HK1196729B - Data transmitting apparatus, data receiving apparatus, and method - Google Patents

Description

Data sending device, data receiving device and method

This application is a divisional application of the invention patent application with application number 201110243178.5, application date October 27, 2003, and invention name “Data sending device, data receiving device and method”.

The original parent case of this application is the invention patent application with application number 200380100279.0, application date October 27, 2003, and invention name “Communication equipment and method, storage medium and program”.

Technical Field

The present invention relates to a communication device and method, a storage medium, and a program, and in particular, to a communication device and method, a storage medium, and a program suitable for determining whether data communication occurs across a WAN such as the Internet or a LAN within a house.

Background Art

In recent years, with the widespread use of public wide area networks (hereinafter referred to as "WANs") such as the Internet and local area networks (hereinafter referred to as "LANs") installed in houses, and with the improvement of communication speeds of these networks, various data are transmitted by using personal computers and various electronic AV equipment on these WANs and LANs.

The widespread use of these networks has made it easy for individuals to sell or share content data, such as video data, audio data, and program data. However, due to this convenience, copyrighted content data is sometimes illegally distributed. To prevent this, various countermeasures have been proposed.

For example, some music download services restrict storage media storing downloaded audio data to storage media having predetermined protection against being copied.

Furthermore, for example, in content data communication via a small network such as a network based on the IEEE 1394 standard, encrypted content data is transmitted after being authenticated to prevent the content data from being transmitted to unauthorized devices.

Unfortunately, there is no established communication solution for the IP protocol commonly used in WAN communications to prevent the illegal distribution of content data. One possible solution is to restrict the communication area to the LAN when distributing content data via the IP protocol. In order to restrict the communication of content data to the LAN, it is necessary to determine whether the other party in the content data communication is located in the LAN or the WAN. However, there is no established method for this determination.

Summary of the Invention

Therefore, an object of the present invention is to provide a scheme for determining whether the other party of content data communication is located in a LAN or across a WAN.

According to the first communication device of the present invention, it includes: a sending device for sending a predetermined number of inspection packets after recording information indicating the order of the inspection packets in the inspection packets; a receiving device for receiving the sent inspection packets; an inspection device for inspecting the order of the predetermined number of inspection packets received by the receiving device; and a determination device for determining whether another communication device is located in the same first network as itself or passes through a second network different from the first network based on the inspection result of the inspection device.

If the inspection device determines that the predetermined number of inspection packets received by the receiving device are in sequence, the determination device can determine that the other communication device is located in the first network. Otherwise, if the inspection device determines that the predetermined number of inspection packets received by the receiving device are not in sequence, the determination device can determine that the location of the other communication device passes through the second network.

The first network may be a local area network (LAN), and the second network may be a wide area network (WAN).

The sending device and the receiving device can work under the UDP protocol.

According to the first communication method of the present invention, the step includes: a step of sending a predetermined number of inspection packets after recording information indicating the order of the inspection packets in the inspection packets; a step of receiving the sent inspection packets; a step of checking the order of the predetermined number of inspection packets received in the receiving step; and a determination step, which determines whether another communication device is located in the same first network as itself or passes through a second network different from the first network based on the inspection result of the inspection step.

According to the first storage medium of the present invention, a program is included, which includes a step of sending a predetermined number of inspection packets after recording information indicating the order of inspection packets in the inspection packets, a step of receiving the sent inspection packets, a step of checking the order of the predetermined number of inspection packets received in the receiving step, and a determination step of determining whether another communication device is located in a first network identical to itself or passes through a second network different from the first network based on a check result of the checking step.

A first program according to the present invention allows a computer to execute the following steps, a step of sending a predetermined number of inspection packets after recording information indicating the order of inspection packets in the inspection packets, a step of receiving the sent inspection packets, a step of checking the order of the predetermined number of inspection packets received in the receiving step, and a determination step, which determines whether another communication device is located in the same first network as itself or passes through a second network different from the first network based on the inspection result of the inspection step.

According to the second communication device of the present invention, it includes: a sending device for sending a predetermined number of inspection packets; a receiving device for receiving the sent inspection packets; an information generating device for generating confirmation information and sending back the confirmation information after the receiving device receives the predetermined number of inspection packets; an obtaining device for obtaining confirmation information sent back from another communication device; a measuring device for measuring the time elapsed from the sending device sending the predetermined number of inspection packets to the obtaining device receiving the confirmation information; and a determining device, which is used to determine whether the other communication device is located in the same first network as itself or passes through a second network different from the first network based on the measurement result of the measuring device.

If the elapsed time measured by the measuring device is less than a predetermined threshold, the determining device can determine that the other communication device is located in the first network; otherwise, if the elapsed time measured by the measuring device is greater than or equal to the predetermined threshold, it can be determined that the location of the other communication device passes through the second network.

The first network may be a local area network (LAN), and the second network may be a wide area network (WAN).The sending device and the receiving device may operate under the TCP protocol or the UDP protocol.

According to the second communication method of the present invention, the steps include: a step of sending a predetermined number of inspection packets; a step of receiving the sent inspection packets; a step of generating confirmation information and sending back the confirmation information after receiving the predetermined number of inspection packets in the receiving step; a step of obtaining confirmation information sent back from another communication device; a step of measuring the time elapsed from sending the predetermined number of inspection packets in the sending step to receiving the confirmation information in the obtaining step; and a determining step, which determines whether the other communication device is located in the same first network as itself or passes through a second network different from the first network based on the measurement result in the measuring step.

The second storage medium includes a program, which includes the steps of sending a predetermined number of inspection packets, receiving the sent inspection packets, generating confirmation information and sending back the confirmation information after receiving the predetermined number of inspection packets in the receiving step, obtaining confirmation information sent back from another communication device, measuring the time elapsed from sending the predetermined number of inspection packets in the sending step to receiving the confirmation information in the obtaining step, and a determining step, which determines whether the other communication device is located in the same first network as itself or passes through a second network different from the first network based on the measurement result in the measuring step.

A second program according to the present invention allows a computer to execute the following steps, a step of sending a predetermined number of inspection packets, a step of receiving the sent inspection packets, a step of generating confirmation information and sending back the confirmation information after receiving the predetermined number of inspection packets in the receiving step, a step of obtaining confirmation information sent back from another communication device, a step of measuring the time elapsed from sending the predetermined number of inspection packets in the sending step to receiving the confirmation information in the obtaining step, and a determining step, which determines whether the other communication device is located in the same first network as itself or passes through a second network different from the first network based on the measurement result in the measuring step.

According to the third communication device of the present invention, it includes: a sending device for sending a predetermined number of check packets and resending the check packets if a communication error occurs; and a determination device, which is used to determine that another communication device is located in the same first network as itself if the sending device does not resend the check packets, otherwise if the sending device resends the check packets, determine that the location of the other communication device passes through a second network different from the first network.

The sending device may operate under the Transmission Control Protocol (TCP).

The first network may be a local area network (LAN), and the second network may be a wide area network (WAN).

The third communication method according to the present invention includes: sending a predetermined number of check packets, and resending the check packets if a communication error occurs; and a determination step, if the check packets are not resent in the sending step, it determines that the other communication device is located in the same first network as itself, otherwise if the check packets are resent in the sending step, it determines that the location of the other communication device passes through a second network different from the first network.

According to the third storage medium of the present invention, a program is included, which includes the steps of sending a predetermined number of check packets, and resending the check packets if a communication error occurs, and a determining step, which determines that the other communication device is located in the same first network as itself if the check packet is not resent in the sending step, otherwise determines that the location of the other communication device passes through a second network different from the first network if the check packet is resent in the sending step.

A third program according to the present invention allows a computer to execute the following steps, a step of sending a predetermined number of check packets, a step of resending the check packets if a communication error occurs, and a determining step, if the check packets are not resent in the sending step, it determines that the other communication device is located in the same first network as itself, otherwise if the check packets are resent in the sending step, it determines that the location of the other communication device passes through a second network different from the first network.

In a first communication device, communication method, and program according to the present invention, a test packet containing information indicating a test packet sequence is received. A predetermined number of test packets are sequenced, and the sequence is checked. The result of the check is used to determine whether another communication device is located in the same first network as the communication device itself or is passing through a second network different from the first network.

In a second communication device, communication method, and program according to the present invention, a predetermined number of check packets are sent to another communication device, and confirmation information sent back from the device is received. Furthermore, the time elapsed from the sending of the predetermined number of check packets to the receipt of the confirmation information is measured. The measurement result is used to determine whether the communication device is located in the same first network as itself or is passing through a second network different from the first network.

In a third communication device, communication method, and program according to the present invention, a predetermined number of check packets are sent to another communication device, and if a communication error occurs, the check packets are resent. If the check packets are not resent, it is determined that the other communication device is located in the same first network as the other communication device. If the check packets are resent, it is determined that the other communication device is located across a second network different from the first network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a block diagram of the structure of a communication system to which the present invention is applied;

FIG2 shows the structure of the personal computer shown in FIG1;

FIG3 shows a first structure of the communication unit 29 shown in FIG2 ;

Figure 4 shows an example of a test package;

FIG5 is a flowchart illustrating a transmission process in the first structure of the communication unit 29;

FIG6 is a flowchart illustrating a receiving process in the first structure of the communication unit 29;

FIG7 shows a second structure of the communication unit 29 shown in FIG2 ;

FIG8 is a flowchart illustrating a receiving process in the second structure of the communication unit 29;

FIG9 is a flowchart illustrating a transmission process in the second configuration of the communication unit 29; and

FIG. 10 is a flow chart illustrating a transmission process through the TCP protocol.

Best Mode for Carrying Out the Invention

1 shows a structure of a communication system according to an embodiment of the present invention, which includes a LAN having a personal computer and AV equipment. In this communication system, LANs 1 and 7 and a server 8 are connected to each other via a WAN 6 such as the Internet.

LAN 1 includes personal computers (PCs) 3 and 4 and AV equipment 5, all connected via a switching hub 2. LAN 1 is used, for example, for communication between individuals or families within a house. Switching hub 2 connects to PCs 3 and 4 and AV equipment 5 via a high-speed interface, such as Ethernet 100BASE-TX. Data communication between PCs 3 and 4 and AV equipment 5 can occur at a rate of approximately 100 Mbps with sufficiently low error rates. PCs 3 and 4 and AV equipment 5 can then communicate with LAN 7 or server 8 via switching hub 2 and WAN 6.

When transmitting content data, the personal computer (PC) 3 can determine whether the other party of the content data communication is located in the LAN 1 , such as the personal computer 4 , or located across the WAN 6 , such as the server 8 .

Likewise, the personal computer 4 and the AV device 5 that transmit content data can determine whether the other party of content data communication is located on the LAN 1 , such as the personal computer 3 , or located across the WAN 6 , such as the server 8 .

LAN 7 has the same structure as LAN 1, but is managed by a different user from that of LAN 1. Server 8 is managed by a different user from that of LANs 1 and 7.

2 shows the structure of a personal computer 3. The personal computer 3 includes a central processing unit (CPU) 21 to which an I/O (input/output) interface 25 is connected via a bus 24. A read-only memory (ROM) 22 and a random access memory (RAM) 23 are connected to the bus 24.

The I/O interface 25 includes: an input unit 26 composed of I/O devices, such as a keyboard and a mouse, through which the user inputs operation commands; an output unit 27, which outputs a video signal to a display operation screen on the display unit; a storage unit 28, which includes a hard disk drive to store programs and other various types of data; and a communication unit 29, which includes an Ethernet interface for sending and receiving data via a 100BASE-TX cable connected to the switching hub 2.

The communication unit 29 may include a universal serial bus (USB), or a high-speed interface such as the Institute of Electrical and Electronics Engineers (IEEE) 1394, instead of the Ethernet interface.

Furthermore, a drive 30 that reads and writes data to a storage medium such as a magnetic disk 31 , an optical disk 32 , a magneto-optical disk 33 , and a semiconductor memory 34 is connected to the I/O interface 25 .

The CPU 21 executes various types of processing, which will be described below, under the control of a program stored in the ROM 22 or RAM 23. The program is read from the magnetic disk 31, optical disk 32, optical-magnetic disk 33, or semiconductor memory 34, stored in the storage unit 28, and then loaded from the storage unit 28 to the RAM 23. The RAM 23 also stores data necessary for the CPU 21 to execute various types of processing.

FIG3 shows a first configuration of functional blocks implemented by the communication unit 29 in response to control by the CPU 21. A control unit 41 controls a transceiver unit 43, which transmits and receives data using the User Datagram Protocol (UDP), one of the communication protocols. The control unit 41 accesses a register 42. Before transmitting content data in response to control by the control unit 41, the transceiver unit 43 sends a predetermined number of check packets to determine whether the other party to the content data communication is located on the LAN 1 or across the WAN 6.

An example of a test packet is shown in FIG4 . Specifically, the payload of the test packet stores the counter value generated by the control unit 41 .

The PC 4 and the AV device 5 have the same hardware or software functional blocks as the communication unit 29 shown in Fig. 3. In addition, various types of devices and the server 8 on the LAN 7 have the same functional blocks.

Now, an overview of how to determine whether the other party of the content data communication is located in the LAN 1 or across the WAN 6 will be described with reference to a first configuration of the communication unit 29.

The UDP protocol defines that in the event of a communication error, packets that have not been correctly sent will be discarded and not resent. Utilizing this feature, it is possible to determine whether the other party of the content data communication is located at LAN1 or passes through WAN6.

More specifically, switching hub 2, which is performing high-speed communication with a peer on LAN 1, sends all packets to the peer without changing the packet order. However, during high-speed communication with the peer across WAN 6, a communication error occurs due to the wide area network connection, and the UDP protocol discards the erroneous packets. As a result, the peer fails to receive some packets or receives packets in a different order than they were sent. This is used to determine whether the other party in the content data communication is located on LAN 1 or across WAN 6.

The transmission process in the first configuration of the communication unit 29 shown in Figure 3 will now be described with reference to the flowchart in Figure 5. This transmission process determines whether the other party of the content data communication is located on LAN 1 or across WAN 6 before communication of content data occurs.

In step S1, the control unit 41 assigns an initial value A to the value of one of the counters (counter value). In step S2, the control unit 41 increments the counter by a constant value X and then outputs the counter value to the transmission and reception unit 43. In step S3, the transmission and reception unit 43, in response to control by the control unit 41, writes the counter value from the control unit 41 into the payload of a check packet and then transmits the check packet to the other party of the content data communication.

In step S4, control unit 41 determines whether transceiver unit 43 has sent all of the predetermined number of inspection packets. If not, the process returns to step S2 and repeats the following steps. If, in step S4, control unit 41 determines that all of the predetermined number of inspection packets have been sent, the sending process is complete. As described above, multiple inspection packets with consecutive counter values are sent to the receiver.

Referring now to the flowchart in FIG6 , the receiving process corresponding to the above-described transmitting process in the first configuration of communication unit 29 will be described. In step S11, control unit 41 stores initial value A in register 42. In step S12, transceiver unit 43 waits until a check packet is received from the transmitter. When transceiver unit 43 receives the check packet, the process proceeds to step S13.

In step S13, the control unit 41 calculates the difference between the counter value in the payload of the inspection packet received in step S12 and the value in the register 42. In step S14, the difference calculated in step S13 is checked to determine whether it is equal to the constant value X. If the difference is equal to the constant value X, the inspection packet is not lost and the packets are received in the order they were sent, and the process proceeds to step S15.

In step S15, control unit 41 stores the counter value recorded in the packet in step S13 in register 42. In step S16, control unit 41 determines whether transceiver unit 43 has received all of the predetermined number of inspection packets. If not, the process returns to step S12 and repeats the subsequent steps. If, in step S16, it is determined that all of the predetermined number of inspection packets have been received, the process proceeds to step S17.

In step S17 , the control unit 41 determines LAN connection, indicating that the transmitter is located in the LAN1 .

In step S14, if the difference calculated in step S13 is not equal to the constant value X, the check packet is lost or the check packets are received in a different order than they were sent. The process then proceeds to step S18. In step S18, control unit 41 determines WAN connectivity, indicating that the transmitter is located on WAN 6. This concludes the description of the receiving process.

For example, if communication is determined to have occurred via a WAN connection during reception, the use of content data subsequently sent from the transmitter is severely restricted. Conversely, if communication is determined to have occurred via a LAN connection, the use of content data subsequently sent from the transmitter is moderately restricted. This prevents content data from being disseminated across the WAN without compromising personal use within the LAN.

FIG7 shows a second configuration of functional blocks implemented by the communication unit 29 in response to control by the CPU 21. A control unit 51 controls a transceiver unit 53, which transmits and receives data using the TCP or UDP protocols. The control unit 51 also accesses a register 52. Before transmitting content data in response to control by the control unit 51, the transceiver unit 53 transmits a predetermined number of check packets to determine whether the other party to the content data communication is located on the LAN 1 or across the WAN 6. A timer 54 measures time in response to control by the control unit 51.

The PC 4 and the AV device 5 have the same hardware or software functional blocks as the communication unit 29 shown in Fig. 7. In addition, various types of devices on the LAN 7 and the server 8 have the same functional blocks.

Now, referring to the second configuration of the communication unit 29, an overview of how to determine whether the other party in content data communication is located on the LAN 1 or is passing through the WAN 6 will be described. In communications on the LAN 1, the switching hub 2 ensures a high communication rate. In contrast, for various reasons, in communications passing through the WAN 6, the communication rate decreases compared to the communication rate on the LAN 1. Based on this, it is determined whether the other party in content data communication is located on the LAN 1 or is passing through the WAN 6.

The receiving process in the second configuration of the communication unit 29 will now be described with reference to the flowchart in Fig. 8. This receiving process starts when the transmitter transmits a check packet.

In step S21, the control unit 51 determines whether the sending and receiving unit 53 has received all the predetermined number of inspection packets. The control unit 51 waits until it is determined that all the predetermined number of inspection packets have been received. If it is determined that all the predetermined number of inspection packets have been received, the process proceeds to step S22. In step S22, the control unit 51 generates a confirmation message indicating that all the predetermined number of inspection packets have been received, and outputs this information to the sending and receiving unit 53. In step S23, the sending and receiving unit 53 sends the confirmation message to the transmitter. For security reasons, it is best that the confirmation message cannot be forged by a third party. For example, the transmitter and receiver share key information as privileged information. All data or part of the data is sent together with a hash and the key information. This is the end of the description of the receiving process.

The transmission process in the second configuration of the communication unit 29 will now be described with reference to the flowchart in Figure 9. In step S31, the control unit 51 sets a waiting time in the timer 54. The waiting time is determined so that after a predetermined number of check packets have been transmitted, the waiting time is sufficient to receive confirmation information sent back from the transmitter located on the LAN 1.

In step S32, the timer 54 begins measuring time in response to control of the control unit 51. In step S33, the transceiver unit 53 transmits a predetermined number of inspection packets in response to control of the control unit 51. For each inspection, a random number may be written into the payload of each inspection packet. The receiver generates confirmation information along with a hash and key information as described above to prevent the confirmation information from being improperly forged.

In step S34, the control unit 51 determines whether the transceiver unit 53 has received confirmation information from the receiver. If the control unit 51 determines that the confirmation information has not been received, the process proceeds to step S35. In step S35, the control unit 51 checks whether the waiting time set in step S31 has passed. If it is determined that the waiting time has not passed, the process returns to step S34 and repeats the subsequent steps.

If, in step S34, control unit 51 determines that confirmation information has been received, the process proceeds to step S36, where control unit 51 verifies whether the confirmation information is correct. If not, the process proceeds to step S38. Otherwise, the process proceeds to step S37. In step S37, control unit 51 determines that communication is occurring via a LAN connection, meaning that the receiver is located within LAN 1. Specifically, to verify the confirmation information, the transmitter can calculate the expected confirmation information, as in the reception process, and compare it with the value received from the receiver.

If in step S35 it is determined that the waiting time has elapsed, the process proceeds to step S38. In step S38, the control unit 51 determines that communication occurs via the WAN connection, ie, the receiver is located across the WAN 6. This is the end of the description of the transmission process.

For example, if it is determined that communication is occurring over a WAN connection during this transmission process, subsequent content data transmission is stopped. Conversely, if it is determined that communication is occurring over a LAN connection, subsequent content data transmission is allowed. This prevents content data from being distributed over a WAN without impairing personal use on the LAN.

The third type of communication using the Transmission Control Protocol (TCP) in the communication unit 29 will now be described. In the TCP protocol, when a communication error occurs, the erroneous packet is retransmitted until all packets are successfully transmitted. If high-speed TCP communication exceeding the speed of the WAN is occurring, retransmission will not occur within the LAN 1, but will occur over the WAN 1.

Now, referring to the flowchart in Figure 10, the transmission process for determining whether the receiver is located in LAN 1 or across WAN 6 by this feature of the TCP protocol will be described. This transmission process is performed before the communication of the content data. In this case, the structure of the communication unit 29 is the same as that in Figure 3.

In step S41, the transmission and reception unit 43 starts transmitting the inspection packet in response to the control of the control unit 41. In step S42, the control unit 41 determines whether the transmission and reception unit 43 retransmits the inspection packet. If it is determined that the inspection packet retransmission occurs, the process proceeds to step S43.

In step S43 , the control unit 41 determines the WAN connection, indicating that the receiver is located on WAN 6 .

If, in step S42, it is determined that the inspection packet has not been retransmitted, the process proceeds to step S44. In step S44, the control unit 41 determines whether the transmission and reception unit 43 has transmitted a predetermined number of inspection packets. If, in step S44, it is determined that the predetermined number of inspection packets has not been transmitted, the process returns to step S42 and repeats the subsequent steps. Subsequently, if, in step S44, it is determined that the predetermined number of inspection packets has been transmitted, the process proceeds to step S45.

In step S45, the control unit 41 determines the LAN connection, indicating that the receiver is located on LAN 1. This is the end of the description of the transmission process.

For example, if it is determined that communication is occurring via a WAN connection during this transmission process, subsequent content data transmission is stopped. Conversely, if it is determined that communication is occurring via a LAN connection, subsequent content data transmission is allowed. This prevents content data from being distributed via the WAN without impairing personal use on the LAN.

In this specification, the steps describing the program stored in the storage medium include not only processes that are executed in the order described above but also processes that can be executed in parallel or independently.

Furthermore, as used in the specification, a "system" refers to the entire apparatus including a plurality of apparatuses.

Industrial Applicability

According to the present invention, it is possible to determine whether the other party of content data communication is located in a LAN or across a WAN.

Claims (11)

1. An electronic device, comprising: A means for outputting a predetermined number of inspection packets to another electronic device using the Transmission Control Protocol (TCP); A means for receiving TCP acknowledgment messages for the predetermined number of verification packets from the other electronic device, the TCP acknowledgment messages including acknowledgment information based on key information shared with the other electronic device; A means for calculating desired confirmation information based on key information shared with the other electronic device; A means for generating a comparison result for the other electronic device based on the confirmation information and the desired confirmation information; A means for calculating the time elapsed since the transmission of the inspection packet; A means for preventing data from being sent to the other electronic device when the comparison result indicates that the confirmation information and the expected confirmation information do not match, or when a predetermined time elapsed since the sending of the verification packet expires before the TCP confirmation message is received. 2. The electronic device of claim 1, wherein the key information is shared between the electronic device and the other electronic device before the verification packet is sent. 3. The electronic device according to claim 2, wherein at least one of the confirmation information and the expected confirmation information is generated using a hash function. 4. The electronic device of claim 3, wherein the time calculation includes the time between the sending of the verification packet and the receiving of the TCP acknowledgment message. 5. The electronic device of claim 1, wherein the electronic device is configured to output a video signal to a display. 6. The electronic device according to claim 1, further comprising: A monitor configured to display the operation screen. 7. The electronic device according to claim 6, further comprising: It is configured as a user interface to receive user input. 8. The electronic device according to claim 7, further comprising: A memory configured to store data to be sent to the other electronic device. 9. The electronic device according to claim 1, wherein the other electronic device is a target device to be locally inspected. 10. A method performed by an electronic device, comprising: The Transmission Control Protocol (TCP) is used to output a predetermined number of verification packets to another electronic device. Receive TCP acknowledgment messages for the predetermined number of verification packets from the other electronic device, the TCP acknowledgment messages including acknowledgment information based on key information shared with the other electronic device; The expected confirmation information is calculated based on the key information shared with the other electronic device; The other electronic device generates a comparison result based on the confirmation information and the expected confirmation information; Calculate the time elapsed since the verification packet was sent; When the comparison result indicates that the confirmation information and the expected confirmation information do not match, or when a predetermined time elapsed since the sending of the verification packet expires before the TCP confirmation message is received, data is prevented from being sent to the other electronic device. 11. A transmitting device, comprising: A user input unit configured to receive user input; It is configured to send a predetermined number of check packets to the communication interface of the receiving device using the Transmission Control Protocol (TCP). And the circuitry is configured as follows: The receiving device receives TCP acknowledgment messages for the predetermined number of verification packets, the TCP acknowledgment messages including acknowledgment information based on key information shared with the receiving device; The expected confirmation information is calculated based on the key information shared with the receiving device; The receiving device generates a comparison result based on the confirmation information and the expected confirmation information; Calculate the time elapsed since the verification packet was sent; When the comparison result indicates that the confirmation information and the expected confirmation information do not match, or when a predetermined time elapsed since the sending of the verification packet expires before the TCP confirmation message is received, data is prevented from being sent to the receiving device.