JP3735631B2 - Mail transmission / reception device and mail transmission / reception method - Google Patents

Description

  The present invention relates to a mail transmission / reception apparatus and a mail transmission / reception method for receiving a mail from a predetermined transmission source apparatus and transmitting the received mail to a predetermined transmission destination apparatus.

  In this specification, “mail” generally includes e-mails that are generally used between personal computers and mobile communication terminals, short message services that are used between mobile communication terminals, and multimedia message services. It is used as a comprehensive means that can be digitized and transmitted to a specific destination. A basic configuration of a conventional mail server is shown in FIG. The mail server 13 receives a mail transmitted from a mobile terminal such as a mobile phone or a personal computer, performs a conversion process of a file format such as a character code as necessary, and a server to which the mobile terminal of the received mail and the personal computer belong When the destination is a mobile terminal or a personal computer belonging to the mail server 13 or the personal computer is the destination, it has a function of sending an email to the destination terminal. The mail server 13 includes an input I / F unit 131, an output I / F unit 132, a recording / conversion unit 133 that performs message conversion processing, a buffer 134 that temporarily stores messages, and a congestion determination unit 136 that determines buffer congestion. The input I / F congestion control unit 137 limits reception processing during congestion. In the mail server 13, for example, the input I / F unit 131 receives a mail from the mail server A, performs a conversion process as necessary, and is transmitted to the destination server by the output I / F unit 132. During the transmission process, the mail is temporarily stored in the buffer 134.

  When mail that exceeds the processing capacity is concentrated on the server at one time and congestion occurs, the resources for establishing and establishing a connection between the server and the transmission source terminal or the transmission source server are insufficient, and mail reception processing is not performed. It becomes difficult. Further, even if the server can receive the mail in a congested state, if the temporary storage capacity of the server is exceeded, the mail is deleted without being transmitted, resulting in a mail loss. Further, on the server side, there is a possibility that the server may stop due to an increase in the number of processes up to the limit of the processing capacity of the server.

  Therefore, in the past, when congestion was assumed, or when congestion occurred, the number of mail processing was limited until congestion was resolved, and mail reception processing exceeding the specified number of processing was not performed. . In the example of FIG. 13, the congestion determination unit 136 restricts reception processing when congestion occurs exceeding the capacity of the buffer 134 or upon reception of a reception restriction instruction from a maintenance terminal (not shown). It was.

  On the other hand, although it is not related to the server, it does not limit the number of processes uniformly, but by partially avoiding or delaying reception of the signal while maintaining signal processing by controlling the signal according to the congestion state, A method for controlling congestion has been proposed. For example, as a method for controlling congestion of a signal transmitted to a CPU, it is proposed to perform predetermined congestion control when the number of interrupts to the CPU per unit time reaches a predetermined set value (for example, patents) Reference 1). More specifically, when two types of setting values are provided and the number of interrupts reaches the first setting value, subsequent transmission / reception is not accepted, and when the number of interrupts reaches the second setting value, an external device is interrupted. Notification is performed so that congestion control can be performed without stopping processing when congestion occurs.

  In addition, in order to detect the congestion state of the input buffer that stores the cell data input from the input line with respect to ATM transmission, the use state of the input buffer is determined in multiple stages, so that the level of the congestion state of the input buffer is determined. It has been proposed to perform congestion control (see, for example, Patent Document 2).

  Further, in the mail server 13 of FIG. 13, the transmission process may be congested due to the concentration of the mail transmission process at once, in addition to the congestion in the reception process and the mail process of the entire server. Further, even when the mail processing number of the mail server 13 itself in FIG. 13 is at a normal level, congestion occurs in the mail transmission destination server or the route connecting to the transmission destination server. Congestion may occur.

  As another background art related to e-mail retransmission control, there is a configuration described in FIG. 14 (FIG. 1 of Patent Document 3 below). In this configuration, the retransmission parameter determined by the client retransmission parameter determination means is transmitted by mail from the client, and the mail management means in the server that receives the parameter determines the retransmission condition for each mail based on the instruction, and the condition Based on the above, retransmission control is performed. That is, in this example, the mail management means manages the mail sender, transmission start time, retransmission parameter, retransmission attempt time, transmission state, etc. for each mail, and sets a retransmission interval and a retransmission cycle for each mail. .

As another background art regarding signal retransmission control, there is a configuration described in FIG. 15 (FIG. 2 of Patent Document 4 below). This configuration is an example of multicast file transmission in a one-to-many system composed of a server and a plurality of terminals connected thereto, and a communication control device for dividing and transmitting a file in units of transmission data blocks DTU It is. Here, retransmission is preferentially performed for a receiving terminal with a small DTU loss, and this is an example in which the retransmission priority is changed for each receiving terminal. Accordingly, communication can be completed earlier at a receiving terminal with better reception status, and multicast communication can be completed earlier as a whole.
JP-A-8-265364 JP-A-11-308247 Japanese Patent Laid-Open No. 11-65961 JP 2000-307676 A

  In the conventional server, when mail exceeding the processing capacity is concentrated at one time and congestion occurs, the number of mail processing is limited until the congestion is eliminated. As a result, the server processing can be maintained, but mails that are not received frequently occur, and when viewed from the mail transmission source user, the situation is equal to the suspension of the processing. Furthermore, when limiting the number of processing or processing capacity, the number of processing is less than the maximum processing capacity of the server, so the server processing capacity is fully exhibited even though there are many mails that you want to process. I couldn't.

  On the other hand, a method of performing control according to the congestion state, such as the above-described signal or ATM cell congestion control, is conceivable. However, the above background art flows into the target device by performing clock control on the transmission side. This is based on the signal control method, and since there are an infinite number of terminals and servers that are the senders of mail, it is impossible to limit the number of transmissions on the side that sends the mail. The control method could not be used. Furthermore, the above background art can be achieved by limiting the number of transmissions of the signal itself on the transmission side, but in order to perform the same processing in the mail, after communication with the transmission source server is established, Since it is necessary to perform control according to an instruction at the application level, it is impossible to perform congestion control that does not depend on the processing number limit of the receiving side device. As described above, depending on the congestion control method of the mail server of the background art, it is extremely difficult to maintain the service without reducing the server processing capacity in the congestion state.

  Further, in order to cope with the congestion of the transmission process, in the first background art, messages are stored and managed in common with a single buffer for a plurality of receiving apparatuses, so that a specific receiving apparatus has a failure, excessive traffic, etc. If it becomes inoperable at the same time, retransmission to the receiving device is frequently performed, and subsequent messages cannot be transmitted until the transmission is completed, so other destinations that arrive after the message for the failed destination device. There is a technical problem to be solved that a message for a device takes a long time to transmit even if the receiving device is normal.

  Although the background art described in Patent Document 4 performs retransmission control in units of mail, there is a drawback in that setting of retransmission conditions is inconvenient because it requires setting from the client one by one. In addition, when a mail receiving device in which the number of retransmissions is set to be broken, there is a disadvantage that it may affect the transmission of subsequent mail.

  In the background art described in Patent Document 3, it is possible to reduce the overall communication time by deferring a receiving terminal having a poor communication status by preferentially performing retransmission control as the receiving terminal has a smaller DTU loss. It is a technique related to file division transfer in multicast communication to the last, and does not transmit a message such as an electronic mail from a plurality of transmission source devices to a plurality of reception devices.

  Therefore, the present invention controls the mail server congestion according to the degree of congestion, so that the server processing capability and service can be maintained even in a congested state, and a plurality of source servers can be changed to a plurality of destination servers. An object of the present invention is to provide a mail transmission / reception apparatus and a mail transmission / reception method as a server capable of performing efficient retransmission control when a message such as an electronic mail is transmitted.

  The mail transmitting / receiving apparatus of the present invention includes (1) a receiving unit that receives a mail from a predetermined transmission source device, (2) a transmission unit that transmits the received mail to a predetermined transmission destination device, and (3) the mail. Processing number measuring means for measuring the number of mail processes per unit time in the transmission / reception device; (4) congestion determination means for determining whether the measured number of mail processes exceeds a predetermined threshold; and (5) congestion determination. A control unit that outputs a control signal to the receiving unit according to the determination result of the unit, and (6) a storage unit that stores the mail transmitted by the transmitting unit. (A) Each threshold corresponds to a different number of mail processes. When the congestion determination means determines that the threshold value exceeds one threshold, the control means performs a predetermined reception restriction so that the reception means corresponds to the one threshold value. Control signal To output.

  According to the mail transmission / reception apparatus of the present invention, even when congestion occurs in mail processing, a plurality of thresholds can be provided based on the number of mail processing per unit time, so that it is matched to the mail congestion state. Reception restriction is possible.

  In the mail transmission / reception apparatus of the present invention, the storage means includes a storage area for storing mail to be transmitted for each destination apparatus, and the control means measures the number of times the mail stored in the storage area is transmitted. It is also preferable to output a control signal to the transmission means so as to retransmit the measured target mail according to the measured number of transmissions. Since retransmission processing is performed according to the number of transmissions for each mail, retransmission control can be performed for each destination of the mail.

  In the mail transmission / reception apparatus according to the present invention, when there are a plurality of transmission destination apparatuses, the congestion determination unit makes a determination for each transmission destination apparatus. As a result, the number of mail processes exceeds one threshold value in one transmission destination apparatus. When it is determined that the transmission means has received the control means, the control means outputs a control signal to the transmission means so that the transmission means performs a predetermined transmission restriction on the one transmission destination device so as to correspond to the one threshold value. It is also preferable. Since retransmission processing is performed for each transmission destination device, it is possible to perform retransmission processing according to the situation for each transmission destination device.

  In the mail transmission / reception apparatus according to the present invention, when the congestion determination unit determines that the number of mail processes exceeds the first threshold, the control unit performs each process for at least one of the reception unit and the transmission unit. If the congestion determination means determines that the number of mail processes exceeds the first threshold and further exceeds the second threshold, the control means outputs a first control signal that instructs to limit the amount. A second control signal for instructing at least one of the reception unit and the transmission unit to further limit the amount of processing is output, and the congestion determination unit determines that the mail processing count is the first threshold value or the first value. If it is determined that the threshold value of 2 has been exceeded and the third threshold value that is lower than the first threshold value is exceeded, the control unit releases the respective processing restrictions on at least one of the receiving unit and the transmitting unit. Do It is also preferable to output a third control signal for instructing urchin. In the case where it is assumed that the mail processing number falls below the first threshold after entering the congestion state and the congestion state is assumed again, for example, the first threshold and the third threshold In order to maintain congestion control even if the number of mail processes per unit time fluctuates around each threshold, the congestion continues until the number of mail processes is less likely to recur. Control can be performed.

  In the mail transmission / reception apparatus according to the present invention, when the congestion determination unit determines that the number of mail processes exceeds the first threshold, the control unit performs each process for at least one of the reception unit and the transmission unit. If the congestion determination means determines that the number of mail processes exceeds the first threshold and further exceeds the second threshold, the control means outputs a first control signal that instructs to limit the amount. A second control signal for instructing at least one of the reception unit and the transmission unit to further limit the amount of processing is output, and the control unit outputs the first control signal or the second control signal to the reception unit. In response to the output of the control signal, a fourth instruction that instructs the transmission source device that cannot receive the mail according to the output of the control signal to transmit the retransmission request for the mail that can no longer be received. control It is also preferable to output No. to the transmission means. Since retransmission of data that cannot be received due to congestion control is requested, the transmission source device can transmit necessary data.

  In the mail transmitting / receiving apparatus of the present invention, the storage means includes a first storage area in which the remaining capacity is less than the first capacity and a second capacity in which the remaining capacity is greater than the second capacity. If there is a storage area, it is also preferable to move the mail stored in the first storage area to the second storage area for storage. Since the mail stored in the first storage area is moved and stored in the second storage area, loss of mail assigned to the first storage area can be avoided.

  Further, in the mail transmitting / receiving apparatus of the present invention, the control means is an average value per unit time from the time when the mail is transmitted to the destination apparatus to the time when the response sent back from the destination apparatus is received according to the transmission. Accordingly, it is also preferable to change the threshold value and output a control signal to the transmission means. For example, even when the destination device is congested, by lowering the threshold accordingly, it is possible to prevent the occurrence of congestion in the output processing due to a significant delay in the transmission processing for a specific destination device.

  The mail transmission / reception method of the present invention is a method of receiving a mail from a predetermined transmission source device and transmitting the received mail to a predetermined transmission destination device, wherein the processing number measuring means has a mail processing number per unit time. A measurement step for measuring the amount of mail processing, a determination step for determining whether or not the measured number of processed mails exceeds a predetermined threshold, and a determination unit for determining whether the number of processed mails exceeds a predetermined threshold. A control step of outputting a control signal so that the control means performs a predetermined reception restriction on the receiving means so as to correspond to the one threshold value when it is determined that one of the threshold values has been exceeded. And including.

  According to the mail transmission / reception method of the present invention, even when congestion occurs in mail processing, a plurality of thresholds can be set based on the number of mail processing per unit time, so that it is matched to the mail congestion state. Reception restriction is possible.

  Further, in the mail transmission / reception method of the present invention, the control unit measures the number of transmissions of the mail accumulated in each storage area for accumulating the mail to be transmitted for each transmission destination device, and performs the measurement according to the measured number of transmissions. It is also preferable to include a retransmission step of outputting a control signal to the transmission means so as to retransmit the target mail. Since retransmission processing is performed according to the number of transmissions for each mail, retransmission control can be performed for each destination of the mail.

  Further, in the mail transmission / reception method of the present invention, when there are a plurality of transmission destination devices, the congestion determination means makes a determination for each transmission destination device in the determination step. When it is determined that the threshold value is exceeded, the control unit controls the transmission unit so that the transmission unit performs a predetermined transmission restriction on the one transmission destination device so as to correspond to the one threshold value. Is preferably included. Since retransmission processing is performed for each transmission destination device, it is possible to perform retransmission processing according to the situation for each transmission destination device.

  According to the present invention, it is possible to maintain the processing capability and service of a server even in a congested state, and in the case where messages such as e-mails are transmitted from a plurality of transmission source servers to a plurality of destination servers, it is efficient. It becomes possible to perform retransmission control.

  The teachings of the present invention can be readily understood by considering the following detailed description with reference to the accompanying drawings shown for illustration only. Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals, and redundant description is omitted.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a communication system to which the present invention is applied.

  The mobile terminal 1 is a mobile terminal that can receive a mobile communication service. The mobile terminal 1 (transmission source device, transmission destination device) can send and receive mail to and from the mobile terminal 61, PHS 62, personal computer 63, and PDA 64. Mail includes e-mail that is generally used between personal computers and mobile communication terminals, short message service used between mobile communication terminals, and multimedia message service. Any means can be used as long as it is a communication means capable of transmitting and receiving the text and the like using the communication system shown in FIG. The wireless communication network 2 includes a wireless station that performs wireless communication with the mobile terminal 1 and communicates with the mail server 3, a communication line, a device that controls them, and the like.

  The mail server 3 (mail transmission / reception device) is a mail server of mobile terminals including the mobile terminal 1. The mail server 3 receives the mail transmitted from the mobile terminal 1, and transmits the mail to the mobile terminal 61, the PHS 62, the personal computer 63, and the PDA 64 that are the destinations of the mail with temporary storage as necessary. . Conversely, the mobile terminal 1 under its own management, or the mobile terminal 61 belonging to the management of another mail server A41 (transmission source apparatus, transmission destination apparatus) and the mail server B42 (transmission source apparatus, transmission destination apparatus). From each of the PHS 62 belonging to the management, the personal computer 63 belonging to the management of the mail server C43 (transmission source device, transmission destination device), and the PDA 64 belonging to the management of the mail server D44 (transmission source device, transmission destination device), A mail transmitted to the mobile terminal 1 under management is received, and the mail is transmitted to the mobile terminal 1 as the destination. Furthermore, if the email source is not the same as the destination file that can be used, such as when the file format is different, if the content cannot be confirmed on the destination device, the email file format is The mail server 3 can be provided with a conversion process and a function for deleting an attached file. The mail server 3 is connected to another mail server B42, a mail server C43, and a mail server D44 via the network 5.

  The mail servers B42 to D44 are examples of mail servers that manage mails that are not controlled by the mail server 3, such as the mail transmission destinations, the PHS 62 that is the transmission source, the personal computer 63, the PDA 64, and the like. is there. The mail servers B42 to D44 are connected to the mail server 3 via the network 5. The network 5 is a communication network that connects the mail servers B42 to D44 and the mail server 3, and includes a dedicated line.

  FIG. 2 shows a configuration diagram of the mail server 3. The input I / F unit 31e (reception unit) has a function of receiving mail transmitted from the mobile terminal 1 belonging to the management of the mail server 3 via the communication network. Further, the input I / F unit 31e has a function of receiving mails directly transmitted from the other mail servers A41 to D44, which are addressed to the mobile terminal 1 belonging to the management of the mail server 3. More preferably, the input I / F units 31a to 31e (reception means) have a function of identifying a destination mail address of the received mail and an identification code for identifying the mail destination apparatus. Here, the identification code may be any one such as a domain name, an IP address, a telephone number, a country code, or the like that is used for specifying a transmission destination device when sending and receiving mail. Although a plurality of input I / F units of the present embodiment are provided as the input I / F units 31a to 31e, they may be configured as a single interface.

  The output I / F units 32a to 32e (transmission means) have a function of transmitting the mail received from the recording conversion unit 33 to a destination mobile terminal or another mail server. One or a plurality of output I / F units are installed, and when a plurality of output I / F units are installed, each output I / F unit can be installed for each server as a mail transmission destination. The example of FIG. 2 shows an example in which a plurality of output I / F units 32a to 32e are installed for each server. Although a plurality of output I / F units of the present embodiment are provided as the output I / F units 32a to 32e, they may be configured as a single interface.

  The recording conversion unit 33 temporarily stores mails transmitted from the input I / F units 31a to 31e during processing, performs character code conversion processing as necessary, and outputs I / F units 32a to 32e. It has the function to transmit to. Further, when a plurality of output I / F units 32a to 32e are installed for each server that is a mail transmission destination, the recording conversion unit outputs the mail according to the mail transmission destination. It has a function to distribute to.

  The buffer 34 (accumulation means) has a function of temporarily storing mails until the processing is completed during mail transmission processing. Further, for example, when there is congestion in the server to which the mail address belongs, or the line leading to the server, or when the mail transmission processing of the output I / F units 32a to 32e increases at one time, the output I The / F units 32a to 32e have a function of temporarily storing e-mails until a transmission resource for e-mails scheduled to be transmitted can be secured.

  FIG. 5 shows a specific configuration example of the buffer 34. The buffer 34 has a function of storing messages for each destination device. It is composed of at least a destination device unit 121, a buffer content unit 122, and a message accumulation number management unit 123, and has a function of storing the contents of messages accumulated in units of destination devices and the number of messages being accumulated. Since messages are individually managed for each destination device in this way, retransmission management can be performed for each destination device individually. Since the number of stored messages is managed for each destination device, the traffic for each destination device can be easily grasped, and the number of messages waiting for transmission can be output to the outside in units of destination devices.

  Further, a mail storage area for each destination device can be set in the buffer 34 in advance. FIG. 6 is an example of a buffer in which a mail storage area is predetermined for each destination device. In the figure, 1 indicates the total capacity of the buffer, and abcdef, ABC, and XYZ indicate mail storage areas for each destination device. Here, abcdef is a storage capacity 1/3 of XYZ, and ABC is a storage capacity 2/3 of XYZ. If XYZ has a storage capacity of 300 GB, ABC and abcdef are 200 GB and 100 GB, respectively. By separately determining the storage capacity according to the destination device in this way, it becomes possible to determine the capacity in consideration of the number of mail transmission processes from the server to the destination device and the length of the temporary storage time associated with the transmission processing. As a result, an efficient buffer can be used.

  As a modified example, the buffer 34 can have a function of switching an area allocated for each destination. That is, when the amount of use of the area (first storage area) directed to a specific destination apparatus may exceed the storage capacity provided in advance for mail directed to the destination apparatus (that is, the first storage area) When the remaining capacity of the area is smaller than the predetermined first capacity), there is an area (second storage area) having a larger storage capacity prepared for another destination apparatus, and an area for the destination apparatus Thus, when all mails stored in the buffer or storage capacity for other destination devices can be stored (that is, when the remaining capacity of the second storage area is larger than the predetermined second capacity), the destination The allocated area can be switched every time. The switching operation will be described with reference to FIGS. 6 (a) and 6 (b).

  For example, when the storage capacity of a shown in FIG. 6A is 100 Gbytes and the usage amount exceeds 80 Gbytes, the usage amount is 50 G for A in ABC with a storage capacity of 200 Gbytes. If it is about bytes, 50% of the storage capacity of A is given to a as shown in FIG. 6B, and a is set to 100 Gbytes. For example, if an area that uses only 50 GB is A, the capacity of A is limited to 100 GB. As a result, even if the storage capacity of abcdef is given, assuming that the capacity of temporarily stored mail is small, the storage capacity temporarily increases due to the concentration of mail to the destination device, failure of the destination device, etc. However, there is no need to prepare an excessive storage capacity in preparation for such a situation without causing lost mail.

  Returning to FIG. 2, the congestion control connection counter unit 35 (processing number measuring means) is configured to receive the number of mails received per unit time at the input I / F units 31 a to 31 e and the output I / F units 32 a to 32 e. Count the number of emails per unit time sent from outside to outside. Here, when a plurality of input I / F units 31a to 31e and a plurality of output I / F units 32a to 32e are provided in the server, the number of processes per unit time is calculated for each I / F unit. . Further, the number of mail processes in the server per unit time is calculated from the number of mails received and transmitted per unit time. Here, when a plurality of destinations are included in a single mail, the number of destinations may be treated as the number of received mails. The congestion control connection counter unit 35 notifies the congestion determination unit 36 of the calculated number of mail processes per unit time.

  The congestion determination unit 36 (congestion determination means) notifies the server of the unit number of times per unit time and the number of mail processes of the input I / F units 31a to 31e and the output I / F units 32a to 32e from the congestion control connection counter unit 35. receive. The congestion determination unit 36 determines that congestion occurs when the number of emails processed per unit time exceeds a preset threshold. The unit time is input from a maintenance terminal (not shown) by a maintenance person of the mail server, for example, and is set in the congestion determination unit 36. The congestion judgment unit 36 notifies the unit time to the congestion control connection counter unit 35.

  The congestion determination unit 36 determines that congestion occurs when the number of mails processed in the server per unit time exceeds a preset threshold. When congestion occurs, the congestion determination unit 36 reduces the number of processes per unit time, so that the input I / F congestion control units 37a to 37e (control means) receive mail as congestion control. Has a function of notifying a predetermined instruction for restricting. Furthermore, the congestion determination unit 36 performs congestion control on the input I / F congestion control units 37a to 37e when the number of mails processed by the server per unit time falls below a preset threshold value. It has a function to instruct to cancel. Here, the threshold value used as a reference for determining congestion is set in two or more stages, and the congestion control method instructed to the input I / F congestion control unit 35 is changed according to each stage. For example, FIG. 3 shows a case where two levels of thresholds are provided.

  FIG. 3 is a graph of the number of mail processes per unit time on the vertical axis and the number of processes on the horizontal axis. Here, when the number of mail processes per unit time does not exceed the primary threshold value (circled number 1), the normal mail is not sent to the input I / F congestion control units 37a to 37e. Process, and if the number of emails processed per unit time exceeds the primary threshold (circled number 1), retry to send the email to the first-stage email source terminal or server. The congestion determination unit 36 performs congestion control by notifying the input I / F congestion control units 37a to 37e so as to return a request signal. Furthermore, when the number of mail processes per unit time exceeds the secondary threshold (circled number 2), the input I / F congestion control units 37a to 37e are notified so as to disconnect the TCP / IP. Thus, the congestion determination unit 36 controls congestion. Even if congestion is occurring, the number of processes up to the primary threshold (circled number 1) is normally received. Next, congestion control and control release in the case of controlling congestion in two stages will be described with reference to FIG.

  FIG. 4 is a graph in which the vertical axis represents the number of mails processed per unit time and the horizontal axis represents unit time. As in the case of FIG. 3, the processing when a threshold value for determining congestion in two stages is provided for the number of processes per unit time is shown. If the primary threshold (circled number 1) is exceeded even once, primary regulation is performed. The congestion determination unit 16 then notifies the input I / F congestion control units 37a to 37e to return a retry request signal to the transmission source, and based on this, the input I / F congestion control units 37a to 37e Create a request signal and send a retry request signal back to the source terminal or server.

  Even if the number of processes per unit time thereafter is less than the primary threshold value (circled number 1), the congestion judgment unit 36 does not perform the above control unless the number of processes is less than the release value (circled number 3). Do not cancel. In other words, the primary regulation is continued until the release value (circled number 3) falls below. Further, the congestion determination unit 36 performs input I / F congestion control units 37a to 37e so as to perform TCP / IP disconnection when the number of processed mails per unit time exceeds a secondary threshold (circled number 2). Notify After this, the congestion determination unit 36 determines that if the number of processed mails per unit time falls below the secondary threshold (circled number 2) but does not fall below the release value (circled number 3), The TCP / IP disconnection congestion control is continued in response to the reception request, and the cancellation of the secondary restriction is not notified to the input I / F congestion control units 37a to 37e. In this way, mail is processed per unit time by providing a width between the primary threshold (circled number 1) or secondary threshold (circled number 2) and the release value (circled number 3). Since the control is continued even if the number fluctuates around each threshold value, it is possible to continuously perform the congestion control until the processing number is low in the possibility that the congestion state will recur.

  Furthermore, the congestion determination unit 36 determines that congestion has occurred when the number of processes per unit time of the output I / F units 32a to 32e exceeds a preset threshold, and outputs the output I / F Congestion control is instructed to the congestion control unit 38 (control means). The instruction is to temporarily store a mail to be transmitted to the output I / F congestion control unit 38 in the buffer 34 and perform a retransmission process after a predetermined time has elapsed. The congestion determination unit 36 further determines the output I / F congestion control unit 36 when the number of mails processed by the output I / F units 32a to 32e per unit time falls below a preset threshold value as a release value. A function to instruct to release the processing restriction.

  As illustrated in FIG. 2, when a plurality of output I / F units 32 a to 32 e are provided, the congestion determination unit 36 performs the congestion control individually for each of the output I / F units 32 a to 32 e. For example, when congestion occurs only in the output I / F unit 32a, the congestion control is performed only for the output I / F unit 32a, and normal transmission processing is performed for the other output I / F units 32b to 32e. Continue. For this reason, when a plurality of output I / F units 32a to 32e are provided and some or all of them are provided for each server to which the mail is sent, about a part of the received mail, As a result, it is possible to control the congestion of the transmission process for each destination server.

  As a modification, when a plurality of output I / F units 32a to 32e are provided, for example, when congestion occurs only in the output I / F unit 32a, the destination is directed to the transmission destination corresponding to the output I / F unit 32a. A function of specifying an identification code for identifying a destination device of the received mail and instructing the input I / F control units 31a to 31e not to perform a mail reception process including the identification code as a destination. You can also.

  FIG. 7 shows an identification code for identifying the output I / F unit and the mail transmission destination device in the congestion determination unit 36, and the management status of the presence or absence of a congestion state. The identification code corresponding to each of the output I / F units 32a to 32e is set by the maintenance person of the mail server, for example, from a maintenance terminal (not shown) and set in the congestion determination unit 36. Here, the identification code may be any one such as a domain name, an IP address, a telephone number, a country code, or the like that is used for specifying a transmission destination device when sending and receiving mail. As a result, even if a server at a specific destination is congested or cannot receive mail due to a failure or the like, the server does not receive mail that is sent to such a server. It is possible to avoid congestion due to stagnation in the server.

  As a modified example, when there are a plurality of output I / F units 32a to 32e and some or all of them are provided for each mail destination device, the congestion judgment unit 36 sends the mail to a specific destination device. It is possible to provide a function of receiving notification from the output I / F congestion control unit 38 that there is a possibility that congestion will occur because the response time of the destination device is longer than the time recorded in advance during transmission. The congestion determination unit 36 may have a function of lowering the threshold value of the number of congestion determination processes of the output I / F congestion control unit 38 corresponding to the destination device when the notification is received. As a result, it is possible to prevent deterioration of congestion due to delay in transmission processing.

  The input I / F congestion control units 37a to 37e receive instructions from the congestion determination unit 36 such as reception restrictions associated with congestion control, and control mail reception for the input I / F units 31a to 31e. It has a function of creating and transmitting a retry signal to the transmission source terminal or server.

  As a modified example, the congestion determination unit 36 instructs the input I / F control units 37a to 37e not to perform a mail reception process including a specific identification code (a code for identifying a mail transmission destination device) as a transmission destination. Even in such a case, the above processing can be performed for them.

  The output I / F congestion control unit 38 temporarily stores the mail scheduled to be transmitted from the congestion determination unit 36 in the buffer 34, receives a control instruction such as performing a retransmission process after a predetermined time has elapsed, and outputs it. The mail that is being processed by the I / F units 32a to 32e is transferred to the buffer 34, and after a predetermined time has elapsed, the output I / F units 32a to 32e are instructed to perform transfer processing again.

  The output I / F congestion control unit 38 functions to individually manage messages for each destination device stored in the buffer 34 and also has a function to manage the number of waiting messages for each destination device. The output I / F congestion control unit 38 has a function of counting the number of message retransmissions for each destination device and stopping the transmission of the message by the output I / F congestion control unit 38 when the number of retransmissions reaches a predetermined number. The output I / F congestion control unit 38 waits for a predetermined timing at the time of retransmission, and retransmits, but determines the timing and manages the timing for each destination device. In some cases, it is possible to change the timing for each destination apparatus and for each retransmission.

  For example, when an e-mail is transmitted from the mobile terminal 1 of FIG. 2 to the mail server B42, a mail signal is received by the input I / F unit 31e, processed by the recording conversion unit 33, and then transmitted to the buffer 34. The received mail is temporarily stored in the part corresponding to B. The output I / F unit 32b that has received the information indicating the reception reads the corresponding mail signal from the buffer 34 and transmits it to transmit the mail signal to the mail server B42. Thereafter, the output I / F congestion control unit 38 waits for a reply signal from the mail server B42, and deletes the corresponding mail signal from the buffer 34 if a normal reception signal is received. In the case of an abnormal reply such as a mail non-reception signal or a reply signal non-reception, the mail is retransmitted after waiting for a predetermined timing, and the information on the number of retransmissions is incremented by one.

  When the output I / F congestion control unit 38 further requests a response request from the output I / F units 32a to 32e to the destination server in the transmission processing of the output I / F units 32a to 32e, the destination server A function for recording the time until the response signal is returned may be provided. In that case, the output I / F congestion control unit 38 also congests the destination server when the response time of the specific destination server is equal to or longer than a predetermined time from the recorded response time. It is determined that a failure or the like has occurred, and a function of instructing to resend the mail to be transmitted temporarily in the buffer 34 and to perform retransmission processing after a predetermined time has elapsed. Furthermore, it is possible to provide a function for notifying the congestion determination unit 36 that congestion has occurred in the destination server.

  8 to 11 show the flow of congestion processing in the mail server 3 of FIG. FIG. 8 shows a flow of a method for determining congestion based on the number of processes of the entire server, and performing congestion control with reception restriction when it is determined that there is congestion. Here, a processing flow in the case where a two-stage threshold is provided as the above-described reference for determining congestion and congestion control corresponding to the threshold is performed is shown. The congestion control connection counter unit 35 is configured such that the number of mails received by the input I / F units 31a to 31e and the output I / F units 32a to 32e are destination terminals or other servers in a unit time designated by the congestion determination unit 36. The number of e-mails sent to is calculated, and the calculation result is notified to the congestion determination unit 36 (S100).

  The congestion determination unit 36 calculates the number of mails processed by the server per unit time based on the number of transmitted / received mails notified from the congestion control connection counter unit 35 (S101), and the calculated number of processes is the primary regulation value. It is determined whether or not the number of processes exceeds a predetermined number (S102). If it is determined that the number of processes exceeds the primary regulation value, it is further determined whether or not the number of processes exceeds the secondary regulation value (S103). In S103, when it is determined that the secondary regulation value is not exceeded, the congestion determination unit 36 instructs the input I / F congestion control units 37a to 37e to perform the primary regulation, and the input I / F congestion control. The units 37a to 37e send control signals to the input I / F units 31a to 31e so as to return a retry request without receiving a subsequent mail to the sender of the mail received by the input I / F units 31a to 31e. (First control signal, fourth control signal) are output (S104). On the other hand, when the secondary regulation value is exceeded in S103, the congestion determination unit 16 instructs the input I / F congestion control units 37a to 37e to perform the secondary regulation, and the input I / F congestion control. The units 37a to 37e output control signals (second control signals) to the input I / F units 31a to 31e so that the input I / F units 31a to 31e do not establish the TCP / IP protocol associated with mail reception. (S105). The control in S104 and S105 is continued until there is an instruction from the congestion determination unit 36 to cancel these controls.

  If it is determined in S102 that the value is equal to or lower than the primary regulation value, it is determined whether primary or secondary regulation is currently being performed (S106). If it is determined in S106 that the primary restriction or the secondary restriction is being performed, it is determined whether the number of processed mails per unit time is below a preset release value (S107). Here, when it is determined that the release value is exceeded, the current regulation is continued. On the other hand, when the release value is less than the release value, the congestion judgment unit 36 determines whether the current regulation is temporarily performed or the secondary regulation. A control signal (third control signal) is output to the input I / F units 31a to 31e so as to cancel all the restrictions and perform normal processing (S108). The congestion determination unit 36 repeats the flow again in the next unit time and performs the same processing.

  Next, a processing flow of the congestion control shown in FIG. 9 will be described as a modification of the congestion control shown in FIG. In addition to the congestion control method shown in FIG. 8, FIG. 9 shows a specific identification code for identifying a mail transmission destination device from the congestion determination unit 36 to the input I / F congestion control units 37a to 37e. The flow of the congestion control method which instruct | indicates not to perform the reception process of the containing mail is shown. The processing up to S208 is the same as the processing up to S108 in FIG. In S209, the input I / F units 31a to 31e specify an identification code for identifying a mail transmission destination device under the primary restriction, the secondary restriction, or in the process of performing normal reception processing. Here, the identification code may be any one such as a domain name, an IP address, a telephone number, a country code, or the like that is used for specifying a destination device when sending and receiving mail.

  Next, since the identification code is congested in the transmission process, it is checked whether or not the identification code is an identification code notified in advance from the congestion determination unit 16 as a target for restricting the reception of mail (S210). . Here, when the identification code of the transmission destination is the target of reception restriction, TCP / IP is disconnected without performing reception processing (S211). On the other hand, if the transmission destination identification code is not subject to reception restriction, reception processing is performed in accordance with the regulations up to S208 (S212). The congestion determination unit 36 repeats the flow again and performs the same processing in the next unit time.

  Next, the congestion control in the output I / F units 32a to 32e will be described with reference to FIG. The congestion determination unit 36 processes the mails of the output I / F units 32a to 32e per unit time based on the number of outgoing mail processes of the output I / F units 32a to 32e notified from the congestion control connection counter unit 35. The number is calculated (S301), and it is determined whether the number of processes exceeds a predetermined number of processes as a primary regulation value (S302). Here, when it is determined that the number of processes exceeds the restriction value, the congestion determination unit 36 instructs the output I / F congestion control unit 38 to restrict the transmission mail to be stored in the predetermined time buffer 34. The output I / F congestion control unit 38 stores the transmitted mail in the predetermined time buffer 34 (S303). The control in S303 is continued until there is an instruction from the congestion determination unit 36 to cancel these controls.

  If it is determined in S302 that the value is equal to or lower than the primary regulation value, it is determined whether regulation is being performed (S304). If it is determined in S304 that the primary restriction is being performed, it is determined whether the number of processed mails per unit time is below a preset release value (S305). Here, when it is determined that the release value is exceeded, the current regulation is continued. On the other hand, when the release value is below the release value, the congestion judgment unit 36 releases the primary regulation currently being performed. The restriction for instructing the output I / F congestion control unit 38 to perform normal processing is released (S306). The congestion determination unit 36 repeats the flow again in the next unit time and performs the same processing.

  Next, a congestion control flow shown in FIG. 11 will be described as a modification of the congestion control method in the output I / F units 32a to 32e shown in FIG. FIG. 11 shows a case where a plurality of output I / F units 32a to 32e are provided, and some or all of them are provided for each mail destination device. FIG. 10 shows a processing flow for lowering the threshold value of the congestion judgment of the output I / F congestion control unit 38 when the response time of the destination device is longer than the pre-recorded time during mail transmission. .

  The output I / F congestion control unit 38 receives the response request from the output I / F unit 32a to 32e when the output I / F unit 32a to 32e transmits mail to the destination server. The time until receiving a reply from the destination device in response to the response request is recorded for each mail transmission (S400), the average value of the recorded processing time per unit time is calculated and notified to the congestion judgment unit 36 ( S401). Next, the congestion determination unit 36 determines whether the average processing time is equal to or greater than a predetermined primary threshold (S402). If the average processing time is equal to or greater than the primary threshold, does the congestion determination unit 36 exceed the predetermined secondary threshold? Determination is made (S403), and if it is determined that the secondary threshold value is exceeded, the threshold value of the processing number of the output I / F units 32a to 32e is set to the minimum value (S404). If the primary threshold value is determined although the secondary threshold value is not exceeded, the threshold value of the number of processes of the output I / F units 32a to 32e is set as an intermediate value (S405).

  On the other hand, when it is determined in S406 that the average processing time does not exceed the predetermined primary threshold, the congestion determination unit 36 determines whether the threshold set for the output I / F is the maximum value. Confirmation is made (S406), and if it is not the maximum value, it is determined whether the processing time is equal to or less than the release value (S407). If it is equal to or less than the release value, the threshold value is returned to the maximum value for normal processing (S408). The output I / F congestion control unit 38 and the congestion determination unit 36 repeat the above processing. As a result, even if the destination server is congested, the output processing congestion can be prevented by significantly reducing the transmission processing for a specific destination by lowering the transmission processing threshold accordingly. Can do.

  Next, transmission congestion control in the output I / F congestion control unit 38 will be described with reference to FIG. The output I / F units 32a to 32e receive the mail scheduled to be transmitted from the recording conversion unit 33 and store it in the buffer 34 (S501). The output I / Fs 32a to 32e determine whether or not the congestion control is performed for the output process (S502), and if the output restriction is performed, the output I / Fs 32a to 32e confirm the number of transmissions of the target mail (S503). If the number of transmissions is less than 1, the mail is transferred to the buffer 34, and the buffer 34 stores the mail for a predetermined time (S505).

  On the other hand, if it is determined in S503 that the output side congestion control is not performed, and if the number of transmissions is one or more in S503, it is determined whether there is a transmission resource available in the output I / Fs 32a to 32e. (S504) If there is no space, the mail is transferred to the buffer 34, and the buffer 34 stores the mail for a predetermined time (S505). If there is an empty transmission resource, the message is transmitted to the destination device (S506). When a reply indicating that the message has been normally received from the destination apparatus is received (S508), a reply indicating that the message has been normally received is returned to the transmission source, and the corresponding message is deleted from the buffer 34 (S509). If it is determined in S507 that the message indicating that the message has been successfully received from the destination device has not been received, it is determined whether or not a predetermined number of retransmissions have been completed, and if not completed (S510). Transfers the mail to the buffer 34, which stores the mail for a predetermined time (S505) and resends the message. Since the message has not been reached when the predetermined number of retransmissions are completed, an error message indicating that the message could not be transmitted is notified to the transmission source (S511), and the corresponding message is deleted from the buffer 34 (S509).

  The present invention is not limited to the above-described embodiment, and various changes can be made. For example, the mail source may be any of a mobile phone, PHS, and PDA, or may be a personal computer. The mail transmission source to the mail server may be connected by either a wireless line or a wired line. The email is not limited to an email, and any email can be used as long as a message is transmitted and received via a server. Furthermore, in the previous example, the threshold of the number of mail processing for determining congestion is set in two stages, but a threshold of two or more stages may be set. In the previous example, as a control method during congestion, transmission of a retry request signal to the transmission source and establishment of TCP / IP are not performed. However, the control method is not limited to this, and unit time Any one can be used as long as it reduces the processing load on the winning server.

  According to the present embodiment, by setting a multi-stage threshold based on the number of mail processes per unit time of the mail server by the apparatus of FIG. 2 and the method of FIG. 8, by using a congestion control method according to this, Congestion can be controlled without stopping the mail processing service while maintaining the server processing capability. Even if mail processing is concentrated at one time, it is possible to time-shift mail processing during congestion by making a retry request to the terminal or server that sent the mail. As a result, the processing capacity of the server can be used in a time-distributed manner, so that it is not necessary to prepare excessive processing capacity in case of congestion. As a result, it is possible to provide a mail server that uses a low cost and minimizes interruption of service for the user, or a mail service using the mail server.

  Furthermore, according to the present embodiment, by taking the response that the request for retry and connection are not established as the congestion control means shown in FIG. 3 and FIG. 4, it is confirmed that the mail transmission processing is not completed at the transmission source terminal. Since the notification can be made, it is possible to notify the sender of the mail transmission failure.

  In addition, by restricting the reception of mail during congestion, it is possible to avoid lost received mail and provide a highly reliable mail system. In addition, since the server does not receive mail during congestion and notifies the sender of transmission failure, it has reached the destination even though the sender has sent mail, which has conventionally occurred during congestion. Therefore, it is possible to eliminate the double transmission in which the mail is repeatedly transmitted. As a result, it is possible to avoid an increase in congestion due to double transmission.

  Furthermore, according to the present embodiment, even when congestion occurs in mail output processing, a threshold is set based on the number of mail output processes per unit time, and a congestion control method corresponding to this is used. The congestion can be controlled while maintaining the mail transmission process.

  In addition, by providing multiple means for output processing and performing congestion control for each means, it is possible to minimize the influence of the congestion on the entire server processing, and it has excessive processing capacity in case of congestion. Eliminates the need for a mail server. As a result, it is possible to provide a mail server that uses a low cost and minimizes interruption of service for the user, or a mail service using the mail server.

  In addition, when a plurality of output I / F units 32a to 32e are provided and some or all of them are provided for each mail transmission destination server, a corresponding output is generated when congestion occurs only for a specific destination. Congestion control may be performed on the I / F units 32a to 32e, and normal processing can be maintained in the output I / F units 32a to 32e directed to other destinations. In addition, when the processing capability of the destination mail server or the capability of the line connecting to the server is clear, by setting a threshold value corresponding to these capabilities, output traffic according to the capability of the destination As a result, transmission processing exceeding the capability of the counterpart device can be suppressed, and congestion of the counterpart server can be prevented beforehand.

  By setting the threshold of the number of mail processing that is the standard for regulation according to the processing capacity and processing status of the server using this congestion control, it does not add excessive processing capacity of the server and conforms to the processing status Congestion control can be performed.

  Furthermore, by setting the input side and the output side congestion control release values with a width between the first threshold value or the second threshold value and the release value, the number of mail processes per unit time can be changed. Since the control is continued even if the vicinity of the threshold value is raised or lowered, the congestion control can be continuously performed until the number of processes with a low possibility that the congestion state will recur.

  According to the present embodiment, since the buffer 34 and the output I / F congestion control unit 38 perform retransmission control of a retransmission message for each destination device, even if there is a destination device with excessive traffic or a fault, other destination devices Therefore, the message transmission can be normally performed without being affected by it.

  According to the modification shown in FIG. 6, the number of mail transmission processes from the server to the destination apparatus and the length of the temporary storage time associated with the transmission process are determined by independently defining a mail storage area for each destination apparatus in the buffer 34. It is possible to determine the capacity in consideration of the above, and it is possible to use an efficient buffer for the entire server.

  According to the modification shown in FIG. 6, when the buffer 34 has a function of switching an area allocated for each destination, a destination to which a relatively small storage capacity is normally allocated for temporary storage is thereby obtained. Even if the storage capacity temporarily increases due to mail concentration on the device or failure of the destination device, it becomes possible to perform processing without causing lost mail, and it is excessive in preparation for such a situation. It is no longer necessary to prepare a large storage capacity.

  The congestion determination unit 36 specifies an identification code of a destination causing congestion (a code for identifying a mail transmission destination device), and sends a specific identification code to the input I / F congestion control units 37a to 37e. 7 and FIG. 9 instructing not to perform the mail receiving process included in FIG. 9, even if congestion occurs only for the mail addressed to the destination due to a failure of a specific destination device or the like, Since the reception of the mail of the destination is restricted, it is possible for the server as a whole to minimize the influence of the congestion.

  In the case where a plurality of output I / F units 32a to 32e are provided and some or all of them are provided for each mail destination device, the congestion determination unit 36 transmits the mail to a specific destination device. Further, when the response time of the destination device takes a predetermined time or more than the time recorded in advance, the congestion judgment threshold value of the output I / F congestion control unit 38 is lowered as a trigger when this takes place as a trigger. According to the variation 9 of the congestion control method, when the destination server is congested, the congestion processing is started in the server early by lowering the threshold value of the transmission processing before the congestion occurs in the own server. In addition, it is possible to prevent the occurrence of serious congestion due to a significant delay in transmission processing for a specific destination.

1 is a configuration diagram of a communication system to which the present invention is applied. It is a block diagram of the mail server of this embodiment. FIG. 4 is a diagram showing the number of mail processes per unit time and the threshold value for congestion control of the mail server in FIG. 3. FIG. 4 is a diagram showing the number of mail processes per unit time and the threshold value for congestion control of the mail server in FIG. 3. FIG. 3 is a configuration diagram of a buffer in FIG. 2. It is a block diagram of the buffer of a modification. The management table of the identification code of a modification is shown. It shows the flow of mail reception. 9 shows a modification of FIG. The flow of mail transmission processing is shown. Fig. 11 shows a modification of Fig. 10. 3 shows a flow of mail transmission processing of the output I / F unit of FIG. 1 shows a conventional mail server. It is FIG. 1 of Unexamined-Japanese-Patent No. 11-65961. It is FIG. 2 of Unexamined-Japanese-Patent No. 2000-307676.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Mobile terminal, 3 ... Mail server, 31a-31e ... Input I / F part, 32a-32e ... Output I / F part, 33 ... Recording / conversion part, 34 ... Buffer, 35 ... Congestion control connection counter part, 36 ... Congestion determination unit, 37a to 37e ... Input I / F congestion control unit, 38 ... Output I / F congestion control unit, 41 ... Mail server A, 42 ... Mail server B, 43 ... Mail server C, 44 ... Mail server D.

Claims (10)

A mail transmitting / receiving apparatus comprising: a receiving means for receiving mail from a predetermined transmission source apparatus; and a transmission means for transmitting the received mail to a predetermined transmission destination apparatus,
A processing number measuring means for measuring the number of mail processes per unit time in the mail transmitting and receiving device;
Congestion determination means for determining whether the measured number of processed mails exceeds a predetermined threshold;
Control means for outputting a control signal to the receiving means according to the judgment result of the congestion judging means;
Storage means for storing mail sent by the transmission means;
With
A plurality of the threshold values are set so as to correspond to different numbers of mail processing, respectively, and when the congestion determination unit determines that the threshold value is exceeded, the control unit corresponds to the one threshold value. Output a control signal so as to perform a predetermined reception limit to
Mail transmission / reception device. The storage means includes a storage area for storing mail to be transmitted for each destination device,
The control means measures the number of transmissions of the mail accumulated in the respective storage areas, and controls the transmission means to retransmit the measured target mail according to the measured number of transmissions. Output,
The mail transmitting / receiving apparatus according to claim 1. When there are a plurality of destination devices, the congestion determination means determines that the number of mail processes exceeds one threshold value in one destination device as a result of making a determination for each destination device. The control means outputs a control signal to the transmission means so that the transmission means performs a predetermined transmission restriction on the one transmission destination device so as to correspond to the one threshold value.
The mail transmitting / receiving apparatus according to claim 1 or 2. When the congestion determination unit determines that the number of mail processes exceeds the first threshold, the control unit limits the amount of processing for at least one of the reception unit and the transmission unit. Output a first control signal instructing
If the congestion determination unit determines that the number of mail processes exceeds the first threshold and further exceeds the second threshold, the control unit determines whether at least one of the reception unit and the transmission unit , Outputting a second control signal instructing to further limit the amount of processing,
When the congestion determination unit determines that the number of mail processes has exceeded the first threshold or the second threshold and then has fallen below a third threshold that is less than the first threshold, the control The means outputs a third control signal instructing at least one of the receiving means and the transmitting means to release the respective processing restrictions.
The mail transmission / reception apparatus according to claim 1. When the congestion determination unit determines that the number of mail processes exceeds the first threshold, the control unit limits the amount of processing for at least one of the reception unit and the transmission unit. Output a first control signal instructing
If the congestion determination unit determines that the number of mail processes exceeds the first threshold and further exceeds the second threshold, the control unit determines whether at least one of the reception unit and the transmission unit , Outputting a second control signal instructing to further limit the amount of processing,
The control means outputs the first control signal or the second control signal to the receiving means, and then, for the transmission source device that cannot receive the mail according to the output of the control signal, The mail transmitting / receiving apparatus according to any one of claims 1 to 3, wherein a fourth control signal instructing to transmit a re-transmission request for mail that can no longer be received is output to the transmission means. The storage means includes a first storage area in which the remaining capacity is smaller than the first capacity and a second storage area in which the remaining capacity is larger than the second capacity in the storage area. The mail transmitting / receiving apparatus according to any one of claims 2 to 5, wherein the mail stored in the first storage area is moved and stored in the second storage area. The control means includes the threshold value according to an average value per unit time from when a mail is transmitted to the destination device to when a response returned from the destination device is received according to the transmission. The mail transmission / reception apparatus according to claim 3, wherein the control signal is output to the transmission unit by changing the password. A mail transmission / reception method for receiving a mail from a predetermined transmission source device and transmitting the received mail to a predetermined transmission destination device,
A measurement step in which the processing number measuring means measures the number of mail processes per unit time,
A determination step in which the congestion determination means determines whether or not the measured number of processed mails exceeds a predetermined threshold;
In the determination step, when the congestion determination unit determines that the number of mail processes exceeds one of a plurality of thresholds, the control unit responds to the reception unit with the one threshold value. A control step for outputting a control signal so as to perform a predetermined reception restriction to
Email sending and receiving method including. The control unit measures the number of mails stored in each storage area for storing the mail to be transmitted for each destination device, and retransmits the measured target mail according to the measured number of transmissions. The mail transmission / reception method according to claim 8, further comprising a retransmission step of outputting a control signal to the transmission means. When there are a plurality of transmission destination devices, the congestion determination means in the determination step makes a determination for each transmission destination device. As a result, the number of mail processes exceeds one threshold value in one transmission destination device. If you decide,
Transmission control in which the control means outputs a control signal to the transmission means so that the transmission means performs a predetermined transmission restriction on the one transmission destination device so that the transmission means corresponds to the one threshold value. The mail transmission / reception method according to claim 8 or 9, comprising a step.

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