JP4656536B2 - Relay server and relay communication system - Google Patents

Description

  The present invention mainly relates to a configuration of a relay server that enables communication between terminals.

Conventionally, a communication technique called a virtual private network (VPN) is known (see, for example, Patent Document 1). This VPN is used, for example, for applications in which terminals connected to LANs of a plurality of branch offices (bases) provided for each region communicate via the Internet. If the VPN is used, another remote LAN can be used as if it were a directly connected network.
JP 2002-217938 A

  In recent years, as a client terminal connected to a LAN, a terminal having a Simple Mail Transfer Protocol (SMTP) transmission / reception procedure has been used. For example, in the Internet facsimile machine, a direct SMTP system is known in which a procedure (SMTP) in which a transmitter transmits to a mail server without directly passing through a mail server is directly notified to the receiver for processing.

  However, although such direct SMTP communication procedures are easy to transmit and receive within the same LAN, it has been difficult to perform between different LANs as in Patent Document 1. A terminal that performs peer-to-peer communication using a dynamic DNS that links a domain name to an IP address is also known, but a special function needs to be implemented, and the configuration is complicated.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize peer-to-peer communication by direct SMTP between client terminals with a simple configuration.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

According to a first aspect of the present invention, a relay server having the following configuration is provided. That is, an account information registration unit and a relay group information registration unit are provided. The account information registration unit stores account information including account information of the client terminal. The relay group information registration unit stores relay group information including information on a group of relay servers that permit connection to each other. The relay server is configured to exchange the account information with another relay server belonging to the same relay group. When the relay server receives from the client terminal having the account information stored in the account information registration unit , a connection request, designation of a source according to the SMTP procedure, and a destination command for designating a destination according to the SMTP procedure detects the account information from the destination command, the stored second relay server is a relay server account information detected from the destination command to the account information registering unit that remembers the relay group information registration unit And specifying the source and destination to the specified second relay server and transmitting a connection request to the specified second relay server, and from the second relay server to the connection request When the OK response is received, a communication path is established with the second relay server. Mail data sent from the client terminal that has made the mail transmission request in the SMTP procedure to the relay server is relayed via a communication path established with the second relay server by the end of the SMTP procedure. while being relayed to the second relay server from the server, that are sent to the client terminal having an account information detected from the destination command.

  Accordingly, peer-to-peer communication by direct SMTP between client terminals stored in the account information registration unit of different relay servers can be realized with a simple configuration.

  In the relay server, it is preferable that the relay transfer of the mail data between the relay servers is performed using an encryption session.

  As a result, mail data exchanged between client terminals is relayed by secure communication, so that eavesdropping can be avoided and secret leakage can be prevented.

  In the relay server, when the relay server of the relay destination of mail data returns an error, it is preferable to return a response code to the client terminal according to the SMTP procedure.

  Thereby, the client terminal can easily perform an appropriate response such as retransmission of mail data based on the response code of the SMTP procedure.

According to the 2nd viewpoint of this invention, the relay communication system of the following structures is provided. That is, a plurality of relay servers are provided, and each of the relay servers includes an account information registration unit and a relay group information registration unit. The account information registration unit stores account information including account information of the client terminal. The relay group information registration unit stores relay group information including information on a group of relay servers that permit connection to each other. The relay server is configured to exchange the account information with other relay servers. When the relay server receives from the client terminal having the account information stored in the account information registration unit a connection request, designation of a source according to the SMTP procedure, and a destination command for designating a destination according to the SMTP procedure detects the account information from the destination command, the stored second relay server is a relay server account information detected from the destination command to the account information registering unit that remembers the relay group information registration unit And specifying the source and destination to the specified second relay server and transmitting a connection request to the specified second relay server, and from the second relay server to the connection request When the OK response is received, a communication path is established with the second relay server, and the second relay server is established. The server is caused to make a connection request, a source designation according to the SMTP procedure, and a destination designation according to the SMTP procedure to the client terminal having the account information detected from the destination command. Mail data sent from the client terminal that has made the mail transmission request in the SMTP procedure to the relay server is relayed via a communication path established with the second relay server by the end of the SMTP procedure. The message is relayed from the server to the second relay server, and transmitted by the second relay server to the client terminal having the account information detected from the destination command by the SMTP procedure. Thus, from the client terminal with the account information stored in the account information registration unit of a certain relay server, the data to the client terminal having the account information stored in the account information registering unit of the other relay servers mail format Configure to send.

  Accordingly, peer-to-peer communication by direct SMTP between client terminals stored in the account information registration unit of different relay servers can be realized with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the overall configuration of a relay communication system according to an embodiment of the present invention.

  As shown in FIG. 1, the relay communication system is composed of a plurality of LANs connected to a WAN. The relay communication system includes an external server S, a relay server R, a client terminal T, and the like.

  A WAN (Wide Area Network) is a network that connects different LANs to each other. In the present embodiment, the Internet is used as the WAN.

  A LAN (Local Area Network) is a relatively small network constructed in a limited place. There are a plurality of LANs, and they are constructed at locations physically separated from each other. In this embodiment, it is assumed that the LAN 1 is constructed in the Tokyo branch and the LANs 2, 3, and 4 are constructed in the Osaka branch, the Nagoya branch, and the Fukuoka branch, respectively. These four LANs 1, 2, 3, 4 are connected to the Internet, which is a global network.

  Next, the external server S will be described with reference to FIG. FIG. 2 is a functional block diagram of the external server S. The external server S is a device used for communication between relay servers R arranged in each LAN, and is installed on the Internet.

  The external server S shown in FIG. 2 has a function as a SIP (Session Initiation Protocol) server. Specifically, the external server S has a function as a SIP proxy server that relays SIP methods and responses, and a function as a SIP registrar server that registers an account of the relay server R.

  As shown in FIG. 2, the external server S includes a WAN interface 201, a control unit 202, and a relay server account information database 203 as main components.

  The WAN interface 201 is an interface that communicates with each device such as a relay server R connected to the Internet using a global IP address.

  The relay server account information database 203 is a database that manages the account of the relay server R that has requested registration in association with the global IP address.

  The control unit 202 is a processing unit that controls various communications performed via the WAN interface 201, and controls communication processing according to protocols such as TCP / IP, UDP, and SIP. The control unit 202 receives, for example, an account of the relay server R from each relay server R and registers it in the relay server account information database 203, various SIP methods and responses transmitted from the relay server R, and the like. The process of relaying the communication data to the other relay server R is performed. Details of each function of the external server S centering on the control unit 202 will be described later.

  Next, the client terminal T will be described with reference to FIG. FIG. 3 is a functional block diagram of the client terminal T.

  The client terminal T is a terminal that can be directly operated by the user. For example, the client terminal T corresponds to a personal computer (PC) used for daily work by the user. Accordingly, a large number of client terminals T usually exist in the LAN. In FIG. 1, only the client terminal 1A is representatively shown in the LAN 1, and similarly, the client terminals 2A, 3A, 4A in the LANs 2, 3, and 4 are shown. Only a representative is shown. The illustrated terminals 1A, 2A, 3A, and 4A are all configured as client terminals capable of SMTP transmission / reception procedures. Each client terminal T is given a private IP address that is uniquely managed in the same LAN.

  As shown in FIG. 3, the client terminal T includes a LAN interface 601 and a control unit 602 as main components.

  The LAN interface 601 is an interface that communicates with each device such as the relay server R connected to the same LAN using the private IP address.

  The control unit 602 is a processing unit that controls various communications performed via the LAN interface 601. The control unit 602 controls communication processing according to protocols such as TCP / IP, UDP, and SIP. The details of the function of each client terminal T centering on the control unit 602 will be described later.

  Next, the relay server R will be described with reference to FIG. FIG. 4 is a functional block diagram of each relay server R.

  As shown in FIG. 1, one relay server R is arranged in each LAN. Specifically, a relay server R1 is arranged in LAN1, a relay server R2 is arranged in LAN2, a relay server R3 is arranged in LAN3, and a relay server R4 is arranged in LAN4.

  The relay server R is connected to a LAN and can communicate with each client terminal T connected to the same LAN. The relay server R is also connected to the Internet, and can communicate with the relay server R connected to another LAN via the external server S. For this communication, each relay server R is assigned both a private IP address and a global IP address.

  As shown in FIG. 4, the relay server R includes a LAN interface 501, a WAN interface 502, a control unit 503, an account information database 504, and a relay group information database 505 as main components.

  The LAN interface 501 is an interface that uses a private IP address for communication with the client terminal T connected to the same LAN as its own device. For example, in the LAN 1, the relay server R1 can communicate with the client terminal 1A using the LAN interface 501.

  The WAN interface 502 is an interface that communicates with each device such as an external server S connected to the Internet using a global IP address.

  The account information database 504 in FIG. 4 is a database that manages the account of the client terminal T that has made a registration request in association with the private IP address. The account information database 504 is not limited to the client terminal T connected to the same LAN as the relay server R, but can also register an account of the client terminal T of another LAN.

  The relay group information database 505 is a database that manages the relay group information related to the client terminal T registered in the account information database 504.

  The control unit 503 is a processing unit that controls various communications performed via the LAN interface 501 and the WAN interface 502, and controls various communication processes according to protocols such as TCP / IP, UDP, and SIP.

  The control unit 503 executes, for example, processing for transmitting an account of the own device to the external server S to request registration, processing for creating relay group information and storing it in the relay group information database 505, and the like. Details of each function of the relay server R centering on the control unit 503 and the like will be described later.

  Next, relay group information, which is information handled in this relay communication system, will be described with reference to FIG. FIG. 5 is a diagram showing an example of the contents of relay group information.

  As shown in FIG. 5, the relay group information 100 stored in the relay group information database 505 includes one group identification information 101 and information on the relay servers R that constitute a relay group by allowing mutual connection ( Relay account information) 102.

  The group identification information 101 is information for identifying the relay group information 100, and is configured to be uniquely identified by being assigned a different ID each time the relay group information 100 is created. Thereby, the operator or the like can specify the relay group based on the group identification information 101, and can easily change the group configuration.

  The relay account information 102 includes account information of each relay server R that constitutes a relay group by allowing connection to each other. Further, the relay account information 102 is connected to the same LAN as each relay server R constituting the relay group, and the account and IP address of the client terminal (SMTP terminal) T registered in the relay server R are registered. Contains information.

  In the relay account information 102, a specific name given to the account of each relay server R is described together to facilitate user identification. For example, in the case of the relay account information 102a of the relay server R1 (relay-server1), the account (relay-server1 @ net) of the relay server R1 and the name (branch office A) assigned thereto are described.

  In the relay account information 102, the account name of the client terminal T connected to the same LAN as the relay server R is described together with a specific name given to the account, so that the user can be easily identified. It has become. For example, in the case of the client terminal (smtp1A), the name (smtp1A) given to the account (for example, smtp1A@relay-server1.net) is described. Further, the account of the client terminal T describes affiliation identification data 103 indicating the affiliation of the client terminal T such as a sales department or a development department.

  As described above, the relay group information 100 is created so as to be uniquely identifiable for each relay group. In addition, the relay group information 100 includes an account (relay account information 102) of each relay server that forms a group (relay group) by allowing mutual connection. Further, the relay account information 102 includes account information of the client terminal T registered and connected to the same LAN as the relay server.

  Therefore, by referring to the relay group information 100, it is possible to know which LAN and which LAN form a group, and which relay server R and client terminal T are registered in those LANs.

  The relay group information 100 shown in FIG. 5 is exchanged between the relay servers R constituting the relay group. Here, since the account information of the client terminal T is also included in the relay group information 100, the account information is also exchanged between the relay servers R.

  The flow of communication processing in the relay communication system configured as described above will be described with reference to the sequence diagram of FIG. Sequence numbers 1 to 3 shown in FIG. 6 indicate an account registration stage of each device.

  In sequence number 1, the relay server R1 transmits an account registration request (REGISTER) to the external server S. Here, the relay server R1 makes a registration request for its own account (sip: relay-server1 @ net). The external server S returns an OK response to the relay server R1, and registers the account of the relay server R1 and the global IP address of the relay server R1 in the relay server account information database 203 in association with each other. Thereafter, the relay server R1 registers the name (smtp1A) of the client terminal 1A and its IP address (192.168.0.1) in the account information database 504.

  Similarly, the relay servers R2 and R3 make a request for registration of their own account (REGISTER) to the external server S, and register their account and the like in the external server S (sequence numbers 2 and 3). Each relay server R2 and R3 registers the names and IP addresses of the client terminals 2A and 3A belonging to the same LAN as its own device in the account information database 504.

  With the above processing, the registration of the account with respect to the external server S of each relay server R and the registration of the account with respect to the relay server R of each client terminal T are completed. The sequence shown above is an example, and the order of the registration is arbitrary as long as the account registration of each device is completed as a result.

  Further, even the relay server R and the client terminal T existing on the network cannot participate in the relay communication system of this embodiment unless the account is registered. For example, the relay server R4 and the client terminal 4A in FIG. 1 cannot participate in the communication described below because the account is not registered in the process of FIG.

  Next, the generation and registration steps of the relay group will be described with reference to sequence numbers 10 to 18 in FIG. Note that the processing of sequence numbers 1 to 3 and 10 to 18 shown in FIG. 6 is generally performed as an initial setting of the network by a user or an operator.

  First, in the relay server R1, a method (createGroup method) for newly forming a relay group with the relay server R2 is executed by the operator. In this createGroup method, the group name (group1), the account of the relay server R2 that forms the relay group (relay-server2 @ net), and the identification ID (groupID0001) to be assigned to the newly created relay group are specified. The

  Then, a message transmission command (MESSAGE method) is executed in the relay server R1, and a group-info message for the partner relay server R2 is transmitted to the external server S (sequence number 10). This message includes the group name specified by the createGroup method, the identification ID of the relay group, and the like.

  In this MESSAGE method, an account (sip: relay-server2 @ net) of the relay server R2 that is the message transmission destination is specified. The external server S refers to the relay server account information database 203 to obtain the global IP address of the relay server R2, and relays the group-info message from the relay server R1 to the relay server R2. The relay server R2 that has received the message returns an OK response to the relay server R1 via the external server S.

  As described above, communication between the relay servers R of this embodiment is performed via the external server S, and this is the same in the following. Therefore, in the following description, a specific description of communication processing via the external server S is omitted.

  Next, the relay server R1 transmits a server information transmission request message (request-server-info message) to the relay server R2 (sequence number 11). The relay server R2 that has received this message, along with the OK response, sends information about the own device (server-info) and account information of the client terminal (smtp2A) connected to the same LAN as the own device to the relay server R1. Return to.

  On the contrary, the relay server R2 transmits a request-server-info message to the relay server R1 (sequence number 12), and the relay server R1 transmits information about the own device (server-info) to the same LAN as the own device. Information on the connected client terminal (smtp1A) is returned to the relay server R2.

  As described above, by exchanging information about each other's servers, relay group information 100 indicating that both relay servers R1 and R2 have formed a relay group is generated, and the relay group information database 505 of each relay server R1 and R2 is created. Remembered. The account information of the client terminal T connected to each of the LANs 1 and 2 is also stored in the relay group information database 505 in a form included in the relay group information 100.

  Next, in the relay server R2, a method (addGroup method) for newly adding the relay server R3 to the previously created relay group (relay group composed of the relay servers R1 and R2) is executed by the operator. In this addGroup method, the group name (group1) of the relay group to be joined, the account of the relay server R3 to join (relay-server3 @ net), and the identification ID (groupID0001) of the relay group to join are designated.

  Then, the relay server R2 transmits a group-info message to the relay server R3 that is a partner to join (sequence number 13). This message includes the group name specified by the addGroup method, the identification ID of the relay group, and the like. Receiving this, the relay server R3 returns an OK response to the relay server R2. Next, server information and the like are exchanged between the relay server R2 and the relay server R3 in exactly the same manner as described with the sequence numbers 11 and 12 (sequence numbers 14 and 15).

  Next, the relay server R2 transmits an update-group-info message notifying that the relay server R3 has joined the relay group to the relay server R1 (sequence number 16). Receiving this, the relay server R1 returns an OK response to the relay server R2. Thereafter, server information and the like are exchanged between the relay server R3 and the relay server R2 (sequence numbers 17 and 18).

  As described above, the relay group information 100 (specifically, the information shown in FIG. 5) indicating that the three relay servers R1, R2, and R3 form a relay group is included in each relay server R1, R2, and R3. It is stored in the relay group information database 505 of R3.

  Next, the operation when the client terminal T and the client terminal T actually exchange data will be described with reference to FIG. Here, an example will be described in which the client terminal 1A connected to the LAN 1 transmits a file to the client terminal 2A of another LAN 2 by the direct SMTP procedure.

  The user operates the client terminal 1A, specifies the destination client terminal 2A, and gives an instruction to transmit data. Then, the client terminal 1A transmits a connection request (tcp command) to the relay server R1 (sequence number 1 in FIG. 7). Receiving this, the relay server R1 returns a response indicating that preparation is complete to the client terminal 1A as if it were an SMTP server.

  The client terminal 1A that has received the response transmits a MAIL FROM command that designates its own device (smtp1A) as a transmission source to the relay server R1 according to the SMTP procedure (sequence number 2). The relay server R1 returns a response indicating the end of execution.

  Furthermore, the client terminal 1A transmits an RCPT TO command designating the client terminal 2A (smtp2A) as a transmission destination to the relay server R1 (sequence number 3). Then, the relay server R1 detects the account of the client terminal 2A from this destination command (RCPT TO), and specifies the relay server to which the client terminal 2A is connected based on the relay group information database 505. Here, it is understood from the relay group information 100 in FIG. 5 that the relay server to which the client terminal 2A is connected is R2.

  Next, the relay server R1 transmits a connection request (INVITE method) to the specified relay server R2 (sequence number 3.1 in FIG. 7). This INVITE method includes designation of the source client terminal 1A and the destination client terminal 2A. The relay server R2 that has received this connection request returns an OK response.

  Subsequently, the relay server R1 transmits a MediaSession command to the relay server R2, and establishes a communication path to both the relay servers R1 and R2 (sequence number 3.2). Note that this communication path is encrypted by, for example, IPsec (IP Security Protocol).

  When the communication path is established, the relay server R2 transmits a connection request (tcp command) to the client terminal 2A (sequence number 3.2.1). Upon receiving this, the client terminal 2A returns a response indicating that preparation has been completed to the relay server R2.

  The relay server R2 that has received the response transmits to the client terminal 2A a MAIL FROM command that specifies the source client terminal (smtp1A) specified by the sequence number 2 as the source (sequence number 3.2.2). The client terminal 2A returns a response indicating the end of execution.

  Further, the relay server R2 transmits an RCPT TO command designating the client terminal 2A (smtp2A) as a transmission destination to the client terminal 2A (sequence number 3.2.3). The client terminal 2A returns a response indicating the end of execution. The relay server R2 relays the received response to the relay server R1, and the relay server R1 further relays it to the client terminal 1A.

  Next, the client terminal 1A transmits a DATA command for transmitting the text to the relay server R1 (sequence number 4). This DATA command is relayed from the relay server R1 to the relay server R2, and further transmitted to the client terminal 2A (sequence numbers 4.1, 4.1.1). The client terminal 2A returns a response to the effect that it has accepted the start of text input to the relay server R2, and this response is sent to the client terminal 1A via the relay server R1.

  Subsequently, the client terminal 1A transmits the data of the mail text to the relay server R1 with a data-transfer command (sequence number 5). The contents of the mail text include contents obtained by MIME encoding the designated transmission target file. The data of the mail text is relayed from the relay server R1 to the relay server R2, and further transmitted to the client terminal 2A (sequence numbers 5.1, 5.1.1).

  When the transmission of the mail text data is completed, the client terminal 1A transmits an EOD command indicating the end of the text transmission to the relay server R1 (sequence number 6). This command is relayed from the relay server R1 to the relay server R2, and further transmitted to the client terminal 2A (sequence numbers 6.1 and 6.1.1). The client terminal 2A returns a response indicating that the input of the text has been accepted to the relay server R2, and this response is sent to the client terminal 1A via the relay server R1.

  Next, the client terminal 1A transmits a QUIT command indicating the end of connection to the relay server R1 (sequence number 7). This command is also relayed from the relay server R1 to the relay server R2 as in the case of the sequence number 6, and transmitted to the client terminal 2A (sequence numbers 7.1 and 7.1.1). The client terminal 2A returns a response to close the connection to the relay server R2, and this response is sent to the client terminal 1A via the relay server R1. Thereafter, the connection is actually closed.

  Next, the relay server R1 transmits a disconnection request (BYE method) to the relay server R2, thereby disconnecting the established communication path (sequence number 8). Thus, the communication is completed, and the file specified in the client terminal 1A is transmitted to the client terminal 2A in the mail format.

  As described above, when the relay server R connected to the LAN in this embodiment receives a mail transmission request in the SMTP procedure from the client terminal T stored in the account information database 504, the SMTP procedure The account information is detected from the destination command (RCPT TO command) of the client, connected to the relay server R to which the client terminal T of the destination is connected, and the mail data received by the SMTP procedure is relayed and transferred. ing.

  Thereby, peer-to-peer communication by direct SMTP between client terminals T existing in different LANs can be realized with a simple configuration.

  In this embodiment, the relay transfer of the mail data between the relay servers R is performed using an encryption session.

  Thereby, since the mail data exchanged between the client terminals T is relayed between the relay servers R by secure communication, eavesdropping can be avoided and secret leakage can be prevented.

  Next, with reference to FIG. 8 and FIG. 9, a communication process in the case of transmitting mail data to a plurality of client terminals T will be described. Here, a case where the client terminal 1A transmits a file to the client terminals 2A and 3A by the direct SMTP procedure will be described as an example.

  In sequence numbers 1 to 3.2.3 in FIG. 8, the client terminal 1A connects to the relay server R1, specifies its own device (client terminal 1A) as the transmission source, and first specifies the client terminal 2A as the transmission destination. Processing is shown. The above processing is exactly the same as sequence numbers 1 to 3.2.3 in FIG.

  Next, the client terminal 1A transmits an RCPT TO command designating the client terminal 3A (smtp3A) as a transmission destination to the relay server R1 (sequence number 4). The relay server R1 then identifies the relay server to which the client terminal 3A is connected based on the relay group information database 505. Here, it can be seen from the relay group information 100 in FIG. 5 that the relay server to which the client terminal 3A is connected is R3.

  Thereafter, the relay server R1 transmits a connection request to the relay server R3 and establishes a communication path (sequence numbers 4.1 and 4.2). After establishing the communication path, the relay server R3 connects to the client terminal 3A, and designates the transmission source and the transmission destination by the SMTP procedure (sequence number 4.2.1 to 4.2.3). The OK response returned by the client terminal 3A is transmitted to the client terminal 1A via the relay server R3 and the relay server R1.

  Thereafter, the client terminal 1A transmits a DATA command for starting text input to the relay server R1 (sequence number 5). The relay server R1 relays this command to the relay server R2 and transmits it to the client terminal 2A, and also relays this command to the relay server R3 and transmits it to the client terminal 3A (sequence numbers 5.1, 5.1.1, 5). .2, 5.2.1). When a response is returned from both client terminals 2A and 3A via the relay servers R2 and R3, the relay server R1 notifies the client terminal 1A of the response.

  The client terminal 1A immediately transmits the data of the mail text to the relay server R1 using the data-transfer command (sequence number 6 in FIG. 9). The data of the mail text is relayed from the relay server R1 to the relay server R2, and further transmitted to the client terminal 2A (sequence numbers 6.1 and 6.1.1). The data of the mail text is relayed from the relay server R1 to the relay server R3, and further transmitted to the client terminal 3A (sequence numbers 6.2 and 6.2.1).

  When the transmission of the mail text data is completed, the client terminal 1A transmits an EOD command indicating the end of the text transmission to the relay server R1 (sequence number 7). This command is relayed from the relay server R1 to the relay server R2, and further transmitted to the client terminal 2A (sequence numbers 7.1 and 7.1.1). Similarly, the command is relayed from the relay server R1 to the relay server R3 and further transmitted to the client terminal 3A (sequence numbers 7.2 and 7.2.1). The client terminals 2A and 3A return to the relay servers R2 and R3 a response indicating that the text input completion has been accepted. Each relay server R2, R3 relays the response to the relay server R1, and the relay server R1 sends the response to the client terminal 1A.

  Next, the client terminal 1A transmits a QUIT command indicating the end of connection to the relay server R1 (sequence number 8). As in the case of sequence number 7, this command is also relayed from relay server R1 to R2 and transmitted to client terminal 2A (sequence numbers 8.1, 8.1.1), and relay server R1 to relay server It is relayed to R3 and transmitted to the client terminal 3A (sequence numbers 8.2 and 8.2.1). The client terminals 2A and 3A return a response to close the connection to the relay servers R2 and R3. Each relay server R2, R3 relays the response to the relay server R1, and the relay server R1 sends the response to the client terminal 1A.

  Next, the relay server R1 transmits a disconnection request (BYE method) to each of the relay servers R2 and R3, whereby the established communication path is disconnected (sequence numbers 9, 10). Thus, the communication is completed, and the data of the client terminal 1A is transmitted to the client terminals 2A and 3A in the mail format.

  Next, an example of communication processing in the case where an error occurs when sending a mail in the same manner as described with reference to FIGS. 8 and 9 will be described with reference to FIG. FIG. 10 shows a case where the client terminal 1A attempts to send a file to the client terminals 2A and 3A by the direct SMTP procedure, as in FIGS. Note that the processing of sequence numbers 1 to 3.2.3 in FIG. 10 is exactly the same as the example in FIG.

  In sequence number 4 in FIG. 10, the client terminal 1A transmits an RCPT TO command specifying the client terminal 3A (smtp3A) as a transmission destination to the relay server R1. Then, the relay server R1 transmits a connection request to the relay server R3 to which the client terminal 3A is connected, and establishes a communication path (sequence numbers 4.1, 4.2).

  After establishing the communication path, the relay server R3 makes a connection request to the client terminal 3A (sequence number 4.2.1). However, it is assumed that a response from the client terminal 3A is not returned for some reason. In this case, the relay server R3 transmits an error message to the relay server R1, and the relay server R1 that has received the message indicates that an error has occurred during processing according to the SMTP procedure, and the requested processing has failed. Is returned to the client terminal 1A.

  The client terminal 1A notified of the process failure stops the file transmission process and transmits a QUIT command for terminating the connection (sequence number 5). This command is relayed from the relay server R1 to the relay server R2, and transmitted to the client terminal 2A (sequence numbers 5.1, 5.1.1). Since the SMTP connection cannot be established with the client terminal 3A, the QUIT command is not transmitted to the client terminal 3A. The client terminal 2A that has received the QUIT command returns a response to close the connection to the relay server R2, and this response is sent to the client terminal 1A via the relay server R1. Thereafter, the connection is actually closed.

  Next, the relay server R1 transmits a disconnection request (BYE method) to each of the relay servers R2 and R3, whereby the established communication path is disconnected (sequence numbers 6 and 7). The communication is thus completed. Thereafter, the user of the client terminal 1A takes appropriate measures depending on the situation, for example, transmitting mail data to the client terminal 2A where no error has occurred.

  As described above, the relay server R1 according to the present embodiment requests the client terminal 1A to send a request to the client terminal 1A when the relay server R3 that is the relay destination of mail data returns an error in the sequence number 4.2 in FIG. A response code indicating that the processed processing has failed is returned in accordance with the SMTP procedure.

  Thereby, the client terminal T can easily perform an appropriate response such as retransmission of mail data based on the response code of the SMTP procedure.

  Although the preferred embodiment of the present invention has been described above, the above configuration can be modified as follows, for example.

  The client terminal T can be changed to, for example, a mail server or a direct SMTP Internet facsimile instead of the personal computer.

  The relay server R constituting the relay group can be arbitrarily selected. Also, a plurality of relay groups can be created and stored in the relay group information database 505.

  When relaying between different LANs as in the above embodiment, the number of LANs is not limited to four as long as it is plural. Further, the WAN can be changed to use a similar network other than the Internet.

  The communication protocol between the external server S and each relay server R in the WAN and between the relay server R and the client terminal T in the LAN can be changed to use a protocol other than SIP.

  The external server S can be omitted, and the relay server R can be configured to communicate directly. In particular, when a protocol other than SIP is used between the relay servers R, communication between the relay servers R may be directly controlled based on the protocol, so that it is easy to omit the external server S. On the other hand, the number of external servers S is not limited to one, and a plurality of external servers S can be configured to function in a distributed manner.

  The WAN interface 502 of the relay server R can be omitted. In this case, the router may be connected to the Internet, and the relay server R may be installed under the router.

  In the above embodiment, the client terminal T connected to the same LAN as the relay server R is stored in the account information database 504 of the relay server R. However, the present invention is not limited to this, and the client terminal T connected to a different LAN from the own device can be stored in the account information database 504. More specifically, the relay server R and the client terminal T registered in the account information database 504 of the relay server R may have any relationship as long as they can communicate with each other via the network.

  A plurality of relay servers R may be connected to the same LAN. For example, three relay servers R are installed in the same LAN, several client terminals T in the LAN are stored in the account information database 504 of the first relay server R, and some other client terminals T can be stored in the account information database 504 of the second relay server R, and so on. In this case, the three relay servers R communicate via the LAN, and the relay is completed within one LAN.

The network block diagram of the relay communication system which concerns on one Embodiment of this invention. The functional block diagram of an external server. The functional block diagram of a client terminal. The functional block diagram of a relay server. The figure which shows the content of relay group information. The sequence diagram which shows the communication processing which registers a relay server and a client terminal, and creates a relay group with three relay servers. FIG. 6 is a sequence diagram showing communication processing for relaying and transferring mail data from a client terminal to another LAN client terminal. The sequence diagram which shows the first half part of the communication processing which relay-transfers mail data from a client terminal to several other LAN client terminals. The sequence diagram which shows the latter half part of the communication process which relay-transfers mail data from a client terminal to several other LAN client terminals. The sequence diagram which shows the example of a communication process when an error generate | occur | produces at the time of the relay transfer of mail data.

Explanation of symbols

S external server T client terminal R relay server 100 relay group information 504 account information database 505 relay group information database (relay group information registration unit)

Claims (4)

In the relay server,
An account information registration unit for storing account information including account information of the client terminal;
A relay group information registration unit for storing relay group information including information of a group of relay servers that permit mutual connection;
With
The account information can be exchanged with other relay servers belonging to the same relay group, and
From the client terminal with account information the stored in the account information registering unit, a connection request, specifying the source in accordance with the SMTP procedure, and receives a destination command to specify the destination according to SMTP procedure, from the destination command It detects the account information, account information detected from the destination command of the second relay server is a relay server account information registering unit that remembers the relay group information stored in the relay group information registration unit And specifying the transmission source and the transmission destination for the specified second relay server, and receiving an OK response to the connection request from the second relay server. Establish a communication path with the second relay server,
Mail data sent from the client terminal that has made the mail transmission request in the SMTP procedure to the relay server is relayed via a communication path established with the second relay server by the end of the SMTP procedure. relay server while being relayed to the second relay server from the server, characterized by being configured to so that is sent to the client terminal having an account information detected from the destination command. The relay server according to claim 1,
A relay server, wherein relay transfer of the mail data between relay servers is performed using an encryption session. The relay server according to claim 1 or 2,
A relay server which returns a response code to a client terminal according to an SMTP procedure when a relay server of a relay destination of mail data returns an error. With multiple relay servers,
Each said relay server
An account information registration unit for storing account information including account information of the client terminal;
A relay group information registration unit for storing relay group information including information on a group of relay servers that permit mutual connection;
With
The account information can be exchanged with other relay servers, and
From the client terminal with account information the stored in the account information registering unit, a connection request, specifying the source in accordance with the SMTP procedure, and receives a destination command to specify the destination according to SMTP procedure, from the destination command It detects the account information, account information detected from the destination command of the second relay server is a relay server account information registering unit that remembers the relay group information stored in the relay group information registration unit And specifying the transmission source and the transmission destination to the specified second relay server, and receiving an OK response to the connection request from the second relay server. A communication path is established with the second relay server, and the destination relay is connected to the second relay server. The client terminal having the account information detected from the command is requested to perform a connection request, a source designation according to the SMTP procedure, and a destination designation according to the SMTP procedure.
Mail data sent from the client terminal that has made the mail transmission request in the SMTP procedure to the relay server is relayed via a communication path established with the second relay server by the end of the SMTP procedure. Relayed from the server to the second relay server, and transmitted by the second relay server to the client terminal having the account information detected from the destination command by the SMTP procedure,
Thus, from the client terminal with the account information stored in the account information registration unit of a certain relay server, the data to the client terminal having the account information stored in the account information registering unit of the other relay servers mail format A relay communication system characterized in that transmission is possible.

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