JP4867756B2 - E-mail transfer system, relay station, and mobile communication network - Google Patents

Description

The present invention is an electronic mail forwarding system, medium Tsugikyoku, and relates to a mobile communication network, for example, ISP over the Internet (Internet Service Provider) and a mail server or corporate mail server, passenger information communication terminal in the train (hereinafter This can be applied to a mail transfer system for train passengers that exchanges e-mail (hereinafter simply referred to as mail) with a user terminal.

  Conventionally, the thing of patent document 1 is proposed as an e-mail transfer system for train passengers.

  The system described in Patent Document 1 is basically based on the fact that the communication between the ground and the train is performed using spot high-speed wireless transmission paths at station buildings and always using low-speed wireless transmission paths at other places.

Here, mail with attachments is transferred using a spot-like high-speed wireless transmission path (hereinafter referred to as spot high-speed wireless transmission path) such as millimeter waves installed in a station building, and text mail without attachments is sent Leaky coaxial cables (hereinafter referred to as LCX cables) installed in other places, low-speed wireless transmission paths (hereinafter referred to as constant low-speed wireless transmission paths) such as mobile phones and satellite communication systems. ) To transfer.
JP-A-2004-356967 (fourth embodiment)

  By the way, there are a wide variety of files attached to e-mails, such as document files represented by Microsoft Office (registered trademark), image files such as moving images and still images, and program execution files. Therefore, the size of the entire mail per message is not always large. Also, in the case of text mail, the received mail may be quoted within the body (in text) when replying, and the size of the mail per mail increases when the mail is exchanged several times.

  In the technology described in Patent Document 1, when the size of text mail per mail is large, the communication time per mail becomes long, and the low-speed wireless transmission path cannot always be used appropriately and effectively. In the case where the total amount of text mail is small, there is a problem that idle time is always generated in communication via the low-speed wireless transmission path, and the low-speed wireless transmission path cannot always be used appropriately and effectively. In such a case, if there are many mails with attached files waiting to be transferred using the spot high-speed wireless transmission path, the problem that the low-speed wireless transmission path cannot always be used appropriately and effectively becomes more conspicuous.

  Therefore, an e-mail transfer system, a relay station, and a mobile communication network that use two types of wireless transmission paths that can appropriately and effectively use a narrow-band wireless transmission path among the two types are desired. Yes.

The first aspect of the present invention comprises a fixed fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a moving body that can move along a predetermined route, In the e-mail transfer system in which the fixed communication network and the mobile communication network transfer e-mails wirelessly via any one of the relay stations, (1) each of the relay stations includes (1-1) first A first wireless communication means for executing wireless communication in accordance with a first wireless communication method capable of wireless communication with the mobile communication network in the communication range of (1-2) from the first communication range Second wireless communication means for executing wireless communication in accordance with a second wireless communication system capable of wireless communication in a wider band than the first wireless communication system and the mobile communication network within a narrow second communication range (1-3) The first wireless communication means A first transfer queue that stores an e-mail waiting to be transmitted to the network; and (1-4) an electronic device that is waiting for the second wireless communication means to transmit to the mobile communication network. Each of the second transfer waiting queue storing mail and (1-5) the electronic mail arriving at the relay station is distributed to the first transfer waiting queue or the second transfer waiting queue. Regardless of whether the email arrived at the relay station has an attached file or not, the size of the email, which is the total data amount of the email, is compared with the queue distribution threshold, and the size of the email is less than the queue distribution threshold. together with distributed to the first transfer queue, and the first mail distribution means for distributing e-mail queue distribution threshold size greater than the said second transfer waiting queue, (1- ) A first threshold value review that switches the queue distribution threshold value to a larger value on condition that the amount of storage in the first transfer queue is less than a predetermined amount due to the transmission of e-mail by the first wireless communication means. (1-7) When the first threshold value reviewing unit switches the queue distribution threshold value to a large value, a new one of the mails already queued in the second transfer queue is sent. An e-mail having a size smaller than a queue distribution threshold value is moved to the first transfer waiting queue .

The second aspect of the present invention comprises a fixed fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a moving body that can move along a predetermined route, In the electronic mail transfer system in which the fixed communication network and the mobile communication network wirelessly transfer an electronic mail via any one of the relay stations, (2) the mobile communication network is (2-1) A third wireless communication means for performing wireless communication according to a first wireless communication method capable of wireless communication with any one of the relay stations within one communication range; (2-2) the first In a second communication range narrower than the communication range, a wireless communication is performed with any one of the relay stations according to a second wireless communication method capable of wireless communication in a wider band than the first wireless communication method. 4 wireless communication means, and (2-3) the third wireless communication A third transfer waiting queue storing an e-mail waiting for transmission to any of the relay stations; and (2-4) the fourth wireless communication means is any of the relay stations. A fourth transfer waiting queue storing e-mails waiting to be transmitted to the e-mail, and (2-5) e-mails given from user terminals in the train, respectively, Regardless of whether the e-mail given from the user terminal in the train is attached with an attached file, the size of the e-mail, which is the total data amount of the e-mail, Compared with the queue distribution threshold, the electronic mail having a size smaller than the queue distribution threshold is distributed to the third transfer queue, and the electronic mail having a size larger than the queue distribution threshold is transferred to the fourth transfer queue. A second mail distribution unit for distributing the waiting queue, a (2-6) by the transmission of e-mail according to the third wireless communication means, the storage amount of the third transfer waiting queue is less than a predetermined amount (2-7) The second threshold value reviewing means switches the queue distribution threshold value to a large value when the queue distribution threshold value is switched to a large value. Of the mails already queued in the transfer queue, an e-mail having a size smaller than the new queue distribution threshold is moved to the third transfer queue .

A third aspect of the present invention includes a fixed fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a moving body that can move along a predetermined route, In each of the relay stations in the electronic mail transfer system in which the fixed communication network and the mobile communication network wirelessly transfer an electronic mail via any of the relay stations, (1-1) the first Within the communication range, the mobile communication network, first wireless communication means for performing wireless communication according to the first wireless communication method capable of wireless communication, and (1-2) narrower than the first communication range Within the second communication range, the mobile communication network, and second wireless communication means for executing wireless communication according to a second wireless communication method capable of wireless communication in a wider band than the first wireless communication method; (1-3) The first wireless communication means is A first transfer queue that stores e-mails waiting to be transmitted to the mobile communication network; and (1-4) awaiting transmission of the second wireless communication means to the mobile communication network. (1-5) sort each of the e-mails that have arrived at the relay station into the first transfer queue or the second transfer queue. Regardless of whether the email arrived at the relay station has an attached file or not, the size of the email, which is the total data amount of the email, is compared with the queue distribution threshold, and the size of the email is less than the queue distribution threshold. the e-mail with distributed to the first transfer queue, and the first mail distribution means for distributing e-mail over the queue sorting threshold size to the second transfer queue (1-6) First, the queue distribution threshold value is switched to a larger value on condition that the amount of storage in the first transfer queue is less than a predetermined amount due to the transmission of e-mail by the first wireless communication means. (1-7) When the queue distribution threshold is switched to a large value, (1-7) the first threshold review unit is configured to store the mail that is already queued in the second transfer waiting queue. Among them, an e-mail having a size smaller than the new queue distribution threshold is moved to the first transfer waiting queue .

A fourth aspect of the present invention includes a fixed fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a mobile body that can move along a predetermined route, (2-1) First communication range in the mobile communication network in the e-mail transfer system in which the fixed communication network and the mobile communication network transfer e-mails wirelessly via any of the relay stations. A third wireless communication means for executing wireless communication according to a first wireless communication method capable of wireless communication with any one of the relay stations, and (2-2) narrower than the first communication range. Fourth wireless communication that executes wireless communication according to a second wireless communication method capable of wireless communication in a wider band than the first wireless communication method with any one of the relay stations within the second communication range And (2-3) the third wireless communication hand A third transfer waiting queue storing e-mails waiting to be transmitted to any of the relay stations, and (2-4) the fourth wireless communication means to any of the relay stations A fourth transfer waiting queue storing e-mails waiting to be transmitted, and (2-5) e-mails given from user terminals in the train, respectively, Regardless of whether or not the email given from the user terminal in the train has an attached file, the size of the email, which is the total data amount of the email, Compared with the distribution threshold, the electronic mail having a size smaller than the queue distribution threshold is distributed to the third transfer waiting queue, and the electronic mail having a size larger than the queue distribution threshold is transferred to the fourth transfer queue. A second mail distribution unit for distributing the Chi queue, the (2-6) by the transmission of e-mail according to the third wireless communication means, the storage amount of the third transfer waiting queue is less than a predetermined amount (2-7) The second threshold value reviewing means switches the queue distribution threshold value to a large value when the queue distribution threshold value is switched to a large value. Of the mails already queued in the transfer queue, an e-mail having a size smaller than the new queue distribution threshold is moved to the third transfer queue .

  According to the present invention, an electronic mail transfer system, a relay station, and a mobile communication network that use two types of wireless transmission paths that can appropriately and effectively use a narrow-band wireless transmission path of the two types. Can be realized.

(A) Main Embodiment Hereinafter, an embodiment in which an electronic mail transfer system, a relay station, and a mobile communication network according to the present invention are applied to an electronic mail transfer system between the ground and a train will be described with reference to the drawings. To do.

(A-1) Configuration of Embodiment FIG. 1 is a block diagram illustrating an overall configuration of an e-mail transfer system according to an embodiment.

  The e-mail transfer system in this embodiment is intended to send and receive e-mail transfer services in a railway train that can move along a predetermined route. The e-mail transfer system is mainly used for stationary systems such as stations and mobile systems such as trains. Separately, it has an upper network 1 and a station network 2 (2-1 to 2-n) belonging to the fixed side, and an in-train network 3 (3-1 to 3-m) belonging to the moving side.

  In FIG. 1, a host network 1 is connected to a plurality of station networks 2 (2-1 to 2-n) as relay stations, and functions such as communication control within a station premises, routes and time control of a plurality of trains. Is responsible. Each station network 2 is provided at each station (including the first and last stations) through which the train providing the mail transfer service passes, and the train network 3 (3-1 to 3) is connected by millimeter wave communication or LCX communication described later. -M)). Each intra-train network 3 is constructed in each train moving on a predetermined route, and performs wireless communication with the station network 2 according to the train position at that time.

  A user terminal 4 used by a passenger of a train (hereinafter also referred to as a user or a user) is connected to the in-train network 3 of the train and uses the Internet 5 connected to the host network 1 via the station network 2. And is connected to an ISP server 51 (51-1 to 51-o) such as an ISP user mail server, and uses a mail transfer service.

  Each component of the host network 1 is installed in a ground station (data center), and the host network 1 performs data transmission / reception between the ISP and the user, user authentication, and train location information management. Management server 11, a plurality of station building side servers 12 (12-1 to 12-p) that hold data to be transmitted to the in-train network 3, and a home in mobile IP that manages packet paths for all the in-train networks 3 An agent (HA) 13 and a router (RT) 14 connected to the station network 2 are included. The upper network 1 is connected to the Internet 5 or the like via a gateway (GW 15).

  It is assumed that the host network 1 and the Internet 5 perform address conversion by NAT (IP masquerade). A certain station building side server 12 and a certain in-train network 3 may correspond one-to-one, or may not necessarily correspond one-to-one. The following description will be made assuming that the former.

  Each station network 2 is fixedly connected to the host network 1 and connected to an in-train network 3 of a train located in its own communication area (jurisdiction area). Each station network 2 includes a router (RT) 21 connected to the host network 1, foreign agents (FA) 22 and 24 in mobile IP, and a millimeter wave that is installed in the station premises and performs high-speed transmission communication using millimeter waves. A spot wireless communication device 23, an LCX cable 26 laid along the track, and an LCX wireless communication device (LCX modem) 25 that performs low-speed transmission communication using the LCX cable 26.

  The millimeter-wave spot wireless communication device 23 has a millimeter-wave communication antenna, and communicates with the in-train network 3 in a wide band using a millimeter-wave frequency band (30 GHz to 300 GHz) suitable for high-speed and large-capacity transmission. Is. The LCX cable 26 transmits a signal and simultaneously radiates a signal radio wave to a space along the cable, or captures a signal radio wave radiated by a network 3 in the train located in the space along the cable. The LCX wireless communication device 25 communicates with the in-train network 3 via the LCX cable 26.

  A communication area (hereinafter referred to as a millimeter wave communication area) covered by the millimeter wave spot wireless communication device 23 is a range in and around the station where the millimeter wave spot wireless communication device 23 is installed. On the other hand, a communication area (hereinafter referred to as an LCX communication area) covered by the LCX wireless communication device 25 is a range along the line where the LCX cable 26 is laid. Here, the LCX cable 26 is laid around a station related to the station network 2, and is laid to almost the midpoint between the station immediately before and immediately after the station. Although FIG. 1 shows that the physical number of LCX cables 26 related to one station network 2 is two, this number may be more or less than two and covers the above-described range. If it does, the number is not limited.

  Further, the network segment (subnet) of the station network 2 is different for each station, and the LCX communication area and the millimeter wave communication area are composed of different network segments (subnets), respectively, and constitute a foreign network.

  Each intra-train network 3 includes a millimeter wave communicating with the LCX wireless communication device 35 communicating with the LCX wireless communication device 25 of the station network 2 via the LCX cable 26 and the millimeter wave spot wireless communication device 23 of the station network 2. A mobile router (MR) that rewrites the address (CoA) each time the communication area (subnet) in which the spot wireless communication device 34 and the LCX wireless communication device 35 or the millimeter wave spot wireless communication device 34 are communicating is switched. 33, a wireless LAN 36 connected to the user terminal 4, and an in-train server 32 that communicates with the user terminal 4 through the wireless LAN 36 and transmits and receives mails and the like.

  In FIG. 1, the user terminal 4 is shown to be outside the components of the wireless LAN 36, but correctly speaking, the user terminal 4 is a component of the wireless LAN 36. The wireless LAN 36 (and the user terminal 4) only needs to be able to communicate at least within the train, and the method is not limited. For example, the wireless LAN 36 may be, for example, a LAN compliant with any of IEEE802.11a, IEEE802.11b, and IEEE802.11g, or may be a network using Bluetooth (registered trademark). Furthermore, it may be one using optical wireless fusion communication (ROF: Radio On Fiber) that optically transmits a radio signal.

  In the mobile IP applied to the e-mail transfer system according to the embodiment having the above-described configuration, two types of addresses, that is, home addresses, are provided to enable transparent access to a moving train. (Hereinafter referred to as HoA) and a care-of address (hereinafter referred to as CoA).

  The in-train server 32 has a HoA that is an invariant address belonging to a network segment that is a home network, and is given a CoA that is an address in the destination network segment as the train moves. Here, HA13, FA22, and 24 link the association between HoA and CoA, respectively. The change in CoA is used to grasp the position of the train. The network segment switching is used in connection switching (handover) between communication areas of the LCX communication area or the millimeter-wave communication area, or during inter-area handover when switching between the station networks 2.

  The arrangement of the mobile IP related devices as described above is organized as follows. In order to manage the home network of all the intra-train networks 3, a home agent (HA) 13 is arranged in the upper network 1. Foreign agents (FA) 22 and 24 are arranged in each station network 2 for millimeter wave radio communication and LCX radio communication, respectively. A mobile router (MR) 33 is arranged in each intra-train network 3. Thereby, the user terminal 4 accommodated in each intra-train network 3 is configured to be able to communicate with a communication partner via the Internet 5.

  The intra-train network 3 also includes a gateway (GW) 37 that transfers information related to electronic mail to the intra-train server 32.

  The GW 37 transfers only the packet from the user terminal 4 related to the electronic mail to the in-train server 32. Here, the packet type is determined based on the port number of the TCP packet passing through the GW 37. That is, when the port number is 110, it is an access to a POP3 (Post Office Protocol version 3) server, and when the port number is 25, it is an access to an SMTP (Simple Mail Transfer Protocol) server. When the TCP packet to be passed matches these port numbers, the GW 37 performs IPinIP encapsulation and transfers the packet to the in-train server 32. Packets relating to other communications are transferred to the upper network 1 via the station network 2 without passing through the in-train server 32.

  In such a system having the GW 37, for the POP3 connection from the user terminal 4, the management server 11 determines which ISP server 51 the e-mail transmission / reception request from the user terminal 4 is for, and An electronic mail is received on behalf of the ISP server 51. The proxy received e-mail is transferred from the management server 11 through the station building side server 12 to the in-train server 32 using the above-described mobile IP mechanism. Further, in response to a request from the user terminal 4, the in-train server 32 performs the role of the ISP server 51 and transfers mail.

(A-2) Operation of Embodiment Hereinafter, the operation of the e-mail transfer system according to the above embodiment is described as follows: (a-1) Location information registration, (a-2) Selection of a station building side server, (a-3) Communication Area switching detection, (a-4) Acquisition of POP3 request, (a-5) Mail reception from ISP server, (a-6) Mail transmission to ISP server, (a-7) Mail transfer to user terminal cannot be performed The process will be described in order, divided into mail processing.

(A-1) Location Information Registration FIG. 2 is a sequence diagram showing operations of location information registration and station building side server selection according to this embodiment, and FIG. 3 is an explanation showing a CoA registration table according to this embodiment. FIG.

  As described above, the LCX communication area and the millimeter wave communication area have different network segments (subnets). Therefore, the CoA in the mobile IP is registered in the HA 13 in order to grasp the network segment with which the user terminal 4 in the train can communicate and appropriately control the route.

  In FIG. 2, each of the FA 22 and FA 24 of the station network 2 periodically transmits an agent advertisement (S1). This agent advertisement is transmitted by including CoA information (for example, the subnet number of the FA) that is different for each subnet.

In the intra-train network 3, the MR 33 that has received the agent advertisement via the LCX radio communication device 35 or the millimeter wave spot radio communication device 34 registers the information on the CoA and the intra-train server 32 of the intra-train network 3. The CoA registration request including the HoA information and the received CoA information is transmitted to the HA 13 of the upper network 1 through the FA 22 or FA 24 that transmitted the agent advertisement (S2) .
The HA 13 associates the HoA of the in-train server 32 included in the received CoA registration request with the CoA of the subnet, registers it in the CoA registration table 100 shown in FIG. 3, and returns a response to the CoA registration request to the MR 33 ( S3).

  As described above, the CoA included in the FA 22 or FA 24 arranged in the station network 2 that is different for each network segment is arranged in the MR 33 of the in-train network 3 communicating in the network segment and the upper network 1. Registered with the existing HA 13.

  Such registered contents are updated every time the CoA received by the MR 33 changes due to the traveling of the train.

(A-2) Selection of station building side server When the HA 13 registers the HoA of the in-train server 32 in the CoA registration table 100 for the first time, the HA 13 has a station building side server 12 for the in-train server 32. An allocation request is transmitted (S4). The management server 11 manages the resource status (for example, HDD free capacity) of each of the station building servers 12-1 to 12-P, and manages the station building server 12-p (hereinafter, simply referred to as “12”) having many free resources. Select (S5). Next, the management server 11 gives an in-train server ID (for example, HoA of the in-train server 32) that is an identifier of the in-train server 32 assigned to the selected station building side server 12 to the selected station building side server 12. The in-train server 32 that notified (S6) and registered the station building server ID (for example, the IP address of the station building server 12) that is the identifier of the selected station building server 12 in the HA 13 and the CoA registration table 100. (S7).

  With such selection of the station building side server 12, in the subsequent communication, the management server 11 transfers the data to each in-train server 32 arranged in each of the plurality of trains to the selected station building side server 12. The station building side server 12 transmits the data transferred from the management server 11 to the notified in-train server 32 or receives the notified data from the in-train server 32. Conversely, the in-train server 32 transmits / receives data to / from the notified station building server 12 (12-p) among the plurality of station building servers 12-1 to 12-P.

(A-3) Communication Area Switching Detection FIG. 4 is a sequence diagram showing a switching operation between LCX communication and millimeter wave spot communication according to this embodiment, and FIG. 5 shows a subnet information list according to this embodiment. It is explanatory drawing shown.

  The station building side server 12 and the train server 32 store in advance a subnet information list 200 as shown in FIG. 5, which is a correspondence table of a wireless communication method (millimeter wave wireless communication or LCX wireless communication) for CoA.

  First, the operation when the train enters the millimeter wave communication area from the LCX communication area will be described.

  In FIG. 4, the FA 22 for millimeter wave communication periodically transmits an agent advertisement, and the MR 33 receives the agent advertisement transmitted from the FA 22 (S11). The MR 33 compares the received CoA information with the registered CoA information, and if they do not match, the MR 33 detects that the communication area has been switched and rewrites the registered CoA information with the received CoA information. The registration request for the CoA is made to the FA 22 and the HA 13 (S12, S13). Further, when the MR 33 detects switching of the communication area, the MR 33 notifies the in-train server 32 of the CoA (S14). For this detection, for example, the SNMP Trap function of SNMP (Simle Network Management Protocol) is used. Upon receiving the CoA notification from the MR 33, the in-train server 32 determines the switching of the CoA of the MR 33, and grasps a new wireless communication system from the subnet information list 200 shown in FIG. In this case, the in-train server 32 recognizes that the train belongs to the millimeter wave communication area.

  On the other hand, the HA 13 that has received the CoA registration request from the MR 33 rewrites the CoA column of the record in the CoA registration table 100 defined by the HoA in the CoA registration request with the CoA included in the received CoA registration request. Is transmitted to the MR 33 (S15), and the HoA and CoA related to the in-train server 32 of the train are notified to the station building side server 12 (S16). For example, by using the SNMP Trap function of SNMP described above, only the station building side server 12 assigned to the in-train server 32 of the train corresponds to this notification. Upon receiving the notification from the HA 13, the station building side server 12 grasps the wireless communication system of the new area from the subnet information list 200 shown in FIG. 5 based on the information on the HoA and CoA. In this case, the station building side server 12 grasps that the train has come to belong to the millimeter wave communication area.

  Next, the operation when the train goes out from the millimeter wave communication area to the LCX communication area will be described.

  When a session (millimeter wave communication) timeout occurs, the MR 33 of the intra-train network 3 sends a CoA transmission request to the FA 24 for LCX communication of the station network 2 (S21). The FA 24 that has received the CoA transmission request returns a CoA response (S22). The MR 33 detects that the communication area has been switched by the same operation as the above-described steps S12 to S14, requests the FA 24 and the HA 13 to register the CoA (S23, S24), and sends the CoA to the in-train server 32. Notification is made (S25). Upon receiving the CoA notification from the MR 33, the in-train server 32 determines the switching of the CoA of the MR 33, and based on the CoA, from the subnet information list 200 shown in FIG. To grasp that it belongs to the communication area.

  On the other hand, the HA 13 that has received the CoA registration request from the MR 33 transmits a response to the CoA registration request to the MR 33 by the same operation as the above-described procedures S15 and S16 (S26), and the station building side server 12 The HoA and CoA of the server 32 are notified (S27). The station-side server 12 that has received the notification from the HA 13 determines that the train belongs to a new communication area (in this case, the LCX communication area) from the subnet information list 200 shown in FIG. 5 based on the information on the HoA and CoA. Know what has become.

  In the above description, the case has been described in which the MR 33 makes a CoA transmission request due to the occurrence of a session (millimeter wave communication) timeout. However, the present invention is not limited to this, and based on the agent advertisement periodically received from the FA 24, the CoA A change may be detected and a CoA registration request may be made.

  In this way, the station building side server 12 and the in-train server 32 grasp that the train belongs to the millimeter wave communication area or the LCX communication area based on the subnet information list 200 held in advance, and the HA 13, The FA 22 and FA 24 can link the association between CoA and HoA that change as the train moves.

(A-4) Acquisition of POP3 Request FIG. 6 is a sequence diagram showing an operation of mail transfer according to this embodiment, and FIG. 7 is an explanatory diagram schematically showing a POP3 request packet structure according to this embodiment. is there.

  The user terminal 4 transmits a POP3 request packet 400 shown in FIG. 7A (S51). In this POP3 request packet 400, the IP address of one of the ISP servers 51 is described in a DA (Destination IP Address) 401, and the IP address of the user terminal 4 is stored in an SA (Source IP Address) 402. An IP address is described, and port number 403 describes 110, which is the port number of POP3.

  The GW 37 confirms the TCP packet header of the POP3 request packet 400 that passes through, and in the case of the packet with the port number 110, as shown in FIG. Transfer to the internal server 32 (S52). In the packet 500, the IP address of the in-train server 32 is described in the DA 501, the IP address of the GW 37 is described in the SA 502, and the POP3 request packet 400 is encapsulated in the data 503.

  The in-train server 32 is information related to user authentication (hereinafter referred to as user account information) by decapsulating the packet 500 transferred from the GW 37 and analyzing the POP3 request packet 400 from the user terminal 4. The IP address, POP3 ID, and POP3 password of the ISP server 51 are acquired (S53).

  Next, the in-train server 32 transmits information regarding a dialog for confirming whether or not to receive a mail with an attached file to the user terminal 4 (S54). A response indicating whether or not mail can be received is acquired (S55).

  Next, as shown in FIG. 7C, the in-train server 32 sets the IP address of the packet transmission source to the ISP server 51 in accordance with the presence / absence of mail to the user terminal 4. A reply packet 600 with the IP address is returned (S56). Here, in the reply packet 600, the IP address of the user terminal 4 is described in DA601, and the IP address of the ISP server 51 is described in SA602.

(A-5) Mail Reception from ISP Server FIG. 8 is an explanatory diagram showing a proxy reception table (user account information table) in this embodiment.

  The in-train server 32 that has received the above-described POP3 request packet 400 requests the management server 11 to perform proxy reception (S61). At this time, the information about the IP address of the ISP mail server, the POP3 ID and the POP3 password, and the information about whether or not the mail with the attached file can be received together with the information about the server ID in the train of the server 32 in the train is obtained. Send.

The management server 11 stores the information of the IP address of the ISP mail server, the POP3ID and the POP3 password, and the information on whether or not to receive the mail with the attached file transmitted from the in-train server 32 in the proxy reception table 700 shown in FIG. Based on the information of the in-train server ID, the POP3 ID is associated with the in-train server ID (S62). Thereafter, the management server 11 uses the IP address of the ISP mail server, the POP3 ID and the POP3 password, and information on whether or not to receive the mail with attached file recorded in the proxy reception table 700 to the desired ISP server 51. , Execute proxy mail reception by the POP3 protocol (S62, S63).

  Next, the management server 11 forwards the proxy received mail to the station building side server 12 to which the server ID in the train associated with the POP3ID of the proxy received mail is assigned (S65). The received mail is transferred to the in-train server 32 (S66). In the train server 32 to which the mail is transferred, the mail is managed using the POP3ID.

  By such an operation, the mail addressed to the user terminal 4 is accumulated in the in-train server 32, and the accumulated mail is transferred to the user terminal 4 at the time of a response by the next POP3 request (S67, S68).

  Details of the mail transfer operation from the management server 11 to the in-train server 32 (downward direction) will be described below. FIG. 9 is a sequence diagram showing the mail transfer operation in the downlink direction and the uplink direction.

  In FIG. 9, the management server 11 receives mail transmitted from the ISP server 51 to the intra-train network 3 via the Internet 5. The management server 11 confirms that the mail has an attached file and that the user terminal 4 associated with the mail destination has not refused to receive the mail with the attached file, and associates it with the user terminal 4 of the destination. The received mail is transferred to the station building side server 12 assigned as described above for the in-train server 32, and the station building side server 12 accumulates the data transferred from the management server 11 (S31).

  FIG. 10 is a flowchart showing the operation of the station building server 12 during accumulation, and FIG. 11 is an explanatory diagram showing the accumulation queue in the station building server 12 according to this embodiment.

  As shown in FIG. 11, the station building side server 12 has a spot high-speed transfer queue Q1 for queuing transfer data (queue) when the communication area is the millimeter wave communication area, and transfer data when the communication area is the LCX communication area. And a constant low-speed transfer queue Q2 for queuing (queue). Here, the high-speed transfer queue Q1 and the constant low-speed transfer queue Q2 are provided in common for all users.

  When the mail from the management server 11 to the in-train server 32 is given to the station building side server 12, the total data amount (mail size) of the mail is set to the queue distribution threshold value (mail size) regardless of whether the mail has an attached file or not. For example, it is determined whether or not 50 KBytes or 100 KBytes; 50 KBytes in the initial state) or more (S100). If the amount of data is equal to or greater than the queue distribution threshold, the station building side server 12 queues the received data to the spot high-speed transfer queue Q1 (S101), and when the amount of data is less than the threshold, the received data is always low-speed. Queuing to the transfer queue Q2 (S102).

  For example, the station-side server 12 starts a new queued mail transmission operation at a predetermined cycle or when the previous mail transfer in the downstream direction is completed. In this transmission operation, the station building side server 12 executes the transmission operation in accordance with the communication area of the train including the destination in-train server 32 detected at that time as described above. The station-side server 12 takes out the oldest stored mail queued in the spot high-speed transfer queue Q1 when the millimeter-wave communication area is valid, and always slows down when the LCX communication area is valid. The oldest stored mail queued in the transfer queue Q2 is extracted and transmitted (S32). At this time, the destination address of the mail is transmitted as HoA of the in-train server 32.

  FIG. 12 is a flowchart showing an operation when the station-side server 12 extracts mail from the accumulation queue and transmits it.

  The station building side server 12 first checks whether the millimeter wave communication area or the LCX communication area is valid at that time (S150).

  If the millimeter wave communication area is valid, the oldest stored mail queued in the spot high-speed transfer queue Q1 is extracted (S151) and transmitted (S152). If there is no mail queued in the spot high-speed transfer queue Q1, the processes in steps S151 and S152 are omitted.

  On the other hand, when the LCX communication area is valid, the oldest stored mail queued in the low-speed transfer queue Q2 is taken out (S153) and transmitted (S154).

  Thereafter, the station building side server 12 determines whether or not the low-speed transfer queue Q2 is always emptied by the current transmission (S155). When the constant low-speed transfer queue Q2 becomes empty, it is determined whether or not the current queue distribution threshold is a small threshold (for example, 50 KBytes) (S156). If the current queue distribution threshold value is a small threshold value, the queue distribution threshold value is updated to a large threshold value (for example, 100 KBytes) (S157), and mails queued in the spot high-speed transfer queue Q1 can be viewed with a new threshold value. For example, what is always inserted into the low-speed transfer queue Q2 is shifted to the constant low-speed transfer queue Q2 (S158).

  If mail remains in the constant low-speed transfer queue Q2 even after the current transmission, it is determined whether or not the current queue distribution threshold is a large threshold (S159), and if it is a large threshold, the constant low-speed transfer queue Q2 It is determined whether or not the used capacity exceeds the quasi-overflow threshold (S160). If the used capacity of the constant low-speed transfer queue Q2 exceeds the semi-overflow threshold, the queue distribution threshold is returned to a small threshold (S161). Even when the queue distribution threshold value is returned to a small threshold value, the mail storage queue that has already been queued may be reviewed.

  Returning to FIG. 9, when the station building side server 12 sets the mail destination address to HoA of the in-train server 32, the HA 13 acquires the mail addressed to the HoA of the in-train server 32 transmitted by the station building side server 12, and Based on the HoA and the information in the CoA registration table 100, the CoA for the HoA is acquired, the mail addressed to the HoA is encapsulated with the packet addressed to the CoA (IPinIP encapsulation), and the CoA is assigned. Transfer to FA22 or FA24 (S33).

  The FA 22 or FA 24 releases the IPinIP encapsulation of the mail received via the RT 14 and RT 21 in order and transfers it to the MR 33 (S34).

  The MR 33 transfers the data to the in-train server 32, and the data is accumulated in the in-train server 32 (S35). The user terminal 4 receives the mail stored in the in-train server 32 at the time of a response to the next POP3 request (S36).

  FIGS. 13A1 and 13A2 show mails queued in the spot high-speed transfer queue Q1 and the constant low-speed transfer queue Q2 at a certain point in time. The queue distribution threshold at this time is 50 Kbytes.

  Since the text mails M22 and M25 have a size of 50 Kbytes or more, they are stored in the spot high-speed transfer queue Q1 even if an attached file is not added. On the other hand, the mails M12 and M15 with attached files are always stored in the low-speed transfer queue Q2 even if attached files are added because the size is less than 50 KB.

In such a state, when the LCX communication area is valid, the mail queued in the low-speed transfer queue Q2 is always taken out from the old one and transmitted. When the low-speed transfer queue Q2 is always emptied by repeating such a transmission operation, the queue distribution threshold is changed to 100 Kbytes.

  As a result, as shown in FIGS. 13B1 and 13B2, the text mails M22 and M25 to which the attached file is not added and the mail M11 with attached file are less than 100 KB, so the spot high-speed transfer queue Q1 Are always stored in the low-speed transfer queue Q2. As a result, these mails M22, M25, and M11 are immediately transmitted using the low-speed wireless transmission line.

(A-6) Mail Transmission to ISP Server FIG. 14 is an explanatory diagram schematically showing a mail transmission packet structure according to this embodiment.

  The user terminal 4 starts mail transmission by the SMTP protocol as shown in FIG. 6 (S71). Here, in the mail transmission packet 800, as shown in FIG. 14A, the IP address of the ISP server 51 is described in the DA 801, the IP address of the user terminal 4 is described in the SA 802, and the port number 803 includes “25”, which is the boat number of the SMTP, is described.

  Next, the GW 37 checks the TCP packet header of the mail transmission 800 that passes through, and in the case of the packet with the port number “25”, as shown in FIG. 900 is transferred to the in-train server 32 (S72). In this packet 900, the IP address of the in-train server 32 is described in DA 901, the IP address of the GW 37 is described in SA 902, and the mail transmission packet 800 is encapsulated in data 903.

  As for the reply in the SMTP session, the in-train server 32 sends a reply packet 1000 shown in FIG. 14C in the SMTP session in which the IP address of the ISP server 51 is the IP address of the ISP server 51 to the user terminal 4. Reply (S73). Here, in the reply packet 1000, the IP address of the user terminal 4 is described in DA1001, and the IP address of the ISP server 51 is described in SA1002.

  The in-train server 32 decapsulates the packet 900 transferred from the GW 37, stores the mail, transfers the stored mail to the management server 11 (S74), and the management server 11 It transmits to the ISP server 51 (S75).

  Next, details of mail transfer from the in-train server 32 to the management server 11 will be described with reference to the sequence diagram of FIG.

  When the user terminal 4 transmits mail to the in-train server 32 as described above and the in-train server 32 accumulates the mail received from the user terminal 4 (S41), the above-described “communication area change detection” is performed. When the millimeter-wave communication area is valid according to the train communication area, the oldest stored mail queued in the spot high-speed transfer queue Q1 is retrieved, and the LCX communication area is valid First, the oldest stored mail queued in the low-speed transfer queue Q2 is taken out and transmitted (S42).

  In the case of this embodiment, the in-train server 32 also includes a spot high-speed transfer queue Q1 and a constant low-speed transfer queue Q2. When a mail to the management server 11 is given to the in-train server 32, the data amount is equal to a queue distribution threshold value (for example, 50 KBytes or 100 KBytes; in the initial state, 50 KBytes) regardless of whether the attached file has an attached file. It is determined whether or not this is the case. The in-train server 32 queues the received data to the spot high-speed transfer queue Q1 when the data amount is equal to or greater than the queue distribution threshold, and always sends the received data to the low-speed transfer queue Q2 when the data amount is less than the threshold. To queue. The mail queued (accumulated) in this way becomes the transmission target in step S42. In addition, after transmitting the mail taken out from the low-speed transfer queue Q2, the queue allocation threshold value review process (see FIG. 12) similar to that performed by the station building side server 12 is executed.

  The in-train server 32 transmits the destination address of the e-mail to the station building side server 12 to which the in-train server 32 is assigned based on the station building side server ID acquired in the “station building selection” described above.

  Next, MR33 transfers mail to FA22 or FA24 arrange | positioned at the network segment of the radio | wireless communication area which the said train can communicate (S43).

  The FA 22 or FA 24 encapsulates the packet addressed to the CoA (IPinIP encapsulation) by reverse tunneling in the mobile IP based on the registered information related to the HoA and CoA, and sends the mail to the HA 13 via the RT 21 and RT 14. Is transferred (S44).

  The HA 13 transfers the mail to the station building side server 12 (S45), and the station building side server 12 transfers the mail to the management server 11 (S46).

  The management server 11 of the upper network 1 transmits the mail transferred in this way to the ISP server 51 via the Internet 5.

(A-7) Mail processing when mail cannot be transferred to the user terminal Next, before the mail stored in the station building side server 12 and the train server 32 is transferred to the user terminal 4, the user terminal 4 stops operating. The mail processing when the mail client cannot be transferred to the user terminal 4 due to (ending the mail client) or the user getting off from the train will be described.

  After sending the POP3 request from the user terminal 4, a time lag occurs before the mail arrives at the user terminal 4. Therefore, before the user terminal 4 receives all the emails transferred to the in-train server 32, the user stops the operation of the user terminal 4 or gets off the train and cannot connect to the in-train network 3. In this case, mail that has not been received by the user terminal 4 (hereinafter referred to as “remaining mail”) remains in the in-train server 32 or the station building side server 12.

  The following cases c1 to c3 can be given as cases where such remaining mail occurs.

(C1) When it does not start again after the operation of the user terminal 4 ends (including the case of getting off the train)
(C2) When starting again after the operation of the user terminal 4 (c3) When switching to another train and connecting to the in-train network 3 built on another train and starting (c1) When the operation does not start again The remaining mail is continuously held until the train arrives at the terminal station that is the end point of the predetermined route. In this case, the following operations are performed when the train arrives at the terminal station.

  When the train arrives at the terminal station, an arrival point arrival signal for identifying the arrival at the terminal station is input to the in-train server 32. Here, the arrival point arrival signal is input to the in-train server 32 by a manual operation by a crew member of the train, a position signal by GPS (Global Positioning System), or an input signal detected by other sensors.

  The in-train server 32 to which the end point arrival signal is input notifies the station building side server 12 to which the in-train server 32 is assigned that the mail transfer is stopped, and a remaining mail list that is information on the remaining mail for each user terminal 4. Is sent to the management server 11 via the station building side server 12, and the mail and user account information accumulated in the in-train server 32 are deleted. Receiving the notice of mail transfer stop, the station building side server 12 deletes the accumulated mail and user account information.

  Next, the management server 11 compares the remaining mail list notified from the in-train server 32 with the list of mails addressed to the user terminal 4 belonging to the in-train server 32 held in the ISP server 51, and The ISP server 51 is notified to delete the mail held in the ISP server 51 without being listed in the mail list. That is, among the mails held in the ISP server 51, mail that has been transferred to the user terminal 4 is deleted when the terminal arrives at the terminal station, and mail that has not been transferred remains in the ISP server 51. After notifying the ISP server 51, the management server 11 deletes the user account information related to the user terminal 4 belonging to the in-train server 32.

  By such an operation, the remaining mail is stored in the ISP server 51, so that the mail can be acquired by a later operation.

(C2) When starting again after the operation of the user terminal 4 As described above, the remaining mail accumulated in the station building side server 12 and the in-train server 32 is the terminal station where the train is the terminal point of the predetermined route. Hold until you arrive. The user account information of each user terminal 4 is continuously recorded in the management server 11, the station building side server 12, and the in-train server 32. Therefore, in this case, after the operation of the user terminal 4 is started again, the remaining mail is transferred from the in-train server 32 to the user terminal 4 by the same operation as described above in response to a reception request from the user terminal 4. The In addition, when the user stops the operation of the user terminal 4 or gets off from the train after the operation is resumed, the arrival at the terminal station arrives in the same manner as in the case “when the user terminal 4 does not start again after the operation of the user terminal 4” described above. Sometimes left mail is deleted.

  By such an operation, even when the user terminal 4 is temporarily stopped, the remaining mail is continuously held in the in-train server 32, and the remaining mail is transferred by the POP3 request from the user terminal 4. Therefore, there is no need to receive mail from the ISP server 51 again.

(C3) When changing to another train and starting by connecting to the in-train network 3 constructed in another train In this case, the in-train server 32 of the train before changing (hereinafter referred to as train A) And the remaining mail accumulated in the station building side server 12 to which the train is assigned is held until the train A arrives at the terminal station, and the case “c. It is deleted by the action of "".

  On the other hand, in another train (hereinafter referred to as train B) that has been transferred from the train A, the user terminal 4 is connected to the in-train network 3 constructed in the train B, and as described above, from the user terminal 4 The in-train server 32 of the train B that has acquired the request for POP3 requests the management server 11 to receive the proxy for mail. Therefore, the management server 11 determines that the request is a proxy reception request from a different in-train server 32, receives all the mail addressed to the user terminal 4 from the ISP server 51 again, and forwards it to the in-train server 32 of the train B. To do. Since the user terminal 4 holds the mail received by the train A, the user terminal 4 receives only the unread mail among all the mails transferred to the in-train server 32 of the train B.

  By such an operation, even if the remaining mail is accumulated in the train A, it is possible to receive mail on the train B.

(A-3) Effect of Embodiment As described above, the station building-side server 12 arranged in the upper network 1 and assigned to each in-train network 3 and the in-train server 32 perform communication using mobile IP. As a result, the management server 11 can communicate without being aware of the position of the in-train server 32. In addition, the in-train server 32 can transmit an e-mail to the same station building side server 12 regardless of the position of the own train. Furthermore, even when straddling between stations, it is not necessary to transfer mail between the station building side servers 12, so the processing load is reduced.

  In addition, the mail transfer between the station building side server 12 and the in-train server 32 is based on the correspondence table between the CoA and the wireless communication method, and the amount of information is large in the case of the millimeter wave communication area according to the communication area of the train. In the case of data in the LCX communication area, by transmitting and receiving data with a small amount of information, efficient information communication can be performed without stagnation of information in LCX communication with a low communication speed. In other words, by selecting a transmission path that distributes mail according to the size of the entire mail per mail, rather than the presence or absence of an attached file, data transmission that matches the characteristics of the transmission path is possible, and depending on the usage status of the transmission path By dynamically changing the mail size threshold, it is possible to improve the usage rate of the transmission path.

  Further, the GW 37 arranged in the in-train network 3 captures data related to the mail, the management server 11 performs the transmission / reception of mail based on the captured data, and the in-train server 32 plays the role of the ISP server 51. By substituting, it is not necessary to pre-register information related to the user, it is not necessary to change the setting of information related to mail transmission / reception of the user terminal, and convenience can be improved.

  Furthermore, it is possible to select whether or not to forward the mail with the attached mail that the management server 11 receives on behalf of the information on whether or not the attached file can be received from the user terminal 4, and the traffic related to this e-mail transfer system is reduced. In addition, the processing load is reduced and network resources can be used effectively.

  In addition, the mail stored in the station building side server 12 and the train server 32 performs the mail processing operation when the mail transfer to the user terminal 4 cannot be performed. While deleting, the user terminal 4 can acquire a mail reliably and efficiently.

(E) Other Embodiments Although various modified embodiments have been mentioned in the description of the above embodiment, modified embodiments as exemplified below can be given.

  In the above-described embodiment, the management server 11 performs transmission / reception of mail on behalf of the ISP server 51. However, the management server 11 may execute only a mail relay function.

  In the above-described embodiment, the case where the always-low-speed wireless transmission path uses an LCX cable has been shown. .

  Further, in the above embodiment, the queue distribution threshold for determining whether to queue the mail waiting for transmission in the spot high-speed transfer queue Q1 or the constant low-speed transfer queue Q2 is one of two types of values. However, you may make it select from three or more types. For example, every time the low-speed transfer queue Q2 is emptied, it may be switched to a queue distribution threshold with a large one-stage size.

  Furthermore, in the above embodiment, the queue distribution threshold is switched on condition that the constant low-speed transfer queue Q2 is empty. However, the storage amount of the constant low-speed transfer queue Q2 is less than a predetermined amount. As a condition, the queue distribution threshold may be switched.

  It may be possible to variably set each type of queue distribution threshold value and a predetermined amount of a boundary for switching the queue distribution threshold value.

  In the above embodiment, immediately after switching the queue distribution threshold, the storage queue for mail that has already been queued is reviewed. However, the switched queue distribution threshold is set to distribute mail that has arrived after switching. You may make it apply only to.

  Moreover, in the said embodiment, although the case where a mobile body was a railroad train was demonstrated, this invention is not restricted to this, What is necessary is just a thing with which the fixed communication network and mobile body communicate, for example, bus Or an airplane etc. may be sufficient.

It is a figure which shows the structure of the electronic mail transfer system which concerns on embodiment. It is a sequence diagram which shows the operation | movement of the positional information registration which concerns on embodiment, and selection of the station building side server. It is explanatory drawing which shows the CoA registration table which concerns on embodiment. It is a sequence diagram which shows the switching operation | movement between LCX communication and millimeter wave spot communication which concerns on embodiment. It is explanatory drawing which shows the subnet information list which concerns on embodiment. It is a sequence diagram which shows the operation | movement of the mail transfer inside and outside the train which concerns on embodiment. It is explanatory drawing which showed typically the POP3 request | requirement packet structure which concerns on embodiment. It is explanatory drawing which shows the proxy reception table (user account information table) which concerns on embodiment. It is a sequence diagram which shows the operation | movement of the mail transfer of the downlink direction which concerns on embodiment, and an uplink direction. It is a flowchart which shows operation | movement of the management server at the time of making mail accumulate | store in the station building side server which concerns on embodiment. It is explanatory drawing which shows the accumulation | storage queue in the station building side server which concerns on embodiment. It is a flowchart which shows the operation | movement at the time of the station building side server in embodiment taking out mail from a storage queue, and transmitting. It is explanatory drawing which shows the example of a change of the accumulation | storage queue in embodiment. It is explanatory drawing which showed typically the mail transmission packet structure which concerns on embodiment.

It is.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Host network, 2 ... Station network, 3 ... In-train network, 4 ... User terminal, 5 ... Internet, 11 ... Management server, 12 ... Station building side server, 13 ... HA, 14 ... RT, 21 ... RT, 22 ... FA, 23 ... millimeter wave spot wireless communication device, 24 ... FA, 25 ... LCX wireless communication device, 26 ... LCX cable, ... 32 ... server in train, 33 ... MR, 34 ... millimeter wave spot wireless communication device, 35 ... LCX Wireless communication device, 36 ... wireless LAN, 37 ... GW, 51 ... ISP server.

Claims (4)

A fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a mobile body that can move along a predetermined route, the fixed communication network and the mobile In an e-mail transfer system in which an e-mail is transferred wirelessly via a communication network via one of the relay stations,
Each of the above relay stations
A first wireless communication means for performing wireless communication in accordance with a first wireless communication method capable of wireless communication with the mobile communication network within a first communication range;
In the second communication range narrower than the first communication range, execute wireless communication with the mobile communication network according to the second wireless communication method capable of wireless communication in a wider band than the first wireless communication method. Second wireless communication means for
A first transfer queue that stores an email waiting for the first wireless communication means to transmit to the mobile communication network;
A second transfer waiting queue storing an e-mail waiting for the second wireless communication means to transmit to the mobile communication network;
Each of the e-mails arriving at the relay station is distributed to the first transfer waiting queue or the second transfer waiting queue, and whether or not the e-mail arriving at the relay station has an attached file. First, the mail size, which is the total data amount of the e-mail, is compared with the queue distribution threshold, and the e-mail having a size smaller than the queue distribution threshold is distributed to the first transfer queue, and the size is equal to or larger than the queue distribution threshold. First mail distribution means for distributing the e-mail to the second transfer queue ,
First threshold value reviewing means for switching the queue distribution threshold value to a larger value on condition that the storage amount of the first transfer waiting queue becomes less than a predetermined amount due to the transmission of e-mail by the first wireless communication means. And
When the first threshold value reviewing means switches the queue distribution threshold value to a large value, among the mails already queued in the second transfer waiting queue, the electronic mail whose size is less than the new value of the queue distribution threshold value. An e-mail transfer system, wherein mail is moved to the first transfer waiting queue . A fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a mobile body that can move along a predetermined route, the fixed communication network and the mobile In an e-mail transfer system in which an e-mail is transferred wirelessly via a communication network via one of the relay stations,
The mobile communication network is
Third wireless communication means for executing wireless communication according to the first wireless communication method capable of wireless communication with any one of the relay stations within the first communication range;
Wireless communication in accordance with a second wireless communication method capable of wireless communication with any one of the relay stations in a wider band than the first wireless communication method within a second communication range narrower than the first communication range. A fourth wireless communication means for executing
A third transfer waiting queue storing e-mails waiting for the third wireless communication means to transmit to any of the relay stations;
A fourth transfer waiting queue storing an e-mail waiting for the fourth wireless communication means to transmit to any of the relay stations;
E-mails given from user terminals in the train are respectively distributed to the third transfer waiting queue or the fourth transfer waiting queue, and the e-mails given from the user terminals in the train are attached files. Regardless of whether it is attached or not, the size of the email, which is the total amount of data of the email, is compared with a queue distribution threshold, and an email having a size less than the queue distribution threshold is distributed to the third transfer queue, A second mail distribution means for distributing an electronic mail having a size equal to or greater than a queue distribution threshold to the fourth transfer waiting queue ;
Second threshold value reviewing means for switching the queue distribution threshold value to a larger value on condition that the amount of storage in the third transfer waiting queue is less than a predetermined amount due to transmission of e-mail by the third wireless communication means. And
When the second threshold value reviewing means switches the queue distribution threshold value to a large value, among the mails already queued in the fourth transfer waiting queue, the electronic mail whose size is less than the new value of the queue distribution threshold value. An e-mail transfer system, wherein mail is moved to the third transfer waiting queue . A fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a mobile body that can move along a predetermined route, the fixed communication network and the mobile In any one of the relay stations in an electronic mail transfer system in which a communication network and an electronic mail is wirelessly transferred via any of the relay stations,
A first wireless communication means for performing wireless communication in accordance with a first wireless communication method capable of wireless communication with the mobile communication network within a first communication range;
In the second communication range narrower than the first communication range, execute wireless communication with the mobile communication network according to the second wireless communication method capable of wireless communication in a wider band than the first wireless communication method. Second wireless communication means for
A first transfer queue that stores an email waiting for the first wireless communication means to transmit to the mobile communication network;
A second transfer waiting queue storing an e-mail waiting for the second wireless communication means to transmit to the mobile communication network;
Each of the e-mails arriving at the relay station is distributed to the first transfer waiting queue or the second transfer waiting queue, and whether or not the e-mail arriving at the relay station has an attached file. First, the mail size, which is the total data amount of the e-mail, is compared with the queue distribution threshold, and the e-mail having a size smaller than the queue distribution threshold is distributed to the first transfer queue, and the size is equal to or larger than the queue distribution threshold. First mail distribution means for distributing the e-mail to the second transfer queue ,
First threshold value reviewing means for switching the queue distribution threshold value to a larger value on condition that the storage amount of the first transfer waiting queue becomes less than a predetermined amount due to the transmission of e-mail by the first wireless communication means. And
When the first threshold value reviewing means switches the queue distribution threshold value to a large value, among the mails already queued in the second transfer waiting queue, the electronic mail whose size is less than the new value of the queue distribution threshold value. A relay station that moves mail to the first transfer waiting queue . A fixed communication network, a plurality of relay stations connected to the fixed communication network, and a mobile communication network constructed in a mobile body that can move along a predetermined route, the fixed communication network and the mobile In the mobile communication network in the e-mail transfer system in which the communication network transfers e-mail wirelessly via any of the relay stations,
Third wireless communication means for executing wireless communication according to the first wireless communication method capable of wireless communication with any one of the relay stations within the first communication range;
Wireless communication in accordance with a second wireless communication method capable of wireless communication with any one of the relay stations in a wider band than the first wireless communication method within a second communication range narrower than the first communication range. A fourth wireless communication means for executing
A third transfer waiting queue storing e-mails waiting for the third wireless communication means to transmit to any of the relay stations;
A fourth transfer waiting queue storing an e-mail waiting for the fourth wireless communication means to transmit to any of the relay stations;
E-mails given from user terminals in the train are respectively distributed to the third transfer waiting queue or the fourth transfer waiting queue, and the e-mails given from the user terminals in the train are attached files. Regardless of whether it is attached or not, the size of the email, which is the total amount of data of the email, is compared with a queue distribution threshold, and an email having a size less than the queue distribution threshold is distributed to the third transfer queue, A second mail distribution means for distributing an electronic mail having a size equal to or greater than a queue distribution threshold to the fourth transfer waiting queue ;
Second threshold value reviewing means for switching the queue distribution threshold value to a larger value on condition that the amount of storage in the third transfer waiting queue is less than a predetermined amount due to transmission of e-mail by the third wireless communication means. And
When the second threshold value reviewing means switches the queue distribution threshold value to a large value, among the mails already queued in the fourth transfer waiting queue, the electronic mail whose size is less than the new value of the queue distribution threshold value. A mobile communication network, wherein mail is moved to the third transfer waiting queue .

Images