JP2004320230A - Transmission station and reception station in in multicast communication system, and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of enhancing the communication efficiency and the reliability of communication with an important reception station in a multicast communication system. <P>SOLUTION: A transmission station 201 in the multicast communication system having a function of retransmitting data to the reception station in response to a retransmission request sent from the reception station on the occurrence of an error in data received by the reception station is provided with: a priority setting section 110 for placing priority denoting a frequency of the permission of transmission of the data retransmission request to each reception station in a way of ranking each reception station; and a retransmission request permission section 104 for permitting the transmission of the data retransmission request to each reception station according to priority set by the priority setting section 110. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transmitting station, a receiving station, and a communication method in a multicast communication system having a retransmission function, and more particularly to a retransmission processing technique for ensuring reliability of a communication path.
[0002]
[Prior art]
(Ensuring communication channel reliability)
2. Description of the Related Art In a data communication technique, there is a technique of detecting an error and retransmitting the data as a technique for correctly transmitting data to be transmitted. This is a technique in which a receiving station detects an error from received data, and when an error is detected, requests the transmitting side to retransmit the data, and the transmitting station receives the retransmission request and retransmits the data. With such a mechanism, the reliability of the communication path can be ensured, and TCP / IP is a well-known method.
[0003]
(Ensuring the reliability of the communication path when there are multiple communication stations)
By the way, it is general that a plurality of stations exist in a communication path, and each station communicates independently. That is, a certain communication band is shared by a plurality of stations. In such a case, if the state of communication between certain stations is bad and retransmission frequently occurs, it affects the communication of other stations sharing the communication path, and the transmission efficiency of communication is significantly deteriorated. In some cases, transmission of important data or data to be transmitted earlier in time is impaired. As a technique for solving the above-mentioned problem, there is a technique in which importance is added to each station in advance, and retransmission is performed in order from the station with the highest importance (for example, see Patent Document 1).
[0004]
(Ensuring reliability of communication path in multicast communication)
When a plurality of receiving stations exist for one transmitting station, there is a communication method in which the same data is transmitted to all of the plurality of receiving stations. Such a communication system is generally called a multicast or broadcast system, and well-known systems include UDP / IP.
[0005]
In these systems, the reliability of a communication path for retransmission or retransmission request is often not ensured.
[0006]
Therefore, as a technique for ensuring the reliability of a communication path in multicast communication, a technique has been proposed in which, when a plurality of retransmission requests are transmitted from a receiving station, the transmitting station performs data retransmission processing in a predetermined order. (For example, see Patent Document 2).
[0007]
Patent Document 3 discloses that, in order to increase the efficiency in a transmitting station in a multicast communication system, when there are a plurality of retransmission requests from the receiving station, a request for retransmission of data transmitted in the past or a larger number of receptions are made. There has been disclosed a configuration (see claims 7 and 8 of Patent Document 3; hereinafter, referred to as a "first configuration of Patent Document 3") that prioritizes and processes a retransmission request for data for which a retransmission request has been issued from a station. I have.
[0008]
Patent Document 3 discloses that, in order to increase efficiency, a transmitting station in a multicast communication system retransmits a previously transmitted data to a receiving station that has issued a retransmission request with higher priority than other receiving stations. A configuration that permits the request (see claim 6 of Patent Document 3; hereinafter, referred to as “second configuration of Patent Document 3”) is disclosed.
[0009]
Furthermore, in a transmitting station in the multicast communication system, if a retransmission request from a certain receiving station is received a predetermined number of times or more within a certain period, a transmitting station that preferentially permits the retransmission request to the receiving station has also been proposed. (See Claim 9 of Patent Document 3; hereinafter, referred to as “third configuration of Patent Document 3”)).
[0010]
[Patent Document 1]
JP 2001-86121 A (page 2, line 2-14)
[Release Date: March 30, 2001]
[0011]
[Patent Document 2]
JP-A-2001-237883 (page 2, line 2-15)
[Release date: August 31, 2001]
[0012]
[Patent Document 3]
JP-A-2002-314626 [Published date: October 25, 2002]
[0013]
[Problems to be solved by the invention]
(Problems of Patent Document 1)
In the technique of Patent Document 1, a transmitting station that has received a retransmission request determines to which receiving station to retransmit based on the importance added to each receiving station in advance.
[0014]
However, in the technique of Patent Document 1, it is the receiving station that determines whether to make a retransmission request, and the receiving station sends the retransmission request without limitation when an error occurs. For this reason, when there is a receiving station in a poor receiving state, that station frequently sends a retransmission request. If the importance of a receiving station with a bad reception status is set to high, retransmission is preferentially performed for the retransmission request. In the worst case, a situation may occur in which retransmission is difficult to be performed in response to the retransmission request and the retransmission is not performed at all. That is, even from a receiving station that is hardly retransmitted or a receiving station that is not retransmitted at all, only a retransmission request frequently occurs, and a retransmission request packet that is not processed at all is transmitted as a useless packet through a communication path. As a result, the efficiency of communication of other stations sharing the communication path is reduced.
[0015]
(Problem when retransmission mechanism is introduced in general multicast communication)
In general multicast communication, if a retransmission mechanism is introduced to ensure the reliability of the communication path, the reception status of multiple receiving stations is independent of each other, and points where errors occur in the received data Are also independent. That is, the location where each receiving station requests retransmission is also independent. As a result, each receiving station sends its own retransmission request to the transmitting station while sharing a limited communication band. In such a state, if the receiving state of a certain receiving station is extremely poor and a retransmission request is frequently transmitted and processed from the receiving station, the retransmission request from the receiving station collides with the retransmission request of another station. As a result, there is a case where a retransmission request from another station for which higher communication reliability is to be ensured is not processed.
[0016]
(Problems of Patent Document 2)
In the technique of Patent Document 2, it is described that the retransmission request from the receiving station does not collide. However, since the details are not clear, it is unclear why the collision does not occur. Therefore, the problem of the collision of retransmission requests has not been solved.
[0017]
Further, in the technique of Patent Document 2, a specific receiving station does not request retransmission more frequently (priority). For this reason, there is a possibility that an important receiving station for which high communication reliability is to be ensured cannot transmit a retransmission request sufficiently.
[0018]
(Problems of Patent Document 3)
In the technique of Patent Document 3, whether or not the receiving station requests retransmission is realized by polling from the transmitting station, so that the problem of collision between retransmission requests as in Patent Documents 1 and 2 is eliminated.
[0019]
However, the first configuration of Patent Document 3 merely changes the order of processing retransmission requests, that is, the order of data retransmission. Further, the priority of the receiving station in the second configuration of Patent Literature 3 merely means that the order in which retransmission requests are permitted is changed and a specific receiving station is retransmitted first. In the first and second configurations of Patent Document 3, the frequency (priority) at which each receiving station is permitted to perform a retransmission request is basically the same, and a higher frequency (priority) is given to a specific receiving station. ) Does not permit retransmission requests. That is, there is no difference in the frequency of performing the retransmission request permission. For this reason, an important receiving station that should ensure high communication reliability may not be able to sufficiently transmit a retransmission request, and may not be able to ensure high communication reliability.
[0020]
In the third configuration of Patent Document 3, as an exceptional process in the case where retransmission requests continue, there is a limited short time (after the retransmission requests are confirmed to be continuous, the retransmission requests become discontinuous). ), The transmission of a retransmission request is temporarily permitted to a specific receiving station continuously. At the beginning of communication or during normal times, the frequency (priority) at which each receiving station is permitted to transmit a retransmission request is Is the same. Therefore, when observation is performed in a relatively long time range, the frequency (priority) at which each receiving station is permitted to perform a retransmission request is almost the same. Further, the third configuration of Patent Document 3 gives priority to one specific receiving station, and permits the other receiving stations to request retransmission completely equally. Therefore, even in this configuration, an important receiving station that should ensure high communication reliability may not be able to sufficiently transmit a retransmission request, and may not be able to ensure high communication reliability.
[0021]
The present invention has been made to solve the above problems, and in a multicast communication system, while improving the communication efficiency, a transmitting station and a receiving station capable of improving the reliability of communication with respect to an important receiving station, And a communication method.
[0022]
[Means for Solving the Problems]
According to the present invention, in a multicast communication system in which a transmitting station transmits the same data packet to all receiving stations, a transmitting station can transmit a specific data packet in addition to general multicast communication system data (multicast data). The information for permitting retransmission is transmitted to one or more receiving stations. When each receiving station receives a packet from the transmitting station, the receiving station analyzes the multicast data and information, and only when the own station is permitted to perform a retransmission request and there is an error in the multicast data, the transmitting station. Sends a retransmission request to. Then, according to the present invention, priorities for permitting transmission of a data retransmission request are set so as to be ranked, and each receiving station is permitted to transmit a data retransmission request according to this priority. For example, if there are three receiving stations A, B, and C, and retransmission can be performed six times within a predetermined period as a whole communication path, three times for receiving station A, two times for receiving station B, and two times for receiving station. C is permitted one retransmission.
[0023]
As can be seen from the above description, the transmitting station of the present invention is a transmitting station in a multicast communication system that performs data transmission from one transmitting station to a plurality of receiving stations that can be individually identified by the transmitting station. And a transmitting station having a function of retransmitting data to the receiving station in response to a retransmission request transmitted from the receiving station when an error occurs in the data received by the receiving station, Priority setting means for setting a priority, which is a frequency at which transmission of a data retransmission request is permitted to the station, so as to give a ranking (so as to give a difference); and the priority setting means sets the priority. Retransmission request permitting means for permitting each of the receiving stations to transmit a data retransmission request in accordance with the priority.
[0024]
Further, the receiving station of the present invention is a receiving station for receiving, from the transmitting station, data including information relating to retransmission request transmission permission, based on the received information relating to retransmission request transmission permission. The retransmission request permission receiving station determining means for determining the retransmission request permission receiving station to which retransmission request transmission is permitted, and the data received when or before receiving the information on the retransmission request transmission permission has an error, A retransmission request unit for transmitting a retransmission request only when the retransmission request permission receiving station determination unit determines that the own station is permitted to transmit the retransmission request is provided. The receiving station may be configured to transmit a retransmission request for error data included in the received packet based on information on retransmission request permission received together with the packet, The retransmission of the included error data may be configured to transmit a retransmission request based on information on retransmission request permission received after the packet.
[0025]
Further, the communication method of the present invention is a multicast communication method in which data transmission is performed from one transmitting station to a plurality of receiving stations that can be individually identified by the transmitting station. In this case, the receiving station transmits a retransmission request, and the transmitting station retransmits data to the receiving station in response to the retransmission request. A priority setting step of setting a priority, which is a frequency of permission, so as to be ranked; and permitting each of the receiving stations to transmit a data retransmission request according to the priority set by the priority setting means. And a retransmission request permitting step.
[0026]
Here, the “priority” is a frequency at which a retransmission request set for each reception is permitted. Therefore, setting the priorities to be prioritized and permitting each receiving station to transmit a data retransmission request in accordance with the set priority does not mean that the order of permitting retransmission is temporarily changed, In contrast, there is a difference in the frequency at which the transmission of a retransmission request is permitted according to the reliability of communication to be secured.
[0027]
According to the present invention, even when the communication path is not stable, only the receiving station that is permitted to transmit the retransmission request transmits the retransmission request. A retransmission request packet is not transmitted through a communication path (the problem of Patent Documents 1 and 2 is solved). Therefore, communication efficiency is improved.
[0028]
Furthermore, according to the present invention, an important receiving station that should ensure high communication reliability can transmit a retransmission request with sufficient frequency, so that high communication reliability can be ensured (Patent Document 1) Solving a few problems).
[0029]
In the communication method of the present invention, typically, the priority setting step is executed at the start of communication or before the communication starts, and the retransmission request permission step according to the priority is always executed during communication. In this way, by making a difference in the frequency of permitting the transmission of the retransmission request on a regular basis, it is possible to maintain high communication reliability of important receiving stations that should ensure high communication reliability.
[0030]
If the transmitting station appropriately determines the receiving stations that are allowed to retransmit by a predetermined algorithm, it is possible to flexibly set which receiving station to assign the retransmission request to, and retransmit important receiving stations and important data. It can be performed flexibly and strictly under the control of the transmitting station. Therefore, it is necessary to carefully consider the priority setting method (priority setting algorithm) in the priority setting step, and various methods are conceivable as follows.
[0031]
That is, in the priority setting step, the priority is determined by, for example, negotiation between the transmitting station and the receiving station performed at the start of communication.
[0032]
According to the above method, at the start of communication, each receiving station knows how much communication channel reliability it can secure. In addition, it is possible to flexibly secure the reliability of the communication path according to the degree of congestion of the communication path at that time.
[0033]
Further, in the priority setting step, the priority may be determined according to a preset attribute of the receiving station.
[0034]
In the above method, for example, as a use scene in a company, a receiving station used by a manager can ensure high reliability, but a setting can be made such that the reliability of a general employee is lower than that of a manager. .
[0035]
Further, the priority may be dynamically changeable. That is, the communication method of the present invention may further include a priority changing step of dynamically changing the priority set in the priority setting step.
[0036]
The condition for changing the priority is, for example, a case where a receiving station is newly added to the network. At a certain point in time, the receiving station A has the first priority and the receiving station B has the second priority, but the receiving station C to which a higher priority should be set has joined the network. This is a usage method in which the priority is changed so that the receiving station C is the first, the receiving station A is the second, and the receiving station B is the third.
[0037]
That is, in the priority changing step, for example, the priority is changed when a new receiving station has joined the network.
[0038]
In the priority changing step, the priority may be changed according to the error rate of each receiving station.
[0039]
Further, if the priority of the receiving station C is the first, the priority of the receiving station A is the second, and the priority of the receiving station B is the third, the communication environment of the receiving station C is poor. At this time, as a result of frequent retransmission by the receiving station C, a situation may occur in which the receiving station A and the receiving station B can hardly make a retransmission request. Alternatively, even if retransmission permission is assigned to the receiving stations A and B, it cannot be said that retransmission is efficient. In such a case, the error rate of each receiving station is calculated from a retransmission request or the like transmitted from each receiving station, and when the calculated error rate is larger than a predetermined value, the priority order is lowered. Is also good. As a result, the priority of the receiving station A is the first, the priority of the receiving station B is the second, the priority of the receiving station C is the third, and the receiving station C can hardly make a retransmission request. However, instead, the receiving station A and the receiving station B can be used to obtain sufficient data reliability.
[0040]
That is, in the priority changing step, the error rate of each receiving station may be calculated, and if a part of the calculated error rate is larger than a predetermined value, the priority may be changed. Further, in the priority changing step, when the calculated error rate is larger than a predetermined value, the priority of a receiving station having an error rate larger than the predetermined value may be lowered.
[0041]
Conversely, in the priority changing step, the error rate of each receiving station may be calculated, and if a part of the calculated error rate is smaller than a predetermined value, the priority may be changed. . In the priority changing step, when the calculated error rate is smaller than a predetermined value, the priority of a receiving station having an error rate smaller than the predetermined value may be increased.
[0042]
According to each of the above methods, a receiving station with a low error rate is preferentially treated, so that a receiving station with an unreliable communication path is not occupied by a retransmission and a receiving station that can further secure the reliability of the communication path. Can be increased. As a result, a receiving station with a higher priority order that does not request retransmission requests frequently can communicate in an almost error-free state. That is, the number of stations that can communicate stably can be increased as much as possible.
[0043]
In the priority changing step in each of the above methods, conditions for changing the priority include a time axis such as an error rate exceeding a predetermined value or a receiving station joining a network (joining a communication group). Although a condition irrelevant to the above is used, the priority may of course be changed at a predetermined time interval. At this time, the priority order may be rearranged, and the above-described error rate may be used as a condition for rearranging the priority order.
[0044]
That is, in the priority changing step, the priority order may be changed at predetermined time intervals.
[0045]
In the above method, the priority is assigned in advance or according to the state of the communication channel, but as a result, the disparity between the receiving station to which the retransmission request is assigned and the receiving station to which no retransmission request is assigned increases. Therefore, it can be said that priority is assigned unfairly. There may be a situation where a certain receiving station is given priority and another receiving station is not given priority for a certain short-term time, but if it is extended to a long-term time, the number of times that retransmission is allowed is limited. It could be closer to equality.
[0046]
In other words, in the priority change step, the error rate of each receiving station is calculated, and the priority order of each receiving station is arranged at predetermined time intervals so that the smaller the error rate, the higher the priority order. The priority may be changed so that the priority can be changed. Further, in the priority changing step, the priority may be changed such that the order of the priority is randomly changed at predetermined time intervals. Further, in the priority changing step, when three or more different priorities exist in the priority order determined in the priority determining step, the priority order of at least one receiving station is set to the highest order. The priority may be changed at predetermined time intervals such that the priority is gradually increased until it becomes the lowest rank, and the highest rank is lowered to the lowest rank. Also, in the priority changing step, when three or more different priorities are present in the priority order determined in the priority determining step, the priority order of at least one receiving station is changed to the lowest order. The priority may be changed at predetermined time intervals so as to gradually decrease until reaching the lowest rank, and to rise to the highest rank when reaching the lowest rank.
[0047]
In the above description, the priority is always set for each receiving station, but there may be a receiving station for which the priority is not set. For example, if there are a large number of receiving stations on the network, it may not be practically possible to prioritize all the receiving stations. In that case, the priority may be set only for a certain number of receiving stations, and the priority may not be set for the other majority of the receiving stations, so that the transmission of the retransmission request may not always be permitted.
[0048]
That is, in the retransmission request setting step, the priority is not always set for some of the receiving stations, and in the retransmission request permitting step, the transmission of the retransmission request is permitted for the receiving station whose priority is not set. It may not be done. Further, in the priority setting step, when a predetermined condition is satisfied, the priority is not set for some of the receiving stations, and in the retransmission request permitting step, the receiving station for which the priority is not set is set. On the other hand, transmission of a retransmission request may not be permitted.
[0049]
Further, it is not necessary that the non-assignment of the priority does not mean that the retransmission request is not permitted. Even if the priority is assigned, the retransmission request may not be permitted. For example, a method of permitting the transmission of a retransmission request from a receiving station with a higher priority order and disallowing a receiving station of a lower priority order from transmitting a retransmission request when the retransmission band is exhausted is used. It may be. According to this method, when a higher-level receiving station leaves the communication thereafter, transmission of a retransmission request is permitted in advance.
[0050]
In the retransmission request permission step, transmission of a retransmission request may not always be permitted to some receiving stations. In the priority setting step, when a predetermined condition is satisfied, transmission of a retransmission request to some of the receiving stations may not be permitted.
[0051]
In the priority setting step, the error rate of each receiving station is calculated, and when the error rate of some of the receiving stations is higher than a predetermined error rate, the error rate of the receiving station having an error rate higher than the predetermined error rate is determined. On the other hand, the transmission of the retransmission request may not be permitted. In the priority setting step, when only some of the receiving stations that expect (permit) higher priority use up the retransmission band, the transmission of the retransmission request to other receiving stations is performed. May not be permitted. In the priority setting step, if there is a receiving station set as a receiving station that is not expected to be retransmitted (in the attribute of the receiving station, user setting, or the like), transmission of a retransmission request to the receiving station is not permitted. It may be.
[0052]
Each of the above configurations will effectively work for effective use of retransmission when the number of receiving stations is large. In addition, if the state of the communication path is poor (the error rate is high) and there is a receiving station that cannot secure the reliability of the communication path with the assigned number of retransmissions, it cannot be used effectively even if retransmission is permitted. Therefore, by not allowing such a receiving station to perform retransmission, retransmission can be used effectively.
[0053]
Of course, all receiving stations may not be permitted to request retransmission. In that case, the band allocated to retransmission can be allocated to data transfer, and the communication band can be used efficiently.
[0054]
BEST MODE FOR CARRYING OUT THE INVENTION
(Summary of the Invention)
In one embodiment of the present invention, unlike a general multicast method, multicast transmission that can secure the reliability of a communication path is adopted. That is, in one embodiment of the present invention, the transmitting station transmits the same data to all the receiving stations, but in the packet, in addition to the multicast data, whether or not a specific receiving station can retransmit is set. The transmitted retransmission request permission flag is also transmitted. Each receiving station, when receiving a packet from the transmitting station, analyzes the flag in addition to the multicast data, and if its own station is permitted to request retransmission, and furthermore, if there is an error in the multicast data, A retransmission request is transmitted to the transmitting station.
[0055]
For example, if there are three receiving stations A, B, and C, and retransmission can be performed six times within a predetermined period as a whole communication path, three times for receiving station A, two times for receiving station B, and two times for receiving station. C is a usage method in which one retransmission is permitted, and the priority of retransmission request permission is set for each station. By the way, as will be described later, this setting is not fixed and can be dynamically changed.
[0056]
By the way, in order to start communication between a transmitting station and a receiving station, a procedure for the transmitting station to uniquely grasp each receiving station is required before actual data transmission. Or Association. Also in the present invention, before actual data transmission is performed between the transmitting station and the receiving station, an association or the like is performed, so that the transmitting station individually recognizes each receiving station and sets so that it can be uniquely handled. Specifically, as an association procedure, the transmitting station assigns a temporary ID valid only during communication to each receiving station, and manages the receiving stations using the ID. The retransmission permission flag described above is managed by this ID.
[0057]
Since the communication is of the multicast type, when there are three receiving stations A, B, and C, even if there is a data error at a certain receiving station A, there is no data error at another receiving station B or C. Sometimes. In this case, a retransmission request is transmitted from the receiving station A, and the transmitting station retransmits the data. Because of the multicast communication, the retransmission data is also received by the receiving stations B and C. However, since the receiving stations B and C have already received the data correctly, the retransmitted data is discarded as meaningless data. You. Alternatively, it may be replaced with correct data received earlier.
[0058]
Also, in the present embodiment described below, the retransmission request permission flag transmitted by the transmitting station is transmitted in the same packet as the multicast data, but since a data error occurring in the receiving station occurs randomly, the retransmission request happens to occur. If an error is detected from a permitted packet, a retransmission request can be transmitted without any problem.However, if an error is detected from a packet for which a retransmission request is not permitted, a retransmission request to the transmitting station is issued. Since it is impossible, it needs to be devised. For example, data error detection results are accumulated for a plurality of packets, wait until a packet whose retransmission request permission flag is the own station is received from the transmitting station, and when that packet is received, the data is accumulated until now. This is an implementation that requests the transmitting station to retransmit the error data that has been set.
[0059]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0060]
(Multicast type communication system)
Here, an embodiment in which the present invention is applied to a communication system (communication environment) as shown in FIG. 2 will be described. That is, a plurality of receiving stations 202, 203, and 204 (receiving station A, receiving station B, and receiving station C) exist for one transmitting station 201, and the same data packet (transmitting packet 108) is transmitted from the transmitting station 201. An embodiment in which the present invention is applied to a so-called multicast communication system for transmitting to a plurality of receiving stations 202, 203, and 204 will be described.
[0061]
Since a multicast communication system transmits one data packet to a plurality of specific receiving stations at the same time, a unicast type communication system that needs to transmit data packets of the same content to each other if there are a plurality of destinations is required. An advantage of the communication system is that only one data packet transmission is required, which saves labor and communication traffic. Also, the multicast communication system differs from the broadcast communication system in that the transmitting station can recognize the receiving station, so that only the specific receiving station that has joined the network (participated in the communication) has data. Can be transmitted, and the transmitting station can control the receiving station.
[0062]
(Configuration of transmitting station)
FIG. 1 is a block diagram illustrating a schematic configuration of transmitting station 201 according to the present embodiment.
[0063]
The transmitting station 201 has a retransmission function of retransmitting data to the receiving stations 202 to 204 in response to a retransmission request transmitted from the receiving stations 202 to 204 when an error occurs in the data received by the receiving stations 202 to 204. Have. As shown in FIG. 1, the transmitting station 201 includes an input data storage unit 101, a transmission packet generation unit 102, a packet transmission unit 103, a retransmission request permission unit (retransmission request permission unit) 104, a retransmission request data processing unit 105, a packet reception And a priority setting unit (priority setting means) 110. All parts of the transmitting station 201 can be realized by hardware.
[0064]
The input data storage unit 101 outputs new input data 107, which is data to be transmitted input from the outside, to the transmission packet generation unit 102. The input data storage unit 101 also serves as a buffer that holds the newly transmitted input data 107 that can be retransmitted when there is a retransmission request from the receiving stations 202 to 204. Packet receiving section 106 receives a packet (reception packet 109) including retransmission request data from receiving stations 202 to 204. The retransmission request data processing unit 105 extracts retransmission request data from the received packet (received packet 109), analyzes the extracted retransmission request data, and outputs it to the input data storage unit 101. When receiving a packet including retransmission request data (reception packet 109) from receiving stations 202 to 204, input data storage section 101 extracts data to be retransmitted (retransmission data) from a buffer and outputs the data to transmission packet generation section 102. I do. However, data to be retransmitted indefinitely may be stored in the buffer (input data storage unit 101), but data stored in the buffer (input data storage unit 101) may be discarded by some algorithm. Good. For example, when the data stored in the buffer is data such as video data and the like, and the receiving stations 202 to 204 reproduce this data as a video or the like, the time required to reproduce the data at the receiving stations 202 to 204 has passed and the data is retransmitted. In particular, it is possible to implement data discarding when it becomes meaningless.
[0065]
The priority setting unit 110 determines which receiving station (one or two of the receiving stations 202 to 204) among the plurality of receiving stations 202 to 204 that can be individually recognized by the transmitting station 201 according to a predetermined priority setting algorithm (described later). (Hereinafter, symbols are omitted) to determine which priority is to be set (perform a priority setting step). At this time, the priorities of the receiving stations 202 to 204 are given a difference (order is given). Although not shown, a priority change unit that dynamically changes the priority determined by the priority setting unit 110 according to a priority change algorithm (described later) (performs a priority change step) may be further provided. .
[0066]
Retransmission request permitting section 104 selects a receiving station to which retransmission request transmission is permitted based on the priority set by priority setting section 110 (dynamically changed in some cases), and selects the selected receiving station. Is output to transmission packet generating section 102 as retransmission request permission data addressed to the receiving station (information on retransmission request transmission permission). The transmission packet generation unit 102 performs transmission based on retransmission request permission data addressed to the receiving station designated by the retransmission request permission unit 104 and transmission data (new input data 107 or retransmission data) output from the input data storage unit 101. A packet is generated and output to the packet transmission unit 103. The packet transmission unit 103 transmits the packet output from the transmission packet generation unit 102 as a transmission packet 108 to the receiving stations 202 to 204. The retransmission function is realized by an input data storage unit 101, a transmission packet generation unit 102, and a packet transmission unit 103.
[0067]
(Format of transmitted packet)
FIG. 3 shows an example of the packet format of the transmission packet 108 transmitted from the transmission station 201. The transmission packet 108 includes a preamble 301, a header 302, a retransmission request permission receiving station setting flag 303, and transmission data 304. The preamble 301 and the header 302 are commonly used in communication and will not be described here. The transmission data 304 is the new input data 107 or retransmission data in FIG.
[0068]
Although not shown, the transmission data 304 and the retransmission request permission receiving station setting flag 303 include an error detection code (CRC or the like) for detecting whether or not the data contains an error. Have been. Further, an error correction code (Reed-Solomon code or the like) may be used for this. Only one of the error detection code and the error correction code may be added to the entire packet, or the packet may be divided into a plurality of blocks and added to each block. Further, a stop flag or the like may be added to the end of the packet.
[0069]
The retransmission request permission receiving station setting flag 303 is a flag that indicates which of the plurality of receiving stations 202 to 204 can transmit a retransmission request, and indicates the receiving station set by the retransmission request permission unit 104. Set the flag. For example, as shown in FIG.
[0070]
Here, the transmission data 304 may be data that is transmitted first before retransmission, retransmission data, or data in which both are mixed. Further, the retransmission data may include a mixture of retransmission data having different numbers of retransmissions, such as first retransmission data and second retransmission data.
[0071]
Further, as shown in FIG. 4, the retransmission permission flag may be set such that retransmission is not permitted to any of the receiving stations 202 to 204.
[0072]
Further, the retransmission permission flag may be set so as to allow all the receiving stations 202 to 204 to accept the retransmission request. However, in that case, a collision may occur in the retransmission request itself, and the request may not be transmitted to the transmitting station 201 correctly. Also, even if the transmitting station 201 can receive a plurality of retransmission request packets by chance, it may be wondering which data should be retransmitted. In such a case, priority is given to a retransmission request from a high-priority receiving station according to the priority of retransmission request permission at that time, or retransmission from a high-priority receiving station is permitted as long as the data transmission capability permits. The request may be processed or the like.
[0073]
Further, one packet may be divided into a plurality of blocks.
[0074]
(Priority setting flowchart at the start of communication)
In the following, a flowchart for setting priorities to the receiving stations 202 to 204 at the start of communication is shown. Here, each of the receiving stations 202 to 204 holds an attribute for determining a priority in advance, and determines a priority by performing negotiation with the transmitting station 201 at the start of communication (priority setting described later). The algorithms A and C) will be described.
[0075]
The attribute for determining the priority is an index for indicating how much the communication reliability is expected to be ensured. For example, the attribute is represented by a numerical value from 1 to 10, and the larger the numerical value, This indicates that the company expects sufficient reliability, but the priorities are relative. For example, assume that the index of the receiving station A is 5. In this case, if the indices of the receiving stations other than the receiving station A are all 4 or less, the highest reliability can be ensured. However, if the indices of the receiving stations other than the receiving station A are all 6 or more, the lowest reliability is obtained. Only sex can be secured. Further, there may be a case where all the indexes of the receiving stations other than the receiving station A are “5”. In that case, all the receiving stations happen to get the same reliability.
[0076]
Also, as a method of specifying attributes for determining priorities, instead of simply indicating how much communication reliability is expected, use something like the capabilities of the receiving station. May be. For example, assume communication with a receiving station having a display unit. There are various types of receiving stations having a display unit, such as a television, a personal computer, a PDA, and a mobile phone. Of course, the display areas of these have various sizes. This is the case with a 20-inch TV, a 12-inch PC, a 4-inch PDA, a 2-inch mobile phone, and the like. In this case, not all receiving stations require the same reliability, a TV with the largest display area will require the highest reliability, and a mobile phone with the smallest display area will require the lowest reliability. I don't mind.
[0077]
Naturally, the index is not limited to this, and a smaller value may be expected to ensure sufficient reliability, or may be at a level relative to other receiving stations. For example, they expect to always ensure the highest reliability. Also, if the number of receiving stations is small and there is room in the band, the reliability is improved by securing the maximum number of retransmissions as much as possible. May be used as an index for distributing the number of retransmissions to the receiving station. That is, as shown in FIG. 11, the receiving station expects the maximum number of retransmissions when the band has a margin and the case where the band has no margin and the number of retransmissions needs to be shared by a plurality of receiving stations. A plurality of indices may be stored in a table, such as a minimum expected number of retransmissions. The number of retransmissions varies depending on various conditions such as a communication band, a communication speed, and a delay time. For example, when the communication speed is 10 Mbps, even if only three retransmissions are allowed in a certain period of time, when the communication speed becomes 1 Mbps, twenty retransmissions are allowed in a certain period. This is the case. Therefore, instead of an index such as an absolute value as shown in FIG. 12, an index such as a ratio to a band may be used. FIG. 12 shows that “1” occupies 100% of the bandwidth. For example, if the communication speed is 1 Mbps and retransmission is allowed up to 20 times in total, the index “1” means 20 retransmissions. However, the index “0.3” means six retransmissions. FIG. 13 shows an example of an index table of a plurality of receiving stations.
[0078]
In addition, it may be a relative index, not an absolute value or a ratio to a band. For example, it is an index such as "securing the maximum number of retransmissions among receiving stations currently participating in communication".
[0079]
FIG. 14 shows a priority setting flowchart when a plurality of receiving stations 202 to 204 holding the above index table start communication with one transmitting station 201. The transmitting station 201 waits for the receiving stations 202 to 204 to participate in the communication (S301). When a new participating receiving station appears (YES in S301), transmitting station 201 receives a retransmission index expected by the newly participating receiving station (S302). Here, the retransmission index is as shown in FIGS. 11 and 12, and is transmitted from the receiving stations 202 to 204 to the transmitting station 201. Next, the transmitting station 201 calculates the number of retransmissions within a fixed time that can be assigned to the newly participating receiving station according to the index transmitted from the receiving station and the communication status at that time ( S303). The priority for the newly participating receiving station is determined from the calculation result, and the priority table is updated (S304).
[0080]
As shown in FIG. 8, the priority table is a table that manages the number of retransmission request grants (priority) within a certain time period assigned to receiving stations participating in communication. This table is updated each time a new participating receiving station appears, and the priority is set. The timing of updating the priority table is not limited to when a new receiving station has joined, but may be updated at various timings as described later.
[0081]
The priority table is a table that manages, for each receiving station, an index (priority) representing the frequency of permitting a receiving station participating in communication to transmit a retransmission request. Examples include the number of permitted retransmission requests within a fixed time, the ratio to the total retransmission band, and a relative index such as “securing the maximum number of retransmissions among receiving stations currently participating in communication”. Instead of the priority table for managing the priority, a table for managing only the priority order may be used.
[0082]
Hereinafter, it is assumed that three receiving stations A, B, and C each have an index table as shown in FIG. 13 and that these receiving stations have participated in communication in the order of receiving stations B, C, and A. In this case, the flow of processing will be described. Here, it is assumed that retransmission can be performed ten times in total within a certain time.
[0083]
First, it is assumed that the receiving station B has joined the communication from a state where no receiving station has joined. Since the retransmission band expected by the receiving station B is 1, the transmitting station permits the receiving station B to perform all possible retransmissions.
[0084]
Thereafter, it is assumed that the receiving station C has participated in the communication. At that point, the transmitting station performs the calculation of S303. As a result of the calculation, even if the minimum expected retransmission bands of the receiving stations B and C are added, not all the bands are used up. In that case, there are various methods for granting the retransmission bands to the receiving stations B and C. If the policy is relatively equal, the receiving station B may be permitted six retransmissions and the receiving station C may be permitted four retransmissions. Further, if the policy is to give priority to a receiving station expecting a larger retransmission band, the receiving station B may be set to eight times and the receiving station C may be set to two times.
[0085]
Next, it is assumed that the receiving station A has joined. At that time, the transmitting station executes the calculation in S303 again, but at this time, it can be seen that the minimum retransmission band expected by all the receiving stations cannot be permitted. In this case, there may be a policy that all receiving stations reduce the bandwidth equally, and a policy that prioritizes receiving stations that expect a larger retransmission bandwidth. In the former case, about 58% of the receiving station A, about 25% of the receiving station B, and about 17% of the receiving station C are permitted. In the latter case, the receiving station is 70% and the receiving station is 70%. B is allowed 30% of the retransmission band, and receiving station C is not allowed to retransmit at all.
[0086]
(Flowchart of operation of transmitting station)
FIG. 7 shows a flowchart of the operation of the transmitting station 201. Hereinafter, for convenience of explanation, the only packet received from the receiving station is a retransmission request packet, but other packets (for example, other control information, etc.) may be received. First, the packet receiving unit 106 checks whether a packet has been received from the receiving stations 202 to 204 (S101). If a packet has not been received (NO in S101), new input data 107 to be input to input data storage unit 101 is extracted, and preparation for creating transmission data is made (S102). If a packet has been received (YES in S101), processing of the retransmission request data received from the receiving stations 202 to 204 is performed (S103). More specifically, the analysis includes preparation for extraction of data stored in the input data storage unit 101 (which data is requested to be retransmitted?). After that, data for which a retransmission request has been received is extracted from the input data storage unit 101 (S104). When transmitting the data for the retransmission request and the newly input data together as the data included in the packet to be transmitted, the step of S102 is always executed regardless of whether or not the packet is received from the receiving station. Is also good. In response to the extraction results in S102 and S104, transmission data is generated (S105) and output to the transmission packet generation unit 102. On the other hand, in the retransmission request data processing (S103), analysis for setting the priority of each of the receiving stations 202 to 204 is also performed from the error rate and the like. Specifically, as described above, the analysis is performed to perform processing such as lowering the priority of a receiving station having a high error rate. In response to the analysis result, the priority setting unit 110 sets the priority for each of the receiving stations 202 to 204 (S106; priority setting step). This setting is stored in the memory as a priority setting table, for example. Of course, this priority setting process does not necessarily have to be continuously performed, but may be performed at the start of communication or when a new receiving station joins. Further, once the priority is set, in this step, the priority is dynamically changed at some timing (for example, when the error rate of a certain receiving station 202 to 204 exceeds a predetermined value). The process may be executed (priority changing step). The priority table set in this process is output to retransmission request permitting section 104, and retransmission request permission setting processing is performed (S107). As described above, since the priority setting process does not always change, the process of outputting the set priority table to the retransmission request permitting unit 104 is performed every time the priority changes. May be implemented. FIG. 8 shows an example of the priority table. As shown in FIG. 8, the receiving stations B, D, and C are permitted a number of retransmissions, but the number of retransmissions allowed as a whole is used up by the top three receiving stations, and the receiving station A has no retransmission at all. It may not be permitted. When there is a receiving station other than the receiving station A, retransmission is not permitted at all, as in the case of the receiving station A. Thereafter, the receiving station that permits the retransmission request in the next packet to be transmitted is determined according to the priority table output from the priority setting process (S107). Then, in response to the results of the transmission data generation process (S105) and the retransmission request permission setting process (S107), the transmission packet generation unit 102 generates a transmission packet as shown in FIG. 3 (S108), and the packet transmission unit 103 Transmits the transmission packet 108 to the receiving stations 202 to 204 (S109).
[0087]
(Transmission of retransmission request packet)
FIG. 10 shows the state of a packet transmitted on a communication channel when the priorities are set for the receiving stations A, B, C, and D as shown in FIG. Here, for convenience, all stations always send retransmission request packets, but if there is no error in the data, the retransmission request packets are naturally not transmitted through the communication path. In a packet transmitted from a transmitting station, data to be transmitted for the first time and retransmission data are mixed. As can be seen from FIG. 10, the retransmission request is permitted six times as a whole, of which the receiving station B is assigned three times, the receiving station D is assigned twice, the receiving station C is assigned once, and the receiving station A is completely assigned. It can be seen that the retransmission request is not permitted.
[0088]
By the way, in the above description, when there is no data to be requested for retransmission, it is described that there is no need to perform communication from the receiving station to the transmitting station. However, the present invention is not limited to this. For example, a packet number (or a block number) is added to all data packets (a block if the packet is divided into small blocks), and if all the data can be received correctly, the last received data correctly The packet number (or block number) or the packet number (or block number) to be received next may be transmitted from the receiving station to the transmitting station, and the transmitting station may surely transmit the data to be transmitted to the receiving station.
[0089]
Also, in FIG. 10, only one response per cycle (assuming one cycle for each packet transmitted by the transmission station) is described from the reception station for data transmission from the transmission station. It is not limited to this. That is, each time one packet is transmitted from the transmitting station, the packet may specify retransmission request permission from a plurality of receiving stations. By permitting retransmission from a plurality of receiving stations in one cycle in this manner, it becomes possible to advance the timing of retransmission. When retransmission from a plurality of receiving stations is permitted in one cycle, the transmitting station can transmit a retransmission request packet transmitted by the receiving station together with retransmission request permission so that retransmission requests do not collide. The timing (a specific period within one cycle) may also be notified to the receiving station.
[0090]
(Operation of receiving station)
When each of the receiving stations 202 to 204 detects an error from the received packet, it checks the retransmission request permission receiving station setting flag 303. If the own station is permitted to perform the retransmission request, the receiving station 202 to 204 transmits the retransmission request packet to the transmitting station 201. However, if the transmission is not permitted, the retransmission request is not transmitted even if an error is detected from the received packet. A flag such as the retransmission request permission receiving station setting flag 303 in FIG. 4 enables the retransmission to each of the receiving stations 202 to 204. That is, as shown in FIG. 6, at the start of communication, an ID is assigned by the transmitting station to each of the receiving stations 202 to 204, and the retransmission request permission receiving station setting flag 303 of FIG. Set. As can be seen from FIG. 6, an ID that is not assigned to any of the receiving stations 202 to 204 may be created. By using the ID, as shown in FIG. 4, it is possible to perform flexible processing such as not permitting any of the receiving stations 202 to 204 to retransmit or permitting all the receiving stations 202 to 204 to retransmit. Become.
[0091]
By the way, the retransmission request permission receiving station setting flag 303 transmitted by the transmitting station is transmitted in the same packet as the multicast data. However, since data errors occurring in the receiving stations 202 to 204 occur randomly, the retransmission request is If an error is detected from the transmitted packet, it is possible to transmit a retransmission request without any particular problem. However, when an error is detected from a packet for which a retransmission request is not permitted, a retransmission request to the transmitting station 201 cannot be made, and thus a device is required. For example, the detection result of the data error is accumulated over a plurality of packets, and the process waits until a packet whose retransmission request permission receiving station setting flag 303 is a flag for permitting the own station is received from the transmitting station 201. Is received, a request is made to the transmitting station to retransmit the error data stored so far.
[0092]
(Block diagram of receiving station)
FIG. 5 shows a block diagram of the receiving stations 202 to 204. Since the other receiving stations 202 to 204 have the same configuration, only one of the receiving stations 202 will be described here.
[0093]
The reception station 202 includes a packet reception unit 501, an error detection unit 502, an output data storage unit 503, a retransmission request permission reception station determination unit (retransmission request permission reception station determination unit) 504, a retransmission request unit (retransmission request unit) 505, A transmission unit 506 and an error accumulation unit 510 are provided. All parts of the receiving station 202 can be realized by hardware.
[0094]
Packet receiving section 501 receives a packet (received packet 507) transmitted from transmitting station 201. Error detecting section 502 determines whether or not a data error exists from the received packet (received packet 507). If the result of the determination is that an error has been detected, data to be requested to be retransmitted to error storing section 510 is transmitted. Accumulate. Further, the error detection unit 502 sends normal data in which no error is detected to the output data storage unit 503. The output data storage unit 503 stores this data and outputs it as received data 509 to the outside when necessary. The retransmission request permission receiving station setting flag 303 in the packet format shown in FIG. 3 is checked from the received packet by the retransmission request permission receiving station determination unit 504. If the own station is permitted to transmit the retransmission request, an error is detected. Data to be requested for retransmission stored in the storage unit 510 is generated by the retransmission request unit 505, and transmitted from the packet transmission unit 506 to the transmission station 201. If the own station is not permitted to transmit the retransmission request, even if an error is detected, the retransmission request packet is not transmitted, and is stored in error storage section 510. Further, as described above, since there is a receiving station to which transmission of a retransmission request is not permitted at all, data to be retransmitted and stored in the error storage unit 510 may not be permanently transmitted. In that case, it may be discarded by some processing (for example, timeout). Also, data may have a time limit to be transmitted. For example, there is a case where data such as video data to be reproduced at a predetermined timing is transmitted, and data has not yet been received at the timing to be reproduced. This can occur when a data error has occurred and the retransmission request is not granted. At that time, even if retransmission is permitted thereafter, the data may not be meaningful and may be deleted from the error accumulation unit 510.
[0095]
Note that the receiving station may have a function of performing error correction. In this case, an error correction code may be added to the above-described transmission packet, and the receiving station may perform error correction based on the error correction code. If the receiving station has a function of performing error correction, the receiving station may request retransmission only when an error occurs in the received data and the error cannot be corrected.
[0096]
(Retransmission request unit)
Incidentally, the retransmission request does not necessarily need to be performed for the entire received packet. The receiving station may divide the received packet into several blocks, perform error detection for each block, and request retransmission of only the block in which the error is detected. If the received packet is divided into a plurality of blocks, the receiving station may detect an error for each block and request retransmission of only the block in which the error is detected.
[0097]
In this case, the receiving station determines the presence or absence of an error in block units by the error detection unit 502, and sends, to the transmitting station, information indicating the block that the receiving station has successfully received among the plurality of blocks included in the packet, together with the retransmission request. Send. Also, the received data of the block determined to be free from errors by the error detection unit 502 is output to the output data storage unit 503 and temporarily stored. Thereafter, the transmitting station retransmits the data in block units based on the retransmission request and the information indicating the correctly received block, and when the receiving station correctly receives the data, the correctly received retransmitted data is output to the output data storage unit. 503 is input. After that, the receiving station sorts the blocks in order and outputs the data as received data 509. Of course, such order arrangement of the blocks may be performed by a processing unit (not shown) at the subsequent stage of the output data storage unit 503.
[0098]
As described above, by performing a retransmission request and retransmission in block units, it is possible to improve packet transmission efficiency.
[0099]
Regardless of whether retransmission is performed in packet units or in block units obtained by dividing a packet into blocks, some kind of number management needs to be used for data requested to be retransmitted. This is because it is not possible to determine what information is included in the packet or block in which an error has been detected because the packet or block is incorrect. It is impossible to request what you do not know what information is included. Therefore, for example, a number such as a sequence number used in TCP or the like is assigned to each packet or each block, and a number that cannot be normally received or a number that can be normally received is transmitted to a transmitting station. The receiving station may request retransmission of data that has not been received normally (erroneously received).
[0100]
(Flowchart of operation of receiving station)
FIG. 9 shows a flowchart of the operation of the receiving station. In the following, for convenience of explanation, the only packet transmitted from the receiving station is a retransmission request packet, but other packets (for example, other control information) may be transmitted. First, the packet receiving unit 502 receives a packet (S201), and the error detecting unit 502 determines whether there is an error in the received data (S202).
[0101]
Naturally, an error in the received packet may be present not only in the data to be transmitted but also in the retransmission requestable receiving station setting flag 303, but in the present embodiment, the error is present in the received packet for convenience. It is assumed that the error is only in the data to be transmitted. By the way, if there is an error in the retransmission requestable receiving station setting flag 303, the process may proceed to S206 as in the case where there is an error in the data to be transmitted. May determine that retransmission is not permitted, and may do nothing. If there is no error (No in S202), the received data is stored in the output data storage unit 503 (S203). As described above, the received data divided for each block may be input to the output data storage unit 503 with the original order changed, so that the output data is stored in the output data storage unit 503 (S204), and the received data 509 is output. (S205). By the way, if an error is detected from the received packet 507 (YES in S202), the error data storage unit 510 stores the error data (S206). On the other hand, from the received packet 507, the retransmission request permission receiving station determining unit 504 determines the retransmission request permission receiving station, and does nothing if the own station is not permitted to retransmit (NO in S207). In other words, no operation is performed unless retransmission is permitted regardless of the presence or absence of accumulation of error data. Thereby, a meaningless retransmission request does not flow to the communication path. If the own station is permitted to retransmit (YES in S207), nothing is performed unless error data is stored in error data storage section 510 (NO in S208). That is, even if retransmission is permitted, nothing is performed unless error data is accumulated. As a result, unnecessary packets do not flow through the communication path. If error data has been stored in error data storage section 510 (YES in S208), retransmission request section 505 prepares to transmit to the transmitting station as retransmission request data (S209), and packet transmission section 506 transmits transmission packet 508 from packet transmission section 506. It is transmitted (S210).
[0102]
(Priority setting algorithm for retransmission request permission)
By the way, the transmission of the retransmission request from the receiving station to the transmitting station cannot be performed indefinitely, but must be performed within a limited transmission band. For example, it is assumed that when the communication environment of the receiving station A is bad, the receiving station A is frequently permitted to transmit a retransmission request, and has transmitted the permitted retransmission request to the maximum using the transmission band. In this case, since the other receiving stations B and C cannot make a retransmission request, the data reliability of the receiving stations B and C may be degraded. In addition, if sufficient reliability of data cannot be obtained only by the retransmission request to which the receiving station A is assigned, the worst case is that the reliability of all data of the receiving station A, the receiving station B, and the receiving station C cannot be secured. It is possible. Therefore, in retransmission request permitting section 104, a method of selecting a receiving station to which a retransmission request is permitted (priority setting method set in the priority setting step) needs to be carefully considered. There is a method. By differentiating the frequency (priority) of retransmission request permission for each receiving station, a plurality of priority setting algorithms and priority changing algorithms for more effective use of communication bandwidth are proposed below.
[0103]
(Priority setting algorithm A)
As a method of determining the priority, first, when the transmitting station and the receiving station start communication, a negotiation is performed between the transmitting station and the receiving station. There is a method in which information about the reliability of data transmission to be transmitted is transmitted to a transmitting station, and the transmitting station sets a priority based on the above information.
[0104]
That is, first, when the transmitting station and the receiving station start communication, negotiations (negotiations) such as association and binding are performed between the transmitting station and the receiving station prior to the original communication. This negotiation means that the transmitting station and the receiving station mutually confirm the conditions for correct communication with each other, and determine in advance the hardware communication conditions (such as how to use signal lines) and the communication procedure (communication protocol). This is the processing to be performed.
[0105]
Each receiving station has its own data transmission reliability (minimum number of retransmissions, etc. within a certain period of time), so any new receiving station that has joined the communication will secure its reliability in negotiations. To be able to do so, a request is made to the transmitting station, that is, the information on the reliability is transmitted to the transmitting station. Next, the transmitting station, by the time the data transmission to the receiving station is started, the information on the reliability and the communication status at that time (such as how many receiving stations are communicating at that time, etc.) Based on the reliability or priority (frequency at which retransmission request transmission is permitted; number of retransmission request transmissions permitted within a certain period, etc.) ) Is determined (examined), and the priority order of the receiving stations is set based on the determination result. In this case, the order of priority of each receiving station is not changed after being set once.
[0106]
(Priority setting algorithm B)
Further, the method of setting the priority may be a method in which the transmitting station is determined based on the attribute of each receiving station and the priority of the attribute, which are set in advance by the user of the communication system. For example, assuming a case where the terminal is used in a company, a plurality of positions are set as attributes of each receiving station, and the priorities of the attributes are set according to the order of the positions. There is a method in which officers are set so as to have a higher priority than managers and have higher priority than managers, and the transmitting station determines based on these settings. In this case, the priority order and priority of each receiving station are not changed once they are set.
[0107]
The attribute of each receiving station may be appropriately set by a user using input means provided in the receiving station, and may be stored in storage means in the receiving station. The priority of the attribute may be stored in advance in a storage unit in the transmitting station, or may be appropriately set by a user using an input unit provided in the transmitting station, and stored in the storage unit in the transmitting station. You should keep it.
[0108]
Further, there may be a receiving station having an attribute that does not request retransmission at all or an attribute that always requests the lowest priority.
[0109]
In the above two methods, once the priority is set, the priority is not changed thereafter. However, the once set priority may be dynamically changed. A method of changing the priority (priority change algorithm) is described below.
[0110]
(Priority change algorithm C)
For example, a method of changing the priority set by the priority setting algorithm A when a receiving station is newly added to the network can be considered. In this method, for example, at a certain point in time, the receiving station A is ranked first in the priority order and the receiving station B is ranked second in the priority order. Is a method of changing the priorities so that the receiving station C is first, the receiving station A is second, and the receiving station B is third.
[0111]
(Priority change algorithm D)
As described above, when the priority of the receiving station C is first, the receiving station A is second, and the receiving station B is third, if the communication environment of the receiving station C is poor, the receiving station C As a result, the receiving station A and the receiving station B can hardly make a retransmission request. In such a case, the error rate of each receiving station is calculated from a retransmission request or the like transmitted from each receiving station, and when the calculated error rate is larger than a predetermined value, the priority setting algorithm A or the like is used. The set priority may be lowered. As a result, the priority order of the receiving station A is the first, the receiving station B is the second, the receiving station C is the third, and the receiving station C can hardly make a retransmission request. The receiving station B can be used to obtain sufficient data reliability. Conversely, when the error rate is smaller than the predetermined value, the priority set by the priority setting algorithm A or the like may be increased. As a result, a receiving station with a higher priority order can communicate in an almost error-free state. In other words, the idea is to increase the priority of stations that do not request retransmission requests frequently and thereby increase the number of stations that can communicate stably as much as possible.
[0112]
It is general that the error occurring in each receiving station is independent for each receiving station (this is not limited to a large external noise (such as a microwave oven)). In this case, as a result of performing many retransmissions to a receiving station having a high error rate, retransmission may not be assigned to a receiving station that can achieve error-free with a slight retransmission. If the number of retransmissions does not improve, the idea is to discard the number of retransmissions and use the limited number of retransmissions as a meaningful retransmission.
[0113]
By the way, regarding the method of calculating the error rate, the value calculated on the receiving station side may be notified to the transmitting station. Also, as a preferred implementation of the error rate measurement, it is better for each receiving station to notify the transmitting station of the independently calculated error rate. This is because the receiving station side can more accurately grasp the error rate. Since retransmission cannot be performed unless permitted, an accurate value may not be calculated from the number of retransmissions.
[0114]
Although there are various error rates such as a bit error rate and a packet error rate, a rate suitable for implementation may be adopted. In actual communication, it is possible to implement processing such as error correction, in which case either the error rate before or after error correction may be used, but if it is used for the presence or absence of retransmission, error correction was performed It may be desirable to use a later error rate (since it is an error rate that requires retransmission). In some cases, a packet is divided into a plurality of blocks, and error correction processing is performed for each block. Therefore, an error rate in units of blocks may be employed. For example, among the ten retransmission request grants, if the receiving station A actually requests retransmission three times and the receiving station B twice, the receiving station A has a higher error rate. Of the 10 retransmission request grants, 10 blocks are transmitted in one packet, and the actual retransmission request is received by the receiving station D with 5 blocks and the receiving station E with 8 blocks. large.
[0115]
Further, in the communication, the error rate may increase instantaneously due to an environmental change, but the communication may return to a stable communication immediately. Therefore, instead of using the error rate in an extremely short time (for example, in packet units), the calculation may be performed with a certain time width (an average value over several packets).
[0116]
(Priority change algorithm E)
In the above description, conditions that are not related to the time axis are used as conditions for changing the priority, such as an error rate exceeding a predetermined value or a receiving station joining a network. The priority may be changed at the time interval of. At this time, the above error rate may be used as a condition for changing the priority.
[0117]
(Priority setting algorithm F)
Also, as described above, the communication environment of a certain receiving station is extremely poor, and even if retransmission is performed, it may be far from ensuring data reliability. In such a case, assigning a retransmission request to the receiving station has little meaning, and merely wastes the communication band. That is, it is possible to more efficiently allocate the retransmission request by not allowing the retransmission request at all to the receiving station having the predetermined error rate or higher.
[0118]
(Priority change algorithm G)
Further, in the above description, the priority assignment is performed according to a predetermined condition, but as a result, the disparity between a receiving station to which a retransmission request is assigned and a receiving station to which no retransmission request is assigned may increase, and It can also be said that priority assignment is performed.
[0119]
Therefore, the priority may not be assigned using the error rate of each receiving station or the like, but may be simply assigned at random. That is, at a certain timing, a retransmission request is assigned very frequently, but after a certain period of time, a retransmission request is not often assigned. As a result, a retransmission request can be equally allocated to each receiving station over a long period of time.
[0120]
In this case, the priorities may be changed so that the priorities are switched at all at random, or the priorities may be changed so that the priorities are gradually raised or lowered.
[0121]
Further, the priority order may be changed according to an instruction from the user. For example, in the case of a brief meeting, leaving the room for a toilet, etc., if the user does not request a retransmission request for a while, the priority of the retransmission request is switched according to the user's instruction. May be.
[0122]
In addition, as a result of equally assigning retransmissions, some errors may occur in all receiving stations without being in an error-free state. However, when retransmission is preferentially performed, there may be a case where almost error-free state can be achieved. Therefore, there may be a case where it is desired to create an error-free state (enhancing communication) even if there is a state in which the number of errors slightly increases rather than a state in which there is always some error (leaving away, CM, so much) Video that you are not interested in).
[0123]
(Priority setting algorithm H)
In the above description, the priority is always set for each receiving station, but there may be a receiving station for which the priority is not set. For example, if there are a large number of receiving stations on the network, it may not be practically possible to prioritize. In that case, the priority may be set only for a certain number of receiving stations, and the priority may not be set for the majority of other receiving stations, that is, the retransmission request may not always be permitted. This will work well for large numbers of receiving stations. Of course, all receiving stations may not be permitted to request retransmission. In that case, the band allocated to retransmission can be allocated to data transfer, and the communication band can be used efficiently.
[0124]
(Packet for sending retransmission request permission flag)
In this embodiment, the retransmission request permission flag is transmitted in the same packet as the data to be transmitted, but may be transmitted as another packet. However, usually, as shown in FIG. 3, since there are additional packets such as a preamble and a header, it is better to transmit the retransmission request permission flag and the data to be transmitted in the same packet as in the present embodiment. Transmission efficiency will be good.
[0125]
(Specific usage scene 1)
A specific usage scene using the priority setting method according to the present invention will be described below. For example, a usage scene in a hot spot. In a hot spot, an unspecified number of receiving stations have access to one or a small number of transmitting stations (access points). In this case, since a large number of receiving stations participate in the communication, the sum of the number of retransmissions expected by all the receiving stations may exceed the retransmission band allowable by the transmitting station. At this time, not all the receiving stations are allowed the expected number of retransmissions. Therefore, it can be said that each receiving station must be differentiated in some way. In hot spots, users often pay for usage and communicate, and all receiving stations share the number of retransmissions equally, so that no receiving station can secure the expected number of retransmissions, that is, expect It is a problem if the reliability of communication cannot be ensured. In a communication environment where a large number of receiving stations are present, it is unlikely that all the receiving stations have a bad communication state, and there is a difference between a receiving station having a good communication state and a receiving station having a bad communication state. There are many. In such a case, the number of retransmissions to a receiving station with a poor communication state is reduced (in the worst case, no transmission is permitted), and allocation is made to a receiving station with a better communication state. It is desirable to increase the number of receiving stations that have no problem. In that case, services such as reducing the usage fee or enabling free use are also conceivable for users of receiving stations with poor communication conditions.
[0126]
(Specific use scene 2)
A specific usage scene using the priority setting method according to the present invention will be described below. This is a usage scene in which a plurality of students receive information from one teacher in a school classroom or the like. Again, as described above, it may be desirable to increase the number of students with better reception status as much as possible, even if the reception status of a particular student is worse than the communication status of all the students being evenly poor. Here, for a student with a poor communication situation, the receiving station may be shared with a student with a good communication situation, or the receiving station in a wired connection environment may be used.
[0127]
Naturally, the use scene according to the present invention is not limited to the above. For example, use in lectures and conferences, use of the whole family at each receiving station, transmission of extra information, transportation such as trains and airplanes It can be applied to various uses, such as use in a movie theater, a video / CD shop, and the like, and ad hoc use by friends gathered. Further, the receiving station possessed by each user is not a single station, and various types of receiving stations may simultaneously participate in communication. For example, a receiving station having various display units such as a television, a personal computer, a PDA, and a mobile phone may simultaneously participate in communication. Here, it is assumed that the television has the largest display area and the mobile phone has the smallest display area. In this case, not all receiving stations require the same reliability, a TV with the largest display area will require the highest reliability, and a mobile phone with the smallest display area will require the lowest reliability. I don't mind.
[0128]
(Program, recording medium)
Further, the above-described communication method can be provided by a program for causing a computer to execute each step of the method.
[0129]
Further, as described above, all of the transmitting station and the receiving station are hardware (generally called baseband and RF units), and in some cases, MAC (Media Access Control) hardware is further included. ), But can be partially realized by software. The components other than the packet transmitting unit 103 and the packet receiving unit 106 of the transmitting station and the packet receiving unit 501 and the packet transmitting unit 506 of the receiving station can be realized by software.
[0130]
Further, the above-described transmitting station can be provided by a program for causing a computer to function as a part related to the communication control, that is, a retransmission request permission unit 104 and a priority setting unit 110.
[0131]
Further, the above-described receiving station can be provided by a program for causing a computer to function as a part related to the communication control, that is, an error detecting unit 502, a retransmission request permission receiving station determining unit 504, a retransmission requesting unit 505, and the like. .
[0132]
Such a program can be recorded on a computer-readable recording medium such as a flexible disk, a CD-ROM, a ROM, a RAM, and a memory card attached to the computer and provided as a program product. Alternatively, the program can be provided by being recorded on a recording medium such as a hard disk incorporated in the computer. Further, the program can be provided by downloading via a network. The programs provided in these modes are installed in a program storage unit such as a hard disk built in the computer, and executed by the computer. Note that the program product includes the program itself and a recording medium on which the program is recorded.
[0133]
The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0134]
【The invention's effect】
According to the present invention, even when the communication path is not stable, only the receiving station that is permitted to transmit the retransmission request transmits the retransmission request. No retransmission request packet is transmitted on the communication path. Therefore, communication efficiency is improved. Furthermore, according to the present invention, an important receiving station that should ensure high communication reliability can transmit a retransmission request with sufficient frequency, so that high communication reliability can be ensured (Patent Document 1) Solving a few problems).
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a transmitting station according to one embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a communication system according to an embodiment of the present invention.
FIG. 3 is a diagram showing a packet format of a packet transmitted from a transmitting station according to an embodiment of the present invention.
FIG. 4 is a diagram showing a retransmission request permission receiving station setting flag according to an embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of a receiving station according to one embodiment of the present invention.
FIG. 6 is a diagram showing IDs assigned to receiving stations according to one embodiment of the present invention.
FIG. 7 is a flowchart showing an operation of the transmitting station according to one embodiment of the present invention.
FIG. 8 is a diagram showing an example of a priority table according to the embodiment of the present invention.
FIG. 9 is a flowchart showing an operation of the receiving station according to one embodiment of the present invention.
FIG. 10 is a diagram showing a state of a packet transmitted on a communication path in the communication system according to the embodiment of the present invention.
FIG. 11 is a diagram illustrating an example of a retransmission index table expected by a receiving station according to an embodiment of the present invention.
FIG. 12 is a diagram showing another example of the retransmission index table expected by the receiving station according to the embodiment of the present invention.
FIG. 13 is a diagram showing still another example of the retransmission index table expected by the receiving station according to the embodiment of the present invention.
FIG. 14 is a flowchart illustrating a priority setting process according to an embodiment of the present invention.
[Explanation of symbols]
104 retransmission request permission section (retransmission request permission means)
110 Priority setting section (priority setting means)
201 transmitting station
202-204 receiving station
504 Retransmission request permission receiving station determination unit (retransmission request permission receiving station determination means)
505 retransmission request unit (retransmission request means)

Claims (29)

The transmitting station is a transmitting station in a multicast communication system that performs data transmission from a single transmitting station to a plurality of individually identifiable receiving stations, and an error occurs in data received by the receiving station. A transmitting station having a function of retransmitting data to the receiving station in response to a retransmission request transmitted from the receiving station when the
For each of the receiving stations, a priority setting means for setting a priority that is a frequency of permitting transmission of a data retransmission request to be ranked.
A transmission station, comprising: a retransmission request permitting unit that permits each of the receiving stations to transmit a data retransmission request according to the priority set by the priority setting unit. A program for causing a computer to function as each unit included in the transmitting station according to claim 1. A receiving station for receiving, from the transmitting station according to claim 1, data including information on permission to transmit a retransmission request,
Retransmission request permission receiving station determining means for determining a retransmission request permission receiving station permitted to transmit a retransmission request by the transmitting station, based on the received information on the retransmission request transmission permission;
Only when the data received before or before receiving the retransmission request transmission permission contains an error and the retransmission request permission receiving station determination means can determine that the own station is permitted to transmit the retransmission request, the retransmission is performed. A receiving station comprising retransmission request means for transmitting a request. A program for causing a computer to function as each unit included in the receiving station according to claim 3. This is a multicast communication method for performing data transmission from one transmitting station to a plurality of receiving stations that can be individually identified by the transmitting station, and when an error occurs in data, the receiving station issues a retransmission request. A communication method in which the transmitting station retransmits data to the receiving station in response to the retransmission request,
For each of the receiving stations, a priority setting step of setting a priority, which is a frequency of permitting transmission of a data retransmission request, to be ranked.
A retransmission request permitting step of permitting each of the receiving stations to transmit a data retransmission request in accordance with the priority set by the priority setting means. The priority setting step is performed at the start of communication or before the start of communication,
The communication method according to claim 5, wherein the retransmission request permission step according to the priority is always executed during communication. The communication method according to claim 5, wherein, in the priority setting step, the priority is determined by negotiation between a transmitting station and a receiving station performed at the start of communication. 6. The communication method according to claim 5, wherein in the priority setting step, the priority is determined according to a preset attribute of the receiving station. The communication method according to claim 5, further comprising: a priority changing step of dynamically changing the priority set in the priority setting step. The communication method according to claim 9, wherein in the priority changing step, the priority is changed when a new receiving station has joined the network. The communication method according to claim 9, wherein in the priority changing step, the priority is changed according to an error rate of each receiving station. The method according to claim 11, wherein, in the priority changing step, an error rate of each receiving station is calculated, and when a part of the calculated error rate is larger than a predetermined value, the priority is changed. Communication method. 13. The method according to claim 12, wherein in the priority changing step, when the calculated error rate is larger than a predetermined value, the priority of a receiving station having an error rate larger than the predetermined value is reduced. Communication method. The method according to claim 11, wherein in the priority changing step, an error rate of each receiving station is calculated, and when a part of the calculated error rate is smaller than a predetermined value, the priority is changed. Communication method. The method according to claim 14, wherein in the priority changing step, when the calculated error rate is smaller than a predetermined value, the priority of a receiving station having an error rate smaller than the predetermined value is increased. Communication method. The communication method according to claim 9, wherein in the priority changing step, the priority is changed at predetermined time intervals. In the priority changing step, the error rate of each receiving station is calculated, and at predetermined time intervals, the order of priority of each receiving station is rearranged into an order in which the smaller the error rate, the higher the priority order. The communication method according to claim 16, wherein the priority is changed in such a manner. 17. The communication method according to claim 16, wherein in the priority changing step, the priority is changed such that the order of the priority is randomly changed at predetermined time intervals. In the priority changing step, when three or more different priorities are present in the priority order determined in the priority determining step, the priority order of at least one receiving station is changed to the highest order. 17. The communication method according to claim 16, wherein the priority is changed at predetermined time intervals so as to gradually increase, and to decrease to the lowest rank when reaching the highest rank. In the priority changing step, when there are three or more different priorities in the priority order determined in the priority determining step, the priority order of at least one receiving station is changed until the priority order becomes the lowest order. 17. The communication method according to claim 16, wherein the priority is gradually changed at predetermined time intervals so that the priority is gradually lowered, and the priority is changed to the highest when the lowest rank is reached. The communication method according to claim 5, wherein in the retransmission request permission step, transmission of a retransmission request is not always permitted to some receiving stations. 6. The communication method according to claim 5, wherein in the priority setting step, when a predetermined condition is satisfied, transmission of a retransmission request to some of the receiving stations is not permitted. 23. The communication method according to claim 21, wherein in the priority setting step, a priority is not set for a receiving station that does not permit transmission of a retransmission request. In the priority setting step, the error rate of each receiving station is calculated, and when the error rate of some of the receiving stations is higher than a predetermined error rate, the error rate of the receiving station having an error rate higher than the predetermined error rate is determined. 23. The communication method according to claim 22, wherein transmission of a retransmission request is not permitted. 23. In the priority setting step, when a total number of receiving stations participating in communication exceeds a predetermined number, transmission of a retransmission request to some of the receiving stations is not permitted. Communication method described in. In the priority setting step, if only some of the receiving stations expecting a higher priority have used up the retransmission band, the transmission of the retransmission request to other receiving stations is not permitted. The communication method according to claim 22, characterized in that: 23. The communication according to claim 22, wherein in the priority setting step, when there is a receiving station set as a receiving station not expecting retransmission, transmission of a retransmission request is not permitted to the receiving station. Method. A program for causing a computer to execute each step included in the communication method according to any one of claims 5 to 27. A computer-readable recording medium on which the program according to claim 2, 4 or 28 is recorded.

Images