence number 5000, the group information notification unit 124 associates each group with the sequence number. Broadcast the group information in the wireless section.

  The broadcast on the wireless LAN is preferably transmitted at a robust transmission rate so that all the wireless STAs 300 can receive the broadcast. As described above, when the group information notification unit 124 periodically notifies the sequence information of all groups, each wireless STA 300 can stably recognize the packet loss.

  The wired communication processing unit 130 wirelessly transmits each data to be transmitted by multicast, unicast, or broadcast transmitted from the data transmission unit 121, the retransmission unit 122, or the group information notification unit 124 via the router 400 and the Internet 500. This is transmitted to the AP 200.

  The retransmission data storage unit 141 stores a copy of transmitted data in order to retransmit multicast data.

  The group information storage unit 142 stores group information that is information related to the multicast group. FIG. 3 is an explanatory diagram illustrating an example of a data structure of group information stored in the group information storage unit 142.

  As shown in the figure, the group information storage unit 142 associates a group name, which is information for uniquely identifying a group, a participating terminal representing the wireless STA 300 participating in the group, and a transmission rate. Stores group information. In the figure, an example is shown in which the wireless STAs 300a, 300b, and 300c belong to the group 1 that is a group that transmits at a high transmission rate (54 Mbps), for example.

  Note that the retransmission data storage unit 141 and the group information storage unit 142 can be configured by any commonly used storage medium such as an HDD, an optical disk, a memory card, and a RAM.

  FIG. 4 is a block diagram illustrating a configuration of the wireless AP 200 according to the first embodiment. As shown in the figure, the wireless AP 200 includes a wired communication processing unit 210, a wireless communication processing unit 220, and an antenna 231 that transmits and receives wireless data.

  The wired communication processing unit 210 receives each data transmitted from the wired communication processing unit 130 of the video distribution server 100 via the router 400.

  The wireless communication processing unit 220 performs communication using a wireless LAN interface such as IEEE802.11a, IEEE802.11b, IEEE802.11g, or IEEE802.11n. The wireless communication processing unit 220 includes a MAC layer processing unit 221 and a physical (PHY) layer processing unit 222.

  The MAC layer processing unit 221 performs wireless communication processing in the MAC layer, and includes a transmission rate management unit 221a.

  The transmission rate management unit 221a determines the transmission rate of multicast data. The transmission rate management unit 221a refers to the correspondence information between the multicast group and the transmission rate stored in the storage unit (not shown) and determines the transmission rate of each group. The correspondence information between the multicast group and the transmission rate is notified from the group management unit 123 of the video distribution server 100 and stored.

  Note that the transmission rate information may be described in the multicast data, and the transmission rate of each multicast data may be determined using the transmission rate information.

  The PHY layer processing unit 222 performs wireless communication processing in the PHY layer on the data received by the antenna 231 and can be realized by the same function as the processing in the PHY layer of a conventionally used wireless communication device. .

  Next, the format of messages transmitted and received in the first embodiment will be described. FIG. 5 is an explanatory diagram showing an example of a configuration of a data packet transmitted and received in the first embodiment.

  FIG. 5 uses a sequence number information field in a transport layer protocol header such as RTP (Real-time Transport Protocol) following an IP header and a UDP (User Datagram Protocol) header, and the data in the sequence number information field. 3 shows a configuration example of a data packet for setting a sequence number (data packet sequence number) for the packet.

  FIG. 6 is an explanatory diagram illustrating an example of a configuration of a group information management packet transmitted and received in the first embodiment. This figure shows a configuration example of a group information management packet for setting group information in a transport layer datagram.

  The group information includes a group information number field indicating the number of group information, a group identifier (multicast address, transmission rate information, etc.) field for uniquely identifying the group, and a group sequence indicating a sequence number for which transmission for each group has been completed. Contains a number field. Although communication efficiency decreases, it is possible to create and transmit a packet including group information for each group identifier.

  FIG. 7 is an explanatory diagram illustrating an example of a configuration of a NACK packet transmitted and received in the first embodiment. This figure shows a configuration example of a NACK packet in which a negative response sequence number (NACK sequence number) is set in the transport layer datagram.

  For example, when the data up to the sequence number 1000 is received in the past and the data No. 1002 is received, the wireless STA 300 indicates 1001 in the NACK sequence number field to indicate that the reception of the data of the sequence number 1001 has failed. Enter the value of.

  Note that the NACK sequence number field may be used to notify the sequence number of multicast data normally received so far. For example, assume that data of sequence number 1005 is received and occurrence of packet loss is detected in a state where data of sequence numbers of 1000, 1001, and 1002 has been received in the past. In this case, the wireless STA 300 transmits the value 1002 in the NACK sequence number field. On the other hand, the video distribution server 100 collectively retransmits a plurality of data (1003, 1004, 1005) from the sequence number 1003 to the sequence number of the last transmitted multicast data. The wireless STA discards duplicate received data.

  FIG. 8 is a block diagram illustrating a configuration of the wireless STA 300 according to the first embodiment. As shown in the figure, the wireless STA 300 includes an application processing unit 310, a multicast processing unit 320, a wireless communication processing unit 330, and an antenna 341 that transmits and receives wireless data.

  The application processing unit 310 executes processing of data transmitted by multicast, and includes a video data output unit 311.

  The video data output unit 311 outputs video stream data transmitted by multicast. The data to be output is not limited to video data, and any data such as audio data and text data can be targeted.

  The multicast processing unit 320 controls various processes of data transmitted by multicast, and includes a data reception unit 321, a sequence number management unit 322, a packet loss detection unit 324, a retransmission request notification unit 325, a group And an information analysis unit 323.

  The data receiving unit 321 receives multicast data from the filtering unit 331a of the wireless communication processing unit 330, passes the received data to the application processing unit 310, and notifies the sequence number management unit 322 of sequence number information.

  In the case of a packet addressed to the higher transmission rate group, the data receiving unit 321 notifies only the sequence number information to the sequence number management unit 322 and then discards the packet.

  The sequence number management unit 322 stores and manages a sequence number reception history for each multicast group in a storage unit (not shown).

  As a sequence number storing method, a method of storing a plurality of sequence numbers received in the past is applied. Other than this, any method such as a method of storing only the sequence number information that has been normally received last is applicable.

  The former method is a method of storing information on the sequence number every time multicast data is received, such as 998, 999, 1001, 1002, and 1004. As a result, when a NACK is transmitted, a retransmission request for a plurality of packets (1000, 1003) can be issued, but the matching processing of a packet in which a necessary storage capacity increase or a packet loss occurs is relatively large. There is a problem.

  The latter method requires a minimum storage capacity (for one packet). However, when a packet loss is detected and a data retransmission request is notified, detailed designation in units of packets cannot be performed. For this reason, it may be necessary to transmit data that has been successfully transmitted in duplicate.

  The group information analysis unit 323 passes group information including a sequence number for each multicast group periodically broadcast from the video distribution server 100 to the packet loss detection unit 324.

  In addition, the group information analysis unit 323 updates the filtering setting according to the group information. Specifically, after the group information analysis unit 323 is changed to the lower transmission rate group, in addition to the data addressed to the group to which the group belongs, the group information analysis unit 323 sets the filtering so that the data of the group to which the group previously belonged can be received. Update. This is necessary in order for the wireless STA that has been reassigned to the lower transmission rate to return to the upper transmission rate group again as the propagation path environment improves.

  The packet loss detection unit 324 detects a packet loss with reference to the reception history of the sequence numbers managed by the sequence number management unit 322. Specifically, for example, when the packet with the sequence number 1002 is received next to the sequence number 1000, the packet loss detection unit 324 detects that the packet with the sequence number 1001 is lost.

  Also, the packet loss detection unit 324 acquires the latest sequence number of the group to which it belongs from the group information passed from the group information analysis unit 323, and receives the sequence number reception history managed by the sequence number management unit 322. Compared with, packet loss is detected.

  For example, when the latest sequence number is 1005 and sequence numbers up to 1004 are stored in the reception history, the packet loss detection unit 324 detects that the packet with the sequence number 1005 is missing.

  The retransmission request notification unit 325 notifies the video distribution server 100 of a retransmission request for the corresponding packet when the packet loss detection unit 324 detects a packet loss.

  The wireless communication processing unit 330 performs communication using a wireless LAN interface such as IEEE802.11a, IEEE802.11b, IEEE802.11g, or IEEE802.11n. The wireless communication processing unit 330 includes a MAC layer processing unit 331 and a PHY layer processing unit 332.

  The MAC layer processing unit 331 performs wireless communication processing in the MAC layer, and includes a filtering unit 331a.

  The filtering unit 331a performs multicast filtering on the multicast data received by the antenna 341 and passed through the PHY layer processing unit 332, and determines whether the data is addressed to the group to which the own device belongs. Is. For data addressed to a group to which the own device does not belong, the filtering unit 331a discards the received data.

  Data addressed to the group to which the own device belongs is notified to the data receiving unit 321 together with additional information such as reception rate information. As will be described later, when belonging to or returning from the higher transmission rate group, the filtering unit 331a passes the received data to the data receiving unit 321 without discarding it.

  The PHY layer processing unit 332 performs wireless communication processing in the PHY layer on the data received by the antenna 341, and can be realized with the same function as the processing in the PHY layer of a conventionally used wireless communication device. .

  Next, data transmission processing by the video distribution server 100 according to the first embodiment configured as described above will be described. FIG. 9 is a flowchart showing an overall flow of data transmission processing in the first embodiment.

  First, the video data generation unit 111 generates a packet to be transmitted for each group (step S901). For example, a packet of an I picture that is the basis of an MPEG video stream is generated for a group having a robust transmission rate, and a packet including a P picture or a B picture that represents a difference from data predicted from a past packet is a high transmission rate. Generate only for groups of Details of generation and transmission processing of an MPEG video stream including an I picture, a P picture, or a B picture will be described later.

  Next, the data transmission unit 121 adds a sequence number to the packet created for each group (step S902). At this time, the data transmission unit 121 refers to the sequence number for each group managed by the group management unit 123. Also, processing such as setting a multicast address is executed here.

  Next, the data transmission unit 121 passes the packet to be transmitted to the wired communication processing unit 130 (step S903). Subsequently, in preparation for retransmission of the multicast data, the data transmission unit 121 stores a copy of the transmitted multicast data in the retransmission data storage unit 141 (step S904). The capacity of data stored in the retransmission data storage unit 141 is implementation-dependent and is not limited to the example of the present embodiment.

  Next, the wired communication processing unit 130 transmits the packet passed from the data transmission unit 121 to the wireless AP 200 (step S905).

  Next, the wired communication processing unit 210 of the wireless AP 200 receives the packet (step S906), and the wireless communication processing unit 220 transmits the received packet to each wireless STA 300 at a different transmission rate for each group (step S907). The transmission rate for each group is determined with reference to information managed by the transmission rate management unit 221a.

  Next, the wireless communication processing unit 330 of the wireless STA 300 receives the packet (step S908), and the data reception unit 321 receives the packet filtered as data addressed to the own device by the filtering unit 331a (step S909).

  Next, the video data output unit 311 outputs the packet received by the data receiving unit 321 and ends the data transmission process (step S910).

  Actually, a packet loss detection recovery process, which will be described later, is executed between step S909 and step S910, and after the packet is normally received, the output process by the video data output unit 311 is executed.

  As described above, in the data transmission processing according to the first embodiment, a conventional wireless communication apparatus is characterized in that a packet with a sequence number added to each group is generated and transmitted, and a means for retransmission is provided to improve reliability. Is different. A process for detecting a packet loss using a sequence number will be described below.

  Next, packet loss detection and recovery processing by the video distribution server 100 according to the first embodiment configured as described above will be described.

  In wireless LAN, when two or more communication devices transmit communication data using the same wireless medium (wireless channel) at the same time, the communication device on the receiving side cannot separate the communication data (collision: Collision ) Occurs. Therefore, the cause of packet loss in the wireless LAN is distinguished between a case where the receiving terminal cannot normally analyze information due to a collision and a case where a packet error occurs due to distance attenuation. In multicast communication in IEEE 802.11, since there is no delivery confirmation from the receiving terminal for multicast data transmitted by the wireless AP 200, detection and recovery when a packet loss occurs in the multicast data cannot be performed.

  On the other hand, in the first embodiment, packet loss can be detected by referring to the sequence number, and a NACK response is returned from the wireless STA 300 that has detected the packet loss, thereby determining whether or not the packet can be received and recovering it. It becomes possible.

  FIG. 10 is a flowchart illustrating an overall flow of the packet loss detection recovery process according to the first embodiment.

  First, the sequence number management unit 322 of the wireless STA 300 acquires the sequence number of the received packet (step S1001). The packet is passed from the data receiving unit 321.

  Next, the packet loss detection unit 324 detects a packet loss with reference to the sequence number acquired by the sequence number management unit 322 and the reception history of the sequence number stored in the storage unit (not shown) (step S1002). ).

  For example, when 1002 is acquired as the sequence number and sequence numbers up to 1000 are stored in the reception history, the packet loss detection unit 324 detects that the packet having the sequence number 1001 cannot be received.

  As described above, when receiving the group information from the group information analysis unit 323, the packet loss detection unit 324 detects the packet loss with reference to the group information and the sequence number of the reception history. For example, when the sequence number in the group information indicates 1002, the reception history management unit of the wireless STA detects that a packet loss has occurred when there is a loss in the sequence numbers up to 1001.

  Next, the packet loss detection unit 324 determines whether or not a packet in which a packet loss has occurred within a predetermined time has been received (step S1003). If received (step S1003: YES), the recovery process need not be executed, and the packet loss detection recovery process is terminated.

  When a packet in which packet loss has occurred within a predetermined time is not received (step S1003: NO), the retransmission request notification unit 325 notifies the wireless communication processing unit 330 of NACK (packet negative response). (Step S1004).

  Next, the wireless communication processing unit 330 transmits NACK to the wireless AP 200 by unicast (step S1005). At this time, the wireless communication processing unit 330 transmits NACK at a robust transmission rate in order to reliably transmit.

  Next, the wireless communication processing unit 220 of the wireless AP 200 receives NACK (step S1006), and the wired communication processing unit 210 transmits the received NACK to the video distribution server 100 (step S1007).

  Next, the wired communication processing unit 130 of the video distribution server 100 receives the NACK (step S1008), and the retransmission unit 122 determines whether or not the packet is received for the first time (step S1009). The retransmission unit 122 determines the number of NACK receptions by storing a past NACK reception history in a storage unit (not shown).

  When the NACK reception is the first time (step S1009: YES), the retransmission unit 122 retransmits the packet by unicast to the wireless STA 300 that has transmitted the retransmission request (step S1010).

  When the NACK reception is not the first time (step S1009: NO), the retransmission unit 122 retransmits the packet by multicast to all the wireless STAs 300 belonging to the group corresponding to the corresponding packet (step S1012). When retransmitting a packet by multicast, it is desirable to transmit at a robust transmission rate in order to reliably transmit information.

  After retransmitting the packet in step S1010, retransmission section 122 determines whether or not a NACK has been received from another wireless STA 300 within a predetermined period (step S1011). This is because when there is a collision on the wireless section, there is a possibility of receiving NACK from a plurality of wireless STAs 300, so that determination is made.

  If a NACK is received from another wireless STA 300 within a predetermined period (step S1011: YES), the retransmission unit 122 sends a packet to all the wireless STAs 300 belonging to the group corresponding to the corresponding packet by multicast. Retransmit (step S1012).

  When no NACK is received from another wireless STA 300 within a predetermined period (step S1011: NO), group reconfiguration processing by the group management unit 123 is executed (step S1016). Details of the group reconfiguration process will be described later.

  Although not shown in FIG. 10, when the retransmission unit 122 retransmits the packet in step S1010 or step S1012, the wired communication processing unit 130 of the video distribution server 100 sends the packet to the wired communication processing unit 210 of the wireless AP 200. Sent.

  Next, the wired communication processing unit 210 of the wireless AP 200 receives the retransmitted packet (step S1013), and the wireless communication processing unit 220 transmits the packet to the wireless STA 300 (step S1014).

  Next, the wireless communication processing unit 330 of the wireless STA 300 receives the packet (step S1015), and ends the packet loss detection recovery process.

  Next, the group reconfiguration process in step S1016 will be described. FIG. 11 is a flowchart illustrating an overall flow of the group reconfiguration process according to the first embodiment.

  First, the group management unit 123 determines whether there is a wireless STA 300 that has been retransmitted continuously a predetermined number of times (step S1101). The group management unit 123 determines the number of retransmissions for each wireless STA by storing a past retransmission history in a storage unit (not shown).

  When there is a wireless STA 300 that has been retransmitted continuously a predetermined number of times (step S1101: YES), the group management unit 123 sets the corresponding wireless STA 300 group to a lower transmission rate than the group to which it currently belongs. To the group (step S1102).

  Next, the group management unit 123 transmits a basic signal for refresh to the wireless STA 300 whose group has been changed by unicast (step S1103). The basic signal refers to data that is a basic signal that does not depend on other data, such as an MPEG I picture. By performing the refresh, it becomes possible to execute the video output process normally by synchronizing the data.

  In addition, when the first embodiment is applied to a technique in which a display screen of a remote PC (Personal Computer) is shared by a plurality of receiving terminals, it is necessary to perform the refresh as described above. In this technique, a basic frame in which one entire screen is encoded by JPEG (Joint Photographic Experts Group) is transmitted first, and after that, only a difference portion in the screen is cut out and JPEG compressed and transmitted.

  In this technology, for example, the video distribution server 100 existing in a remote place transmits a high-resolution compressed screen for a high transmission rate group, and a relatively low-resolution compressed screen for a robust transmission rate group. Send information. When a group is changed, it is not synchronized with the screen information distributed to the group to which the change is made. Therefore, for the purpose of refreshing, a compressed image of the entire screen is only transferred to the wireless STA 300 whose group has been changed. Must be sent in a cast.

  If it is determined in step S1101 that there is no wireless STA 300 that has been retransmitted continuously a predetermined number of times (step S1101: NO), the group management unit 123 does not need to reconfigure the group, so The configuration process ends.

  Next, the group participation request process performed by the video distribution server 100 according to the first embodiment configured as described above will be described. The group participation request processing is, for example, high when the wireless STA 300 moved to the low transmission rate group by the above-described group reconfiguration processing approaches a short distance from the wireless AP 200 or when the channel state becomes good. This process is executed in order to return to the transmission rate group and enable efficient multicast data transmission.

  FIG. 12 is a flowchart illustrating an overall flow of the group participation request process according to the first embodiment.

  First, the wireless communication processing unit 330 of the wireless STA 300 receives a packet (step S1201). Note that this packet means a packet transmitted from the video distribution server 100 via the wireless AP 200 by the same processing as in steps S901 to S907 of the data transmission processing of FIG.

  Next, the filtering unit 331a determines whether the packet is for a group other than the group to which the own device belongs (own group) (step S1202). If it is not a packet addressed to another group (step S1202: NO), the video data output unit 311 outputs a packet addressed to the own group (step S1213), and ends the group participation request process.

  If the packet is addressed to another group (step S1202: YES), the data reception unit 321 passes the packet to the sequence number management unit 322 (step S1203). Next, the sequence number management unit 322 stores the reception history for each group in the storage unit (step S1204). At this time, the sequence number management unit 322 stores not only the sequence number of the data of the own group but also the sequence number of the data addressed to other groups including the upper group.

  Next, the data receiving unit 321 discards packets addressed to other groups (step S1205).

  According to the IEEE 802.11 standard, when a MAC frame destined for a destination other than the multicast group to which the wireless STA 300 belongs is received, the NAV (Network Allocation Vector) is set and the data payload portion is not analyzed. , Discard the entire MAC frame.

  In the first embodiment, in order to determine whether or not the wireless STA 300 can stably receive a packet of a multicast group to which the wireless STA 300 belongs in the past, the internal packet is also transmitted with respect to a packet other than the multicast group to which the own device belongs. Analyze the data payload.

  That is, the sequence number management unit 322 analyzes the multicast data sequence number information inside the data (the MSDU: MAC Service Data Unit unit as the unit of the MAC layer) and stores it in the reception history. The only information necessary for the received multicast data is the destination group and sequence number, and the data payload body is discarded after packet analysis.

  After discarding the packet in step S1205, the group information analysis unit 323 refers to the reception history and determines whether or not the packet addressed to the upper group has been normally received for a predetermined number of times (step S1206). .

  If it cannot be received normally (step S1206: NO), the group participation request process is terminated.

  If the reception is successful (step S1206: YES), the group information analysis unit 323 transmits a request for participation in the upper group to the video distribution server 100 (step S1207). Although omitted in FIG. 12, the participation request is transmitted to the wireless communication processing unit 220 of the wireless AP 200 by the wireless communication processing unit 330 of the wireless STA 300. Further, it is desirable to transmit the participation request at a robust transmission rate in order to reliably transmit information.

  The transmitted participation request is received by the wireless communication processing unit 220 of the wireless AP 200 (step S1208), and is transmitted to the video distribution server 100 by the wired communication processing unit 210 (step S1209).

  Next, the wired communication processing unit 130 of the video distribution server 100 receives the participation request (step S1210).

  Next, the group management unit 123 changes the group of wireless STAs that transmitted the participation request to the group requested to participate (step S1211).

  In addition, you may comprise so that a participation request may be performed with respect to not only the group which has belonged in the past but arbitrary groups. As shown in FIG. 6, each wireless STA 300 can acquire sequence number information of an arbitrary group. Further, when the configuration is such that the sequence number information of a large number of groups is acquired, the data processing load at the time of reception increases, so that only the sequence numbers of some groups may be acquired.

  Further, the group management unit 123 may be configured not to perform group reconfiguration when a predetermined condition for stably receiving a message is not satisfied even when a participation request is received. . For example, in a situation where the radio wave condition is unstable and frequent changes between the high transmission rate group and the low transmission rate occur, the group may not be reconfigured until the radio wave condition stabilizes. desirable.

  Next, the group management unit 123 transmits a basic signal for refresh to the wireless STA 300 whose group has been changed by unicast (step S1212), and ends the group participation request process.

  Next, a specific example of communication processing by the video distribution server 100 according to the first embodiment will be described. FIG. 13 is an explanatory diagram showing an example of a group to which the wireless STA 300 belongs.

  In the first embodiment, a multicast group is formed for each wireless LAN transmission rate. FIG. 1 shows an example of a wireless network in IEEE 802.11a.

  In the example shown in the figure, the wireless STA 300a, the wireless STA 300b, and the wireless STA 300c at a distance close to the wireless AP 200 belong to the group 1 (54 Mbps high transmission rate group), and the wireless STA 300d and the wireless STA 300e are the group 2 (24 Mbps robust transmission rate group). ). In the first embodiment, the wireless STA 300 in the high transmission rate group also belongs to a lower transmission rate group. For example, in the example shown in the figure, the wireless STA 300a, the wireless STA 300b, and the wireless STA 300c also belong to the group 2.

  When grouped in this way, group information as shown in FIG. 3 is stored in the group information storage unit 142.

  Note that IEEE 802.11 does not define an algorithm for determining a transmission rate in a wireless LAN. Therefore, in the first embodiment, from the result of RSSI (Received Signal Strength Indicator) measurement in the wireless LAN, the wireless STA 300 whose strength is relatively stable at the start of multicast communication is received as a high transmission rate group. A method is adopted in which wireless STAs 300 having low strength are allocated in advance to robust transmission rate groups.

  Note that a method may be adopted in which communication is started at the highest transmission rate group in which all wireless STAs 300 can be transmitted within a BSS (Basic Service Set). Further, a method of starting communication by grouping to the lowest robust transmission rate may be employed.

  FIG. 14 is an explanatory diagram showing an example of a transmission state of wireless multicast data according to IEEE 802.11a.

  The figure shows an example in which packet loss occurs in the wireless STA 300d and the wireless STA 300e that are far from the wireless AP 200 when multicast data is transmitted at a transmission rate of 54 Mbps.

  In IEEE802.11a, a plurality of transmission rates from 6 Mbps to 54 Mbps are defined depending on the modulation method. Basically, it is possible to perform communication over a longer distance as the transmission rate is lower. Accordingly, when the wireless AP 200 communicates with a nearby wireless STA 300 at a high transmission rate and communicates with a remote wireless STA 300 by switching to a low transmission rate, the wireless AP 200 can efficiently communicate over a wide area. . Note that IEEE 802.11 does not define an algorithm for selecting an appropriate transmission rate.

  FIG. 15 is an explanatory diagram illustrating an example of a video stream transmitted in the first embodiment. In the example of the figure, it is shown that the video distribution server 100 transmits a video stream by MPEG.

  An MPEG stream is an I (Intra) picture for intra-frame coding of all the screens using DCT (Discrete Cosine Transform), a P (Predictive) picture for forward predictive coding from a past frame, and two past and future pictures. There are three types of B (Bidirectional) pictures that perform inter-frame prediction in two directions from a frame and encode a difference. As shown in the figure, in the first embodiment, a video stream using an I picture and a P picture among the three types of pictures is transmitted. Note that a B picture may be transmitted, or video data other than an MPEG stream may be transmitted.

  In the first embodiment, different information data is transmitted to the multicast group for each transmission rate. For example, high-frequency component information such as an I picture that is the basis of an MPEG video stream is reliably distributed at a robust transmission rate, and low-frequency component information such as a P picture is transmitted at a high transmission rate.

  In the example shown in the figure, since the wireless STA 300d and the wireless STA 300e belong to a robust transmission rate group, only the MPEG I picture is received. Since the wireless STA 300a, the wireless STA 300b, and the wireless STA 300c receive not only the I picture but also the P picture addressed to the high transmission rate group, complete video stream reproduction can be realized.

  Note that the wireless STA 300d and the wireless STA 300e receive only I pictures and are smooth because there is no P picture, but it is possible to reproduce video in a state where there is little influence of image quality degradation due to packet loss. .

  FIG. 16 is an explanatory diagram showing an example of a sequence number and NACK to be transmitted. As shown in the figure, the video distribution server 100 manages the sequence number information for each group divided by the transmission rate, and increments the number by one each time data is transmitted. When the number reaches a predetermined maximum value, the number is cyclically returned to the minimum value. For example, when managing a sequence number with 16 bits, it starts from 0, and when it reaches 65535, the next starts from 0 again.

  In the example of the figure, data up to sequence number 1000 is transmitted for a high transmission rate (54 Mbps) group, and data of sequence numbers up to 5000 is transmitted for a robust transmission rate (24 Mbps) group. It shows that.

  As described above, each wireless STA 300 that receives the multicast data stores a sequence number history for each group (step S1204).

  In the figure, it is shown that the wireless STA 300a and the wireless STA 300b have successfully received the multicast data of the high transmission rate group up to the sequence number 1000, and have successfully received the multicast data to the group of the robust transmission rate up to the sequence number 5000. Has been. Since the wireless STA 300d and the wireless STA 300e belong only to a multicast group having a robust transmission rate, the stored information is one type (only 5000).

  Here, when the wireless STA 300c in the figure fails to receive the data of the sequence number 1000 of the high transmission rate group, the last received sequence number information is 999. When wireless STA 300c detects that reception of data of sequence number 1000 has failed, NACK 1601 for prompting the transmission source to retransmit is transmitted by unicast (step S1004).

  FIG. 17 is an explanatory diagram showing an example of recovery processing when a packet loss occurs. The figure shows an example in which the video distribution server 100 transmits the multicast data 1701 of sequence number 1 to the wireless STA 300a, the wireless STA 300b, and the wireless STA 300c.

  In this example, it is assumed that the wireless STAs 300a, 300b, and 300c belong to a group with a high transmission rate (for example, 54 Mbps), and the wireless AP 200 also performs transmission processing at a transmission rate based on this.

  Here, when an arbitrary packet is transmitted from the wireless STA 300 at the same timing as the multicast data transmission by the wireless AP 200, a collision on the wireless channel occurs and reception of all the packets fails. That is, the wireless STAs 300a, 300b, and 300c fail to receive multicast data transmitted via the wireless AP 200.

  Thereafter, assuming that packet loss is detected by receiving group information, each wireless STA 300 waits for a random time and then transmits NACK to the video distribution server 100 by unicast. In the figure, an example in which the wireless STA 300a first transmits a NACK 1702 is shown.

  When receiving the NACK from the wireless STA 300a, the video distribution server 100 transmits the retransmission data 1703 to the wireless STA 300a by unicast. The reason why the first retransmission is not performed by multicast is to distinguish between a packet loss due to collision and a packet loss due to distance attenuation (deterioration of channel conditions) accompanying movement.

  When a retransmission request (NACK) of the same sequence number is received from another wireless STA 300 after the unicast retransmission to the wireless STA 300a is completed, it can be detected that a collision has occurred on the wireless channel. Therefore, the video distribution server 100 that has received the NACK twice or more retransmits the data by multicast. In the figure, an example in which NACK 1704 is transmitted again from the wireless STA 300b and multicast data 1705 is transmitted from the video distribution server 100 is shown.

  In the example shown in the figure, if the wireless STA 300a successfully receives the first retransmission data 1703, duplicate data will be received during the second retransmission using the multicast data 1705, so the duplicate information is discarded. .

  In addition, the wireless STA 300c cancels transmission of NACK when the multicast data 1705 is received.

  As shown in the second half of FIG. 17, after the wireless STA 300c cannot receive the multicast data 1706 and transmits NACK 1707, if another wireless STA 300 does not transmit NACK after a certain period of time, only the wireless STA 300c transmits data. This means that reception has failed.

  As described above, when a situation in which only a specific wireless STA 300 cannot normally receive data continues for a predetermined period or longer, the video distribution server 100 reconfigures the multicast group.

  FIG. 18 is an explanatory diagram of an example of group reconfiguration. In the figure, an example is shown in which the wireless STA 300c has moved from a high transmission rate group to a robust transmission rate group.

  Therefore, the wireless STA 300a and the wireless STA 300b belong to the high transmission rate (54 Mbps) group, and the wireless STA 300a, the wireless STA 300b, the wireless STA 300c, the wireless STA 300d, and the wireless STA 300e belong to the robust transmission rate (24 Mbps) group. To do.

  FIG. 19 is an explanatory diagram showing an example of group information in the state of grouping in this way. As shown in the figure, the wireless STA 300c is deleted from the group 1.

  FIG. 20 is an explanatory diagram illustrating an example of the group reconfiguration process. This figure shows an example in which a group is reconfigured by transmitting a request to join a high transmission rate group from a state in which the wireless STA 300c is changed to a low transmission rate group.

  In the figure, the wireless STA 300c that has moved to the robust transmission rate group monitors the multicast data 2001, 2002, and 2003 corresponding to the sequence numbers 1000, 1001, and 1002 addressed to the high transmission rate group. It is determined whether it has been received stably depending on whether it has been received.

  When the wireless STA 300c is able to stably receive, the wireless transmission STA 300c notifies the video delivery server 100 of the request for participation in the higher transmission rate group 2004 by unicast (step S1207).

  After receiving the participation request 2004, the video distribution server 100 reconfigures the multicast group and adds the wireless STA 300c to the high transmission rate group. As a result, as shown in the figure, the wireless STA 300c can receive multicast data 2005 and 2006 transmitted at a high transmission rate.

  In the above, the description has been made on the premise of an example (FIGS. 5 to 7) in which the transmitted / received message is set in the header or datagram of the transport layer protocol. The message format is not limited to this, and the message may be set by an IP layer protocol, an application layer protocol, or the like.

  FIG. 21 is an explanatory diagram illustrating another example of the configuration of the data packet transmitted and received in the first embodiment.

  The figure shows a configuration example of a data packet in which a field (multicast header) including a source port number, a destination port number, a data packet sequence number, and a checksum for detecting these information errors is added to the field following the IP header. Show. Note that data of an upper layer (for example, a transport layer) than the IP layer is added after the multicast header.

  FIG. 22 is an explanatory diagram illustrating another example of the configuration of the group information management packet transmitted and received in the first embodiment.

  This figure shows a configuration example of a group information management packet for setting group information in an IP datagram. As shown in the figure, unlike the group information management packet of FIG. 6, group information is set in the IP datagram. As described above, the group information may be created for each group and notified separately, instead of collecting the group information in one packet.

  FIG. 23 is an explanatory diagram illustrating another example of the configuration of the NACK packet transmitted and received in the first embodiment.

  This figure shows a configuration example of a NACK packet for setting a NACK sequence number in an IP datagram. As shown in the figure, unlike the group information management packet of FIG. 7, a NACK sequence number is set immediately after the IP header.

  As described above, in the video distribution server according to the first embodiment, at the time of multicast distribution in wireless communication, the cause of packet loss by using the reply status of the negative response from the receiving terminal that has detected the loss of data Can be distinguished from collision or distance attenuation, and reconfiguration of the multicast group for each transmission rate can be performed accordingly. For this reason, it is possible to improve the reliability of data distribution accompanying the discrimination of the transmission rate, and to ensure the communication efficiency according to the channel state.

(Second Embodiment)
In the first embodiment, the configuration example is described in which the function for wirelessly communicating data is executed by the wireless AP and the function is divided so that the other processing is executed by the video distribution server. You may comprise so that it may execute within. In the second embodiment, a communication apparatus (wireless AP) configured as described above will be described.

  FIG. 24 is a block diagram illustrating a configuration of a wireless AP 2400 that is a communication device according to the second embodiment. As shown in the figure, the wireless AP 2400 includes an application processing unit 110, a multicast processing unit 120, a wireless communication processing unit 220, a retransmission data storage unit 141, and a group information storage unit 142.

  In the first embodiment, since the functions are divided into the video distribution server 100 and the wireless AP 200, the wired communication processing units 130 and 210 are provided to transmit and receive data between the two. On the other hand, in the second embodiment, the functions are concentrated in the wireless AP 2400, so that a wired communication processing unit is not necessary.

  Therefore, as shown in the figure, the wireless AP 2400 is connected to all the functional units other than the wired communication processing unit 130 of the video distribution server 100 in the first embodiment and the wired communication of the wireless AP 200 in the first embodiment. The configuration includes all the functional units other than the processing unit 210.

  Since the function of each functional unit is the same as that of the configuration of the first embodiment, the same reference numerals are given and the description thereof is omitted here. The data transmission process, the packet loss detection recovery process, and the group participation request process are the same as those in the first embodiment except that data is transmitted and received directly using the wireless communication processing unit 220 without using the wired communication processing unit. Since this is the same, the description thereof is omitted.

  In the above-described configuration, the multicast processing unit 120 is separated from the MAC layer processing unit 221 and realized in higher layers including the IP layer. However, the MAC layer processing unit 221 has a function of the multicast processing unit 120. You may comprise. In this case, it is necessary to use a packet format that can process a message in the MAC layer.

  FIG. 25 is an explanatory diagram illustrating another example of the configuration of the data packet transmitted and received in the second embodiment.

  This figure shows a configuration example of a data packet in which a sequence number information field and a fragment number information field existing in an IEEE802.11 MAC header are used and a data packet sequence number is set in the sequence number information field. This makes it possible to execute sequence number acquisition processing and the like in the MAC layer.

  FIG. 26 is an explanatory diagram showing another example of the configuration of the group information management packet transmitted and received in the second embodiment.

  As shown in the figure, when the MAC layer processing unit 221 has the function of the multicast processing unit 120, the packet format is set in which group information is set after the MAC header. As described above, the group information may be created for each group and notified separately, instead of collecting the group information in one MAC frame.

  FIG. 27 is an explanatory diagram illustrating another example of the configuration of the NACK packet transmitted and received in the second embodiment.

  As shown in the figure, when the MAC layer processing unit 221 has the function of the multicast processing unit 120, the packet format has a MAC header followed by a NACK sequence number.

  FIG. 28 is an explanatory diagram showing still another example of the configuration of the NACK packet transmitted and received in the second embodiment.

  When the wireless STA 300 is configured to store the history of sequence numbers for a plurality of reception times, data that has failed to be received can be individually specified, so that it is possible to selectively specify retransmission of a plurality of data. . This figure is a diagram showing a configuration example of a NACK packet when a plurality of data retransmission requests can be transmitted in this way.

  As shown in the figure, following the MAC header, there are a number of NACK sequence number fields (number of NACK frames) and a plurality of NACK sequence number fields for prompting retransmission of a plurality of data.

  For example, when the wireless STA 300 has received data with sequence numbers 1000, 1002, 1003, and 1005 in the past, an NCK packet in which NACK frame number field is set to 2, NACK sequence number 1 is set to 1001, and NACK sequence number 2 is set to 1004 Send.

  The configuration example in FIG. 28 is an example in a configuration in which the function of the multicast processing unit 120 is provided in the MAC layer processing unit 221, but a plurality of sequences may be used when multicast processing is performed in the IP layer, transport layer, and application layer. It can be configured to specify a number.

  As described above, since the wireless AP 2400 according to the second embodiment can consolidate all the sequence number management processing and retransmission processing, the network load on the Internet or the wired LAN can be reduced.

  FIG. 29 is an explanatory diagram of a hardware configuration of the communication device according to the first and second embodiments.

  The communication device according to the first and second embodiments communicates with a control device such as a CPU (Central Processing Unit) 51 and a storage device such as a ROM (Read Only Memory) 52 and a RAM 53 by connecting to a network. A communication I / F 54 to be performed, an external storage device such as an HDD and a CD (Compact Disc) drive device, a display device such as a display device, an input device such as a keyboard and a mouse, and a bus 61 for connecting each part are provided. The hardware configuration uses a normal computer.

  The communication program executed by the communication apparatus according to the first and second embodiments is a file in an installable format or an executable format, and is a CD-ROM (Compact Disk Read Only Memory), a flexible disk (FD), The program is provided by being recorded on a computer-readable recording medium such as a CD-R (Compact Disk Recordable) or a DVD (Digital Versatile Disk).

  The communication program executed by the communication device according to the first and second embodiments is stored on a computer connected to a network such as the Internet, and is provided by being downloaded via the network. May be. The communication program executed by the communication device according to the first and second embodiments may be provided or distributed via a network such as the Internet.

  Further, the communication programs of the first and second embodiments may be provided by being incorporated in advance in a ROM or the like.

  The communication program executed by the communication device according to the first and second embodiments has a module configuration including the above-described units (application processing unit, multicast processing unit, and wired communication processing unit), and the actual hardware As hardware, the CPU 51 (processor) reads out and executes a communication program from the storage medium, whereby the above-described units are loaded onto the main storage device, and the above-described units are generated on the main storage device.

  As described above, the communication device, the communication method, and the communication program according to the present invention are suitable for a wireless communication device that transmits multicast data to an external wireless terminal grouped in transmission rate units.

It is explanatory drawing which shows an example of a structure of wireless LAN containing the video delivery server which is a communication apparatus concerning 1st Embodiment. It is a block diagram which shows the structure of the video delivery server concerning 1st Embodiment. It is explanatory drawing which shows an example of the data structure of the group information stored in the group information storage part. It is a block diagram which shows the structure of the wireless AP concerning 1st Embodiment. It is explanatory drawing which shows an example of a structure of the data packet transmitted / received in 1st Embodiment. It is explanatory drawing which shows an example of a structure of the group information management packet transmitted / received in 1st Embodiment. It is explanatory drawing which shows an example of a structure of the NACK packet transmitted / received in 1st Embodiment. It is a block diagram which shows the structure of the radio | wireless STA concerning 1st Embodiment. It is a flowchart which shows the whole flow of the data transmission process in 1st Embodiment. It is a flowchart which shows the whole flow of the packet loss detection recovery process in 1st Embodiment. It is a flowchart which shows the whole flow of the group reconfiguration | reconstruction process in 1st Embodiment. It is a flowchart which shows the whole flow of the group participation request | requirement process in 1st Embodiment. It is explanatory drawing which shows an example of the group to which radio | wireless STA belongs. It is explanatory drawing which shows an example of the transmission condition of radio | wireless multicast data. It is explanatory drawing which shows an example of the video stream transmitted in 1st Embodiment. It is explanatory drawing which shows an example of the sequence number and NACK which are transmitted. It is explanatory drawing which shows an example of the recovery process at the time of packet loss generation | occurrence | production. It is explanatory drawing which shows an example of group reconstruction. It is explanatory drawing which shows an example of group information. It is explanatory drawing which shows an example of a group reconstruction process. It is explanatory drawing which shows another example of a structure of the data packet transmitted / received in 1st Embodiment. It is explanatory drawing which shows another example of a structure of the group information management packet transmitted / received in 1st Embodiment. It is explanatory drawing which shows another example of a structure of the NACK packet transmitted / received in 1st Embodiment. It is a block diagram which shows the structure of wireless AP which is a communication apparatus concerning 2nd Embodiment. It is explanatory drawing which shows another example of a structure of the data packet transmitted / received in 2nd Embodiment. It is explanatory drawing which shows another example of a structure of the group information management packet transmitted / received in 2nd Embodiment. It is explanatory drawing which shows another example of a structure of the NACK packet transmitted / received in 2nd Embodiment. It is explanatory drawing which shows another example of a structure of the NACK packet transmitted / received in 2nd Embodiment. It is explanatory drawing which shows the hardware constitutions of a communication apparatus.

Explanation of symbols

51 CPU
52 ROM
53 RAM
54 Communication I / F
61 Bus 100 Video distribution server 110 Application processing unit 111 Video data generation unit 120 Multicast processing unit 121 Data transmission unit 122 Retransmission unit 123 Group management unit 124 Group information notification unit 130 Wired communication processing unit 141 Retransmission data storage unit 142 Group information storage Part 200 Wireless AP
210 Wired communication processing unit 220 Wireless communication processing unit 221 MAC layer processing unit 221a Transmission rate management unit 222 PHY layer processing unit 231 Antenna 300 Wireless STA
310 Application processing unit 311 Video data output unit 320 Multicast processing unit 321 Data reception unit 322 Sequence number management unit 323 Group information analysis unit 324 Packet loss detection unit 325 Retransmission request notification unit 330 Wireless communication processing unit 331 MAC layer processing unit 331a Filtering unit 332 PHY layer processing unit 341 Antenna 400a, 400b, 400c, 400d, 400e Router 500 Internet 1601 NACK
1701 Multicast data 1702 NACK
1703 Retransmission data 1704 NACK
1705, 1706 Multicast data 1707 NACK
2001, 2002, 2003 Multicast data 2004 Participation request 2005, 2006 Multicast data

Claims (11)

Group information storage means for storing group information in which first group identification information for identifying a first multicast group is associated with identification information for identifying another communication device belonging to the first multicast group;
Transmission means for multicast transmission of a message with a sequence number corresponding to the first multicast group to the other communication device belonging to the first multicast group;
A retransmission means for receiving a retransmission request message for requesting retransmission of the message from the other communication apparatus, and for retransmitting the message requested for retransmission to the other communication apparatus that has received the retransmission request message;
When the retransmission means determines whether or not the retransmission request message has been continuously received from the other communication device a predetermined number of times or more, and determines that the retransmission request message has been received continuously or more than the number of times is the identification information of the other communication apparatus, in association with a second group identification information for identifying the second multicast group and updates the group information stored in the group information storage unit, the second A movement request message for requesting movement to a multicast group is received from the other communication apparatus, and the identification information of the other communication apparatus that has transmitted the movement request message is associated with the second group identification information. Group management means for updating the group information stored in the group information storage means ;
A communication apparatus comprising: The group information storage means further stores a first transmission rate used for communication with the first multicast group and a second transmission rate used for communication with the second multicast group,
The transmission means multicasts the message to the first multicast group at the first transmission rate, and multicasts to the second multicast group at the second transmission rate. The communication apparatus according to 1.   The retransmission means unicasts the message requested to be retransmitted to the first communication apparatus that first receives the retransmission request message among the other communication apparatuses belonging to the first multicast group. When the retransmission request message of the message to which the same sequence number is added is received from a second communication apparatus other than the first communication apparatus and belonging to the first multicast group, the other The communication apparatus according to claim 1, wherein the message requested to be retransmitted is multicast-transmitted to the communication apparatus.   When the group management unit determines that the retransmission request message has been received continuously more than the number of times, the identification information of the other communication device belongs to the other communication device when the retransmission request message is received. Updating the group information stored in the group information storage means in association with the second group identification information for identifying the second multicast group associated with a transmission rate lower than that of the first multicast group. The communication apparatus according to claim 1, wherein:   It further comprises notification means for broadcasting a notification message including a sequence number corresponding to the transmitted message for each of the first multicast groups to the other communication device at a predetermined time. The communication device according to claim 1.   The notifying means broadcasts a message including a sequence number corresponding to a transmitted message for each of the first multicast groups in a payload part of the transport layer, network layer, or data link layer of the message to the other communication device. The communication device according to claim 5, wherein the communication device transmits.   The communication apparatus according to claim 1, wherein the transmission unit adds the sequence number to a header part of a transport layer, a network layer, or a data link layer of the message.   The communication apparatus according to claim 1, wherein the transmission unit adds the sequence number to a payload portion of an application layer of the message.   The retransmission means receives the retransmission request message including at least one sequence number to be retransmitted in the payload part of the application layer, transport layer, network layer, or data link layer of the message from the other communication device. The communication apparatus according to claim 1. A transmission step of multicast transmission of a message with a sequence number corresponding to the first multicast group to another communication device belonging to the first multicast group;
Receiving a retransmission request message requesting retransmission of the message from the other communication device, and retransmitting the message requested to be retransmitted to the other communication device that has received the retransmission request message;
Group management means, wherein the retransmission step is continuously over a predetermined number of times from the other communication apparatus determines whether it has received the retransmission request message, receiving the retransmission request message continuously the number of times or more If it is determined that the first multicast group is identified, the identification information for identifying the other communication device is associated with the second group identification information for identifying the second multicast group, and the first multicast group is identified. Updating group information storage means for storing group information in which group identification information is associated with the identification information of the other communication devices belonging to the first multicast group, and requesting movement to the second multicast group The movement request message is received from the other communication apparatus and the movement request message is transmitted from the other communication apparatus. And group management step serial identification information in association with the second group identifier to update the group information stored in the group information storage means,
A communication method comprising: A transmission procedure for multicast transmission of a message with a sequence number corresponding to the first multicast group to another communication device belonging to the first multicast group;
A retransmission procedure for receiving a retransmission request message for requesting retransmission of the message from the other communication apparatus, and retransmitting the message requested to be retransmitted to the other communication apparatus that has received the retransmission request message;
When it is determined whether the retransmission procedure has received the retransmission request message continuously from the other communication device a predetermined number of times or more, and when it is determined that the retransmission request message has been received more than the number of times Associates the identification information for identifying the other communication device with the second group identification information for identifying the second multicast group, the first group identification information for identifying the first multicast group, and the Updating a group information storage means for storing group information in association with the identification information of the other communication device belonging to the first multicast group, and sending a movement request message requesting movement to the second multicast group The identification information of the other communication device that has received the other request from the other communication device and that has transmitted the movement request message. And Group Management procedure group identification information in association with the updating the group information stored in the group information storage means,
A communication program that causes a computer to execute.

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