JP2001156782A - Method for transmitting data to a plurality of destinations - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system that transmits data to a plurality of destinations that can reduce a data transmission time while keeping reliability of data transfer. SOLUTION: A transmission source station #1 transmits data A to a wireless station #2. The wireless station #2 transmits the received data A to a wireless station #3. After that, the data A are sequentially transmitted to a lowermost stream wireless station #n according to a broadcast list. Each wireless station (transmission source station #1) can receive data transmitted from a wireless station (wireless station #2) that is installed next to the wireless station #1 downward. When each wireless station (transmission source station #1) cannot receive the data A sent from the next downward wireless station (wireless station #2) to a next wireless station (wireless station #3), each wireless station (transmission source station #1) transmits again the data A to the wireless station (wireless station #2) installed downward by one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a system for transmitting data to a plurality of destinations, and more particularly to a technique for transmitting a packet to a plurality of destinations in a wireless data transmission system.

[0002]

2. Description of the Related Art In recent years, wireless data transmission has rapidly spread. In particular, mobile phones, wireless LANs, and the like have become indispensable in ordinary life and business.

In a wireless data transmission system, data is generally stored in a packet and transmitted. The packet includes "destination address", "source address", "packet type" and "data to be transmitted" as shown in FIG. 9 (a). A network basically sends a packet transmitted from a source station to all wireless stations existing in a wireless area. Then, when the destination address set in the received packet matches the address of its own, each wireless station captures the packet. As a result, data is transmitted from the source station to the desired destination station.

However, in a wireless data transmission system,
The packet may be discarded without reaching the destination station due to the deterioration of the transmission path environment or the like. For this reason, especially a wireless LAN or the like has a data retransmission function.

In a system having a data retransmission function, generally, when a destination station receives a packet, the destination station notifies the source station of the packet (hereinafter referred to as “ACK (acko)”.
wledgment) packet. ) Is returned to the source station. On the other hand, the source station waits for the return of the ACK packet from the destination station for a certain period of time after transmitting the packet. At this time, as shown in FIG. 9B, when the ACK packet is received, the source station determines that the packet has arrived at the destination station. On the other hand, if the ACK packet cannot be received, the source station considers that the packet has not arrived at the destination station, and retransmits the previously transmitted packet. Thereby, deterioration of communication quality due to packet discarding and the like is avoided.

In a wireless data transmission system,
Demands for transmitting certain data to multiple destination stations often arise. In this case, the source station sets a value indicating "broadcast (broadcast communication)" as the destination address of the packet, and transmits the packet to the network. The net is
This packet is sent to all wireless stations existing in the wireless area. On the other hand, each wireless station is set to take in all the packets for which the value indicating “broadcast” is set as the destination address. With the above configuration, data is transmitted from the source station to the plurality of destination stations.

[0007]

However, in response to the broadcast packet, each destination station sends an A to the source station.
When trying to return a CK packet, there is a possibility that a plurality of ACK packets will collide with each other, as shown in FIG. In this case, the source station cannot recognize whether the packet has arrived at each destination station. For this reason,
In a wireless data transmission system, each destination station often does not return an ACK packet in response to a broadcast packet.

However, in a system that does not return an ACK packet, the data retransmission function cannot be used efficiently. For example, a method of repeatedly broadcasting the same packet a predetermined number of times irrespective of whether or not the packet has arrived at each destination station can be considered. However, this method has a disadvantage that radio resources are occupied more than necessary. . On the other hand, if the data retransmission function is not used at the time of broadcasting, the reliability of data transmission naturally decreases.

FIG. 11 is a diagram showing another conventional method for transmitting data to a plurality of radio stations. In this method, the source station executes the processing shown in FIG. 9B for each of a plurality of destination stations. Therefore, the reliability of data transmission is high. However, in this method, the source station needs to repeatedly execute the packet transmission processing according to the number of destination stations. For this reason, the load on the source station becomes excessive. Also,
The time required for all the destination stations to receive the packet becomes longer.

An object of the present invention is to improve the reliability of data transfer in a system for transmitting data to a plurality of destinations. Another object of the present invention is to reduce communication time in a system for transmitting data to a plurality of destinations, prevent waste of communication resources, and reduce the load on a transmission source station.

[0011]

According to the data transmission method of the present invention, when data is transmitted from a first station to a second station and a third station, the data is transmitted from the first station to the second station. ,
The second station sends data received from the first station to the third station, and the first station transmits data from the second station to the third station within a predetermined time. Is not detected, the data is retransmitted to the second station.

The data transmitted from the first station is transmitted to the second station and also transmitted to the third station via the second station. In this way, the first station can send data to a plurality of destination stations. If the first station cannot detect data transmission from the second station to the third station, the first station considers that data transmission from the first station to the second station has failed and considers the data transmitted earlier. To the second station. This implements a data retransmission function.

According to the data transmission method of the present invention, in addition to the above-described procedure, when a third station receives the data from the second station, it notifies the second station of the fact, However, when the notification cannot be received from the third station within a predetermined time, the data may be retransmitted to the third station.

When the third station, which is the most downstream station, receives the data from the second station, which is the upstream station, the third station notifies the second station of the same as in the case of the normal data retransmission function. This implements a data retransmission function.

In a data transmission method according to another aspect of the present invention, when data is transmitted from a source station to a plurality of destination stations, the data is broadcast from the source station to the plurality of destination stations,
When each destination station receives the data from the source station, the destination station notifies the source station of that fact, and the source station sends a notification to a destination station other than the destination station that sent the notification. Only resend the above data.

According to this configuration, data is not retransmitted to a communication station that has already received data by the previous broadcast. Therefore, unnecessary load does not occur on those destination stations due to data retransmission.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a diagram for explaining a data transmission method according to a first embodiment of the present invention. Here, wireless station # 1 to wireless station # 2
To #n.

The wireless stations # 1 to #n are not particularly limited, but are, for example, mobile terminals constituting a wireless LAN, and transmit and receive packets of a predetermined format, respectively. The wireless stations # 1 to #n may have the same configuration as each other, or may have a parent-child relationship (in the example of FIG.
Wireless station # 1, slave unit: wireless stations # 2 to #n) may be set.

Packets transmitted and received between the radio stations # 1 to #n include "destination address", "source address", "packet type", and "broadcast flag" as shown in FIG.
Includes "data to be transmitted". As the packet type, in this embodiment, "data" indicating that data to be transmitted is stored in the packet, or "ACK" indicating that the packet is an ACK packet is used. The broadcast flag is set to “0” when data is transmitted to one wireless station, and is set to “1” when data is transmitted to a plurality of wireless stations. Hereinafter, “broadcast = 0”
Is called a normal packet, and a packet with "broadcast = 1" is called a broadcast packet.

When data is transmitted to a plurality of wireless stations using the method of the first embodiment, as shown in FIG.
Data is not transmitted from a source station to a plurality of destination stations all at once, but is transmitted in sequence like a bucket brigade. Therefore, the transmission method of the first embodiment is as follows.
Strictly different from the original broadcast communication, the method of the present embodiment is hereinafter referred to as “broadcast” for convenience.

Each of the radio stations # 1 to #n has a broadcast list shown in FIG. This broadcast list indicates the order of data transmission. In the list of FIG. 3, it is registered that the wireless station # 1 is the most upstream station and the wireless station #n is the most downstream station. The method of generating and updating this list will be described later.

When data A is transmitted from the wireless station # 1 to the wireless stations # 2 to #n, the wireless station # 1 stores the data A in a packet, and the packet “Broadcast flag =
1 ”is set. Thereby, the data A is stored in the broadcast packet. Also, referring to the broadcast list, “destination address = wireless station # 2” is set in the packet. Further, “source address = wireless station # 1” and “data type = data” are set in the packet. Then, the wireless station # 1 sends this packet to the network (network), and the network transmits the packet to all wireless stations existing in the wireless area.

Each wireless station fetches the data stored in the packet when the destination address set in the received packet matches its own address. Here, since “destination address = wireless station # 2” is set, data A is taken in by wireless station # 2. Further, when the received packet is a broadcast packet, each wireless station, when the source address set in the received packet is the address of the wireless station one downstream of itself, Fetch the data stored in the packet. Here, “source address = wireless station # 1” is set, but wireless station #
Since 1 is the most upstream station, there is no radio station other than the radio station # 2 that takes in the data A.

Thus, the data A transmitted from the wireless station # 1 is received by the wireless station # 2. Radio station # 2
Updates the “destination address” and “source address” of the received packet. That is, with reference to the broadcast list, “destination address = wireless station # 3” is set in the packet, and “source address = wireless station #”
2 ”is set. Then, the wireless station # 2 transmits the packet to the network, and the network transmits the packet to all wireless stations existing in the wireless area.

As in the case described above, each wireless station fetches the data stored in the packet when the destination address set in the received packet matches the address of the wireless station itself. Here, "destination address =
Since the wireless station # 3 is set, the data A is taken in by the wireless station # 3. Also, when the source address set in the received packet is the address of the wireless station one downstream of itself, each wireless station fetches the data stored in the packet. Here, since “source address = wireless station # 2” is set, data A is also captured by wireless station # 1.

Thus, data A transmitted from wireless station # 2 is received by wireless station # 1 and wireless station # 3. Then, by receiving the data A from the wireless station # 2, the wireless station # 1 recognizes (detects) that the data transfer from the wireless station # 1 to the wireless station # 2 has succeeded.

Thereafter, as shown in FIG. 1, the radio stations # 3 to #n successively transmit the data A in the order registered in the broadcast list. At this time, each wireless station functioning as a relay station confirms whether or not the data transmitted by itself has been received by the downstream wireless station, as described as the operation of wireless station # 1. Then, the wireless station #n which is the most downstream station is a wireless station # (n-1)
Receives the data A from the base station, the ACK packet is returned to the wireless station # (n-1) without sending the packet storing the data A to the network.

As described above, in the system of this embodiment,
The data A transmitted from the wireless station # 1 is transmitted to the most downstream station while sequentially passing through the destination station.
The data A is transmitted to 2 to #n.

In the system of this embodiment, when data is not transmitted between arbitrary radio stations due to packet discarding or the like, a data retransmission function is used. Here, a data retransmission operation when data transmission from the wireless station # 1 to the wireless station # 2 fails will be described with reference to FIG.

The radio station # 1 receives the message “destination address = wireless station #
When a broadcast packet in which "2" is set is transmitted to the network, a timer is started and the corresponding packet is transmitted from the wireless station # 2. If the packet is received from the wireless station # 2 before the time T elapses, as described above, the wireless station # 1 determines that the data transfer from the wireless station # 1 to the wireless station # 2 has been completed. Recognize. In this case, the operation of the wireless station # 1 ends.

On the other hand, if the packet cannot be received from the wireless station # 2 before the time T has elapsed since the start of the timer, the wireless station # 1 switches from the wireless station # 1 to the wireless station # 2. It is assumed that the data transfer has failed. Then, the previously transmitted packet is retransmitted to the wireless station # 2. Thus, when the wireless station # 2 receives the data A from the wireless station # 1, the data A is sequentially transmitted to the wireless station #n in the same manner as in the sequence described with reference to FIG.

As described above, in the system of this embodiment,
Since it is recognized whether data transmission from a certain wireless station to a wireless station on the downstream side is successful, and data retransmission is performed according to the result, the reliability of data transmission is high. In addition, since unnecessary data retransmission is not performed, utilization efficiency of the data retransmission function is high. Further, in the system of the present embodiment, A
Since the data retransmission function is realized without using the CK packet, compared to the conventional method shown in FIG. Communication resources are saved.

FIG. 5 is a flowchart for explaining the operation of the radio station. This flowchart shows the operation of each wireless station except the most downstream station. In addition, this flowchart describes only processing related to data transfer.

When a packet is received in step S1, it is checked in step S2 whether the received packet is a broadcast packet and whether the received packet is a packet transmitted from an upstream wireless station. . In the former determination, the “broadcast flag” set in the received packet is referred to. In the latter determination, the “source address” set in the broadcast list and the received packet is referred to.

If the received packet is a broadcast packet transmitted from the upstream side, the process proceeds to step S3, and if not, another process is executed in step S9. Here, "other processing"
For example, it is a process of returning an ACK packet to the source station. In the operation of the most upstream station, the above steps S1, S1
2, S9 is omitted.

In step S3, the data stored in the packet received in step S1 is extracted, and after updating the destination address and the source address, the packet is transmitted to the downstream radio station. At this time, the destination address is determined with reference to the broadcast list. Then, in step S4, a timer is started.

In step S5, it is determined whether or not a packet corresponding to the packet transmitted in step S3 has been received from the downstream wireless station (the destination station in step S3) within a predetermined time after the timer is started. In this case, the address of the destination station in step S3 is compared with the source address set in the received packet.

If the corresponding packet can be received, it is considered that data transmission to the downstream wireless station has been successful, and
The process ends. On the other hand, if the corresponding packet cannot be received within the fixed time, it is considered that data transmission to the downstream wireless station has failed, and in step S6, the packet transmitted in step S3 is retransmitted.

In step S7, it is checked whether or not the number of executions of the data retransmission processing to the downstream radio station has reached a predetermined number. If the number has not reached the predetermined number, the process returns to step S4 after incrementing the counter for counting the number of retransmissions in step S8. On the other hand, if the number of retransmissions has reached the predetermined number, the processing is ended in order to avoid infinite repetition of data retransmission.

FIG. 6 is a flowchart for explaining the operation of the most downstream radio station. The processing in steps S1, S2, and S9 is the same as the operation of the wireless station other than the most downstream one. However, if the received packet is a broadcast packet transmitted from the upstream side, the most downstream wireless station sends an ACK packet to the upstream wireless station in step S11. In step S11, the ACK packet may be transmitted not only to the upstream wireless station but also to the most upstream wireless station.

As described above, in the system of the first embodiment, the broadcast list is provided for each wireless station, and each wireless station forwards a packet coming from the upstream side to the downstream side according to the list. Thereby, data is transmitted to a plurality of wireless stations. Therefore, the broadcast lists provided in each wireless station need to match each other.

The broadcast list is set, for example, by a system user or an administrator according to the configuration of the system. In this case, this setting operation is performed every time a new wireless station is added to the system or every time an arbitrary wireless station is removed from the system.

Also, the broadcast list may be automatically updated. In this case, for example, the master station (basically, the most upstream station) is determined, and the master station adds (including turning on the power of the wireless station) / deletes (including the wireless station) the wireless station in the wireless area. (Including that the power is turned off). Then, upon detecting the addition of the wireless station, the master station generates a new broadcast list including the added wireless station, stores the list in the broadcast packet described above, and sends the list to the downstream wireless station. Thereby, a new broadcast list is transmitted to each wireless station, and each wireless station updates its own list accordingly. At this time, the master station sends the above-described new broadcast list to the newly added wireless station by point-to-point communication. On the other hand, when detecting the deletion of the wireless station, the master station generates a new broadcast list accordingly. Then, the list is transmitted by point-to-point communication for each wireless station.

The method of creating and updating the broadcast list is not limited to the above method, and various other methods are conceivable. Second Embodiment FIG. 7 is a diagram for explaining a data transmission method according to a second embodiment of the present invention. Here, wireless station # 1 to wireless station # 2
To # 5. Note that data is stored in packets and transmitted between wireless stations. This packet includes a “destination address”, a “source address”, and a “data type” as described with reference to FIG. 9A.

When data is transmitted from the wireless station # 1 to the wireless stations # 2 to # 5, the wireless station # 1 first sets a value indicating "broadcast" as a destination address, similarly to the existing broadcast communication. The packet is sent to the network. Then, upon receiving the packet, the wireless stations # 2 to # 5 return an ACK packet to the wireless station # 1. At this time, the wireless stations # 2 to # 5 transmit ACK packets at different timings so as to prevent a plurality of ACK packets from colliding with each other.

The wireless station # 1 is connected to all destination stations (wireless station # 1).
If an ACK packet can be received from 2 to # 5), the process is terminated. If an ACK packet from one or more destination stations cannot be received, a data retransmission process is executed. The data retransmission processing differs depending on the number of ACK packets that could not be received. That is, the wireless station # 1 retransmits data by point-to-point communication when the number of unreceivable ACK packets is smaller than a certain threshold, and re-executes broadcast communication when the number is larger than the threshold. I do.

Here, an example will be shown with reference to FIG. 7 assuming that the above-mentioned threshold value is “2”. In the example shown in FIG. 7, in the broadcast communication from the wireless station # 1 to the wireless stations # 2 to # 5, data arrives at the wireless stations # 2, # 3, and # 5, but the data is transmitted to the wireless station # 4. No data has arrived. In this case, the wireless station # 1 is the wireless station # 2, # 3, #
5, but cannot receive an ACK packet from wireless station # 4. That is, the number of ACK packets that could not be received is “1”, which is smaller than the threshold. Therefore, the wireless station # 1 retransmits the packet to only the wireless station # 4 by the point-to-point communication.

As described above, in the method of the second embodiment,
When the number of stations that could not receive the data transmitted by the broadcast communication is small, the data is retransmitted only to the station that could not receive the data, instead of re-executing the broadcast. Therefore, it is expected that the load on the destination station is reduced as compared with the method of repeating the broadcast. In other words, despite the fact that data is being received at most of the destination stations, if the broadcast is repeated, most of the stations that have already received data will receive the previously received data and newly received data. It is necessary to determine whether the data is the same or not, and an extra load is generated. According to the method of the second embodiment, this extra load on the destination station is removed.

FIG. 8 is a flowchart for explaining the operation of the source station. In this flowchart, only the process related to the broadcast transfer is described.
In step S21, a packet is broadcast, and in step S22, an ACK packet from each destination station is received. In step S23, it is checked whether ACK packets have been received from all destination stations. Then, if ACK packets can be received from all the destination stations, the process is terminated; otherwise, the process proceeds to step S2.
Proceed to step 4 to execute retransmission processing.

In step S24, A that could not be received
It is checked whether the number of CK packets is equal to or less than a threshold. If it is equal to or smaller than the threshold value, in step S25, the packet is retransmitted by point-to-point communication to the destination station that has not transmitted the ACK packet. Thereafter, in step S26, it is checked whether or not the number of executions of step S25 has reached a predetermined number. If the number has reached the predetermined number, the process ends. If not, the process returns to step S23 after incrementing a counter for counting the number of times step S25 has been executed in step S27.

If the number of unacknowledged ACK packets is larger than the threshold value (step S24: No),
In step S28, it is checked whether the number of times the broadcast has been executed has reached a predetermined number. And
If the number has reached the predetermined number, the process is terminated. On the other hand, if the number of times the broadcast has been executed has not reached the predetermined number, the counter for counting the number of times the broadcast has been executed is incremented in step S29, and then the operation returns to step S21. Go back and rerun the broadcast.

In the above-described embodiments (both the first and second embodiments), wireless data transmission is assumed, but the present invention is not necessarily limited to this.
The present invention is applicable to non-wireless networks, for example, when a packet transmitted from a terminal such as Ethernet is transmitted to all terminals connected to the network.

[0053]

According to the system of the present invention, data transmitted from a source station is transmitted to a plurality of destination stations by being sequentially transmitted through one or more destination stations. Each destination station has a data retransmission function. Therefore, the reliability of data transmission is improved. Also,
Since the data retransmission function is distributed to each station, the load on the source station is reduced.

In a system according to another aspect of the present invention, data is retransmitted only to a destination station that cannot receive data transmitted by broadcast communication. For this reason,
The load on the destination station is reduced as compared with the method of repeating the broadcast.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a data transmission method according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration of a packet used in the first embodiment.

FIG. 3 is an example of a broadcast list used in the first embodiment.

FIG. 4 is a diagram illustrating a data retransmission function according to the first embodiment.

FIG. 5 is a flowchart illustrating an operation of a wireless station (excluding the most downstream wireless station).

FIG. 6 is a flowchart illustrating the operation of the most downstream wireless station.

FIG. 7 is a diagram illustrating a data transmission method according to a second embodiment.

FIG. 8 is a flowchart illustrating an operation of a transmission source station.

FIG. 9A is a diagram showing the structure of a packet, and FIG.
FIG. 3 is a diagram illustrating a data retransmission function.

FIG. 10 is a diagram illustrating a problem of a conventional broadcast.

FIG. 11 is a diagram showing another conventional method for transmitting data to a plurality of wireless stations.

Claims (6)

[Claims] 1. A method for transmitting data from a first station to a second station and a third station, comprising: transmitting data from the first station to the second station; Transmitting data received from a station to the third station, wherein the first station, when it cannot detect data transmission from the second station to the third station within a predetermined time, A data transmission method for retransmitting data to the second station. 2. The method according to claim 1, wherein the third station notifies the second station when the third station receives the data from the second station. Retransmits the data to the third station when the notification cannot be received from the third station within a predetermined time. 3. The method according to claim 2, wherein the second station, when the notification is not received from the third station despite the retransmission processing being repeated a predetermined number of times, is performed. To the first station. 4. The method according to claim 1, wherein the third station notifies the first station when the third station receives the data from the second station. 5. A communication station as an arbitrary communication station in a system for transmitting data in order through a plurality of communication stations, wherein data received from an upstream communication station is transmitted to a downstream communication station. Data transmitting means for transmitting; detecting means for detecting data transmission from the downstream communication station to the next communication station; and said data transmission not being detected by the detecting means within a predetermined time. Retransmission means for retransmitting the data to the downstream communication station when the data is transmitted. 6. A method for transmitting data from a source station to a plurality of destination stations, wherein the data is broadcast from the source station to the plurality of destination stations, and each destination station transmits the data from the source station. A data transmission method in which, when received, the transmission source station is notified of the fact, and the transmission source station retransmits the data only to destination stations other than the destination station that has transmitted the notification.