JP3560508B2 - ISDN terminal adapter - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ISDN terminal adapter, and more particularly to an ISDN terminal adapter having a function of performing point-to-point protocol (PPP: Point-to-Point Protocol) synchronous / asynchronous conversion and capable of connecting a plurality of PPP terminals. Regarding terminal adapter.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, some ISDN terminal adapters used for connecting to an integrated services digital network (ISDN network) can accommodate telephones and data terminals that cannot be connected to the ISDN network. This type of ISDN terminal adapter is disclosed, for example, in Japanese Patent Application Laid-Open No. Hei 10-13567. Japanese Patent Application Laid-Open No. H10-70588 discloses an ISDN terminal adapter which accommodates an asynchronous PPP terminal and has a PPP synchronous / asynchronous conversion function.
[0003]
This type of ISDN terminal adapter includes a data port interface for controlling an interface with a non-ISDN terminal such as an asynchronous PPP terminal, an ISDN interface for controlling an interface with an ISDN network, and a PPP synchronous / asynchronous conversion for performing PPP synchronous / asynchronous conversion. And a unit.
[0004]
A conventional ISDN terminal adapter having a synchronous / asynchronous PPP conversion function having such a configuration transmits a call (call) to ISDN in response to a line connection request issued from a non-ISDN / asynchronous PPP terminal connected to the ISDN terminal adapter. Setting) operation to occupy one or a plurality of B channels for data communication, and perform communication with a synchronous PPP terminal connected to the Internet via an ISDN network.
[0005]
In a device such as a conventional dial-up router, a communication function capable of performing channel multiplexing in the router is realized. This type of dial-up router includes an ISDN interface for controlling an interface with an ISDN network, an interface for controlling connection to a LAN using a LAN interface represented by 10Base-T, and a line using a routing table. And a routing control unit that performs control of IP packets on the LAN side and multiplexing in a channel.
[0006]
This type of dial-up router transmits a call to a public line such as ISDN when it is necessary to connect to a WAN or the Internet via a public line in response to an IP packet from a LAN interface connected to the dial-up router. (Call setting) operation, occupying one or a plurality of B channels, and communicating with a synchronous PPP terminal connected to the Internet via the ISDN network. At this time, the IP packets transmitted from the unspecified number of data terminals on the LAN side to the once connected line are logically multiplexed with the line side by the routing control unit using the routing table.
[0007]
[Problems to be solved by the invention]
However, even if the conventional ISDN terminal adapter described above can accommodate a plurality of asynchronous PPP terminals, one of the asynchronous PPP terminals establishes a call with the synchronous PPP terminal via the ISDN network and connects to the Internet. In this case, there is a disadvantage that the Internet cannot be connected from another asynchronous PPP terminal. The reason is that two B channels used for data communication are prepared in the basic interface of the ISDN, but if one asynchronous PPP terminal performs multilink PPP, the two B channels are used together. Therefore, the Internet connection cannot be made from another asynchronous PPP terminal.
[0008]
In order to enable multilink PPP from all the asynchronous PPP terminals in the conventional ISDN terminal adapter, it is conceivable that the ISDN terminal adapter can accommodate the same number of ISDN lines as the asynchronous PPP terminals. However, in this case, there is a disadvantage that costs such as communication costs are extremely high. The reason is that there is no standard scheme for multiplexing PPP or a scheme that can be independently extended, and one or two B channels are occupied by one dial-up.
[0009]
Also, in a conventional router having a dial-up function, the method of performing intra-channel multiplexing using one logical channel on the line side is a function that requires a network-related setting such as a LAN using an IP address as a precondition. However, it is difficult for a novice user in a general home not to use a LAN. The reason for this is that for a novice user in a general home who only knows the procedure of dial-up connection, the setting dedicated to the LAN is complicated and the setting cannot be performed easily.
[0010]
In a conventional system configuration using a router having a dial-up function, an IP address is determined to determine whether to perform intra-channel multiplexing to a logical channel on a line side. Since it is presupposed that a data terminal is connected, it is necessary to add a device such as a LAN card to the data terminal. In addition, it is necessary for the router to analyze the IP address and prepare a routing table, resulting in an increase in hardware cost as a whole. Therefore, there is a disadvantage that the overall hardware cost is extremely high, and it is difficult to introduce the hardware for an individual user.
[0011]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to logically multiplex a plurality of PPP links in an ISDN terminal adapter so that a synchronous PPP terminal to which the connection is made can appear to have only one PPP link. To provide an ISDN terminal adapter that can be used.
[0012]
Another object of the present invention is to provide an ISDN terminal adapter capable of simultaneously connecting a plurality of asynchronous PPP terminals to the Internet using a single basic interface line (two B channels) of one contained ISDN.
[0013]
Still another object of the present invention is not to use a complicated routing table based on an IP address to determine whether connection (transmission) operation to a line side or multiplexing in a channel is to be performed or not, but to be based on a destination telephone number. An object of the present invention is to provide an ISDN terminal adapter capable of performing connection (transmission) operation and intra-channel multiplex communication using simple multiplex logic.
[0014]
Still another object of the present invention is that simultaneous communication can be performed at a relatively low cost as a whole without preparing a complicated routing table and without preparing a LAN device on the data terminal side. It is another object of the present invention to provide an ISDN terminal adapter that can construct an environment that can be used as well as realize multiplexing in a channel by a simple dial-up connection procedure that has been used in ordinary homes.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an ISDN terminal adapter for connecting to an ISDN line and a plurality of data terminals to perform data communication via an ISDN network, wherein the connection between the data terminal and an access point on the ISDN line is provided. Asynchronous / synchronous conversion means for performing point-to-point protocol (PPP) asynchronous / synchronous conversion, IP multiplexing means for logically multiplexing a plurality of PPP links to the same connection destination, and dial-up connection as the data terminal Interface means for passing an asynchronous PPP frame for connection to an asynchronous PPP terminal having the protocol of the asynchronous PPP procedure , wherein the IP multiplexing means comprises a plurality of data terminals and a synchronous terminal which is an access point on the ISDN line. For connection with a PPP terminal, the synchronization An IP address assigned by negotiation between the PP terminal and the IP multiplexing means is passed to the data terminal, and a TCP / UDP port number of a packet transmitted from the data terminal using the IP address is set to Well known. By performing conversion to a port number other than the port and transmitting the port number to the synchronous PPP terminal and returning the port number of the packet from the synchronous PPP terminal to the port number before the conversion, logical multiplexing of a plurality of PPP links is performed . Features.
[0016]
According to a second aspect of the present invention, there is provided an ISDN terminal adapter for performing data communication via an ISDN network by connecting to an ISDN line and a plurality of data terminals, wherein a point in a connection between the data terminal and an access point on the ISDN line is provided. An asynchronous / synchronous conversion unit for performing asynchronous / synchronous conversion of a point-to-point protocol (PPP); and an IP multiplexing unit for logically multiplexing a plurality of PPP links to the same connection destination, wherein the IP multiplexing unit comprises a plurality of Passing the IP address assigned by negotiation between the synchronous PPP terminal and the IP multiplexing means to the data terminal with respect to the connection between the data terminal and the synchronous PPP terminal which is an access point on the ISDN line, TC of a packet transmitted from the terminal using the IP address By converting the port number of / UDP to a port number other than the Well known port and transmitting it to the synchronous PPP terminal, and returning the port number of the packet from the synchronous PPP terminal to the port number before the conversion, a plurality of Performs logical multiplexing of a PPP link, and when the asynchronous / synchronous conversion unit detects the link control protocol Config-Request transmitted by the data terminal, if there is a PPP link to the same destination already connected, A required signal including a link control protocol Config-Ack and a link control protocol Config-Request is generated and transmitted to the data terminal.
[0017]
The present invention according to claim 3 is an ISDN terminal adapter for performing data communication via an ISDN network by connecting to an ISDN line and a plurality of data terminals, wherein a point in a connection between the data terminal and an access point on the ISDN line is provided. An asynchronous / synchronous conversion unit for performing asynchronous / synchronous conversion of a point-to-point protocol (PPP); and an IP multiplexing unit for logically multiplexing a plurality of PPP links to the same connection destination, wherein the IP multiplexing unit comprises a plurality of Passing the IP address assigned by negotiation between the synchronous PPP terminal and the IP multiplexing means to the data terminal with respect to the connection between the data terminal and the synchronous PPP terminal which is an access point on the ISDN line, TC of a packet transmitted from the terminal using the IP address By converting the port number of / UDP to a port number other than the Well known port and transmitting it to the synchronous PPP terminal, and returning the port number of the packet from the synchronous PPP terminal to the port number before the conversion, a plurality of It is characterized in that logical multiplexing of a PPP link is performed .
[0018]
In the ISDN terminal adapter according to the present invention, when the asynchronous / synchronous conversion unit detects the link control protocol Config-Request transmitted by the data terminal, a PPP link to the same destination already connected is detected. If necessary, a necessary signal including a link control protocol Config-Ack and a link control protocol Config-Request is created and transmitted to the data terminal .
[0019]
The present invention according to claim 5 is an ISDN terminal adapter for performing data communication via an ISDN network by connecting to an ISDN line and a plurality of data terminals, wherein a point in a connection between the data terminal and an access point on the ISDN line is provided. An asynchronous / synchronous conversion unit for performing asynchronous / synchronous conversion of a point-to-point protocol (PPP); and an IP multiplexing unit for logically multiplexing a plurality of PPP links to the same connection destination, wherein the IP multiplexing unit comprises a plurality of Passing the IP address assigned by negotiation between the synchronous PPP terminal and the IP multiplexing means to the data terminal with respect to the connection between the data terminal and the synchronous PPP terminal which is an access point on the ISDN line, TC of a packet transmitted from the terminal using the IP address / UDP port number is converted to a port number other than the Well known ports (0 to 1023) and transmitted to the synchronous PPP terminal, and the port number of the packet from the synchronous PPP terminal is returned to the port number before the conversion. Accordingly, a plurality of PPP links are logically multiplexed, and among the plurality of data terminals, one or more data terminals have already been connected, and a connection request has been received from the second and subsequent data terminals. In this case, it is determined whether or not the telephone number of the destination of the connection request is the same as the telephone number of the destination already connected. If the telephone number is the same, the IP multiplexing means is sent to the same channel. It is characterized by further comprising a multiplex determination means for performing a determination to execute multiplexing.
[0020]
In the ISDN terminal adapter according to the present invention, when the multiplexing judging means judges that the telephone number of the destination of the connection request is different from the telephone number of the destination already connected, the multiplexing determining means is free. Communication control means for making a call using the channel.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an ISDN terminal adapter according to an embodiment of the present invention. Referring to FIG. 1, an ISDN terminal adapter 10 of the present embodiment accommodates a data terminal 20 performing an asynchronous PPP procedure and an ISDN line 30. And a data terminal interface unit 11 for controlling the data terminal 20, an ISDN line interface unit 12 for controlling the ISDN line 30, an asynchronous PPP frame exchanged with the data terminal interface unit 11, and a synchronous PPP frame exchanged with the ISDN line interface unit 12. Asynchronous / synchronous PPP conversion unit 13 that converts and controls frames, and a destination that determines whether to perform transmission on another channel or multiplex communication on the same channel according to the destination telephone number The system includes a telephone number determining unit 14, an IP multiplexing control unit 15 for performing IP (Internet Protocol) multiplexing control, and a communication control unit 16 for integrally controlling these components. In FIG. 1, only the characteristic configuration of the present embodiment is described, and the description of other general configurations is omitted.
[0022]
In the above configuration, the data terminal interface unit 11 performs transmission and reception of commands and data for communication from the data terminal 20, and performs control such as flow control while interfacing with the communication control unit 16.
[0023]
The ISDN line interface unit 12 controls the ISDN line 30 and also interfaces with the communication control unit 16 to distribute data to be transmitted and received between the D channel and the B channel as needed.
[0024]
The asynchronous / synchronous PPP conversion unit 13 interfaces with the communication control unit 16, converts and controls an asynchronous PPP frame and a synchronous PPP frame, and controls LCP (link control protocol), IPCP (Internet Protocol control protocol), and the like. Of the negotiation.
[0025]
Upon receiving a connection request from the second data terminal, the destination telephone number determination unit 14 determines whether the number is the same as the first destination, and if another number is available, another channel that is free. And if it is the same number, it is determined to multiplex to the existing same channel.
[0026]
The IP multiplexing control unit 15 interfaces with the communication control unit 16 and emulates the second and subsequent LCP, Authentication, IPCP, and other phases to be multiplexed, and manages the storage and allocation of parameters required at that time. , The distribution of data multiplexed on the ISDN line 30 to the data terminals 20 is controlled.
[0027]
The communication control unit 16 sends a command analysis, a response, and a data analysis to the data terminal interface unit 11, the ISDN line interface unit 12, the asynchronous / synchronous PPP conversion unit 13, the destination telephone number determination unit 14, and the IP multiplex control unit 15. Overall control of transmission and reception. In data transmission / reception, bulk communication using a plurality of channels simultaneously and multilink PPP using the same can be performed.
[0028]
Next, the operation of this embodiment will be described in detail with reference to the sequence chart of FIG. In the following description, it is assumed that the asynchronous PPP terminals 20a and 20b are the data terminals 20 shown in FIG. 1, and that the synchronous PPP terminals 31 exist on the ISDN line 30 in FIG.
[0029]
Referring to FIG. 2, first, the asynchronous PPP terminal 20a issues an initial connection request by an ATD command. Next, in response to the connection request, the ISDN terminal adapter (hereinafter, abbreviated as TA) 10 sends a SETUP message to the ISDN network on the D channel, and starts a transmission operation.
[0030]
When the synchronous PPP terminal 31, which is the communication partner, responds, a CONNECT message is returned via the ISDN network. Therefore, the TA 10 sends out a CONNECT result indicating that the call has been connected to the asynchronous PPP terminal 20a.
[0031]
The asynchronous PPP terminal 20a transmits an LCP Config-Request (hereinafter abbreviated as C-Req) on the B channel of the call connected via the TA 10 for LCP negotiation. In response, the synchronous PPP terminal 31 returns an LCP Config-Ack (hereinafter abbreviated as C-Ack).
[0032]
Further, C-Req is transmitted from the synchronous PPP terminal 31, and the asynchronous PPP terminal 20a returns C-Ack213. After that, negotiations such as Authentication Phase and IPCP Phase are performed, and the process proceeds to a data transfer phase (normal mode). With the above operation, the asynchronous PPP terminal 20a is connected to the WAN such as the Internet via the synchronous PPP terminal 31.
[0033]
Here, when the asynchronous PPP terminal 20b issues a connection request to the same synchronous PPP terminal 31 by an ATD command, the TA10 makes the destination telephone number determination unit 14 based on the destination telephone number of the ATD command. It is determined that the connected IP packets can be multiplexed on the same channel. The asynchronous / synchronous PPP conversion unit 13 sends a CONNECT result to the asynchronous PPP terminal 20b without entering the ISDN network transmission operation.
[0034]
Similarly, the asynchronous PPP terminal 20b sends a C-Req to the TA 10 for LCP negotiation, but the TA 10 does not send the C-Req to the ISDN network, and the asynchronous / synchronous PPP conversion unit 13 The C-Ack is returned to the terminal 20b. Further, the C-Req is transmitted from the TA 10 to the asynchronous PPP terminal 20b, and the asynchronous PPP terminal 20b returns a C-Ack.
[0035]
Thereafter, negotiations such as an Authentication Phase and an IPCP Phase are also terminated at the TA 10 and locally transmitted and received to and from the asynchronous PPP terminal 20b, and the process proceeds to a data transfer phase (multiplexing mode) 228.
[0036]
Next, in the above-described operation of the TA 10, it is determined whether the destination telephone number determination unit 14 performs the same PPP link multiplexing in response to an ATD command connection request from the asynchronous PPP terminal 20b, or starts independent PPP on another channel. The determination operation will be described with reference to the flowchart of FIG.
[0037]
When there is a connection request from the data terminal 20 (step 301), it is determined whether a PPP link already exists (step 302). If the call does not exist, the process proceeds to a new call process to generate a new call, and a call to the ISDN is started (step 303).
[0038]
On the other hand, if the PPP link exists, it is determined whether the connection request is a connection request to the same number as the already connected connection destination (step 304). If the numbers are different, the process proceeds to a new call process (step 303). If the numbers are the same, a pseudo call process is started (step 305). In this case, without transmitting anything to the ISDN network, the data terminal 20 performs processing to make it appear as if it were connected to the ISDN network, and proceeds to the multiplexing mode.
[0039]
In order to realize this function, it is necessary to terminate the PPP in the TA 10 and perform independent negotiation for each interface. The asynchronous / synchronous PPP conversion unit 13 designates and stores negotiation parameters for realizing the subsequent multiplexing function for the asynchronous PPP terminal 20a and the ISDN network at the time of the first call shown in FIG. . FIG. 4 shows an example of the relationship between parameters stored at the time of the first call and stored values used at the time of the second call. When performing a local sequence with the asynchronous PPP terminal 20b, local negotiation is performed using parameters (stored values) stored at the time of the first call with the asynchronous PPP terminal 20a.
[0040]
Next, with reference to FIGS. 5 and 6, a logical multiplexing method for transmitting and receiving IP packets by the IP multiplexing control unit 15 will be described.
[0041]
The IP multiplexing control unit 15 sends the IP address assigned by negotiation with the dial-up server 501 located at the synchronous PPP terminal 31 shown in FIG. 2 to the client located at the asynchronous PPP terminals 20a and 20b shown in FIG. Pass it to 502. The IP multiplex control unit 15 itself does not have an IP address.
[0042]
The client 502 transmits a packet using the IP address assigned in the IPCP negotiation as it is (seq. 1). At this time, since the IP multiplexing control unit 15 does not have an IP address and the IP address used by the client 502 is a formal one, the IP multiplexing control unit 15 converts the TCP / UDP Only the port number is converted to a port number (1024 to 65535) other than the Well known Port (0 to 1023), and the packet is transmitted (Seq. 2). At this time, the conversion pattern is stored internally.
[0043]
The dial-up server 501 transmits the Seq. A Reply Packet is transmitted for the packet converted in step 2 (Seq. 3).
[0044]
The IP multiplexing control unit 15 that has received the Reply Packet sends the Seq. The port number of the Reply Packet is returned to the original one based on the conversion pattern stored in step 2 and transmitted to the client 502 (seq. 4).
[0045]
In the present embodiment, the asynchronous PPP terminal of the client is configured to use a dial-up procedure for controlling a modem or the like using a COM port using RS-232C or USB. In other words, the Windows (R) or Macintosh (R) OS is a mechanism that is prepared as a standard, so that even a novice user in a general home can easily use it. Also, since the already connected line channel is used, the communication fee can be reduced.
[0046]
Further, in the present embodiment, the configuration does not use a special device such as a LAN card, and the terminal adapter does not need to prepare complicated routing tables and IP address analysis logic. Therefore, an increase in hardware cost can be significantly reduced.
[0047]
As described above, the present invention has been described with reference to the preferred embodiments, but the present invention is not necessarily limited to the above embodiments.
[0048]
【The invention's effect】
As described above, according to the ISDN terminal adapter of the present invention, data transmission and reception are logically multiplexed and performed by the IP multiplex conversion means, so that only one PPP link is connected to the synchronous PPP terminal at the connection destination. There is an effect that a plurality of terminals can be connected to the Internet while appearing to exist.
[0049]
In addition, since data transmission and reception are performed by logically multiplexing, there is no need to newly accommodate another ISDN line for connecting a plurality of terminals to the Internet, so that there is an effect that communication charges can be reduced. .
[0050]
In addition, since a normal dial-up connection procedure is used, there is an effect that no setting is required and the introduction and use of the system are easy.
[0051]
Furthermore, since a special device such as a LAN card is not required, and a complicated analysis logic such as a dial-up router and a memory for managing the logic are small, a hardware configuration for realizing the function can be reduced in cost. effective.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an ISDN terminal adapter according to an embodiment of the present invention.
FIG. 2 is a sequence chart showing an operation of the embodiment.
FIG. 3 is a flowchart illustrating an operation of a destination telephone number determining unit according to the embodiment.
FIG. 4 is a diagram showing a specific example of a mode of storing and using parameters required in the operation of the present embodiment.
FIG. 5 is a data flow diagram showing a flow of an IP packet in the embodiment.
FIG. 6 is a table showing a specific example of a relationship between an IP address and a port number in the embodiment.
[Explanation of symbols]
Reference Signs List 10 ISDN terminal adapter 11 Data terminal interface 12 ISDN line interface 13 Asynchronous / synchronous PPP conversion unit 14 Destination telephone number judgment unit 15 IP multiplex control unit 16 Communication control unit 20 Data terminals 20a, 20b Asynchronous PPP terminal 30 ISDN line 31 Synchronous PPP Terminal

Claims (6)

An ISDN terminal adapter for connecting to an ISDN line and a plurality of data terminals to perform data communication via an ISDN network.
Asynchronous / synchronous conversion means for performing an asynchronous / synchronous conversion of a point-to-point protocol (PPP) in a connection between the data terminal and an access point on an ISDN line;
IP multiplexing means for logically multiplexing a plurality of PPP links to the same connection destination;
Interface means for passing an asynchronous PPP frame for connecting to an asynchronous PPP terminal having a protocol of a dial-up connection asynchronous PPP procedure as the data terminal ;
The IP multiplexing means, for connection between the plurality of data terminals and a synchronous PPP terminal which is an access point on the ISDN line, assigns an IP address allocated by negotiation between the synchronous PPP terminal and the IP multiplexing means. Handover to a data terminal, convert a TCP / UDP port number of a packet transmitted from the data terminal using the IP address into a port number other than a well-known port, and transmit the port number to the synchronous PPP terminal; An ISDN terminal adapter for performing logical multiplexing of a plurality of PPP links by returning a port number of a packet from a PPP terminal to the port number before the conversion . An ISDN terminal adapter for connecting to an ISDN line and a plurality of data terminals to perform data communication via an ISDN network.
Asynchronous / synchronous conversion means for performing an asynchronous / synchronous conversion of a point-to-point protocol (PPP) in a connection between the data terminal and an access point on an ISDN line;
IP multiplexing means for logically multiplexing a plurality of PPP links to the same connection destination,
The IP multiplexing means, for connection between the plurality of data terminals and a synchronous PPP terminal which is an access point on the ISDN line, assigns an IP address allocated by negotiation between the synchronous PPP terminal and the IP multiplexing means. Handover to a data terminal, convert a TCP / UDP port number of a packet transmitted from the data terminal using the IP address into a port number other than a well-known port, and transmit the port number to the synchronous PPP terminal; By returning the port number of the packet from the PPP terminal to the port number before the conversion, logical multiplexing of a plurality of PPP links is performed,
When the asynchronous / synchronous conversion means detects the link control protocol Configure-Request transmitted by the data terminal, if there is a PPP link to the same destination already connected, the link control protocol Config-Ack and the link An ISDN terminal adapter, which generates a necessary signal including a control protocol "Configure-Request" and sends it to the data terminal. An ISDN terminal adapter for connecting to an ISDN line and a plurality of data terminals to perform data communication via an ISDN network.
Asynchronous / synchronous conversion means for performing an asynchronous / synchronous conversion of a point-to-point protocol (PPP) in a connection between the data terminal and an access point on an ISDN line;
IP multiplexing means for logically multiplexing a plurality of PPP links to the same connection destination,
The IP multiplexing means, for connection between the plurality of data terminals and a synchronous PPP terminal which is an access point on the ISDN line, assigns an IP address allocated by negotiation between the synchronous PPP terminal and the IP multiplexing means. Handover to a data terminal, convert a TCP / UDP port number of a packet transmitted from the data terminal using the IP address into a port number other than a well-known port, and transmit the port number to the synchronous PPP terminal; An ISDN terminal adapter for performing logical multiplexing of a plurality of PPP links by returning a port number of a packet from a PPP terminal to the port number before the conversion . When the asynchronous / synchronous conversion means detects the link control protocol Configure-Request transmitted by the data terminal, if there is a PPP link to the same connection destination already connected, the link control protocol Config-Ack and the link The ISDN terminal adapter according to claim 3, wherein a necessary signal including a control protocol "Configure-Request" is generated and transmitted to the data terminal. An ISDN terminal adapter for connecting to an ISDN line and a plurality of data terminals to perform data communication via an ISDN network.
Asynchronous / synchronous conversion means for performing an asynchronous / synchronous conversion of a point-to-point protocol (PPP) in a connection between the data terminal and an access point on an ISDN line;
IP multiplexing means for logically multiplexing a plurality of PPP links to the same connection destination,
The IP multiplexing means, for connection between the plurality of data terminals and a synchronous PPP terminal which is an access point on the ISDN line, assigns an IP address allocated by negotiation between the synchronous PPP terminal and the IP multiplexing means. The packet is passed to the data terminal, and the TCP / UDP port number of a packet transmitted from the data terminal using the IP address is converted to a port number other than the Well known port (0 to 1023), and the packet is transmitted to the synchronous PPP terminal. Transmitting and returning the port number of the packet from the synchronous PPP terminal to the port number before the conversion to perform logical multiplexing of a plurality of PPP links;
When one or more data terminals are already connected among the plurality of data terminals, and a connection request is received from a second or subsequent data terminal, the telephone number of the destination of the connection request is The apparatus further comprises a multiplex determining means for determining whether the telephone number is the same as the telephone number of the destination already connected and, if the number is the same, the IP multiplexing means for performing multiplexing to the same channel. An ISDN terminal adapter. When the multiplex determination means determines that the telephone number of the destination of the connection request is different from the telephone number of the destination already connected, the communication control means for making a call using another available channel. The ISDN terminal adapter according to claim 5, further comprising:

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