JP3559349B2 - Connection method between LANs via public network - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a connection method between LANs via a public network.
2. Description of the Related Art In recent years, systems for sharing and distributing resources by connecting many processing devices to a LAN have been increasing. There is also adopted a system in which a LAN is extended to connect a plurality of LANs via a public area WAN (Wide Area Network) to establish a LAN / WAN / LAN connection.
[0002]
When the LAN is connected via the public network, when the calling LAN calls the other LAN via the public network, and when the line is busy, the calling side may send a message. In many cases, the calling operation is repeated, resulting in unnecessary operation, and its improvement is desired.
[0003]
[Prior art]
FIG. 10 is an explanatory diagram of a conventional example.
In FIG. 10, reference numeral 60 denotes a public network, 61 and 62 constitute a LAN1, 61 is an inter-LAN connecting device provided for connecting the LAN1 to the public network 60, and 62 is a personal computer, workstation, and printer of the LAN1. And the like, 63 and 64 constitute the LAN2, 63 is an inter-LAN connecting device provided for connecting the LAN2 to the public network 60, and 64 represents a terminal.
[0004]
The inter-LAN connecting device 61 includes a line device (or port) 61a connected to the public network 60, and the inter-LAN connecting device 62 includes two line devices (or ports) 63a and 63b connected to the public network 60. I have. When a request for communication with the terminal 64 of the LAN 2 is generated in response to a request from the terminal 62 of the LAN 1, the inter-LAN connecting device 61 calls the public network 60 from the line device 61 a and communicates with the partner requested by the terminal 62. In order to call, selection information for accessing LAN1 is transmitted. In this case, as the selection information, one of the line numbers of the line devices 63a and 63b connected to the LAN-to-LAN connecting device 63 of LAN2 is registered in advance, and in this example, the line number of the line device 63a is registered. . The public network 60 receiving this selection information performs an operation of capturing the line device 63a. If the line device 63a is free, the public network 60 receives the signal at the LAN connection device 63, and transmits the terminal 64 of the other party from the LAN connection device 63. By calling, the terminal 64 and the terminal 62 are connected. This connection is called LAN, WAN (public network 60), or LAN connection.
[0005]
When the line device 63a is connected to a line in which calls from a number of other inter-LAN connecting devices (not shown) or terminals connected to the public network 60 are concentrated, the probability of being used is high. In this case, a signal (connection rejection) indicating busy is sent from the public network 60 to the line device 61a on the calling side, and when the inter-LAN connecting device 61 or a terminal connected to the public network detects busy, a certain time later. A re-call is performed, and this operation is repeated.
[0006]
[Problems to be solved by the invention]
In the connection of LAN, WAN, and LAN described as the above-mentioned conventional example, when access (calling) to the line number of the line device 63a of the LAN connection 63 of LAN 2 is concentrated, calls from other LAN connection devices are transmitted. Connections are often refused. Conventionally, the following (1) or (2) exists as a method for dealing with this.
[0007]
{Circle around (1)} The inter-LAN connecting device 61 stops the call using the first line number and manually inputs another line device 63b of the partner inter-LAN connecting device 63 to make a call.
[0008]
{Circle around (2)} In the case of an automatic call, the call is repeated and the communication partner of the line device 63a of the inter-LAN connecting device 63 is disconnected and then connected.
The method (1) requires a lot of time and effort for connection, and the method (2) requires a long time for connection.
[0009]
Even if the public network is compatible with ISDN, the same problem as described above occurs when the channel of the destination line (two channels in the case of the 2B + D basic interface) is busy.
[0010]
The present invention relates to an ISDN public network capable of securing a connection with a calling LAN (or terminal) even if connection refusal occurs due to concentrated access to a specific line number in a LAN-to-LAN connection using a public network. It is an object of the present invention to provide an inter-LAN connection method.
[0011]
[Means for Solving the Problems]
FIG. 1 shows a first principle configuration of the present invention, and FIG. 2 shows a second principle configuration of the present invention.
In FIG. 1, reference numeral 1 denotes an inter-LAN connecting device having two line devices, 10 denotes a control unit, 11 to 15 constitute means of the control unit 10, 11 denotes an incoming call rejection notification detecting means, and 12 denotes an idle line identifying means. , 13 are call instructing means, 14 is table updating means, 15 is a channel table storing the channel state corresponding to the line, 16 is calling means, and 17-1 and 17-2 are line numbers a and b, respectively. A certain line device (or line set), 2 is a LAN connected to the LAN connection device 1, 3-1 and 3-2 are ISDN lines connected to the public network and each of the line devices 17-1 and 17-2, 4 Is a public network compatible with ISDN, 5 is a LAN-to-LAN connecting device connected to the public network 4 and connected to another LAN, and 6 is another LAN. Although two line devices are provided in the LAN connection device 1 in FIG. 1, any two or more line devices can be provided. In addition, the LAN connection device 5 may be a terminal connected to a public network.
[0012]
2 shows a configuration in which a plurality of inter-LAN connecting devices are provided in the same LAN. In FIG. 2, reference numeral 1a denotes an inter-LAN connecting device in which incoming rejection occurs, and 1b denotes the same LAN 2 as 1a. , Other control units of the LAN connection devices 1a and 1b, 11 to 14 correspond to the units having the same reference numerals in FIG. 1, and 15a and 15b correspond to the respective units. 9 is a channel table for storing the states of the line of the own LAN connection device and the line of another LAN connection device.
[0013]
Reference numeral 18 in the control unit 10a denotes a call requesting unit, 19 denotes an update notification unit, 110 denotes a call request detection unit, and 111 denotes a response notification unit. Line devices 17a and 17b are line devices, respectively, 2 is a LAN, 3a and 3b are lines connected to the line devices 17a and 17b, respectively, and 4 is a public network. Similarly, the LAN connection device 5 and the LAN 6 on the calling side are connected to the public network 4. Although only one line device 17b and one corresponding line 3b are shown in the LAN connection device 1b, a plurality of line devices 17b and a plurality of corresponding lines 3b may be provided. Further, the inter-LAN connecting device 5 on the calling side may be a terminal connected to the public network 4.
[0014]
The present invention relates to a method for connecting to a LAN on a receiving side even if connection rejection due to concentration of access (calling) to a specific line number occurs in connection to a LAN connecting apparatus via a public network of ISDN. The connection is established by calling the LAN (or terminal) of the other party to which the connection has failed by the device or the LAN connection device.
[0015]
[Action]
In the following description, it is assumed that the lines 3-1 and 3-2 and 3a and 3b in FIGS. 1 and 2 are lines of the basic interface (2B + D). In the case of FIG. 1, when the inter-LAN connecting device 5 of the LAN 6 makes a request to connect to the terminal of the LAN 2 according to a request from a terminal under the same, the inter-LAN connecting device 5 is registered to access the LAN 6 via the public network 4. Make a call using the line number. The public network 4 performs a process of arriving at the line device 17-1 corresponding to the other party's line number. However, since the two channels (B channels) of the line of the line number are being used by another call, the call is received. Can not. At this time, the public network 4 attaches the line number of the calling side (the line number of the line device of the LAN-to-LAN connecting device 5) to the line device 17-1 via the ISDN control channel (D channel) and rejects the incoming call. Notification information indicating (connection failure) is sent. This notification information is transmitted from the public network 4 as one of the ISDN supplementary services.
[0016]
When the incoming call rejection notification detecting means 11 of the control unit 10 of the LAN-to-LAN connecting device 1 detects this notification information, the idle line identifying means 12 is driven. The vacant line identification means 12 has a vacant channel with reference to the channel table 15 in which the use state of each of the plurality of lines 3-1 and 3-2 provided in the LAN connection apparatus 1 is stored. Identify the line. In this case, among the lines 3-1 and 3-2, the line 3-1 has two B channels in a busy state, and the line 3-2 has an empty channel.
[0017]
When the vacant line identification unit 12 identifies that the line device 3-2 is vacant, the calling instruction unit 13 instructs the calling unit 16 to make a call using the line device 17-2 of the identified line 3-2. In response, the calling means 16 executes a call with the line number c of the calling side as the destination via the line device 17-2, is connected to the LAN connection device 5 via the public network 4, and further makes a call. Connected to the called terminal. The table updating means 14 updates the channel state of the corresponding line in the channel table 15 when the calling instruction means 13 confirms that the call is executed and the connection is successful.
[0018]
In the case of FIG. 2, when an incoming call is made from the inter-LAN connecting device 5 (not shown) of another LAN to the inter-LAN connecting device 1a as in FIG. 1, the incoming call is rejected because two channels of the line 3a are in use. When notification information indicating incoming call rejection (connection failure) is sent from the public network 4, the incoming call rejection notification detecting means 11 is activated, and the free line identifying means 12 identifies a free line. In this configuration, the channel state of the line 3a (own line) of the own LAN connection device 1a and the line 3b (other line) of another LAN connection device 1b connected to the same LAN 2 are stored in the channel table 15a of the control unit 10a. The usage status of is stored. As a result of the identification, when it is identified that there is an empty channel in the line (other line) of the other inter-LAN connecting device 1b, the calling requesting means 18 sends the calling line to the other inter-LAN connecting device 1b via the LAN 2. A call request including the number c is made.
[0019]
In the inter-LAN connecting apparatus 1b, when this is received by the call request detecting means 110, the vacant line identifying means 12 refers to the channel table 15b to identify the channel state of the line 3b of the own apparatus, and reports the result to the response notifying means. 111 notifies the LAN connection device 1a. When it is determined that there is a free line, the call instructing means 13 instructs to make a call by the line device 17b of the free line 3b, and the calling means 16 makes a call to the line number c of the calling side. A call is made and a connection is made to the partner LAN connection device. When a call is executed by the call instructing means 13, the table updating means 14 updates the channel state of the corresponding line 3 b in the channel table 15. Next, the update notifying means 19 is activated, and notifies the inter-LAN connecting device 1a connected to the same LAN 2 of the update content of the own line 3b.
[0020]
In the description of FIG. 2, the channel tables 15a and 15b are updated by notifying the other inter-LAN connecting device each time the updating is performed by the own inter-LAN connecting device as described above. It issues a request to read the contents of the channel table of another LAN connection device, and receives and updates the read contents, or sends its own channel table to another LAN connection device at regular time intervals. The other party can update it.
[0021]
【Example】
FIG. 3 shows a configuration example of the LAN connection device.
In the figure, reference numeral 20 denotes a LAN connection device, 21 denotes a control unit including a CPU, a RAM, and a ROM, 22 denotes a memory having a channel table 22a, 23 denotes a LAN interface connected to the LAN, and 24 and 25 denote line sets (FIG. 1). , The line set interfaces (LSIFs) 26, 27 connected to the line devices 17-1, 17-2, 17a, 17b in FIG. 2 are respectively ISDN public networks (4 in FIGS. 1, 2). Is a line set connected to the lines 3-1 and 3-2.
[0022]
The configuration in FIG. 3 corresponds to the inter-LAN connecting device 1 in FIG. 1 and is provided with two lines and a line set (line device). However, the configuration is changed to include only one line and a line set. Corresponds to the LAN connection device 1a in FIG.
[0023]
FIG. 4 illustrates an example of a network connection configuration according to the first embodiment. In the first embodiment, an inter-LAN connecting device shown in FIG. 3 corresponding to the first principle configuration shown in FIG. 1 is used. In FIG. 4, a plurality of inter-LAN connecting devices A to C are connected to a public network (4 in FIG. 1) by lines to which line numbers (a) to (c) are assigned, respectively. Connected to LAN. The inter-LAN connecting device D has the configuration shown in FIG. 4 described above. One is connected to the LAN, the other is connected to two line sets d1 and d2, and each line set has a line number (d1) and a line number (d2), respectively. Is connected to the line of the public network 4 having. The internal configuration of the LAN-to-LAN connecting device D shows only a control unit and a line set, and other configurations are the same as those in FIG. 4 and are not shown.
[0024]
FIG. 5 shows the configuration of the channel table of the LAN connection apparatus according to the first embodiment. This channel table is shown as 22a provided in the memory (22 in FIG. 3) of the LAN connection device D in FIG. 4, and for each line set d1, d2, a line number, an IP (Internet Protocol) address, respectively. Is stored, and the current state of two channels included in each line set, that is, channel 1 and channel 2 are stored. In this example, the line 3-1 of the line set d1 has the channel 1 and the channel 2 occupied (in use), and the line 3-2 of the line set d2 has both the channels idle.
[0025]
FIG. 6 shows an operation sequence according to the first embodiment, and shows an operation in the connection configuration shown in FIG. FIG. The figure shows a state in which the line set d1 of the inter-LAN connecting device D is communicating with the inter-LAN connecting device A and the inter-LAN connecting device B using channel 1 and channel 2, respectively. At this time, the contents of the channel table of the inter-LAN connecting device D are as shown in FIG.
[0026]
In this state, when the inter-LAN connecting device C (line number c) makes a call to the public network 4 to connect to the inter-LAN connecting device D in which the line number (d1) is registered as a destination, B. FIG. As shown in (2), the connection fails because the two channels of the line 3-1 are occupied (in use). At this time, the ISDN public network notifies the D channel (control channel) that the incoming call has been rejected. This notification includes the line number c of the calling party.
[0027]
Next, C. of FIG. As shown in FIG. 5, upon receiving the notification of the rejection of the incoming call, the inter-LAN connecting device D detects that the incoming call from the line number c has failed, and refers to the channel table of FIG. Instruct d2 to place a call using channel 1. As a result, the line set d2 is connected to the inter-LAN connecting device C via the line 3-2 and the public network 4, and a terminal connected to the LAN of the inter-LAN connecting device C and a LAN terminal of the inter-LAN connecting device D are connected. Communication between LANs becomes possible. Thereafter, an update is performed to set the channel used for communication among the two channels of the line set d2 in the channel table shown in FIG. 5 to the exclusive state.
[0028]
When there are a plurality of line sets connected to the public network in addition to the line set d2, when referring to the channel table in the LAN connection apparatus D, the order of the line sets to be referred to is set in advance by designation. . If there is no available channel when the channel table is referred to in the inter-LAN connecting device D, the system waits for a channel to become available for a certain period of time, and when it becomes available, issues a call instruction to the line set. . If there is no free space, the process ends after a certain waiting time.
[0029]
FIG. 7 illustrates an example of a network connection configuration according to the second embodiment. In the second embodiment, an inter-LAN connecting device corresponding to the second principle configuration shown in FIG. 2 is provided as a receiving-side inter-LAN connecting device, and one line set in the inter-LAN connecting device shown in FIG. This corresponds to a configuration having only one.
[0030]
In the connection configuration shown in FIG. 7, a plurality of inter-LAN connecting devices A to C are connected to the public network (4 in FIG. 1) by lines to which line numbers (a) to (c) are assigned. With the respective LANs, the inter-LAN connecting devices D and E are connected to the same LAN, and the inter-LAN connecting device D has one line set of the line number (d) and is connected to the public network 4 by the line 3a. The inter-LAN connecting device E includes at least one line set e with the line number (e), and is connected to the public network 4 via the line 3b. The internal configuration of the LAN connection devices D and E includes only the control unit and the line set, and other configurations are not shown.
[0031]
FIG. 8 shows a channel table of the second embodiment and a frame format between LAN-connected devices via LAN.
FIG. And B. 7 shows the configuration of the channel tables of the LAN connection device D and the LAN connection device E in FIG. The line number and the IP address of the line set d of the LAN-to-LAN connecting device D, which is its own device, are stored as the reference order 1, the statuses of the channels 1 and 2 are stored, and then the reference order 2 Similar information is stored for the line set e of the inter-connection device E. B. Sets the line set e of the LAN-to-LAN connecting device E, which is its own device, to the reference rank 1 and sets the line set of the LAN-to-LAN connecting device D to the reference rank 2. The same contents as are set. Note that the IP address includes an address (d) 'in the LAN and an address (d) via the WAN, and both have partially different addresses.
[0032]
FIG. And B. The channel table shown in FIG. 7 is obtained by the control units of the LAN-to-LAN connecting device D and LAN-to-LAN connecting device E notifying each other of the vacant state of the line set of each other periodically via the LAN in the configuration of FIG. Always updated to the correct content. The transmission interval is specified by the setting.
[0033]
C. of FIG. Indicates a frame format of information to be notified between LAN connections via the LAN, and a notification of an empty state of the channel of the line set is also performed in this format. The notification of the channel state is based on the identifier of the identifier provided at the end of the format. Represented by a numerical value, "1" is set. C. In the format, DA and SA respectively indicate the MAC (Media Access Control) address of the notification partner and the transmission source, TYPE indicates the protocol identifier (in this case, 08800 indicating the IP protocol is set), and then the IP header, UDP ( Following an “User Datagram Protocol” header, an identifier indicating the type (function) of information transmitted by the frame is set last.
[0034]
FIG. 9 shows an operation sequence according to the second embodiment, and shows an operation in the connection configuration shown in FIG. First, FIG. The figure shows a state in which the line set d of the inter-LAN connecting device D is communicating with the inter-LAN connecting device A and the inter-LAN connecting device B using channel 1 and channel 2, respectively. On the other hand, the line set e of the inter-LAN connecting device E has two channels both in an idle state, and the contents of the respective channel tables are the same as those shown in FIG. And B. It is like.
[0035]
In this state, when the inter-LAN connecting device C (line number c) makes a call to the public network 4 to connect to the inter-LAN connecting device D in which the line number (d) is registered as the destination, B. FIG. As shown in (2), the connection fails because the two channels of the line 3a are in the exclusive state (in use). At this time, the inter-LAN connecting device D is notified that the incoming from the line number c has failed (the incoming call has been rejected) via the D channel (control channel) from the ISDN public network.
[0036]
Next, C. of FIG. As shown in FIG. 8, upon receiving the notification of the rejection of the incoming call, the LAN-to-LAN connecting apparatus D detects that the incoming call from the line number c has failed. First, it is determined whether there is a vacancy in the line set of its own device according to the reference order, and if there is no line set as in this example, the next reference order is identified, and the other LAN connecting device E is identified. It is identified that the line set e has a free space. As a result, a frame for requesting another inter-LAN connecting apparatus E via the LAN to make a call to the line number c is transmitted. This frame corresponds to C.I. in FIG. And its identifier is “2”. This identifier indicates that the frame is a call request frame, and information on the line number of the call partner (line of the LAN connection device C) is also transmitted.
[0037]
Upon receiving this frame, the inter-LAN connecting device E refers to its own channel table (B in FIG. 8), confirms the vacancy status of the channel of the specified line set e, and according to the vacancy status, Perform processing.
[0038]
(1) If there is a vacancy in the channel, in order to notify that the call request has been accepted, the transmission source (inter-LAN connecting apparatus D) of the above-mentioned call request frame is sent to C. of FIG. And updates the channel table of its own device (inter-LAN connecting device E). In this case, the channel 1 of the line set e is changed from “empty” to “hold”. The identifier of the transmitted frame is "3".
[0039]
(2) If the channel is occupied, if there is another line set in the own device, check if there is a free line in that channel, and if there is a free line, indicate that a call can be made from that other line set. The frame to be notified is transmitted to the transmission source (the LAN connection device D). The identifier of the frame at this time is “4”. Next, the channel table of the own device is updated. In this case, the corresponding channel is changed from “empty” to “hold”.
[0040]
(3) If there is no vacancy in the channel of the own device (the LAN connection device D), it is notified that a call cannot be made. In this case, the frame identifier is “5”.
[0041]
According to the above (1), (2), and (3), the control unit of the source LAN connection apparatus D that has received the frames with the identifiers “3”, “4”, and “5” respectively has the following configuration. Perform processing.
[0042]
a. When the frame with the identifier "3" is received, a frame requesting a call to the LAN-to-LAN connecting device C is sent to the transmission source of the frame (the LAN-to-LAN connecting device E), and the corresponding portion of the channel table is transmitted. From "empty" to "hold". The identifier of the frame at this time is “6”.
[0043]
b. When the frame with the identifier “4” is received, a frame requesting a call to the LAN-to-LAN connecting device C is sent to the source of the frame, and the corresponding part of the channel table is changed from “empty” to “reserved”. ". The identifier of the frame transmitted at this time is “7”.
[0044]
c. When the frame with the identifier "5" is received, the channel table is referred to, and the apparatus and the line set having the highest reference order except for the inter-LAN connection apparatus D and the line set previously requested are referred to. A frame for requesting a call to C is transmitted, and one of the above-mentioned processes (1) to (3) is performed in the partner LAN connection device.
[0045]
When receiving the frames with the identifiers "6" and "7", the LAN connection apparatus E makes a call to the LAN connection apparatus C having the line number c. If the call is successful, the calling LAN connection device E sends a frame with an identifier of "8" to the LAN connection device D to notify the success of the call, and checks the channel table of the own device. Update from "pending" to "proprietary".
[0046]
Upon receiving the frame with the above identifier “8” from the inter-LAN connecting device D, the inter-LAN connecting device D updates the corresponding portion of the channel table of the own device from “pending” to “exclusive”.
[0047]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the present invention, when a call from another terminal or an inter-LAN connecting device via the public network is concentrated on a specific inter-LAN connecting device connected to the ISDN public network, the connection may fail. Can be reduced.
[0048]
Further, when another LAN connecting device for connecting to the public network is provided on the same LAN as a specific LAN connecting device on which calls are concentrated, the connection is effectively used by using the other LAN connecting device. It is possible to connect to the failed calling terminal or LAN connection device.
[Brief description of the drawings]
FIG. 1 is a first principle configuration diagram of the present invention.
FIG. 2 is a configuration diagram of a second principle of the present invention.
FIG. 3 is a diagram illustrating a configuration example of an inter-LAN connection device;
FIG. 4 is a diagram illustrating an example of a network connection configuration according to the first embodiment;
FIG. 5 is a diagram illustrating a configuration example of a channel table of the LAN connection apparatus according to the first embodiment;
FIG. 6 is a diagram illustrating an operation sequence according to the first embodiment.
FIG. 7 is a diagram illustrating an example of a network connection configuration according to a second embodiment;
FIG. 8 is a diagram illustrating a channel table and a frame format between LAN connection apparatuses via a LAN according to the second embodiment.
FIG. 9 is a diagram showing an operation sequence according to the second embodiment.
FIG. 10 is an explanatory diagram of a conventional example.
[Explanation of symbols]
Reference Signs List 1 inter-LAN connecting device 10 control unit 11 incoming call rejection notification detecting means 12 available line identifying means 13 calling instruction means 14 table updating means 15 channel table 16 calling means 17-1 line device 17-2 line device 2 LAN
3-1 Line 3-2 Line 4 Public network 5 compatible with ISDN 5 LAN connection device 6 Other LAN

Claims (3)

In a LAN connection system via a public network in which a plurality of LANs are respectively connected to an ISDN public network by a LAN connection device,
When an incoming call is rejected due to the use of a line when a specified line number of the inter-LAN connecting device having a plurality of lines arrives on the line, a notification of the incoming call rejection including the calling-side line number is sent from the public network. Sent to the called line,
The inter-LAN connecting device on the receiving side identifies a line table having a vacant channel by identifying a channel table storing a use state of the plurality of lines in a control unit and identifying the channel table upon detecting the notification of the rejection of the incoming call. Free line identification means, call instruction means for instructing a call from the line identified by the empty line identification means, and table updating means for updating the channel table when connection by the call instruction is successful. A connection method between LANs via a public network characterized by the following. In a LAN connection system via a public network in which a plurality of LANs are respectively connected to an ISDN public network by a LAN connection device,
When an incoming call is rejected due to the use of a line when the line number of the inter-LAN connecting device having one line on the receiving side arrives at the line, a notification of the incoming call rejection including the line number of the calling side is sent from the public network. And
The other LAN connecting device having a line connecting to the public network is connected to the same LAN connected to the receiving side LAN connecting device, and the control unit of each LAN connecting device is connected to the line of the own LAN connecting device. A channel table for storing the use status of each line of the other LAN connection device;
The inter-LAN connecting device on the receiving side and the other inter-LAN connecting device periodically update their respective channel tables by periodically notifying each other of the line vacancies of the respective lines via the LAN. Channel table updating means ,
The control unit of the inter-LAN connecting device on the receiving side, upon detecting the notification of the rejection of the incoming call, identifies a line having an empty channel of the other inter-LAN connecting device from the channel table. Sends a call request to the calling-side LAN connecting device,
The inter-LAN connection method via a public network, wherein the control unit of the other inter-LAN connection device makes a call to the requested partner via an empty line. In claim 2,
Upon receiving the call request specifying the line, the other inter-LAN connecting device on the receiving side refers to the channel table, and determines whether the specified line is idle or the specified line is in use and is connected to another line. Identifying whether there is a vacant state or whether the specified line and all other lines are in use, and notifies a response frame including a corresponding identifier to the requesting LAN connection device;
The inter- LAN connection system via a public network , wherein the requesting inter-LAN connection device transmits a corresponding call request to the other inter-LAN connection device when the response frame is identified .

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