JPH10112739A - Modem - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mode which enables the connection confirmation of a packet data link and the transmission and receiving confirmation of packet data between a terminal computer and a modem by using a communication application of the terminal computer even without connecting the modem to a network interface and a network. SOLUTION: A pseudo-host function processing part 9 which analyzes packet data that is sent from a communication application of a terminal computer 1 and performs loop back which simulates connection with a host computer is installed. In the case of a TCP/IP application, the part 9 analyzes IP packet data without sending it to a network interface 4 and converts only an IP header in the IP packet data and a header part of data of an upper protocol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem device provided on a terminal computer for communicating with a host computer.

[0002]

2. Description of the Related Art A conventional modem device, for example, a modem card device is a TCP / IP (Transmission Control Protocol) of a terminal computer, for example, a personal computer.
/ Internet Protocol) When receiving IP packet data sent from an application, it is transmitted to the network interface as it is. To confirm the communication operation of the TCP / IP application of the personal computer, the modem card device must be connected to the network. Had to connect.

[0003]

That is, the TCP / IP application of a personal computer can function by transmitting and receiving IP packet data to and from a host computer at the network destination. In order to establish communication with the computer, a network interface must be connected to the modem card device and connected to the network via this. Unless the connection is made, the communication operation of the TCP / IP application can be confirmed. Did not.

Therefore, if the connection environment and connection conditions from the personal computer to the host computer at the network destination are completely prepared and the host computer is not actually accessed, even if the personal computer and the modem card device are connected to each other, the personal computer cannot be used. T
The connection confirmation of the IP packet data link and the transmission / reception confirmation of the IP packet data using the CP / IP application could not be performed. In addition, if you try to check it in a situation where the connection environment and connection conditions etc. in advance with the host computer side and the network are not established, you can not do it, so if you purchase a modem card device in such a situation Is a personal computer TCP / IP
The application, the communication system, and the modem card device itself could not sufficiently check the operation.

[0005] The above-mentioned problems are the same in modem board devices other than modem card devices and ordinary box-type modem devices.

Accordingly, an object of the present invention is to provide a communication application (T) for a terminal computer without connecting a modem device to a network interface and a network.
Another object of the present invention is to provide a modem device capable of confirming connection of a packet data link between a terminal computer and a modem device and confirming transmission / reception of packet data using a CP / IP application or the like.

[0007]

SUMMARY OF THE INVENTION A modem device according to the present invention is a pseudo host means for analyzing packet data sent from a communication application of a terminal computer and performing a loopback to the terminal computer to simulate a connection with a host computer. It is provided with.

If the communication application of the terminal computer is a TCP / IP application, the pseudo host means analyzes the IP packet data sent from the TCP / IP application without sending it to the network interface, converts the data, and converts it. Reply to the terminal computer. The conversion may be performed only on the IP header in the IP packet data and the header part of the data of the upper protocol.
The invention is particularly useful for modem card devices.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In the embodiment shown in FIG. 1, a terminal computer 1 is a notebook personal computer (hereinafter referred to as "PC") incorporating a TCP / IP application, and a modem device 2 is a card type (hereinafter referred to as "modem card").
These are connected by a serial signal line (RS232C) 3 having a PCMCIA-compliant interface. In addition, the signal line 5 between the modem card 2 and the network interface 4 serves as a control line and a communication / data signal line.

The modem card 2 is equipped with a microprocessor and incorporates communication control software. Five processing units, namely, a data terminal communication control processing unit 6, a modem control command processing unit 7, and a T
It is divided into a CP / IP protocol unit 8, a pseudo host function processing unit 9, and a signal control unit 10, and a line connecting each processing unit is a logical signal line. Of these five processing units, the emphasis of the present invention is particularly on the pseudo host function processing unit 9.

The layer of the communication protocol between the PC 1 and the modem card 2 is such that layer 1 is PCMCIA and layer 2 is PP
P (Point-to-Point Protocol), Layer 3 is IP (Int
Internet Protocol), Layer 4 is TCP (Transmission C)
ontrol Protocol), on which the upper application is located.

Before the TCP / IP application of the PC 1 is operated, it is necessary to establish a link between the PC 1 and the modem card 2 by the layer 2 PPP. P
The link establishment by the PP is performed by exchanging data between the PC 1 and the TCP / IP protocol unit 8 via the data communication control processing unit 6. At this time, the conversion method of asynchronous data, the maximum number of received bytes, and the like are negotiated.

When the link by PPP is established, the modem card 2 and the PC 1 can receive the IP packet data. However, the connection between the PC 1 and the modem card 2 is confirmed by using the TCP / IP application of the PC 1. In the conventional modem card, a call connection must be made via a network to actually access a host computer. When a conventional modem card receives IP packet data from the PC 1, the data is transmitted to the network interface 4 via the data terminal communication control processing unit 6, the TCP / IP protocol unit 8 and the signal control unit 10. At this time, the data is HDLC (High level Data).
Although it flows in the form of a Link Control procedure frame, the conventional modem card transmits the HDLC frame to the network interface 4 without changing the information part (IP packet data) of the HDLC frame.

Therefore, in the modem card 2 shown in FIG. 1, a pseudo host function processing section 9 is provided. Here, the information section (IP packet data) of the HDLC frame is changed in the same manner as the processing on the host computer side, and is changed to the PC 1. By sending it back, the TCP / IP application of the PC 1 appears to be communicating with the host computer. Next, the operation will be described.

As shown in FIG. 2, the information portion of the HDLC frame, that is, the IP packet data, is further divided into an IP header and user data, and the user data is data of a higher protocol indicated by the IP header. Since the data of the upper protocol differs depending on the TCP / IP application, the pseudo host function processing unit 9 converts the data into data corresponding to the upper protocol. Here, ICMP (Internet) is used to switch between real processing and pseudo processing.
Control Message Protocol) and a packet transmission / reception diagnostic program using the echo function of ICMP.
ING will be described as an example.

The PING is for transmitting and receiving packet data to and from a host to diagnose the state of a line.
In FIG. 2, in the case of PING, [RFC (Request For Comments) 1
340], the ICM of protocol number 1
P is adopted. That is, when the upper protocol field in the IP header is “1”, the user data contains an ICMP message. ICM
The P message is also divided into a header part and a data part, and the first byte of the header part indicates the type of the message. The message types are: 0: echo response, 3: destination unreachable notification, 4: start point suppression request, 5:
Route change request, 8: echo request, 11: timeout notification,
12: parameter error notification, 13: time request, 14: time response, 15: information request, 16: information response.

Since the pseudo host function processing section 9 returns an echo response (number 0) in response to the echo request (number 8) from the PC 1, the type of the first byte is changed from "8" to "0", that is, "echo". The request is converted into an "echo response", and the third byte checksum is recalculated only for the ICMP message. If this checksum is calculated differently, PING
Discards the data, assuming that a communication fraud has occurred.
The checksum is the complement of the sum of each one's complement when the data is viewed as a sequence of 16-bit integers. In the calculation, the checksum field is assumed to be "0". The remaining data is not converted. Here, the conversion method when the upper protocol is ICMP has been described. However, when the upper protocol is TCP or the like, the conversion method differs.

The pseudo host function processing section 9 also partially changes the IP header. The change is performed irrespective of the upper layer protocol.
After replacing the 6th byte with the receiving side Internet address, the 10th byte checksum is recalculated for only the IP header part. The checksum algorithm is I
Similar to CMP.

In the above, the embodiment in which the terminal computer 1 is a notebook personal computer and the modem device 2 is a modem card has been described. However, the terminal computer 1 is a desktop personal computer or the like, and the modem device 2 is a modem board or box-type modem. The present invention can be applied in the same manner as described above. As a communication application, a TCP / IP application is optimal for practical use, but another communication protocol may be used.

[0021]

As described above, the modem device of the present invention has a pseudo host function of performing a loopback to the terminal computer simulating the connection with the host computer, so that the modem device can be connected without connecting to the network. That is, it is possible to confirm the connection of the packet data link and the transmission / reception of the packet data only with the terminal computer using the communication application of the terminal computer, regardless of the host computer.

Further, in the modem device, transmission and reception of lines on the terminal computer and the network and transmission / reception of packet data can be separately checked, so that reliability and maintainability can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration and a data flow of an embodiment of a modem device according to the present invention.

FIG. 2 is a diagram showing IP packet data (including an ICMP message) in an HDLC frame communicated using the modem device of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Terminal computer 2 Modem device 4 Network interface 6 Data terminal communication control processing part 7 Modem control command processing part 8 TCP / IP protocol part 9 Pseudo host function processing part (pseudo host means) 10 Signal control part

Claims (4)

[Claims] A modem provided on a terminal computer side for performing communication with a host computer, a loop simulating connection with the host computer by analyzing packet data sent from a communication application of the terminal computer. A modem device comprising pseudo host means for performing back-up on a terminal computer. 2. The pseudo host means according to claim 1, wherein the pseudo host means analyzes the IP packet data sent from the TCP / IP application of the terminal computer without transmitting it to the network interface, converts the data, and returns it to the terminal computer. Modem device. 3. The modem device according to claim 2, wherein the pseudo host means converts only an IP header in the IP packet data and a header portion of the data of the upper protocol. 4. The modem device according to claim 1, wherein the modem device is a card which is removably mounted on a terminal computer.