Communication control method, communication control apparatus and storage medium

The present invention relates to a communication control method for a communication system in which a plurality of data terminals can communicate with each other through a wired or wireless communication network, a communication apparatus for implementing the communication control method and a storage medium for storing communication control programs embodying the communication control method.

A communication system is prevalent in which a plurality of data terminals, such as personal computers, communicate with each other through a wired or wireless communication network for data transmission to or from another data terminal. In such a communication system, each data terminal has a communication module. This communication module is a module executed by a control part provided in the data terminal in order to perform communication with another data terminal through a communication network.

While a data terminal is performing a data communication with another data terminal, however, the communication is sometimes interrupted for an unexpected cause, for instance, an occurrence of a trouble in the network or steep deterioration of the quality of the communication line. In such cases, the communication module in the data terminal receives a notification that the communication has been interrupted and then ends the communication. Therefore, when a communication is interrupted, the user has to do the same operations allover again from the beginning to start the communication module to reconnect the data terminal with the other data terminal through the communication network.

For example, during downloading of desired data with a personal computer, if the communication is interrupted for an unexpected cause, the user has to start again the application program for the downloading to download the desired data from its beginning. Also, during access to a homepage on the Internet, using a browser, if the communication is interrupted, the user has to reestablish the communication to access the homepage again. Therefore, the user is sometimes prevented from doing continuous surfing on the Internet.

As described above, if the communication is interrupted, the user has to do the same procedures for reestablishing the communication and start downloading data allover gain from the very beginning. This problem increases the load on the user and makes expensive charges to be paid to the operator operating the personal computer communication.

The present invention is made, considering the above-described circumstances, and an object of the present invention is to provide a communication control method, a communication control apparatus and a storage medium which, even if a communication is interrupted, can reestablish the communication without increasing the load on a user.

In order to attain such an object, the present invention is to provide a communication control method for data terminals with data communication module for transmitting data or receiving data between data terminals over a communication network. The method includes steps of detecting an interruption of a communication and, when an interruption of the communication is detected, reestablishing the communication without notifying the data communication module of the interruption of the communication.

According to this communication control method, even if a communication is interrupted, the data communication module in the data terminal does not recognize the interruption of the communication. Therefore, when the communication is reestablished, the data communication can be restarted with the data that remained to be communicated at the time when the communication line was interrupted.

This communication control method may include a step of judging whether to reestablish the interrupted communication. The interrupted communication is reestablished without notifying the data communication module of the interruption of the communication when the interruption of the communication is detected, and it is judged that the communication can be reestablished.

In the judging step, the judgment as to whether or not the communication can be reestablished is made based on a cause for the interruption of the communication. Therefore, attempts can be avoided that would be made to reestablish the communication despite the fact that it is impossible to reestablish the communication.

In addition, the communication control method may further include a step of diagnosing the condition of the network. The judgement as to whether or not the interrupted communication can be reestablished is made based on the diagnosed condition of the network. Therefore, attempts can be avoided that would be made to reestablish the communication despite the fact that the condition of the network is not good.

On the other hand, the present invention can be realized by a communication control apparatus for implementing the communication control method. In addition, the present invention can be realized by a storage medium for storing a communication control program embodying the communication control method.

FIG. 1 is a block diagram showing the principle of the present invention.

FIG. 2 is a flowchart showing operations for reestablishing a communication.

FIG. 3 is a flowchart showing operations for reestablishing a communication after the communication is interrupted.

FIG. 4 is a block diagram showing the constitution of a communication system adopting the communication control method according to the first preferred embodiment of the present invention.

FIG. 5 is a sequence chart showing operations for establishing and reestablishing a communication according to the same embodiment.

FIG. 6A is a block diagram showing that a client data terminal is downloading data from a server data terminal through a communication network; FIG. 6B is a block diagram showing a situation where the communication is interrupted; and FIG. 6C is a block diagram showing a situation where the interrupted communication is reestablished; and FIG. 6D is a block diagram showing a situation after the reestablishment of the communication is completed.

FIG. 7 is a block diagram showing the constitution of a communication system adopting the communication control method according to a second preferred embodiment of the present invention.

FIG. 8A is a block diagram showing a situation where a facsimile is sending image data to another facsimile through a communication network; FIG. 8B is a block diagram showing a situation where the communication is interrupted; and FIG. 8C is a block diagram showing a situation where the interrupted communication is reestablished.

FIG. 9 is a block diagram showing the constitution of a communication system adopting the communication control method according to a third preferred embodiment of the present invention.

FIG. 10 is a flowchart showing operations of the same communication system.

The preferred embodiments of the present invention will hereinafter be discussed with reference to the attached drawings.

FIG. 9 shows the constitution of a communication system adopting the communication control method according to the present invention.

The communication system, as shown in FIG. 9 , includes a portable telephone 33 , a communication adapter (PC card) 31 , a cable 32 , a portable data terminal 30 , a radio base station 34 , mobile radio communication control stations 35 and 37 , a home memory station 36 , a gateway station 38 , a telephone network 39 and a data terminal 40 . The portable data terminal 30 is a notebook-type personal computer, for example. The portable telephone 33 and the portable data terminal 30 are connected to each other through the cable 32 and the communication adapter 31 . More specifically, one end of the cable 32 is connected to the portable telephone 33 , and the other end of the cable 32 is connected to the communication adapter 31 inserted in a card slot of the portable data terminal 30 . This communication adapter 31 functions to modulate data outputted from the portable data terminal 30 into radio signals and demodulate radio signals received through the portable telephone 33 . In the constitution described above, the portable data terminal 30 can perform data communication with the data terminal 40 through a communication network comprised of the portable telephone 33 , the radio base station 34 , the mobile radio communication control stations 35 and 37 , the gateway station 38 and the telephone network 39 .

A: The principle of the present invention

Before getting into the details of embodiments of a communication system adopting the communication control method according to the present invention, the present invention should be discussed in general.

First, the conceptual constitution of a communication system adopting the communication control method according to the present invention will be discussed with reference to FIG. 1 . As shown in FIG. 1 , this communication system includes data terminals 1 A and 1 B, DCE (Data Circuit terminating Equipment) 4 A, DCE 4 B and a communication line 5 . FIG. 1 illustrates a situation where the data terminals 1 A and 1 B are connected to each other through the communication line 5 established in a network. The data terminal 1 A is connected to the DCE 4 A. The DCE 4 A relays data between the data terminal 1 A and the communication line 5 . The data terminal 1 B is connected to the DCE 4 B. The DCE 4 B relays data between the data terminal 1 B and the communication line 5 . The DCE 4 A and DCE 4 B are equivalent to the communication adapter 31 in the communication system shown in FIG. 9 . One data terminal can transmit data to and receive data from the other data terminal over a connection through the DCE 4 A, the communication line 5 and the DCE 4 B.

The data terminal 1 A has a communication module 3 A and a communication control module 2 A. The communication module 3 A and the communication control module 2 A are programs executed by a control part provided in the data terminal 1 A. More specifically, the communication module 3 A is a module for transmitting data to or receiving data from the data terminal 1 B connected to the data terminal 1 A through the communication line 5 . The communication control module 2 A is a module for controlling data communication performed by the communication module 3 A. The data terminal 1 B has a communication module 3 B and a communication control module 2 B similar to those in the data terminal 1 A.

FIG. 2 illustrates operations for connecting the data terminal 1 A to the data terminal 1 B through the communication line 5 .

First, receiving from a user a command to perform a data communication with the data terminal 1 B, the communication module 3 A in the data terminal 1 A sends a connection request to the communication control module 2 A (step S 1 ). When the communication control module 2 A receives this connection request, it requests to the DCE 4 A information on the present condition of the network (step S 2 ). When the DCE 4 A receives this request, it diagnoses the present condition of the network (step S 3 ). For example, the DCE 4 A diagnoses the condition of the network, based on control signals sent from the network. More specifically, the DCE 4 A determines whether or not traffic congestion has occurred on the network, whether or not a trouble has occurred in the network, whether or not any line is available or the like. If the receiving data terminal 1 B is the portable computer as shown in FIG. 9 that is connected to the network through the portable telephone 33 , the DCE 4 A also detects whether or not the portable telephone 33 is found within the wireless zone formed by the radio base station 34 . Similarly, if the sending data terminal 1 A is the portable data terminal as shown in FIG. 9 that is connected to the network through the portable telephone 33 , the DCE 4 A detects whether or not the portable telephone 33 is found within the wireless zone formed by the radio base station 34 . The DCE 4 A sends results of the detection (network information) to the communication control module 2 A (step S 4 ).

When the communication module 2 A receives the network information (step S 5 ), it analyzes it and judges, based on the network information, whether or not the present condition of the network is good (step S 6 ). “The condition of the network is good” means that there are no problems with establishing a communication between the data terminals 1 A and 1 B. More specifically, the communication control module 2 A determines that the condition of the network is good when the following are true:

(1) there is no traffic congestion on the network; (2) there are no troubles in the network; (3) the portable telephone 33 is found within the wireless zone formed by the radio base station 34 in a case where the receiving data terminal 1 B is the portable data terminal connected with the portable telephone 33 as shown in FIG. 9 ; and (4) the portable telephone 33 is found within the wireless zone formed by the radio base station 34 in a case where the sending data terminal 1 A is the portable data terminal connected with the portable telephone 33 as shown in FIG. 9 .

In contrast, “The condition of the network is not good” means that there is a problem with connecting the data terminal 1 A to the data terminal 1 B through the communication line 5 . More specifically, the communication control module 2 A determines that the condition of the network is not good when any one of the following is true:

(1) There is traffic congestion on the network; (2) there is a trouble in the network; (3) the portable telephone 33 is not found within the wireless zone formed by the radio base station 34 in a case where the receiving data terminal 1 B is the portable data terminal connected with the portable telephone 33 as shown in FIG. 9 ; or (4) the portable telephone 33 is not found within the wireless zone formed by the radio base station 34 in a case where the sending data terminal 1 A is the portable data terminal connected with the portable telephone 33 as shown in FIG. 9 .

If the communication control module 2 A determines in step S 6 that the condition of the network is good, it sends a connection request to the DCE 4 A (step S 7 ).

In contrast, if the communication control module 2 A determines that the condition of the network is not good, it sends DCE 4 A a directive to watch the condition of the network (step S 8 ). In this step, the communication control module 2 A does not inform the communication module 3 A that there is a problem with establishing a communication.

When the DCE 4 A receives this directive, its operation mode switches over to a watching mode (steps S 9 to S 11 ). More specifically, this is done as follows;

It has been detected in step S 3 that the condition of the network is not good. The DCE 4 A performs the same detection operation in step S 9 and repeats the operation at regular intervals until it detects that the problem of the network has been cleared (steps S 9 and S 10 ). If the DCE 4 A determines that the problem of the network is cleared, that is to say, if the condition of the network has turned good, the DCE 4 A sends a watch result to the communication control module 2 A (step S 11 ). This watch result indicates that the condition of the network is now good.

On the other hand, the communication control module 2 A switches its operation mode to a waiting mode (steps S 12 to S 14 ) after the communication control module 2 A sends the DCE 4 A the directive to watch the condition of the network in Step 8 . That is to say, the communication control module 2 A waits for a fixed time (described below as “a waiting time”) from the time when it sends the directive. If the communication control module 2 A receives the watch result from the DCE 4 A, that is to say, if the condition of the network turned good, before the waiting time lapses (step S 13 ; Yes), it outputs a connection request to the DCE 4 A (step S 7 ).

In contrast, if the communication control module 2 A does not receive the watch result, that is to say, if the condition of the network does not turn good, within the waiting time (step S 14 ; Yes), it informs the communication module 3 A that it is impossible to establish the communication (step S 16 ). When the communication module 3 A is so informed, it informs the user that it is impossible to establish the communication and ends the operations for data communication.

On the other hand, when the DCE 4 A receives the connection request from the communication control module 2 A in step S 7 , it forwards this connection request to the network (step S 15 ). The communication control module 2 B in the receiving data terminal 1 B receives this circuit connect request through the network. The communication line 5 between the data terminals 1 A and 1 B is established after a series of operations such as a negotiation, an authentication and the like are performed. After this, the communication module 3 A in the data terminal 1 A and the communication module 3 B in the data terminal 1 B transmit data to and receive data from each other through this communication line 5 .

The operations performed in this communication system will be discussed with reference to FIG. 3 . Suppose that the communication is interrupted for an unexpected cause after the data terminals 1 A and 1 B are connected to each other through the communication line 5 according to the processes described above.

First, when the communication line 5 is interrupted, an interruption response code is sent from the network to the data terminals 1 A and 1 B. The interruption response code includes information indicating the fact that the communication line is interrupted and the cause for the interruption.

A possible cause for an interruption of a communication is as follows:

(1) there is traffic congestion on the network; (2) there is a trouble in the network; (3) the portable telephone 33 moves out of the wireless zone formed by the radio base station 34 in a case where the receiving data terminal 1 B is the portable data terminal connected to the portable telephone 33 as shown in FIG. 9 ; or (4) the portable telephone 33 moves out of the wireless zone formed by the radio base station 34 in a case where the sending data terminal 1 A is the portable data terminal connected to the portable telephone 33 as shown in FIG. 9 .

The communication control module 2 A in the data terminal 1 A receives this interruption response code through the DCE 4 A (steps S 20 and S 21 ). The communication control module 2 A then judges, based on the interruption response code, whether or not it is possible to reestablish the interrupted communication (step S 22 ). More specifically, if the cause of the interruption is such that the interruption is temporary, or the problem can be solved in a time, the communication control module 2 A determines that it is possible to reestablish the communication.

For example, the communication control module 2 A determines that it is possible to reestablish the communication if the interruption was caused by one of the following:

(1) there is traffic congestion on the network; (2) the portable telephone 33 shown in FIG. 9 moved out of the wireless zone formed by the radio base station 34 in a case the receiving data terminal 1 B is the portable data terminal connected to the portable telephone 33 as shown in FIG. 9 ; or (3) the portable telephone 33 shown in FIG. 9 moved out of the wireless zone formed by the radio base station 34 in a case where the sending data terminal 1 A is the portable data terminal connected to the portable telephone 33 as shown in FIG. 9 .

On the other hand, if the cause of the interruption is such that there is no or very little hope that the problem will be solved in a time, the communication control module 2 A determines that it is impossible to reestablish the communication.

For example, the communication control module 2 A determines that it is impossible to reestablish the communication if the cause of the interruption is any one of the following;

(1) the receiving data terminal 1 B rejects a data communication with the data terminal 1 A; (2) the receiving data terminal 1 B has broken down; (3) no response has been sent back from the data terminal 1 B; or (4) an insoluble problem has happened in the network.

If the communication control module 2 A determines in step S 22 that it is impossible to reestablish the communication, it informs the communication module 3 A that the communication line 5 is disconnected (step S 23 ). When the communication module 3 A receives this notification, it informs the user that the communication line is disconnected and ends the operations for the data communication between the data terminals 1 A and 1 B.

In contrast, if the communication control module 2 A determines that it is possible to reestablish the communication, it performs operations for reestablishing the interrupted communication without informing the communication module 3 A of the interruption of the communication. More specifically, these operations are as follows:

First, the communication control module 2 A requests to the DCE 4 A information on the condition of the network (step S 24 ). When the DCE 4 A receives this request, it diagnoses the condition of the network (step S 25 ) and sends results of the diagnosis (network information) to the communication module 2 A (step S 26 ).

When the communication control module 2 A receives the network information (step S 27 ), it judges whether or not the present condition of the network is good (step S 28 ). If the communication control module 2 A determines that the condition of the network is good, it sends the DCE 4 A a directive to perform a retransmission (step S 29 ).

On the other hand, if the communication module 2 A determines in step S 28 that the condition of the network is not good, it sends the DCE 4 A a directive to watch the condition of the network (step S 30 ).

When the DCE 4 A receives this directive, its operation mode switches to a watching mode (steps S 31 to S 33 ). That is to say, the DCE 4 A diagnoses the condition of the network at regular intervals. As a result of this diagnosis, if the DCE 4 A determines that the problem that happened in the network has now been solved (step S 32 ; Yes), it sends this watch result to the communication control module 2 A (step S 33 ). In contrast, if the problem in the network has not been solved, the DCE 4 A repeats the same diagnosis at regular intervals (steps S 31 and S 32 ).

On the other hand, when the communication control module 2 A in step S 30 sends the DCE 4 A the directive to watch the condition of the network, its operation mode switches to a waiting mode, and it waits for the waiting time to lapse (steps S 34 to S 36 ). If the communication control module 2 A receives the watch result before the waiting time elapses (step S 35 ; Yes), that is to say, if the condition of the network has turned good, it outputs a connection request to the DCE 4 A (step S 29 ).

In contrast, if the communication control module 2 A does not receive the watch result from the DCE 4 A before the waiting time elapses, that is to say, if the condition of the network would has not turned good (step S 36 ; Yes), it informs the communication module 3 A that the communication has been disconnected (step S 37 ). When the communication module 3 A receives this notification, it informs the user that it is impossible to reestablish the communication and ends the operations for performing the data communication.

On the other hand, if the connection request is sent from the communication control module 2 A in step S 29 , the DCE 4 A forwards the connection request to the network (step S 38 ). The communication control module 2 B in the receiving data terminal 1 B receives this connection request through the network. Thereafter, a series of operations such as a negotiation, an authentication of the sender and the like are performed, and the communication line 5 between the data terminals 1 A and 1 B is reestablished.

As described above, according to the present invention, even if the communication is unexpectedly interrupted, the communication module 3 A is not informed of the interruption of the communication in a case where it is possible to reestablish the communication. That is to say, since the communication module 3 A does not recognize the interruption of the communication line 5 , it will proceed to perform the same operation that has been halted since the communication circuit was interrupted. Therefore, when the communication is reestablished, the data communication will be restored retrospectively to the time of the interruption.

In addition, since establishing or reestablishing of the communication is performed only if the condition of the network is good, it is possible to eliminate the execution of the unnecessary operations for attempting to re-send data despite the fact that the condition of a network is not good.

The following describes preferred embodiments of a communication system adopting the communication control method according to the present invention.

B: First Preferred Embodiment

FIG. 4 illustrates the constitution of a communication system adopting the communication control method according to the present invention. As shown in FIG. 4 , this communication system includes data terminals 1 C and 1 S which are, for instance, personal computers, DCE 4 C, DCE 4 S and the communication line 5 . In this embodiment, the data terminal 1 C operates as a client. On the other hand, the data terminal 1 S operates as a server which sends data in response to a request from the data terminal 1 C operating as a client. The data terminal 1 C is connected to the communication line 5 through the DCE 4 C. The data terminal 1 S is connected to the communication line 5 through the DCE 4 S. The DCE 4 C and DCE 4 S are modems, for example.

The data terminal 1 C includes a communication application 61 C, a TCP 62 C, a PPP 63 C, a communication port 7 C and a port driver 8 C. The communication application 61 C is an application program executed by a control part provided in the data terminal 1 C when data communication is performed between the data terminals 1 C and 1 S. The TCP 62 C is a protocol that functions to receive from the communication application 61 C data to be sent to the data terminal 1 S, determine to which application in the receiving data terminal 1 S the data should be sent and add to the data information on its determination. The PPP 63 C is a protocol for establishing an IP connection through a public telephone network. In the following, the communication applications 61 C, TCP 62 C and PPP 63 C are collectively indicated as “an upper application 6 C”. This upper application 6 C is equivalent to the communication module 3 A as shown in FIG. 1 .

The DCE 4 C is connected to the communication port 7 C in the data terminal 1 C. The port driver 8 C functions to process signals outputted from the upper application 6 C to the communication port 7 C and signals inputted from the DCE 4 C to the communication port 7 C and to control data communication between the data terminals through the communication port 7 C. In addition, the port driver 8 C functions to reestablish the communication line 5 when the communication line 5 is interrupted (details are described later). This port driver 8 C is equivalent to the communication control module 2 A as shown in FIG. 1 .

On the other hand, like the data terminal 1 C described above, the server data terminal 1 S includes an upper application 6 S comprised of (a communication application 61 S, TCP 62 S and PPP 63 S,) a communication port 7 S and a port driver 8 S.

With reference to FIG. 5 , an explanation will be given of operations for establishing a communication and reestablishing the communication when the established communication line has been interrupted for an unexpected cause.

The operations for establishing a communication are as follows;

First, when a user of the client data terminal 1 C gives the communication application 61 C a command to start a data communication, it outputs a connection request specifying the server data terminal is (step S 40 ). When the port driver 8 C receives this connection request, it asks the DEC 4 c about the condition of the network (step S 41 ). The DCE 4 C diagnoses the condition of the network in response to this inquiry. The DCE 4 C sends a result of the diagnosis (network information) to the port driver 8 C (step S 42 ).

The port driver 8 C judges whether or not the condition of the network is good, based on the network information sent from the DCE 4 C. If the port driver 8 C determines that the condition of the network is good, it forwards the connection request to the network (step S 43 ). At the same time, the port driver 8 C writes a telephone number of the server in a memory provided in the data terminal 1 C. This telephone number of the server is included in the connection request described above. In this embodiment, the telephone number of the server is written in the memory in step S 44 . Please note, however, that such information is not only the information to be written in the memory in step S 44 . That is to say, the information to be memorized in the memory may include information for use in specifying the server data terminal is, such as the name of the server and its IP address.

On the other hand, the port driver 8 S in the receiving data terminal 1 S receives the connection request from the data terminal 1 C through the network. The port driver 8 S writes a telephone number of the client in a memory provided in the data terminal 1 S (step S 45 ). This telephone number of the client is included in the connection request. After this, a series of operations for establishing a communication, such as a negotiation and an authentication of the client, are performed by the DCE 4 C and DCE 4 S, and the data terminal 1 C is thereafter connected to the data terminal 1 S through the communication line 5 (step S 46 ).

Next, if the communication line 5 established in this way is interrupted for an unexpected cause, operations, which will be described below in detail, for reestablishing the communication are performed.

First, when the communication is interrupted for an unexpected cause (step S 47 ), an interruption response code is sent to the data terminals 1 C and 1 S from the network (steps S 48 and S 49 ). This interruption response code, as described above, includes information indicating the fact that the communication has been interrupted and the cause for the interruption.

The port driver 8 S in the server data terminal 1 S judges, based on the interruption response code received through the DCE 4 S, whether or not it is possible to reestablish the communication line 5 (step S 51 ). If the port driver 8 S determines that it is possible to reestablish the communication, it waits, without informing the upper application 6 S of the interruption of the communication, until a request for reestablishing the communication is sent from the data terminal 1 C (step S 53 ). On the other hand, if the port driver 8 S determines in step S 51 that it is impossible to reestablish the communication, it informs the upper application of the disconnection of the communication. As a result, the data communication is ended.

On the other hand, when the port driver 8 C in the client data terminal 1 C receives the interruption response code through the DCE 4 C (step S 48 ), it judges, based on this interruption response code, whether or not it is possible to reestablish the communication (step S 50 ). If the port driver 8 C determines that it is impossible to reestablish the communication, it informs the upper application 6 C of the disconnection of the communication.

In contrast, if the port driver 8 C determines that it is possible to reestablish the communication, it asks the DCE 4 C about the condition of the network (step S 52 ). After this, the port driver 8 C switches its operation mode to the waiting mode. The port driver 8 C does not inform the upper application of the interruption of the communication circuit 5 .

The DCE 4 C diagnoses the condition of the network in response to the inquiry from the port driver 8 C as described above. As a result of this diagnosis, if the DCE 4 C determines that the condition of the network has turned good, it sends the port driver 8 C a watch result indicating that the condition of the network is now good (step S 54 ).

When the port driver 8 C receives this watch result, it reads the telephone number of the server memorized in step S 44 and it sends a connection request to the data terminal 1 S, which is identified by the read out telephone number (step S 55 ).

On the other hand, if the port driver 8 S in the data terminal 1 S being in the waiting mode receives this request, it compares the telephone number of the sender memorized in step S 45 with the telephone number notified this time (step S 56 ). If both of the telephone numbers are the same, the port driver 8 S in the data terminal 1 S performs an off-hook operation (step S 57 ). As a result, the communication between the data terminal 1 C and the data terminal 1 S is reestablished (step S 58 ).

In this embodiment, as described above, even if a communication is interrupted for an unexpected cause, the communication is reestablished without notifying the upper applications 6 C and 6 S of the interruption of the communication in a case where it is possible to reestablish the communication. That is to say, for the upper application 6 C and the upper application 6 S, the connection has been maintained. Therefore, when the communication is reestablished, the data communication is restored retrospectively to the time of the interruption of the communication.

Next, operations of this embodiment are described with reference to FIGS. 6A to 6D in which a communication is interrupted while the client data terminal 1 C is downloading data from the server data terminal 1 S.

FIG. 6A shows a situation where the client data terminal 1 C is downloading files stored in a memory in the server data terminal 1 S. Data outputted from the communication application 61 S in the data terminal 1 S is sent to the data terminal 1 C by the PPP 63 S and the TCP 62 S during the course of the operation. This data is sent to the communication application 61 C by the PPP 63 C and the TCP 62 C in the data terminal 1 C. The communication application 61 C writes data thus received in a memory provided in the data terminal 1 C in order.

FIG. 6B shows a situation where the communication line 5 is interrupted for an unexpected cause while the data terminal 1 C is downloading data from the data terminal 1 S. Under the conventional technology, when such an interruption happens, an interruption response code indicating the interruption of the communication circuit is sent to the communication applications in the data terminals. As a result, the data communication between them is ended.

FIG. 6C shows a situation where the interrupted communication line 5 is reestablished. As described above, the operations for reestablishing the communication are performed only by the port driver 8 C in the data terminal 1 C and the port driver 8 S in the data terminal 1 S.

That is to say, even if the communication line 5 is interrupted, and an interruption response code is sent from the network, the port driver 8 S in the server data terminal 1 S does not inform the upper application 6 S, i.e., the TCP 62 S, the PPP 63 S and the like, that the communication line has been interrupted. More specifically, the TCP 62 S in the data terminal 1 S does not recognize the interruption of the communication. Therefore, as it was doing before the communication was interrupted, the TCP 62 C, for example, requests the communication port 7 S to send data. A signal indicating an acknowledgement (ACK), however, is not sent back to the TCP 62 S in response to the above request because the communication has been interrupted. As a result, until informed by the port driver 8 S of a reestablishment or a disconnection of the communication, the upper application 6 S repeats the operations to try to send the data that it was sending when the communication was interrupted.

Likewise, even if an interruption response code is sent from the network, the port driver 8 C in the client data terminal 1 C does not inform the upper application 6 C that the communication has been interrupted. As a result, the TCP 62 C and others repeat the same receiving operations that it was performing when the communication was interrupted.

FIG. 6D shows a situation after the reestablishing of the communication is completed. As shown in FIG. 6D , when the communication line 5 is reestablished, the data terminal 1 S starts sending data to the data terminal 1 C again. While the communication was interrupted, the upper application 6 S in the data terminal 1 S repeated the same sending operations that it had been performing at the time of the interruption. When the communication is reestablished, the upper application 6 S starts sending the data that remained to be sent at the time of the interruption. Likewise, while a communication was interrupted, the upper application 6 C in the data terminal 1 C repeated the same receiving operations that it had been performing at the time of the interruption. When the communication is reestablished, the upper application 6 C starts receiving the data that remained to be received at the time of the interruption. That is to say, the communication can be restored retrospectively to the time of the interruption of the communication line 5 .

As described above, according to this embodiment, even if a communication is interrupted while the client data terminal is downloading data, a user of the data terminal does not need to start the same operations for downloading the data allover again from the beginning. Thus, this embodiment has an advantage of reducing a communication time and a communication charge.

C: Second Preferred Embodiment

The following describes a communication system using the communication control method according to the present invention. In this communication system, a facsimile transmits image data to or receives image data from another facsimile.

As shown in FIG. 7 , this communication system includes facsimiles 10 A and 10 B and the communication line 5 , which connects the facsimile 10 A and the facsimile 10 B.

The facsimile 10 A includes an image outputting part 11 A, an image reading part 12 A, a central control part 13 A, a FAX protocol control part 14 A and a communication control part 15 A. The image outputting part 11 A receives from the central control part 13 A image data sent from another facsimile and prints out this image data on a paper. The image read part 12 A reads an image printed on a paper as an object of transmission by means of a CCD sensor and outputs the image data to the central control part 13 A. The central control part 13 A includes a CPU, a RAM and a ROM, and functions as a central controlling means. More specifically, the central control part 13 A outputs to the image output part 11 A image data sent from another facsimile through the communication line 5 . The central control part 13 A sends the image data from the image read part 12 A to another facsimile through the communication line 5 . The FAX protocol control part 14 A functions to control an image transmission protocol in the facsimile 10 A. In the following, the FAX protocol control part 14 A, the central control part 13 A, the image reading part 12 A and the image outputting part 11 A are collectively indicated as an upper application. This upper application is equivalent to the communication module 3 A as shown in FIG. 1 .

On the other hand, the communication control part 15 A controls establishing or reestablishing of the communication line 5 between the facsimile 10 A and the other facsimile 10 B. This communication control part 15 A is equivalent to the communication control module 2 A as shown in FIG. 1 .

The configuration of the facsimile 10 B is similar to the configuration of the facsimile 10 A. That is to say, the facsimile 10 B includes an image outputting part 11 B, an image reading part 12 B, a central control part 13 B, a FAX protocol control part 14 B and a communication control part 15 B. Because the functions of these parts are similar to those of the corresponding parts in the facsimile 10 A, their explanations are omitted.

With reference to FIG. 7 , operations of this embodiment will be described in which the facsimile 10 A sends image data to the facsimile 10 B.

First, when a user gives the facsimile 10 A a command to send image data, the communication control part 15 A sends a connection request to the facsimile 10 B. When the communication control part 15 B in the facsimile 10 B receives this request, it writes ID information of the sender in a memory provided in the facsimile 10 B (as shown by “A” in FIG. 7 ). The facsimile 10 A is connected to the facsimile 10 B through the communication line 5 after a series of operations such as a negotiation, an authentication and the like, are performed.

If the communication line 5 is interrupted for an unexpected cause, following processes are performed. First, an interruption response code such as “NO_CARRIER” is sent from the network to the communication control part 15 A in the facsimile 10 A and the communication control part 15 B in the facsimile 15 B (as shown by “B” in FIG. 7 ).

The communication control part 15 B in the receiving facsimile 10 B judges, based on the informed interruption response code, whether or not it is possible to reestablish the communication. If the communication control part 15 B determines that it is possible to reestablish the communication, it starts waiting for a transmission from the sending facsimile 10 A without informing the upper application of the interruption of the communication line 5 (as shown by “C” in FIG. 7 ). Likewise, the communication control part 15 A in the sending facsimile 10 A judges whether or not it is possible to reestablish the communication line. If the communication control part 15 A determines that it is possible to reestablish the communication, it diagnoses the condition of the network. As a result of this diagnosis, if the communication control part 15 A determines that the condition of the network has turned good, it sends a connection request to the facsimile 10 B (as shown by “D” in FIG. 7 ). When the communication control part 15 B in the facsimile 10 B receives this request (as shown by “E” in FIG. 7 ), it compares the ID information of the sender included in this connection request with the ID information stored at the time of the first connection of the communication line (as shown by “F” in FIG. 7 ). If both of them are the same, the communication control part 15 B performs the operations for reestablishing the communication line 5 .

Next, with reference to FIGS. 8A to 8C , operations will be described that are taken when the communication line 5 is interrupted while the facsimile 10 A is sending image data to the facsimile 10 B.

FIG. 8A shows a situation where the facsimile 10 A is sending image data representing a letter “A” to the facsimile 10 B. During the course of sending the data, even if the communication line 5 is interrupted for a cause (as shown in FIG. 8B ), the upper application in each facsimile does not recognize the interruption of the communication in a case where it is possible to reestablish the communication. Therefore, the central control part 13 A in the sending facsimile 10 A repeatedly outputs the image data that remains to be sent at the time of the interruption of the communication line 5 . Likewise, the central control part 13 B also repeats the same operation that it was performing at the time of the interruption. Therefore, when the communication line 5 is reestablished, as shown in FIG. 8C , the sending facsimile 10 A starts sending the image data that remained to be sent at the time of the interruption. The facsimile 10 B starts receiving the image data that remained to be received at the time of the interruption. That is to say, the communication can be restored retrospectively to the time of the interruption of the communication.

Therefore, even if a communication is interrupted while image data is transmitted, a user of a facsimile does not need to start the operations for establishing a communication and send the image data allover again from the very beginning. Therefore, it is possible to reduce the load on a user and a charge required for re-sending data.

D: Third Preferred Embodiment

The following describes a communication system using the communication control method according to the present invention. In the system, data communication can be performed through portable telephones.

As shown in FIG. 9 , this communication system includes a portable telephone 33 , a communication adapter (PC card) 31 , a cable 32 , a portable data terminal 30 , a radio base station 34 , mobile radio communication control stations 35 and 37 , a home memory station 36 , a gateway station 38 , a telephone network 39 and a data terminal 40 . The portable data terminal 30 is a notebook-type personal computer, for example. Each of the portable data terminal 30 and the data terminal 40 includes the upper application 61 comprised of the communication application 61 , the TCP 62 and PPP 63 , the communication port 7 and the port driver 8 , such as those provided in the data terminals 1 C and 1 S shown in FIG. 4 . The portable data terminal 30 is connected with the portable telephone 33 through the cable 32 and the communication adapter 31 . More specifically, one end of the cable 32 is connected to the portable telephone 33 . The other end of the cable 32 is connected to the communication adapter 31 , which is inserted in a card slot of the portable data terminal 30 and connected to the communication port 7 . This communication adapter 31 functions as a modem to convert into radio signals data outputted from the portable data terminal 30 . With the configuration described above, the portable data terminal 30 can transmit data to or receive data from the data terminal 40 through the communication network formed from the portable telephone 33 , the radio base station 34 , the mobile radio communication control stations 35 and 37 , the gateway station 38 and the telephone network 39 . The home memory station 36 has a database storing information regarding the present location of the portable telephone 33 .

With these constructions in mind, processes for establishing a communication between the portable data terminal 30 and the data terminal 40 will be discussed below. In the following discussion, the portable data terminal 30 sends data to the data terminal 40 .

First, given by a user a command to start a data communication, the communication application 61 in the portable data terminal 30 outputs a connection request. The portable telephone 33 sends this connection request to the radio base station 34 , which form a wireless zone in which the portable telephone 33 is located. This connection request is sent to the data terminal 40 through the mobile radio communication control stations 35 and 37 , the gateway station 38 , the telephone network 39 and the like. After this, a series of operations including a negotiation, an authentication and the like are performed, and a communication between the portable data terminal 30 and the data terminal 40 is established.

FIG. 10 illustrates operations that are performed in the communication system according to this embodiment when a communication is interrupted for an unexpected cause.

First, when a communication is interrupted for an unexpected cause, the communication adapter 31 sends to the port driver 8 in the portable data terminal 30 an interruption response code including notification of the fact that the communication has been interrupted and the cause for the interruption. The port driver 8 judges, based on this interruption response code (step S 60 ), whether or not it is possible to reestablish the communication (step S 61 ).

If the port driver 8 in the portable data terminal 30 determines that it is impossible to reestablish the communication, it informs the upper application of the disconnection of the communication. Thereafter, the data communication between the portable data terminal 30 and the data terminal 40 ends (step S 69 ). In contrast, if the port driver 8 determines that it is possible to reestablish the communication, it performs operations for reestablishing the communication without informing the upper application of the interruption of the communication. That is to say, these operations are as follows.

First, the port driver 8 sends to the communication adapter 31 an AT command to inquire the current condition of the portable telephone 33 (step S 62 ). In response to this AT command, the communication adapter 31 sends to the port driver 8 a response code indicating whether or not the portable telephone 33 is within the wireless zone formed by the radio base station 34 . The port driver 8 analyzes this response code (step S 63 ), and it judges whether or not the portable telephone 33 is within the wireless zone (step S 64 ). If the port driver determines that the portable telephone 33 is within the wireless zone, it sends a connection request to the communication adapter 31 (step S 67 ).

In contrast, if the port driver 8 determines in step S 64 that the portable telephone 33 is not within the wireless zone, it starts counting a waiting time. In addition, the port driver 8 repeatedly sends at regular intervals the AT command for inquiring the condition of the portable telephone 33 . In response to the AT command sent from the port driver 8 , the communication adapter 31 returns to the port driver 8 the response code indicating whether or not the portable telephone 33 is currently within the wireless zone.

If the port driver 8 receives the response code indicating that the portable telephone 33 moves within the wireless zone before the port driver 8 counts up to the waiting time (steps S 65 and S 66 ; Yes), the port driver 8 sends the connection request to the communication adapter 31 (step S 67 ).

In contrast, if the port driver 8 does not receive the response code indicating that the portable telephone 33 moves within the wireless zone before the port driver 8 counts up to the waiting time (step S 68 ; Yes), the port driver 8 informs the upper application of the disconnection of the communication. As a result, the operations for the data communication between the portable data terminal 30 and the data terminal 40 are ended (step S 69 ).

On the other hand, if the connection request is sent from the port driver 8 in step S 67 , the communication adapter 31 forwards this connection request to the data terminal 40 . The communication between the portable data terminal 30 and the data terminal 40 is thereby reestablished.

According to this embodiment described above, the same effects as the first preferred embodiment described above can be obtained. In addition, in this embodiment, the judgment as to whether to reestablish a communication is made based on whether or not the portable telephone 33 is within the wireless zone. Therefore, it is possible to eliminate the execution of the unnecessary operations in which a transmission for reestablishing the communication is repeated despite the fact that the portable telephone is not within the wireless zone.

In this embodiment, the AT command is used for inquiring the condition of a portable telephone, but other kinds of command may of curse be used instead of the AT command.

E: Variation Examples

The embodiments according to the present invention are described above, but variations may be added to these embodiments without departing from the gist of the present invention. Some of the variations are discussed below, for example.

(1) The functions of the communication control module as shown in FIG. 1 may not reside in the data terminal but may reside in the DCE, for example. The functions of the port drivers 8 C and 8 S as discussed in first preferred embodiment may reside in the PPP 63 C and PPP 63 S, the TCP 62 C and TCP 62 S or the communication applications 61 C and 61 S.

(2) The present invention can be applied to a communication through a leased line, a network of CATV or a LAN, a satellite communication, a radio communication, an infrared communication or the like, in addition to a communication through a public telephone network.

(3) In the first preferred embodiment, the data terminal has the PPP and the TCP, but it is possible to use, in place of the PPP, another protocol such as XMODEM, YMODEM, B_Plus, Kermit, Quick-VAN or the like.

(4) In the third preferred embodiment, the portable telephone is connected to the portable data terminal, but in place of the portable data terminal, other kinds of communication terminal such as a personal handy phone, a personal digital assistant or the like may be used.

(5) An arrangement may be possible in which a communication control program embodying the communication control method according to the present invention is store in a storage medium, and that the data terminal reads out the communication control program from the storage medium and execute it to implement the communication control method according to the present invention. That is to say, as shown in FIG. 9 , a floppy disk 41 is provided for recording the communication control program. The communication control program recorded on the floppy disk is installed and executed in the data terminal. The communication control method according to the present invention may be realized in the form of the storage medium that stores the communication control program embodying the communication control method according to the present invention.

In the examples described above, the communication control program is recorded on the floppy disk, but a storage medium for storing this program is not limited to a floppy disk. Of course, various kinds of recording medium such as a CD-ROM may be available for storing the program.